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© International Telecommunication Union OMITE CoNSULTATIF INTERNATIONAL DES COMMUNICATIONS TELEPHONIQUES A GRANDE DISTANCE

Plenary Session, Berlin> yrd-ioth June3 1929

\

ENGLISH EDITION

Issued by The International Standard Electric Corporation, London, 1930. PREFACE TO THE ENGLISH EDITION.

This volume contains an unofficial translation of the official French text of the Proceedings of the CO MITE CONSULTATIF INTERNATIONAL DES

C ommunications T elephoniques a G r a n d e D i s ­ t a n c e (c .c .i .) at its Plenary Session in Berlin, 3 rd -io th June, 1929.

I nternational S t a n d a r d

, E l e c t r i c C o r p o r a t io n . CONTENTS.

Page I.—LIST OF DELEGATES...... i

II.—MINUTES OF THE OPENING SESSION 6

HI.—QUESTIONS OF GENERAL ORGANISATION ...... n Organisation and Working of the International Consultative Committee for Loilg-Distance Telephone Communications .-...... n Distribution of the Expenses incurred in the Operations of the International Consultative Committee ...... 13 Distribution of Expenses for the Maintenance of the European Master Reference System for Telephone Transmission ...... 13 Representation on the International Consultative Committee of Private1 Telephone Organ­ isations operating in Countries where a State Telephone Administration exists . . 14 Membership of the International Consultative Committee of Private Telephone Adminis­ trations which operate in Countries where there is no State Telephone Administration 14 Technical Collaboration between the International Consultative Committee and Technical Organisations dealing with Questions likely to have a bearing on International Telephony 15 Methods to be followed in the Study of Questions of interest both to the International Consultative Committee and to other International Organisations ...... 15 Collaboration between the C.C.I. and the International Bureau of the Telegraph Union . . 16 Committee on Revision of the International Regulations (Telephone Section) .. .. 16

IV.—QUESTIONS OF TRANSMISSION, MAINTENANCE AND SUPERVISION OF LINES AND INSTALLATIONS .. ’ . . 18 A. Advice of the International Consultative Committee on Long-Distance Telephone Communications ...... < 19

(A.a.) G en eral...... ; ...... 19 (A.a.l.) Transmission Standards and Definitions ...... 19 Transmission Unit ...... 19 Method of expressing Frequency ...... 19 Conversion Table of Transmission Units (Nepers and Decibels)...... 20 Definition of some Expressions used in Questions of Telephone Transmission . . .. 20 (a) Nepers and Decibels ...... 20 (b) Special Definitions . •...... 21 Telephone Transmission Reference Systems...... 23 Object of Telephone Transmission Reference Systems ...... 23 The Setting up of Telephone Transmission Reference Systems...... 23 Conditions which should be fulfilled by the Telephone Transmission Reference Systems . . 23 I.—The Master Telephone Transmission Reference System '...... 23

II.—Telephone Transmission Reference Systems ...... 23 (1) Transmitting System ...... 23 (2) Reference Artificial Line ...... 25 (3) Reference Receiving. System .\ ...... 26 IV,— Questions of Transmission, Maintenance and Supervision, &c.— continued. Page III.—Working Standards : . , . . ,...... 27 Recommendations regarding the Calibration of Reference Systems and Working Standards 28 A.—Comparison of Reference Systems with the Master Reference System, and the Periods at which such Comparisons should be made...... 28 B.—Calibration of Working Standards referred to the “ SFERT ” ...... 28 C.—Normal adjustment of the " SFERT ...... 28 A p p en d ix I. Notes on Working Standards employing Carbon Transmitters (" SETAC ”)— A.—Description of the Working Standard ...... 32 B.—Comparison of the “ SETAC ” with the “ SFERT ” ...... 33 C.—Instructions for the use of a “ SETAC ” ...... 36 D.—General Remarks concerning the Carrying out of the Tests ...... 43 E.—Periodic Calibration of the Standard Instruments by the “ SFERT ” Laboratory . . 46

Addendrtm No. 1 to A p p en d ix No. 1. Essential Clauses of a Specification for the Supply of Repeating Coils (Toroidal Coils). . . .• ...... 48 Addendum No. 2 to A p p en d ix No. 1. Sample Calibration Sheets ...... 50

■Addendum No. 3 to A p p en d ix No. 1. Experiments to Determine the Normal Calling Intensity to be used in Phonometric Tests . , ...... 51 A p p en d ix II. Note on Working Standard Systems using Electro-magnetic Transmitters (“ S E T 'E M ” ) ...... '. .. 51 A.—Description of the “ SETEM ” Working Standard System ...... 51 B.—Comparison of the “ SETEM ” with the “ SFERT ” ...... 54 C.—Instructions for using a “ SETEM ” ...... 57 D.—General Remarks concerning the Carrying out of Tests ...... 59 E.—Periodic Calibration of Standard Instruments by the “ SFERT ” Laboratory . . . . 59

General Method to be employed for Testing Syllable Articulation ...... 60

A ppendix. Comparative Articulation Tests in Various Languages. (Technical Report No. 4 of the “ SFERT ” Laboratory) ...... 62 I.—Normal Articulation Tests ...... 62 II.—International List Test ...... 64 (A.a.2 .) Recommendations of Principle ...... 66 Practical Limits of Transmission Equivalents ...... 66 T ran sien t Phenom ena ...... 67 Possibility of Standardisation of Long-Distance Telephone Systems ...... 67

(A.b.) General Rules concerning the Composition of Transmission System s...... 69 (A.b.2.) Carrier Current Telephony ...... 69 (A.b.3.) Radio-broadcast Transmission ...... 69 Maximum and Minimum Transmission Levels to be adopted for Radio-broadcast Transmissions 69 Conditions which Open-wire Lines must fulfil in order to be used for Radio-broadcasting.. 70 Alterations to be made in Cable Circuits in order that they may be suitable for Broadcast T ransm ission ...... ’...... 70 Electrical Conditions to be considered as a Criterion for the good Condition of Lines for relaying Radio-broadcast Transmissions ...... 71 (A.b.4.) Picture Transmission ...... ' ...... 72 Conditions relating to Picture Transmission over Telephone circuits - ...... 72

(A.c.) Apparatus . . ' . . 73 (A.C.l.) Subscribers’ Instruments ...... 73 Tests of Subscribers’ Instruments and Lines in Operation ...... 73

(A.C.2.) Local Exchanges ...... 74 General Conditions which should be satisfied by the new Bourse Exchanges regarding the use of International Circuits ...... 74 iv IV.—Questions of Transmission, Maintenance and Supervision, &c.—continued. Page (A.C.3.) Toll Exchanges. Conditions to be satisfied by Cord Circuit Repeater Positions from the Point of View of Facilities for Regulation of the Repeater, as well as for Supervision, and Charging of Calls ...... 75 Conditions to be satisfied by International positions as regards the Type of Operator’s Set and the Transmission Losses due to the Operator listening on the Line ...... 75

(A.C.4.) Repeater Stations ...... 76 Compensation of the Effects due to Temperature Variations ...... 76

(A.d.) Lines ...... 77 (A.d.l.) Open-wire Lines ...... 77 Loading of Open-wire Lines ...... 77 Setting up of Open-wire Lines ...... 77 (A.d.3.) Mixed Lines. Rules for the Construction and Loading of Cables inserted in Open-wire Lines . . . . 79

(A.e.) Maintenance and Supervision of Lines and Installations...... 80 Extract from the List of Periodical Tests for the Maintenance of International Circuits . . 80 A p p en d ix I. Definition and Measurement of Attenuation due to Echo (“ Singing Point”). . 81 A p p en d ix II. The Measurement of Impedance Unbalance ...... 84 Suggested Instructions for putting into service and maintaining International Telephone C ircuits ...... 96 A.—Setting up and putting into service International Circuits...... 96 B.—Routine Tests to be made in. order to ensure satisfactory Operation of the Circuits . . 98 Application of the Instructions for putting into service and maintaining International Telephone Circuits ...... •...... '. 101 A ddendum I. Crosstalk Tests ...... 110 Maintenance of Circuits used for the relaying of Broadcast Transmission ...... 111 Division of Responsibility between Telephone Administrations and Radio-broadcast Services (State or Private) regarding the maintenance of Circuits used for the relaying of Broadcast Transmissions ...... in Technical Responsibility in connection with the renting of International Telephone Circuits to Broadcasting Authorities ...... in Instructions to Broadcasting Organisations and to Terminal Exchanges or Repeater Stations of Telephone Administrations for putting into Operation a Connection to be used for Broadcast Transmission and for the Re-establishment of this Connection in its Normal Service ...... 112 A p p en d ix to the Questions concerning Supervision and Maintenance of International Telephone Lines...... 113 Description of Apparatus for making Transmission Measurements ...... 113

(A.f.) Coexistence of Telephone and Telegraph Circuits in the same Cable ...... 119 I.—Simultaneous Telegraphy and Telephony (over the same Conductors) or Infra- Acoustic Telegraphy ■ ...... 119 II.—Coexistent Telegraphy and Telephony (over separate Conductors) ...... 120 III.—Voice Frequency Telegraphy ...... 120

(A.g.) Co-ordination o£ Radio Telephony and Telephone Systems ...... 120

B. Essential Clauses of Typical Specifications ...... 123 A p p en d ix B.b.2. No. 1. Instructions for drawing up a typical Specification for the Supply of a Multiple Telephone Installation using High Frequency Carrier Currents for International Service ...... 123 A p p en d ix B.b.2. No, 2. Instructions for drawing up a Specification for the Supply of a , ‘ High Frequency Repeater Station ...... 125 A p p en d ix B.b. No. 3. Essential Clauses of a Typical Specification for the Supply of Repeaters and Special Correctors for the Relay of Radio Broadcast Transmission .. 126

V IV.— Questions of Transmission, Maintenance and Supervision, &c.— continued. Page A p p en d ix B.C.4. No. 1. Essential Clauses for a Typical Specification for the supply of Two-wire Telephone Repeaters ...... 127 A p p en d ix B.c.4. No. 2. Essential Clauses for a Typical Specification for the Supply of Four-wire Telephone Repeaters ...... 128 A p p en d ix B.d.2. No. 1. Essential Clauses for a Typical Specification generally applying to Factory Lengths of International Telephone Cables of the Quadded Type . . . . 129 A ppendix B.d.2. No. 3. Essential Clauses for a Typical Specification for Repeater Sections of Loaded International Telephone Cable ...... 134 System No. Ia ...... 135 System No. Ib ...... ' ...... 138 System No. II ...... ' ...... 141 A p p en d ix B.d.2. No. 5. Essential Clauses for a Typical Specification of General Application to Loading Coils for International Telephone Cables ...... 143

C. Appendices. List of Appendices on Transmission Questions ...... 145 A p p en d ix A.c.3. No. 1. Cord Circuit Repeaters used at Amsterdam, operating always at the same gain ...... 145 A p p en d ix A.C.3. No. 2. System of Cord Circuit Repeaters used in Great Britain . . 146 A p p en d ix A.C.3. No. 3. Automatic Gain Control of Cord Circuit Repeaters . . . . 150 A p p en d ix C.c.i. No. la. British Post Office Method of Measuring the Transmission Efficiency of a Subscriber’s Installation from the Central Office ...... 154 A p p en d ix C.c.i. No. 1/3. British Post Office Method for Measuring the Efficiency of a Subscriber’s Station from the Central Office by means of Alternating Current. . . . 156 A p p en d ix C.C.I. No. 1y. A Method of Measuring by Speech Test, the sending and receiving efficiency of a Subscriber’s Installation in situ (alternative to the method described in A ppendix C.C.I. No. 1/3.) '...... 157 A p p en d ix C.C.I. No. 2. Methods adopted by the French Telephone Administration for testing Subscribers’ Installations in Operation ...... 162 A p p en d ix C.c.i. No. 3. Method used by the German Administration for testing a Complete Subscriber’s Installation from the Local Telephone Exchange ...... 168 A p p en d ix C.c.i. No. 4. Information concerning Methods utilised in the U.S.A. for testing Subscribers’ Instruments and Lines in Operation ...... 169

D. Bibliography...... 170 (a) German Publications ...... 170 (b) English Publications ...... 173 . (c) F rench P ublications ...... 176

V.—QUESTIONS OF TRAFFIC, OPERATION AND TARIFFS...... 177 A. General. Recommendation No. 4a. Establishment of the Nomenclature of the International Circuits and the Schematic Plan of the Cables...... 177 I. Form under which the Nomenclature of the International Circuits should be arranged 177 A p p en d ix 1. Form of Table for Establishing the Nomenclature of the International Circuits 179 A p p en d ix 2. Form of the General Summary of the International Circuits to be attached to the Nomenclature of the International Circuits ...... 180 . A p p en d ix 3. Form of List of Terminal Exchanges having several Designations to be attached to the Nomenclature of International Circuits ...... 181

II. Form under which the Schematic Plan of the Cables should be set up . . . . 181 Recommendation No. 6 a. Emergency Lines ...... 182 Recommendation No. 7a. Recommendations concerning the Establishment of Telephone Directories and the Conditions under which these may be purchased by the Public .. 184 vi V.—Questions o£ Traffic > Operation and Tariffs—continued. Page B. Various Glasses of Conversations and Facilities available to the Public. Recommendation No. 9a. Fixed-Time Calls by Subscription during the Heavy Traffic Period (except during the Hours of Maximum Traffic) 184 Recommendation No. 10a. Establishment of a Subscription Call with or from Telephone Stations other than those indicated in the Subscriber’s Agreement 185 Recommendation No. 14a. Calls demanded by Aeroplane Pilots in Cases of Forced Landings 185 C. Methods of Operation. Recommendation No. 18a. Method of establishing Calls with Preavis or Avis d’appel 185 Recommendation No. 21a. Bourse Calls 190 Recommendation No. 23a. Enunciation of Subscribers’ Numbers .... 192 Recommendation No. 24a. General Principles for Equalising Waiting Times in both D irections 193 D. Rates and Tariffs. Recommendation No. 35a. Rates applicable between Primary Zones of two Contiguous Countries ...... 194 Recommendation No. 35b. Rates applicable to Calls originating from, or to be completed at, a Public Call Box . . 194 Recommendation No. 35c. Rates applicable to Press Calls 194 Recommendation No. 37a. Picture Transmission between Correspondents over General Service Circuits (Conditions relating to Acceptance and Tariffs) . . 195 Recommendation No. 40a. Recording the Chargeable Duration of Calls 196 Recommendation No. 40b. Maximum Duration of a Call 196 Recommendation No. 41a. Checking the Number of Minutes of Conversation between Terminal Exchanges on International Lines...... 197 E. Typical'Form of Agreement between Administrations for International Telephone Service 197 F. Traffic Statistics. Recommendation No. 43a. Supervision of International Telephone Traffic 198

VI.—QUESTIONS CONCERNING THE PROTECTION OF LINES ...... 200 Modifications to be made to the “ Guiding Principles concerning measures to be taken in order to protect telephone lines against the disturbing influences of heavy-current or high- tension power lines ” (1926 Edition) . . 2bo Recommendations of the C.C.I. on the following points :— How can the Disturbing Effect of Harmonics from Direct Current Traction Installations be defined ? .. 200 Steps to be taken in the Case of Parallelism between International Telephone Lines and Direct Current Traction Lines 201 Permissible Limits for Induced Noise on Open-wire Circuits and on Cable Circuits 201 How can the Disposition of the Conductors of a TwoTvire Single-phase Line, and of a Three-phase Line, be taken into account in the calculation of the Noise Voltage on a neighbouring Telephone Line ? . . . . ., . . . . 201 Should Consideration be given to the Danger caused by a double accidental Earth on a Three phase Line with Neutral Point insulated ? 204 Comparative Study of various Protective Devices against Acoustic Shocks by means of Exchange of Apparatus between interested Administrations 205 Determination of the Coefficient of Mutual Induction 205 Length of Telephone Circuits to be used in the calculation of noise voltage 206

Vn.—MINUTES OF THE CLOSING S E SSIO N ...... 207 Appendix A. Definition of Noise at the End of an International Circuit 223 A p p e n d ix B. Various Methods of measuring Noise Voltages 223 A p p en d ix C. Permissible Limit for Induced Noise ...... 226 A p p e n d ix D. Arrangements for Collective Communications (Conference Calls) 227 A p p en d ix E. Suggestion by the International Standard Electric Corporation concerning the use of “ Noise Ratio ” as a Measure of the Balance of a Cable from the Point of View of Noise Induction ...... 229 VIII.—Index .. - • ,...... 235 vii COMITE CONSULTATIF INTERNATIONAL DES COMMUNICATIONS TELEPHONIQUES A GRANDE DISTANCE.

Plenary Session: Berlin: June 3rd-ioth, 1929.

L—LIST OF DELEGATES.

A.—DELEGATES FROM TELEPHONE ADMINISTRATIONS AND OPERATING COMPANIES.

1 . Administrations and Companies represented on the Committee.

A l b a n ia Not represented.

G e r m a n y Professor Doctor Breisig, Ministerial Councillor. Mr. Stegmann, Ministerial Councillor. Mr. Hopfner, Ministerial Councillor. Mr. Dohmen, Councillor, Higher Grade of Posts. Mr. Wiehl, Councillor, Higher Grade of Posts. Dr. Jager, Councillor, Higher Grade of Posts. Mr. Mentz, Councillor, Higher Grade of Posts. Dr. Klewe, Councillor of Posts. Dr. Craemer, President, German Long-Distance Cable Company. Dr. Liischen. Mr. Kaehler, Director of Telegraphs.

A u s t r ia Mr. R. Heider, Engineer, Ministerial Councillor. Dr. R. Oestreicher, Ministerial Councillor. Mr. H. Pfeuffer, Engineer, Councillor.

B e l g iu m Mr. Sadzot, Chief Engineer, Director General of Telegraphs and Telephones. Mr. Van Ubbel, Chief Engineer, Director of Telephones Mr. H. Fossion, Head of Department. Mr. Haemers, Engineer. C u b a Cuban Telephone Company. Mr. Frank Gill. Mr. P. E. Erikson. D e n m a r k (a) Delegates of the Administration. Mr. Christiansen, Chief of the Technical Division, Posts and Telegraphs. Mr. Gredsted, Chief of Division, Chief of International Service Telegraphs. Mr. Gottlieb, Telegraph Engineer. D e n m a r k (cont.) (.b) Delegate from the Commission of State Supervision over Private Telephone Companies. Mr. A. Petersen. (c) Delegate from the Copenhagen Telephone Company. Mr. L. Saltoft, Engineer. (d) Delegate from the Jutland Telephone Company. Mr. Nyholm, Engineer. D a n z ig . [Free City of) ■. . Dr. Eppich, Councillor, Higher Grade of Posts. Professor Kupfmiiller, Danzig Polytechnic University. •

S p a in . . .. Mr. A. Nieto y Gil, Chief of the Telegraph Service. Mr. G. Hombre y Chalbaud, Head of Department., Telegraph Administration.

E s t iio n ia Not represented.

F in l a n d Mr. L. T. Stahlhammar, Engineer in the Posts and Telegraphs Department.

F r a n c e .. Mr. Milon, Director of the Telephone Service. Mr. Drouet, Inspector-General, Director of Investigation and Technical Research. Mr. Rochas, Inspector-General. Mr. Barillau, Deputv-Director of the Telephone Service. Mr. Lange, Chief Engineer, Director of Long-Distance Underground Line Service. Mr. Le Corbeiller, Chief Engineer of the Investigation Service. Mr. Collet, Engineer in the Investigation. Service. Mr. Chavasse, Engineer in the Investigation Service. Mr. Pellenc, Chief Engineer, Director of the Broadcasting Service.

G r e a t B r it a in .. Colonel Sir T. F. Purves, the Engineer-in-Chief, British Post Office. Mr. H. Townshend, Principal, Secretary's Office, British Post Office. Mr. H. G. Trayfoot, Inspector of Traffic, British Post Office. Mr. S. C. Keyte, Accountant-General’s Office, British Post Office. Captain B. S. Cohen, Staff Engineer, .British Post Office. Mr. A. B. Hart, Staff Engineer, British Post Office. Mr. C. Robinson, Engineer, British Post Office. Mr. S. C. Bartholomew, Engineer, British Post Office. Dr. R. V. Hansford, Engineer, British Post Office (since deceased). -Mr! B. J. Stevenson, Engineer, British Post Office. Mr. A. J. Aldridge, Engineer, British Post Office.

H u n g a r y Dr. I. Tomits, Technical Adviser, Head of the Electrical Section in the Experimental Department. I t a l y Mr. C. Albanese, Head of Department, Experimental Institute of Communications. Mr. Baldini, Engineer, Chief of Section, Experimental Institute of Communications.

L e t t o n ia ...... Not represented.

L it h u a n ia .. .. Mr. B. Banaitis, Engineer. 2 L u x e m b o u r g .. .. Mr. L. Klein, Engineer, Inspector of Telegraphs. Mr. L. Hamus, Official in the Department of Posts, Telegraphs and Telephones. M e x ic o . (a) Ericsson'Telephone Company. Dr. M. Vos. Mf. T. Laurent, Transmission Expert. (b) Mexican Telephone and Telegraph Company. Mr. G. H. Nash. • - Mr. M. K. McGrath.

M o z a m b iq u e Not represented.-'' "" '

N o r w a y Mr. S. Abild, Chief Engineer to the Telegraph Administration. Mr. M. Wahl, Secretary to the Telegraph Administration.

H o l l a n d Jhr. W. M. de Brauw, Engineer-in-Chief of Telegraphs (since deceased). Mr. H. J. Claasen, Chief of the Telephone Division. Mr. A. H. de Voogt, Engineer, Telegraphs. Mr. F. Nauta, Secretary of Posts and Telegraphs. Mr. G. C. Snijders, Engineer, Director- of the Rotterdam Municipal Telephone Service.

P o l a n d Mr. S. Zuchmantovicz, Engineer, Chief of the Cable Bureau, Ministry of Posts and Telegraphs. Mr. J. Gize, Engineer, Director of the Tele-technical Laboratory, Ministry of Posts and Telegraphs.

P o r t u g a l Not represented.

R o u m a n ia Mr. J. Constantinesco, Engineer, Director of the Telegraph and Telephone Service. Mr. S. Condrea, Engineer, Head of the Investigation and Inspection Service. Mr. B. Paslaru, Head of Lines and Installations Service.

S e r b s , C r o a t s a n d Not represented. S l o v e n e s .

S w e d e n Mr. P. J. W. Llallgren, Head of Lines Section, Swedish Telegraph Administration. ■ Mr. A. Lignell, Director of Telephones, Stockholm. Mr. A. V. A. Holmgren, Head of Department, Telegraph Adminis­ tration, Mr. A. H. Karlsson, First Secretary to the Telegraph Administration. Mr. G. E. Swedenborg, Engineer in the Telegraph Administration.

S w it z e r l a n d , Mr. A. Muri, Head of Technical Section, General Administration of Telegraphs. Dr. J. Forrer, Head of Electro-technical Experimental Section and of Control of Material. Mr. A. Moeekli, Head of Telephone Department.

C z e c h o -S l o v a k ia Mr. S. Chocholin, Engineer, Ministerial Councillor. Mr. V. Kucera, Ministerial Councillor. Mr. F. Schneider, Engineer, Chief Technical Adviser. U n io n o f S o v ie t Mr. Ermolov, Chief of the Telephone Department. S o c ia l is t R e p u b l ic s Professor Jouriew, Director of the Central Laboratory of Posts, Telegraphs and Telephones. Mr. Lakhmann, Deputy-Director of Posts, Telegraphs and . Telephones, North-West Area. Mr. Botcharov, Head of Division on International Electrical Relations. <

2 . Representatives of Telephone Organisations, not belonging to the C.C.I., but invited to be present at the Plenary Session.

(a) American Telephone and Telegraph Company. Mr. H. E. Shreeve. Mr. W. H. Martin. Mr. C. H. G. Gray.

(b) Telephone Administration of Japan. Mr. Nagashima, District Chief Engineer. Mr. Yamada, Ministerial Councillor. Mr. Abiko, Legal Adviser, Interpreter.

(c) •Telephone Administration of Persia. Mr. Assadollah Khan Dariusch.

3 . Representing the International Bureau of the Universal Telegraph Union. Dr. J. Raber, Director of the Bureau.

4 . Representing the International Consultative Technical Committee on Radio Communications. Dr. de Vos, Chief Engineer of the Radio-Electric Service of the Royal Dutch Telegraph Administration.

5 . Representing the International Consultative Committee for Telegraph Communications. Mr. Stahl, Director of Posts (Germany).

B.—DELEGATES FROM ELECTRO-TECHNICAL ASSOCIATIONS.

1 . International Electro-technical Commission (Observer). Dr. Heidecker, Member of the German Electro-technical Committee.

, 2 . International Union of Railways.

G e r m a n y . . . . Mr. Schulze, Chief Technical Adviser to the German Railways. Mr. Schieb, Technical Adviser to the German Railways, Dr. Wechmann, Director of the German Railways. Mr. Staeckel, Director of the German Railways. 4 F r a n c e .. ... Mr.' Leboulleux, Chief Engineer, Permanent Way Department, Paris-Orleans Railway Company. Mr. Villeneuve, Chief Engineer of the Technical Service, Midi Railway Company.

I t a l y ...... Mr. Dorati, Chief Inspector of the Italian State Railways. Mr. Micarelli, Chief Inspector of the Italian State Railways.

S w e d e n .. .. Mr. Billing, Chief Engineer of the Telegraph and Telephone Service of the Swedish State Railways.

S w it z e r l a n d .. .. Mr. Muller, Assistant to the Chief Engineer of the Electrification Division of the Swiss Federal Railways.

3. International Union of Producers and Distributors of Electrical Energy.

Mr. Garczynski, Chief Engineer of the Compagnie Generale du Gaz pour la France et l’Etranger.

4. Electrical Engineering Societies.

Mr. C. W. Marshall, Representing The Institution of Electrical Engineers.

C — SECRETARIAT OF THE C.C.I.

Mr. Valensi, Secretary-General. Mr.' Bigorgne, Assistant Secretary. Mr. Gosselin, Assistant Secretary. Mr. Hubert, Assistant Secretary. Mr. Mocquard, Assistant Secretary. Mr. Rebillat, Assistant Secretary. Mr. Lavoignat, Office Manager.

5 A 3 II.—MINUTES OF THE OPENING SESSION.

The meeting opened at 10 a.m.

Dr. Breisig : According to our rule and to the tradition of several years, I have the honour, as chief delegate of the inviting Administration, to open the Sixth Plenary Session of the C.C.I. in Berlin. Since the last Plenary Session, we have had the misfortune to lose three of our most estimable and amiable colleagues. They are Messrs. Van Embden, Dethioux and Bocquet. Their ability, zeal and high qualities of character make us realise the extent of our loss, and I feel certain that all their colleagues will keep them in pious and unalterable remembrance.

Gentlemen, I have the honour to extend to you all, delegates of the Foreign Administra­ tions who have made tiring journeys in order to give us the honour of holding the C.C.I. Plenary Session in Germany, a most cordial welcome on behalf of the German delegation. I am happy to state that the membership of our committee has been considerably increased since our last meeting. Among telegraph Administrations who have notified their adhesion we may mention that of the Free City of Danzig. . Further, as a result of the advice given by the A.P. of Paris, 1928, with respect to the participation of private companies exploiting telephone services, we are pleased to notice among us the delegates of the Cuban Telephone Company, and of the two telephone companies of Mexico, i.e. the Ericsson Telephone Company and the Mexican Telephone and Telegraph Company. We are also glad to welcome, as the guests of the Plenary Session, engineers of the American Telephone and Telegraph Company, and of the Japanese and Persian Administrations. The American engineers have already collaborated with the C.C.I. With regard to the Japanese engineers, we hope that the impression created by our work will incline their Administration to decide to be represented on the C.C.I., because the Japanese system will, before long, be connected to the system of Administration, either in Europe or in America, which are represented on our committee. In addition to the delegates of the Administrations, 1 welcome the representatives of the Allied Institutions of the Universal Telegraph Union, namely, of the International Bureau of Berne and of the International Consultative Committees for Telegraph and Radio-telegraph Communications. Then we shall have, as from this evening, the pleasure of welcoming delegates of the international electro-technical associations with whom we are now accustomed to collaborate in the most friendly manner. We hope that the sixth A.P. will follow the happy and honourable example of the five preceding A.P.s, of which ah those who have been present retain happy memories. These .A.P.s. have contributed considerably to the valuable progress that has been made in the realm of long-distance telephony. They have left with us the memory of happy hours in which we have experienced the progressive strengthening of the personal bond between the members of the great fraternity of international telephone engineers. On our side we have done everything possible to provide a suitable environment for the present A.P., and to arrange for our esteemed guests recreations which may enable them to

6 maintain their efficiency for the strenuous work which lies before them. Fortunately, you are here in the spring, the season in which the charms of our country are seen at their best. . I hope that the weather will be good enough, on the occasion of the technical visits, to enable us to show you some of the beautiful country in which the Marches of Brandenburg are so rich. The sixth A.P. of the C.C.I. in Berlin in 1929 is now opened, and its first task is to elect its President. Sir Thomas Purves : Several times before, in Paris, I have had the honour, of proposing • as President of the C.C.I., the beloved name of Mr. Milon—Mr. Milon, upon whom we all look as our Standard President: but here in Berlin we are in the homeland of our dear Doctor Breisig. Dr. Breisig, who has contributed so much, has frequently shown that he possesses all the qualities of an ideal president, and I am sure, gentlemen, that I shall have the assent of the entire assembly in proposing that Dr. Breisig be invited to fill, in his own country, the duties of President.' (Applause.) Dr. Breisig : Gentlemen, I am deeply touched by the kind words of Colonel Sir Thomas Purves, and by your applause. I accept with sincere thanks the honour of being President. I shall do my very best to justify the confidence shown in me. I imagine that the Plenary Session is prepared, as hitherto, to sub-divide the work into three main parts; and I propose as Vice-Presidents : Colonel Sir Thomas Purves, for meetings dealing with transmission questions; Mr. Milon, for meetings dealing with questions of traffic, operation and tariffs. If you will allow me, I shall myself preside over the sessions dealing with questions of protection, in addition to presiding over the opening and closing sessions. Are these suggestions acceptable ? (Applause.) . Sir Thomas Purves : I did not expect to be called upon so quickly; I feel honoured * by your choice, and accept with pleasure.' Mr. Milon : I wish to associate myself with the thanks expressed by Sir Thomas Purves; I shall endeavour to merit the confidence of Colonel Sir Thomas Purves,- and I accept the Vice-Presidency. Dr. Breisig : I shall now ask the Secretary-General to give you the details of the reports contained in the records on the special questions.

Mr. Valensi : Allow me, in the first place, to express my pleasure at meeting again our worthy colleagues of previous Plenary Sessions, and at making the acquaintance of new delegates or guests, who are present for the first time at the C.C.I. meetings. I should like also to express to the Minister of Posts, Telegraphs and Telephones of Germany, also to the Assistant Secretaries and High Officials of the German Reichspost the deep gratitude of the Secretariat of the C.C.I. for the spacious and well-furnished premises which we found on our arrival in Berlin. I would also ask Dr. Breisig to express to the German Reichspost our thanks for its generous contribution towards the expenses of the journey, and of the sojourn in Berlin of the personnel attached to the Secretariat of the C.C.I. Allow me now to give you some explanation and information regarding the notes which the heads of the Delegations have found at their respective places : The first note is the suggested time-table for the Plenary Session in Berlin, 1929; it only differs from that sent to the Telephone Administrations in May, 1929* in that the

'7 A 4 Plenary Session on transmission, intended to be held on Monday, June 3rd, between 11 a.m., and noon, has been cancelled. This session will be replaced by meetings of commissions. The second note is the list of questions submitted for consideration by the Plenary Session in Berlin. The third note relates to the meetings of commissions proposed for the first days of the Plenary Session. A general meeting will first be held of the First and Third Commissions of Assessors for the examination of questions regarding unbalance in telephone circuits, and of induced noises on telephone circuits—these questions having been studied separately by the two Commissions, each one taking a different point of view. Further, a report on administrative questions, which appears in the notes presented to the Heads of the Delegations, sets forth numerous questions of organisation, for the settlement of which it would appear desirable to call a meeting this morning of an Organisation Committee, which will prepare a report for the meeting of the Heads of Delegations which is to decide everything in connection with the organisation of the C.C.I. and of the budget. This proposal being accepted, the Organisation Committee is constituted in the following manner :— President: Dr. Breisig [Germany). Members : Mr. Heider (Austria). Mr. Sadzot (Belgium). Mr. Gill (Cuba). Mr. Milon. (France). Col. Sir Thomas Purves (Great Britain). Mr. Nash (Mexico). Mr. Hallgren (Sweden). Mr. Muri (Switzerland). Mr. Botcharov (U.S.S.R.) Mr. Raber (Director of the International Bureau of the Telegraph Union, Berne). Mr. Valensi : Furthermore, as a result of the proposals of the Sixth Commission of Assessors assembled at Copenhagen in April, 1929, it is desirable to set up a Special Committee' to decide upon :— (a) Emergency lines for use in cases of breakdown on the normal routes, to maintain telephone communication between the different European countries, taken two at a time ; , (&) The tariffs applicable to these emergency lines. Heads of Delegations are requested to fill in, on the special form attached to the notes which have been supplied to them, the name of the member of their Delegation who will attend the meetings of this Special Committee. Finally it is necessary definitely to establish the Mixed Commission of Telegraph and Telephone Engineers which was proposed at the last Plenary Session of the C.C.I., Paris (June, 1928), for the solution of questions regarding the transmission of pictures, and simultaneous or co-existent telephony and telegraphy. The International Consultative Committee for Telegraph Communications has appointed its representatives in this Mixed Commission of Telegraph and Telephone Engineers, as follows :— ■ Messrs. Hopfner, Stahl, Kunert (Germany). Messrs. Lange, Montoriol, Belin, Mesny (France). Colonel Sir Thomas Purves (Great Britain). Mr. De Boer (Holland). Mr. Holmgren (Sweden). Mr. Muri (Switzerland).

8 Similarly, the International Consultative Committee for Long-Distance Telephone Communications must nominate representatives for this Commission; it seems natural that the members of the Third Commission of Assessors, who study all questions respecting transmission, should represent the C.C.I. Telephones. This suggestion was adopted. • Mr. Valensi : The notes handed to .the Heads of Delegations contain, among other things, various particulars relating to visits to the works of the Allgemeine Elektrizitats Gesellschaft, and of Messrs. Siemens & Halske, as well as to the official visit to the Reichspostzentralamt. Finally these notes contain a report on the budget of the C.C.I. and a report of the management for the year 1928-1929. There now remains the establishment of a Bureau of the Secretariat for the Plenary Session in Berlin, 1929. I have the honour to propose to the Assembly as Secretaries :— For questions concerning the protection of telephone lines Mr. Hubert. For questions of transmission, and of maintenance of lines :— Mr. Mocquard, Mr. Gosselin and Mr. Bigorgne. For questions of traffic, operation and tariffs :— Mr. Rebillat. For questions of both a technical and operating character - Mr. Bigorgne. These suggestions were accepted;

The President : I thank the Secretary-General for the explanation which he has just given. It is obvious that he is always equal to his task. The session will be adjourned for a few minutes in order to allow the Heads of Delegations to acquaint themselves with the contents of their notes. The session re-assembled at 10-45 a.m.

Mr. Arendt, representing the Minister of Posts, Telegraphs and Telephones of Germany, came to greet the Plenary Session. Mr. Arendt : If you will allow me, gentlemen, I will interrupt your work for a few minutes. You have just inaugurated the Sixth Meeting of the International Consultative Committee for Long-Distance Telephone Communications. During the last five years, we have observed remarkable developments in the international telephonic service. It was not so very long ago that international telephone communications were restricted to relatively short distances, and that the idea of communicating between the various capitals in Europe could not be looked upon as being capable of realisation. It was thought that with loaded cables and repeaters, all difficulties had been overcome, and that all obstacles which prevented the telephone from being used over the same distance as the telegraph had been surmounted. In practice, however, fresh obstacles seemed constantly to appear, and the International Consultative Committee for Telephone Communications has alone been able to overcome them. It is to the work of the technical and operating experts attached to the C.C.I. that we owe the great success which enables us to telephone from one corner of Europe to the other. This progress is being continued. New inventions h'ave been submitted, by means of which it is possible to surpass anything that has been done already, to telephone over practically unlimited distances. In London, Paris, The Hague, and Beilin, radio telephone communications are maintained for commercial service between 9 Europe and North America, South America and the Dutch Indies. Tests have been made with Persia, with Siam, and even with Australia. Discussions have begun on the question of laying trans-Atlantic cables for simultaneous telephone and telegraph services, and one of these cables is the subject of serious study, as it is hoped to put it into service in the near future. This, then, represents a great amount of important work for the development of the international service, and, one may even say, of a world-wide system. The International Consultative Committee for Telephone Communications, started as a Pan-European organisation, is about to enlarge its scope, by including representatives of all members of the great Universal Telegraph Union. At the last Plenary Session in Paris, in 1928, you decided to meet in Germany in 1929, and you have entrusted the Presidency of this meeting to Dr. Breisig, the representative of the German Administration. The German Reichspost, gentlemen, has asked me to thank you for your choice, and my Minister has asked me to express to you the great honour and pleasure which is his in welcoming you to Berlin. I hope that your work will leave you sufficient time to visit our city and to see some of its surroundings. Our Minister invites you to join him at dinner on Wednesday evening, as he has a great desire to know you personally. If you wish to visit the technical installations, as well as the Telegraph and Telephone Offices of our Administration, all facilities will be given you. I think, however, that it is inadvisable for a man to do nothing but work when he is in a foreign country. The great importance of all kinds of international meetings lies in the fact that they give to participants an opportunity of getting to know each other personally. We know one another through our work, we know the requirements of our calling. One can know a man, and his strong and weak points, only by meeting and knowing him. To know one another is to understand one another. It is my opinion that where such reciprocal understanding exists it naturally leads to collaboration in mutual efforts to develop the technique. In this sense, my dear colleagues and friends, I hold out the hand of welcome to you, and wish you every success. (Loud applause.) The President : Dear Mr. Arendt, in the name of the Plenary Session, I thank you very much for your kind words. The C.C.I. is proud of being generally regarded as the Consulting Engineer to. the Administrations, devoted to its task, but leaving to the Administrations the final decision whether the recommendation of the Committee can be applied, in practice, by every country. The fact that the recommendations *of the Committee have been adopted almost without exception, shows at once that the Committee has kept strictly to the principle laid down, and illustrates the confidence which the Administrations have felt in the results of its deliberations. I would ask Mr. Arendt to give our thanks to the Minister for his greetings and kind invitation. (Loud applause.) The opening session closed at 11 a.m.

10 III.—QUESTIONS OF GENERAL ORGANISATION.

A dvice of the International C onsultative C ommittee concerning Q uestions of G eneral O rganisation.

Organisation and Working of the International Consultative Committee for Long- Distance Telephone Communications.*

The International Consultative Committee comprises three divisions : (a) The Plenary Assembly (AP); (b) The Secretary-General (SG); (c) The Commissions of Assessors {Rapporteurs) (CR).

{a ) The Plenary* Assembly. 1. The AP meets normally once a year, so far as possible between the ist of April and the 15th of June. ' Such Administrations, belonging to the International Consultative Committee, as wish to be represented at a certain AP are obliged to advise by telegram or letter addressed to the SG the names of the members of their delegations, and particularly the names of the chiefs of the delegations. Each delegation thus introduced has one vote. No person shall be authorised to attend a Plenary Session of the C.C.I. as the representative of a manufacturing company (manufacturing telephone material). The resolutions put to the vote are considered as accepted if they obtain a majority of votes. The minutes will indicate the results of the voting without indicating the delegations which have voted for or against. The corresponding resolutions will also refer to these results in the following form :— “ The International Consultative Committee .... unanimously advises ....”, or, " The International Consultative Committee .... passes by ... . votes, against.... votes, the resolution . . . It is not permitted that a delegation shall vote on behalf of an Administration not represented. 2. The first meeting of the AP is opened by the Administration of the country where it is held. • . It begins by electing the President and the Vice-Presidents and, on the proposal of the Secretary-General, nominates the Secretaries. 3. The function of the AP is to approve, reject, or modify the reports presented, after having, if necessary, referred them to the competent Commission. 4. The AP decides what further questions shall be specially studied.

* This text replaces that under the same heading on pages 19-22 of the Green Book; English translation, 1928, pages 11-12. II 5- At the closing meeting the SG gives a summary of the work of the Conference, containing particularly the resolutions approved and the list of questions which have yet to be examined; the AP appoints until the following meeting the Administrations who will be asked to nominate members of the various Commissions. In addition, it will decide the town where the next. meeting will be held. 6. Experts belonging to other groups or organisations dealing with questions likely to have a bearing on international telephony may be invited by the AP to be present at certain meetings. 7. The AP appoints three Auditors of Accounts, entrusted with examining the budget proposals for the ensuing year and the accounts of the past year.

(b) The Secretary-General. 1. The SG is the Director of the Office of the International Consultative Committee. He is elected by the AP for an indefinite period, but with reciprocal powers of terminating his engagement at the end of each calendar year. As confidant of all the Administrations it is desirable that, for the period of his office, he should not be entrusted with any active service in his Administration. His salary as Secretary-General is payable out of the budget of the International Consultative Committee and is fixed by the AP. His residence is decided by the AP. An office, maintained out of the budget of the C.C.I., shall be at his disposal for his work. 2. The SG conducts the entire correspondence of the International Consultative Com­ mittee. When required, the SG will get in touch with the Chief Assessor (Rapporteur) of the Commission of Assessors to which a question raised would belong, according to its nature. 3. In order that he may always remain in direct contact with the progress of engineering questions, the SG is authorised to attend the special meetings of the Commission of Assessors. The Administrations will allow the SG to visit their installations and will procure for him all the necessary information. The expense incurred on this account will be chargeable to the International Consultative Committee. 4. The SG makes arrangements for the next conference of the AP. He prepares the agenda for this meeting in accord with the reports submitted by the Commissions. In agree­ ment with the Administration of the country where the next plenary meeting will be held, he fixes the date of the meeting, and takes all necessary steps in this connection. . 5. The SG will report to the AP on the activities of the Committee since the' last AP. During the first quarter of each year he prepares an account of the preceding year, drawn up as at'31st December, and approximate budget proposals for the following year, which he submits for the previous approval of the auditors before submitting them to the next AP. The expenses of the current year are met by means of contribution levies requested during the previous year. An emergency fund enables the period between two budgetary periods to be covered and to meet any unforeseen expenditure or expenditures in excess of the forecast of the budget.

(c) The Commissions of Assessors (Rapporteurs). 1. The AP appoints each year, the Commissions of Assessors (Rapporteurs)necessary to deal with the questions which it has submitted for study. 2. The function of the CR is to make a detailed study of new questions and present to the following AP a detailed report on each question complete, with proposed recommendations. 3. During the "meeting of. the AP, the CR holds itself at the disposal of the AP,

1 2 4. Membership of a CR is conferred for one year by the AP on certain Administrations. The latter appoint the persons who will represent them and advise the SG of their names. The choice of any Administration represented on a CR can be renewed without restriction. 5. Each CR elects a Chief Assessor [Rapporteur) who assumes the direction of the work of the CR. A CR meets at a convenient place in order to discuss the questions which it has-been entrusted to study, if the Chief Assessor considers this to be necessary. In such cases the travelling expenses of the representatives of an Administration are borne by that Administration. The CR are authorised to invite experts to participate in their deliberations. 6. The report drawn up by a CR, as well as all the documents which have been used to prepare this report, are sent to the Administration as early as possible, and always at least one month before the date of the AP. The Administrations will be asked to communicate this information to all the experts whom it considers may usefully be consulted. Questions which have not formed the subject of a report, prepared under the conditions indicated above, cannot be placed on the agenda of the AP.

Distribution of the Expenses incurred in the Operations of the International Consultative Committee.* The expenses incurred by the work of the C.C.I. will be divided between the partici­ pating countries in accordance with the following table, in conformity with that adopted by the Universal Telegraph Union in 1925 :— First Class.—Germany, United States of America, France, Great Britain, Italy and Union of Soviet Socialist Republics. Second Class.—Spain and Poland. Third Class.—Belgium, Cuba, Finland, Norway, Holland, Roumania, Sweden, Czecho­ slovakia, Jugo-Slavia. Fourth Class.—Austria, Denmark, Hungary, Mexico and Switzerland. Fifth Class.—Albania, Esthonia, Latvia, Lithuania and Portugal. Sixth Class.—Danzig, Luxembourg and Mozambique.

The nations in the first class shall each pay 25 units; those of the second class 20 units; those of the third class 15 units; those of the fourth class 10 units; those of the fifth class 5 units; and those of the sixth class 3 units. The contributing shares will be paid in advance on the first of January of each year, by cheque or warrant [virement de compte). The total annual expenditure shall not exceed 150 000 Swiss francs.

Distribution of Expenses for the Maintenance of the European Master Reference System for Telephone Transmission, f The expenses involved in the maintenance of the European Master Reference System for Telephone Transmission will be covered by means of the contributions made by the different Administrations attached to the International Consultative Committee.

* This text replaces that under the same heading on page 22 of the Green Book; English translation, 1928, page 13. f This text replaces that under the same heading on page 23 of the Green Book; English translation, 1928, page 13. Representation on the International Consultative Committee of Private Telephone Organisations operating in Countries where a State Telephone Administration exists.

The International Consultative Committee—

Considering :— .

The first paragraph of Article 91 of the International Service Regulations (Paris Revision, 1925) Unanimously advises

1. That the private telephone enterprises operating within the boundaries of an Administration belonging to the International Consultative Committee, be regarded as forming an integral part of the telephone system of that Administration with which lies the decision whether it is desirable to include representatives of these . private telephone enterprises in the delegation of the country interested in the Plenary Sessions of the International Consultative Committee; ■ 2. That at the meetings of the International Consultative Committee a single country can only have one delegation, representing at the same time both the State and the private telephone enterprises operating within the confines of that State ; the members of this delegation all being nominated by the State Administration of that country.

Membership of the International Consultative Committee of Private Telephone Administrations which operate in Countries where there is no State Telephone Administration.*

The International Consultative Committee—

Considering:—

That new telephone connections- may be opened between countries who are members of the C.C.I. and countries iri which no State Telephone Administration exists and where the operation is in the hands of private companies;

That one of these private companies may ask to collaborate in the work of the C.C.I.,

Unanimously advises :—-

That when the C.C.I. receives an application for membership from a private company controlling international terminal exchanges, the Government concerned should be approached in the usual manner, in order to ascertain :

(a) Which are the different companies operating such terminal stations in its. country;

(b) The companies wishing to collaborate with the C.C.I.

(c) The name of the head of the delegation representing these companies at the Plenary Assemblies of the C.C-.I., the head of the delegation having been' chosen by common agreement between the interested companies, or if such agreement. has not been attainable, by the Government concerned.

* This text replaces that under the same heading on page 28 of the Green. Book ; English translation, 1928, page' 14. Technical Collaboration between the International Consultative Committee and Technical Organisations dealing with Questions likely to have a bearing on International Telephony.

The International Consultative Committee unanimously advises :— (1) That it is. desirable to establish technical collaboration between the C.C.I. and all the technical organisations which deal with questions likely to have a bearing on International Telephony:—- International Consultative Committee for Telegraph Communications. International Consultative Technical Committee for Radio-electric Communications. International Union of Railways. International Electro-technical Commission. International Conference of the Chief Power Systems. International Union of Producers and Distributors of Electrical Energy. Committee on International Telephony of the International Chamber of Commerce. i International Union of Tramways, Local Railways and Public Motor Transport. Advisory and Technical Commission on Communications and Transit of the League of Nations Union. . Etc. (2) That it is desirable- to send to all these organisations the reports of the work of the C.C.I. which may interest them.

Methods to be followed in the Study of Questions of Interest both to the International Consultative Committee and to other International Organisations. ~ The International Consultative Committee— Considering :— That collaboration is desirable between International Organisations studying questions bearing on telephony. That the networks formed by long distance international telephone lines represent considerable capital. That the C.C.I. has taken the initiative in the studies and has been continuously engaged with questions relating to the establishment and maintenance of these networks. That, in particular, joint adaptation of these networks and of the various methods of transmission may give rise to important problems, of interest both to “telephone engineers and to engineers of other international organisations.

Unanimously advises (1) That— (1) Questions concerning the protection of telephone lines against the disturbing effects of electric power installations and the protection of cables against electrolytic coriosion continue to be studied by the Commissions of Assessors of the C.C.I. to which the experts of the organisations and groups interested are attached; (2) The question of loaning lines and telephone installations to 'broadcasting authorities for the relaying of broadcast transmissions continues to be studied by the Commissions of Assessors of the C.C.I., who could co-opt representatives of the International Consultative Technical Committee for Radio-electric Communications ■ and experts of the International Union of Broadcast Transmission. -

1 5 (3) That the C.C.I. is ready to take over or follow up studies concerning picture transmission and simultaneous or co-existent telephony and telegraphy, and that the best method in this respect would be to form a Mixed Commission of Assessors, nominated respectively by the Plenary Assemblies of the C.C.I. for Telephony and of the C.C.I. for Telegraphy. To avoid delay it is desirable that the joint report of • these experts should be submitted for approval, with the authority of the Administrations interested, to only one of these two Plenary Assemblies. (4) That the C.C.I. is willing to study the question of the co-ordination of broadcast telephony and of telephony for commercial purposes, and that the best method to be adopted would be the forming of a Mixed Commission of Assessors chosen by the Plenary Assemblies of the International Consultative Technical Committee for Radio-electric Communications and the International Consultative Committee for Telephone Communications.

Collaboration between the C.C.I. and the International Bureau of the Telegraph Union. The C.C.I., in agteement with the International Bureau of the Telegraphic Union, Considering:— That the development of telephony demands, in the interest of the Telegraph Union, a close collaboration between the International Bureau and the C.C.I.; That Articles 71, Section S, 83, 84, 85 and 86 of the Regulations of the International Telegraph Service (Paris Revision, 1925) define the respective activities of the International Bureau, and of the C.C.I., Unanimously advises:— 1. That the C.C.I. is to undertake the study of all questions concerning the technique and exploitation of international telephony as described in Article 71, S (2) of the Regulations, and make recommendations on these subjects; The International Bureau is authorised to participate, as consultant, in the deliberations at the Plenary Session of the C.C.I., and if it deems it advisable, at meetings of the Commission of Assessors dealing with traffic, operation, tariffs, and questions of organisation relating to the co-operation between the International Bureau of Berne and the C.C.I. 2. The recommendations of the Plenary Session of the C.C.I. are to be submitted by the Secretary-General for approval by the Administrations represented on the C.C.I.* 3. The Secretary-General of the C.C.I. is to send to the International Bureau all the documents of the C.C.I., and of its Commissions of Assessors dealing with questions of traffic, operation, tariffs, and questions of organisation concerning relations between the International Bureau and the C.C.I. Similarly/the International Bureau is to send to the Secretary-General of the C.C.I., circulars, notices and publications of the International Bureau relating to telephony.

Committee on Revision of the International Regulations (Telephone Section). The C.C.I., in agreement with the International Bureau of the Telegraph Union, Considering :— That the C.C.I. has made, in recent years, a great number of recommendations which have found practicable application;

* In the case of countries represented on the C.C.I. by private telephone companies, the Secretary - General will communicate with the Head of the Delegation in each of these countries, in order to ascertain whether the private companies approve of the C.C.I. proposals.

1 6 That it would be advantageous that these suggestions should be incorporated, in part, in the regulations of the International Telegraph Service ; That it might be useful to the Administrations, in view of the coming International Telegraph Conference in Madrid (1932), to have the proposed revision of the regulations, including the C.C.I; suggestions which have been approved by the participating Administra­ tions ; That a committee, specially set up for this purpose, and composed of representatives of the C.C.I. and of the International Bureau, could assist the Administrations.

Unanimously advises :— 1. That such a committee be constituted, in order to carry out the necessary work and to communicate its suggestions, as soon as possible, to the Administrations of the Telegraph Union. 2. That the International Bureau of Berne should examine the possibility of including, in the expenses of the International Telegraph Conferences, those of the Committee for the Revision of the Regulations.

B 1 7 IV. QUESTIONS OF TRANSMISSION, MAINTENANCE AND SUPERVISION OF LINES AND INSTALLATIONS.

Advice of the International Consultative Committee. (a) General. 1. Transmission Standards and Definitions. 2. Recommendations of Principle.

(b) General Rules concerning the Composition of Transmission Systems. 1. Ordinary Telephony. 2. Carrier Current Telephony. 3. Radio-broadcast Transmission. 4. Picture Transmission.

(c) Apparatus. 1. Subscribers’ Instruments. 2. Local Exchanges. 3. Toll Exchanges. 4. Repeater Stations.

(d) Lines. 1. Open-wire Lines. 2. Cables. (a) General. (/3) Aerial cables. (y) Underground cables. (8) Submarine cables. 3. Mixed Lines. (e) Maintenance and Supervision of Lines and Installations. (/) Co-existence of Telephone and Telegraph Circuits in the same Cable. (g) Co-ordination of Radio-telephony and Telephone Systems.

Essential Clauses of Typical Specifications.

Appendices.

Bibliography. A. ADVICE OF THE INTERNATIONAL CONSULTATIVE COMMITTEE ON LONG DISTANCE TELEPHONE COMMUNICATIONS.

(A.a.) General.* (A.a.i.) Transmission Standards and Definitions. Transmission Unit.

The International Consultative Committee— Considering that there is a general agreement regarding the nature and object of the transmission unit, that is to say, that it serves to express the ratios of apparent or real powers, voltages or currents in transmission systems, and that in practice the logarithms of these ratios shall be used. Considering that, as regards the use-of Napierian or decimal logarithms, the various Administrations reserve their opinions in favour of the one for which they have, for some time, presented numerous arguments. Considering, on the other hand, that a majority vote should not compel any Admini­ stration, belonging to the C.C.I., to adopt a unit of which it does not approve. Considering, finally, that converting test results from one system to another presents no difficulties,f because of the agreement reached in regard to the reference system.

Unanimously advises :— • 1. That, though in principle it is desirable, it does not appear to be possible, for’ the present, to adopt a common transmission unit. The Napierian or the decimal system of logarithms may therefore be used provisionally, as desired, by the Administrations, it being understood that, in international traffic, the two units shall be used indiscriminately, and no Administration shall claim the exclusive use of the unit it adopts. 2. That in the technical literature and particularly in the C.C.I. documents the trans­ mission equivalents, losses or gains, etc., shall be expressed in both units. •

Method of expressing Frequency. The International Consultative Committee— Considering :— That it is desirable to adopt a uniform method of expressing frequency, and of making selection between the expression of frequency in periods per second and the expression of the angular velocity in radians per second; That the first method has the advantage of. giving a physical representation more precise than the second, Unanimously advises :— That, all things considered, it is preferable to express frequency in periods per second, in accordance with common practice.

* This text replaces that on pages 32-62 of the Green Book; English translation, 1928, pages 20-43. f See Conversion Table of Transmission Units, Nepers and Decibels, page 20. i q . B 2 Definition of some Expressions used in Questions of Telephone Transmission. The International Consultative Committee proposes unanimously the. following definitions :— (a) Nepers and Decibels. In telephone transmission the relation between two magnitudes having the same physical dimensions is expressed by the logarithm of the relation. For instance, one speaks of the logarithm of the relation of two powers, leal or imaginary, of two voltages, of two currents, of two acoustic pressures, etc. In practice either the Napierian or decimal system of logarithms is used. If two powers P 1 and P 2 are concerned, the number of units is : In the Naperian system. In the decimal system. P P k loge y ; 10 log,, y ■

If two voltages V 1 and V 2 or two currents I x and /2 are concerned, the number of units is : In the Napierian system. In the decimal system.

i i Ji i Fi i 1 °g e 1V 7% or l°g e l2 T ; 20 lo8io W v 2 or 20 lo8io 12T •

Conversion Table between Napierian Logarithmic Units of Transmission (Nepers) and Decimal. Units (Decibels).

Nepers. Decibels. Nepers. Decibels. Nepers. Decibels. Nepers. Decibels.

O-T 0-869 2-6 22-584 5-i , 44-299 7-6 66-014 0-2 1-737 2-7 23-452 5-2 45-167 7.7 66-882 o -3 .2 • 606 2-8 24-321 5-3 46-036 7-8 67-751 o-4 3-474 2-9 25-189 5-4 46-904 7-9 68-619 o -5 4-343 3-0 26-058 5’5 47-773 8-o 69•488 o-6 5-212 3-i 26-927 5-6 48•642 8-i 70-357 o -7 6-080 3-2 27-795 5-7 49-510 8-2 71-225 o-8 6-949 . 3-3 28•664 5-8 50-379 8-3 72•094 o -9 . 7-817 3-4 29-532 5-9 5I -247 8-4 72-962 I -o 8-686 3-5 3° -4°i 6-o 52•116 8-5 73-83I I ■ I 9-555 3-6 31-270 6-1 52-985 8-6 74-700 1-2 10-423 3-7 32-138 6-2 53-853 8-7 75•568 1-3 11-282 3-8 33-oo7 . 6-3 54-722 8-8 76-437 i -4 12-160 3-9 33-875 6-4 55-590 8-9 77-305 i ’5 13-029 4-0 34•744 , 6-5 56-459 9-° 78-174 i -6 13-898 4 -i 35-613 6-6 57-328 9-i 79-043 i -7 14-766 4-2 36-481 6-7 58-196 9-2 79-911 i-8 I5-635 4 ’3 37-350 6-8 59-065 9-3 80-780 1-9 16-503 4 ’4 38-218 ■ 6-9 59-933 9-4 81•648 2-0 17-372 4'5 39-087 7-0 60•802 9-5 82-517 2 • I 18•241 4-6 39-956 7-1 61•671 9-6 83-386 2-2 19•109 4‘7 4.0-824 .7-2 62-539 9-7 84-254 2-3 19-978 4-8 41-693 7-3 63-408 9-8 85-123 2-4 20-84.6 4-9 42-561 7'4 64-276 9-9 85-991 2-5 21-715 5-o 43-430 7‘5 65-I45 10 ■ 0 86-86o

It is usual to call the results obtained with the Napierian logarithms “ nepers ” and those obtained with the decimal logarithms “ decibels.” These units give, therefore, an indication of the system of logarithms used. " "In 'th e official documents of the C.C.I. the units of transmission will be expressed in both nepers and decibels; as for example :

2 0 A transmission of 3 nepers or 26 decibels will be written in full thus “ nepers” or “ decibels.” In documents other than official C.C.I. literature, the symbols “ n ” for nepers, “ db ” for decibels, and “ dn ” for decineper, are sometimes used. In special cases hereafter the term “ determined ” means that the calculation must be carried out by means of the formulae given above.

(b ) Special Definitions. 1. The acousto-electric index (efficacite absolue, akustoelektrisches Verhaltnis) of any transmitting system at any frequency is the ratio of the voltage measured at the output of the system to the acoustic pressure measured on the. diaphragm of the transmitter at the frequency considered; the output of the system is assumed to be closed with an impedance of 600 ohms with zero angle; this ratio is expressed in volts per bar. 2. The electro-aeoustic index (efficacite absolue, elektroakustisches Verhaltnis) of any receiving system at any frequency is the ratio of the acoustic pressure to half the electro­ motive force of the generator, having an internal impedance of- 600 ohms with zero angle, connected to the input terminals of the system; this ratio is expressed in bars per volt. 3. The reference equivalent (equivalent de reference, Bezugsdampfung) of a transmission system (systeme de transmission, Ubertragungsystem) is the reading given by the Master Telephone Transmission Reference System when this Master Reference System is adjusted so as to give the same volume of sound at the receiver terminals as the system under consideration—the acoustic power supplied being identical in both instances. The sign of the reference equivalent is so chosen that a positive sign indicates that the system is less efficient than the Master Reference System. 4. The reference equivalent of a principal part of a transmission system (systeme emetteur—transmitting system—Sender ligne — line —Leitung systeme recepteur — receiving system ■—Empfanger) is the reading indicated by'the corresponding part of the Master Reference System when adjusted to give the same volume of sound at the receiving end before and after the substitution of the part under test for the corresponding part of the Master Reference System, the acoustic power supplied being identical in both instances. The sign of the reference equivalent is so chosen that a positive sign indicates that the part under test is less efficient than the corresponding part of the Master Reference System. 5. The relative equivalent (equivalent relatif, relative Dampfung) of a system A compared to another system B, or of a part of system A compared to the corresponding part of another system B, is the difference : a — b, where a represents the reference equivalent of A and b the reference equivalent of B. 6. The level (niveau de transmission, Pegel) of the power, of the current, or of the voltage at one point in a system is determined by the ratio of the value of one of these quantities to the value of the corresponding quantity which is chosen as zero reference. 7. The crosstalk (diaphonie, Nebensprechdampfung) between two systems—disturbing and disturbed—is determined by the ratio between the apparent powers obtained at given points on the disturbing and disturbed systems under specified terminal conditions (for example, by means of image impedances). 8. Image attenuation (affaiblissement image, Vierpoldampfung). This expression applies to a quadripole electric system terminated by its image impedances; it is determined by the ratios of the apparent powers at the ends of the system so terminated. 21 B 3 In the special case in which a homogeneous line, or more generally a line made up of identical symmetrical units, such as a coil-loaded line terminated at mid-section, is terminated by impedances equal to its characteristic impedance and is traversed by a sinusoidal current which has reached its steady state, we have—

v 2 h w 2 l o Se = l o Se = I l 0 g e F i h w x where V x, I x and W x represent the voltage, current and power respectively at one point, and V 2, 12 and W 2 the voltage, current and power respectively at another point. These expressions represent the attenuation (affaiblissement, Dampfung) of the line in question between the given points. The attenuation constant (constante d’affaiblissement or affaiblissement lineique, Dampfungskonstante) of a homogeneous line is the quotient of the image attenuation between its terminals divided by its length. It follows that the attenuation constant of a line made up of a number of similar units, such as a coil-loaded line terminated at mid-section, is the quotient of the image attenuation between its terminals divided by its length. ,

9 . Effective attenuation (affaiblissement effectif, Betriebsdampfung). The effective attenuation of a part of a system terminated by impedances Z x and Z 2 is determined by the ratio between the apparent power delivered by a generator of impedance Z x to a receiver of impedance Z i and the apparent power delivered byothe same generator through the part of the system in question to a receiver of impedance Z2. If this ratio is negative it is called the effective amplification (amplification effective, Betriebsverstarkung). In the particular case in which Z x — Z 2 — 600 ohms with zero angle, the effective attenuation is represented by the same number of units as the reference equivalent, as defined above. 10. The loss, or gain, introduced by a part of a system between an input impedance Z x and an output impedance Z2, is determined by the ratio of the apparent powers received in the impedance Z2, before and after the insertion of the part of the system between Z x and Z2. If the apparent power received by the impedance Z2 is greater than before the insertion of the part of the system, the result is a gain, and, conversely, a loss. If Z x — Z2 = 600 ohms with zero angle, the loss or gain thus defined is expressed by the same magnitude as the reference equivalent of the part of the system considered.

1 1 . Damping (amortissement, zeitliche Dampfung). This is a general term, indicating the decrease in a certain quantity (current, voltage, power, pressure, etc.) as a function of time. 12. Articulation and intelligibility.—The “ articulation ” (nettete pour les logatomes, Silbenverstandlichkeit) is characterised by the percentage of syllables in standard lists, correctly leceived, with respect to the total number of syllables transmitted; by “ syllable ” is understood the smallest possible vocal combination, i.e. the shortest possible element of speech. (Etymology :—Xoyos, element of speech; arofios, indivisible.) The “ intelligibility of words ” (nettete pour les mots, Wortverstandlichkeit) is characterised by the percentage of words forming standard lists correctly received with lespect to the total number of words transmitted. The "intelligibility of phrases” (nettete poui les phrases, . Satzveistandlichkeit) is characterised by the percentage of sentences of any text .correctly received with respect to the total number of sentences transmitted. The " intelligibility ” (intelligibilite, Sinnver- standlichkeit) is characterised by the percentage of words correctly received with respect to the total number of words transmitted in a continuous conversation. 22 TELEPHONE TRANSMISSION REFERENCE SYSTEMS. Object of Telephone Transmission Reference Systems. The International Consultative Committee— Unanimously advises :— That a Master Telephone Transmission Reference System, capable of being rigorously defined and of being reproduced exactly, is essential for procuring a constant base for trans­ mission measurements and for the co-ordination of the transmission data relating to the systems of telephony utilised in all countries. In addition, other systems must be adopted to determine—- 1. Transmission equivalents. 2. Relative equivalents. 3. Transmission losses and gains. 4. The articulation of a system or of one of its parts. 5. The coefficient of experimental practice of a team engaged in transmission measurements.

THE SETTING UP OF TELEPHONE TRANSMISSION REFERENCE SYSTEMS. The International Consultative Committee recommends that the number of types of Telephone Transmission Reference Systems should be reduced to three, as follows :— I. Master telephone transmission reference systems. Systeme Fondamental de Reference pour la Transmission telephonique. Ureichkreis fur die Fernsprechiibertragung. (The European Master System is referred to, briefly, as “ SFERT.”) II. Telephone transmission reference systems. Systemes .de reference pour la transmission telephonique. Haupteichkreise. III. Working standards. Etalons de travail. Arbeitseichkreise.

CONDITIONS WHICH SHOULD BE FULFILLED BY THE TELEPHONE TRANSMISSION REFERENCE SYSTEMS. I. THE MASTER TELEPHONE TRANSMISSION REFERENCE SYSTEM. This system is rigorously defined in the documents kept by the Secretary-General of the C.C.I. and at the Master Telephone Transmission Reference System Laboratory (Conservatoire des Arts et Metiers, 292, rue Saint-Martin, Paris).

II. TELEPHONE TRANSMISSION REFERENCE SYSTEMS. Each system is composed of a transmitting system, an artificial line and a receiving system complying with the following conditions :—

(1) TRANSMITTING SYSTEM. Definition of the Acoustic Input to the Transmitter. In order to simplify the definition of the referepce system, it is useful to start with the sound pressure rather than with the acoustic power. For the transmitter the ratio of the 23 B 4 voltage delivered to the input of the reference artificial line to the uniform sound pressure on the diaphragm of the reference transmitter is chosen as the measure of efficiency. Hence it is necessary to fix the essential external mechanical dimensions of the reference transmitter and the manner in which it is to be used. (See below.) .

Method of measuring the Acoustic Input to the Transmitter.

For the measurement of sound pressure any reliable method may be used {e.g., Thermo­ phone, Rayleigh Disc, or compensation methods).

Section of Electro-dynamic Receiver, Condenser Transmitter, and Acoustic Coupling Regulating Device.

24 Maximum permissible Acoustic Power for which the Transmitter is to be constructed. The maximum acoustic pressure depends upon the permissible non-linear distortion. It has been found that when the types of transmitters and receivers mentioned below, together with suitable amplifiers, are used, no appreciable non-linear distortion is produced over th,e range of sound pressures normally occurring.

The value of the Output Impedance of the Transmitting System. In order to have all required corrections in a positive direction it is convenient to select 600 ohms (zero angle) as the output impedance of the transmitting system. A tolerance of it 5 per cent, and an angle not greater than ±10° may be permitted over the frequency range 100 to 5 000 p.p.s.

Adjustment of the Efficiency of the Transmitting System. The output of the transmitting system must be adjustable in such a manner that its value can be assured with an accuracy of at least 0-02 neper or 0-2 decibel. This adjustment must be possible between limits of — 1 to -\- 1 neper or between the limits — 10 to -j- 10 decibels.

Ratio between the Acoustic and Electric Power (taken respectively at the Input and Output of the Transmitting System) defining the Zero Point of the Transmitting System. The zero point of the transmitting sj^stem should approximate to that of commercial standard systems in general use. (See p. 28. Normal adjustment of the “ S F E R T /’)

Band of Frequencies in which this Ratio must be Constant. Permissible Variations of this Ratio within this Band of Frequencies. The variations of this ratio must not exceed 31 0*2 neper or ^ 2 decibels in the frequency range between 100 to 5 000 p.p.s.

Maximum permissible Non-linear Distortion (a ) for the Maximum Power, (&) for a given Fraction of this Power. The maximum acoustic pressure on the transmitter depends on the permissible non­ linear distortion. Experience has shown that for normal intensity the use of the types of transmitter and of receiver specified below and associated with suitable amplifiers, does not give rise to any appreciable non-linear distortion.

Method of Construction of Transmitting System satisfying the required Conditions. A transmitting system composed of a condenser transmitter with stretched metallic diaphragm, and associated with a suitable amplifier would satisfy the above conditions. Any other type of transmitter satisfying equally well the above conditions would be accepted. The essential dimensions of the condenser transmitter are indicated in Fig. 1. To compensate for the variations which may occur a regulating device should be included in the transmitting system.

(2 .) REFERENCE ARTIFICIAL LINE. Characteristic Impedance of the Reference Artificial Line. The reference artificial line must have a characteristic impedance of 600 ohms (zero angle). A tolerance of 1 per cent, and an angle not greater than d; 2° may be permitted, over the frequency range 100 to 5 000 p.p.s. 25 • Adjustment of the Attenuation of the Reference Artificial Line. The attenuation of the reference artificial line must be adjustable by steps of 0*02 neper or o-2 decibel between the limits o — 6-nepers or o — 60 decibels.

(3 .) REFERENCE RECEIVING SYSTEM. Definition of the Acoustic Output furnished by the Receiver. The sound pressure delivered at the end of a metallic acoustic coupler should be regarded as a measure of the acoustic output. The essential dimensions, of this coupler are given in Fig. 2. It is necessaty to fix certain essential dimensions of the receiver in the same way as for the transmitter, and these are also given in Fig. 2.

Method of measuring the Acoustic Output of the Receiver. The measurement of the sound pressure, as in the case of the transmitter, may be carried out by means of any reliable method (calibration by means of a condenser transmitter and the sound pressure compensation method are in practical use).

The Value of the Electrical Impedance at the Input of the Receiving System. The impedance of the receiving system must be 600 ohms (zero angle). A tolerance of i 5 per cent, and an angle not greater than io° over the frequency range 100 to 5 000 p.p.s. may be permitted.

Adjustment of the Efficiency of the Receiving System. The efficiency of the receiving system must be adjustable in such a manner that its value can be assured to an accuracy of at least 0-02 neper or 0-2 decibel. This adjustment must be possible between limits of — 1 to -f- 1 neper or — 10 to -(- 10 decibels.

Ratio between the Electric and Acoustic Powers (taken respectively at the Input and Output of the Receiving System) defining the Zero Point of the Receiving System. The efficiency of the reference receiving system is determined by the ratio of the sound pressure of the acoustic coupler to the input voltage across the receiving system. The zero point of the receiving system should approximate to that of the commercial standards in general use. (See p. 28. Normal adjustment of the “ SFERT.”)

Frequency Range over which this Ratio must remain Constant. Permissible Variations of the Ratio in this Frequency Range. The variations of this ratio must not exceed ^ o • 4 neper or ^ 4 decibels for frequencies lying between 300 to 3 000 p.p.S. or ^ 1 neper or 10 decibels for frequencies lying between 100 to 5 000 p.p.s.

Maximum Non-Linear Distortion permissible in the Receiving System. (a) For Maximum Power, (b) for a given Fraction of this Power. The maximum acoustic pressure on the transmitter depends on the permissible non-linear distortion. It has been found that for sounds of normal intensity the use of the types of transmitter and receiver specified below, when associated with suitable amplifiers, does not give rise to any appreciable non-linear distortion. 26 Method of Construction of a Receiving System satisfying the required Conditions. Any system satisfying the above conditions is admissible. The earpiece of the receiver must have certain essential dimensions which are indicated in Fig. 2. Also the volume of the cavity bounded by the receiver diaphragm, the walls of the earpiece and the plane of contact with the acoustic coupler must be approximate^ the same as indicated in Fig. 2.

III. WORKING STANDARDS. Working standards are systems calibrated by voice and ear tests with a telephone transmission reference system. They are composed of a transmitting system, an artificial line and a receiving system. The transmitting and receiving systems should have transmission characteristics similar to those of commercial apparatus. Although it is more convenient to obtain working standards by choosing them from the usual types of commercial apparatus, it is permissible to use apparatus different from commercial types. Appendix I, p. 32. describes a working standard employing a carbon transmitter (“ SETAC ”), the method of comparing this standard with the “ SFERT ” gives advice on ' the use of such a standard, together with all information necessary for its periodic re- :alibration, and despatch, for this purpose, to the “ SFERT ” Laboratory. Appendix II, p. 51, describes a working standard without a carbon transmitter (“ SETEM ”), and using amplifiers, the method of comparing this standard with the “ SFERT,” and gives advice on the use of such a standard, togethei with all information necessary for its periodic re-calibration.

2 7 RECOMMENDATIONS REGARDING THE CALIBRATION OF REFERENCE SYSTEMS AND WORKING STANDARDS.

A. COMPARISON OF REFERENCE SYSTEMS WITH THE MASTER REFERENCE SYSTEM, AND THE PERIODS AT WHICH SUCH COMPARISONS SHOULD BE MADE. As a reference system, complying with the above-mentioned conditions, may differ from the Master System, the first calibration should be made, in the Master System Laboratory, using the complete transmitting and receiving systems (including the amplifiers) of the system to be calibrated. The first calibration will indicate whether subsequently it will be sufficient to calibrate only the transmitters and receivers of the reference system by comparison with those of the Master System. Until thorough experience of these tests has been obtained, it is desirable to repeat these calibrations every nine months, in order that they may be carried out under varying atmospheric conditions.

B. CALIBRATION OF WORKING STANDARDS REFERRED TO THE *“ SFERT.”

(See Appendices I, p. 32, and II p. 51.)

C. NORMAL ADJUSTMENT OF THE “ SFERT.”

Determination of zero levels 'of the transmitting and receiving systems of the Master Reference System. The characteristic curves of the transmitter and receiver of the “ SFERT ” will be . expressed, respectively, in terms of one volt per bar for the transmitting system, and one bar per volt for the receiving system. The values, for the different frequencies to be considered, of the ratios of volts per bar and of bars per volt, proposed for characteiising the zero level of the transmitting system and receiving system, with and without distortion, and the values in bars per bar for the complete reference system containing a line of zero decibels, are given in Tables I to V below. With each of these values is given the numbei of decibels corresponding to one volt per bar for the transmitting system, and to one bar per volt for the receiving system, and to one bar for the complete system. The maximum permissible deviations of the characteristic curves of the system, and of its components, for any frequency must not exceed ^0*1 neper or + 1 • o decibel from the values given in the tables attached. (For frequencies between 100 and 5 000 p.p.s.) The arithmetic means of the values given in Tables I to V, for frequencies between 200 and 3 600 p.p.s. inclusive, will be taken as the specification for regulation of the Master System without distortion, and for its components. In cases of deviation between the characteristic. curves of the transmitting and receiving systems without distortion, referred to the values given in the attached tables, the setting of the potentiometer for'each element will be changed by a quantity equal to the mean of the differences, in decibels, between the test results at the time considered, and the values given in the attached tables .(for frequencies given in these tables and between 200 and 3 600 p.p.s.) For the transmitting system and for the receiving system with distortion, the maximum permissible deviation for any frequency is the same as in the preceding case for components without distortion. To ensure that regulation at any instant takes into account deviations with respect to the values given in the attached tables, the arithmetic mean in decibels of the deviations obtained for the three frequencies 800, 1 100 and 1 300 p.p.s., will be taken. 28 In order to reduce the noise in the Master System to a negligible quantity, periodic tests will be made, in accordance with the proposals contained in the memorandum entitled “ Measurement of Noise induced in the components of the ' SFERT/ " dated May 23rd, 1929, to ascertain a measure of the noise, which can be produced by a condenser transmitter under service, conditions. Rules will be laid down for obtaining the characteristic curves of the “ SFERT ” and its components, and for exchanging test results every six months between New York and Paris. For these purposes it will be necessary to possess the following information : 1. Characteristic curves of each condenser transmitter and of its associated amplifier. 2. Combination of the characteristic curve of one of the condenser transmitters with that of its associated amplifier. 3. Characteristic curves of each electro-magnetic receiver (moving-coil type) and of its associated amplifier. 4. Combination of the characteristic curve of one of the ‘ electro-magnetic receivers with that of the associated amplifier. 5. The characteristic curves obtained with one of the condenser transmitters and one of the moving coil receivers, when attenuators are inserted in the corresponding amplifiers. The characteristic curves should be expressed in decibels, and referred to one volt per bar for the transmitters, and to one bar per volt for the receivers. Further, the test results of one of the condenser transmitters with four thermophones will be given.

TABLE I

C haracteristic V a l u e s o f t h e T ransmitting S y s t e m .

F requency. Volts per bar. D ecibels. Frequency. Volts per bar. Decibels.

100 0-0272 - 31-3 1 800 0-0263 —31 -6 200 0-0272 - 3i -3 2 100 0-0269 - 3i -4 300 0-0260 . ' — 3 1 ■ 7; 2 400 0-0269 - 3i -4 400 0-0257 - 3 1 - 8 2 700 0-0275 - 3 1 - 2 500 0-0253 — 31 ’ 9 3 000 0-0284 - 3° -9 600 0-0253 - 3i -9 3 300 0-0294 - 3 0 - 6 700 0-0253 - - 3i -9 3 600 0-0305 - 30-3' 800 0-0253 - 3J '9 4 000 0-0323 — 29-8 900 0-0257 - 3 1 - 8 5 000 0-0337 - 2 9 - 4 1 000 0•0257 - 3 1 - 8 6 000 0-0309 — 30-2 1 100 0-0257 - 31-8 7 000 0-0229 - 3 2 - 8 1 200 0-0257 - 31-8 8 000 0-0165 - 35‘7 . 1 300 0-0260 - 3i -7 9 000 O-0121 - 3 8 - 4 1 500 0-0263 — 31 ' 6 10 000 0-0092 - 4 0 - 7

Decibels referred to 1 volt per bar.

Average value Average value Frequency range in volts per bar. in decibels. '500-2 500 p.p.s. 0-0259 - 3i -7 200-3 600 p.p.s. 0-02656 - 3i -5 29 TABLE II

C haracteristic V a l u e s o f t h e R e c e iv in g S y s t e m .

Frequency. Bars per volt. Decibels. F requency. Bars per volt. Decibels.

100 16-4 24-3 1 800 17 • 6 24-9 200 I 7'4 24-8 2 100 17-8 25-0 300 17-6 24-9 2 400 16-2 24-2 ' 400 17-2 24-7 2 700 14-7 23-3 500 17-0 24-6 3 000 13-3 22-5 600 16- 8 24-5 3 300 12-3 21 • 8 700 16-8 24*5 3 600 11 • 1 20 • 9 800 16-8 24-5 4 000 10-5 20-4 900 16-8 24-5 5 000 12-3 21-8 1 000 17-0 24-6 ' 6 000 17-2 24 -7 1 100 17-0 24-6 7 000 1-4 -5’ 23-2 1 200 17-2 24-7 8 000 14-5 23-2 1 300 17 • 2 24-7 9 000 14-5 23-2 1 500 17-2 24-7 10 000 10 • 9 20-7

Decibels referred to 1 bar per volt.

Average value in Average value Frequency range. bars per volt. in decibels. 500-2 500 p.p.s. 17-03 24-6 200-3 600 p.p.s. 16-28 24-2

TABLE III

C haracteristic V a l u e s o f t h e S f e r t w it h o d e c i b e l in C i r c u it .

Frequency. Bar per bar. Decibels. F requency. Bar per bar. Decibels.

100 0 • 446 - 7 - 0 1 800 0-462 - 6 - 7 200 0-474 - 6 - 5 . 2 100 0-479 - 6 - 4 300 0-458 - 6 - 8 2 400 o -435 - 7 - 2 400 0-441 - 7-1 2 700 0 • 404 - 7 - 9 500 0-431 - 7'3 3 000 0-378 - 8 - 4 600 0-426 - 7 - 4 3 3oo 0-362 - 8 - 8 700 0-426 - 7 - 4 3 600 0-338 —9 -4 800 0-426 - 7-4 4 000 0-338 - 9 - 4 900 0-431 - 7’3 5 000 0-415 - 7 - 6 1 000 0-436 - 7 - 2 6 000 o - 53i - 5’5 1 100 0-436 - 7-2 7 000 0-332 — 9-6 1 200 0-441 - 7-i 8 000 0-239 - 1 2 - 5 1 300 0-446 - 7*0- 9 000 0-175 - 1 5 - 2 1 500 0-452 — 6-9 10 000 o -io o — 20-0

Decibels referred to 1 bar per bar.

Average value Average value Frequency range. in bar per bar. in decibels. 500-2 500 p.p.s. 0-441 —7-1 200-3 600 p.p.s. ' 0-429 — 7-4

3 0 TABLE IV

C haracteristic V a l u e s o f t h e T ransmitting S y s t e m w it h D is t o r t io n N e t w o r k N o . i .

F requency. Volts per bar. D ecibels. Frequency. Volts per bar. Decibels.

100 0•0618 — 24 • 2 1 800 0-0x69 - 35’5 200 ’ 0-0275 - 3 1 - 2 2 100 0-00977 — 40-2 300 0•0090 — 40-9 2 400 o -00610 - 44'3 400 0-0143 - 36-9 2 700 0-00408 - 4 7 - 8 500- 0-0204 - 33-8 3 000 0-00299 - 50-5 600 0-0263 ■ -3 1 -6 3 300 0-00202 — 53-9 700 0-0316 — 30-0 3 600. 0-00133 - 57-6 800 0-0390 —28-2 4 000 o-000611 '' - 6 4 - 3 900 0-0483 —26-3 4 400 0-0000751 - 8 2 - 5 1 000 0-0741 — 22-6 5 000 0-000531 - 6 5 - 5 1 100 0-139 - I 7 -I .6 000 0-00104 - 59-7 1 160 0-185 — 14-6 7 000 o-ooioo —6 0 -o' 1 200 0-182 — 14-8 8 000 0-000824 — 61-7 1 300 o - 118 —18 • 6 9 000 0•000684 - 63-3 1 500 0-039 — 28-2 10 000 0-000575 . - 6 4 - 8

Referred to i • o volt per bar.

TABLE V

C haracteristic V a l u e s o f t h e R e c e iv in g S y s t e m w it h D is t o r t io n N e t w o r k N o . i .

F requency. Bars per volt. D ecibels. F requency. Bars per volt. Decibels.

100 2-79 8 -9 1 200 43-5 32-8 200 - 5 ’4 14-6 1 300 24-0 27 ■ 6 300 ' 7-8 17-8 1 500 12-0 21-6 400 10-4 20-3 1 800 5-93 15'5 500 13-3 22-5 2 100 3-39 io -6 600 17-4 24-8 2 400 2-07 6-3 700 22-5 27-0 2 700 1-259 2-0 800 29-3 29-3 3 000 0-813 - i - 8 900 44-5 33-2 4 000 • 0-248 — I 2 - I 1 000 96-3 39-7 5 000 o - i 33 - 17-5 1 060 150-0 43‘5 6 000 o -io o — 20-0 x 100 116-3 4i -3

Decibels referred to 1 • 0 bar per volt. j

3i APPENDIX i.

NOTES ON WORKING STANDARDS EMPLOYING CARBON TRANSMITTERS ( “ SETAC ”).

A. DESCRIPTION OF THE WORKING STANDARD (Fig. i, below). The “ SETAC ” consists of a transmitting system, a receiving system, and an artificial line. The components of the transmitting system (or receiving system) are as follows :—

(a) A transmitter standard.—The transmitter should be of the carbon, solid-back, central-battery type, selected from the point of view of stability. (b) A receiver standard.—The receiver should be of the Bell type, with a nominal resistance of 60 ohms, selected from the point ol view of stability. Note.—The “ solid back ” transmitter standards and the Bell receiver standards are of the same type as the reference standards normally employed by the British and French Administrations in their Departments of Telephonometry, where good results are obtained. A sufficient number is kept at the Laboratory of the " SFERT ” to satisfy any sudden demand.

TRANSMITTING SYSTEM RECEIVING SYSTEM.

INDUCTION REPEATING ARTIFICIAL REPEATING INDUCTION COIL COIL LINE. COIL COIL TYPE 20. 300 TYPE 27-A. TYPE 27-A. 300“ TYPE 20. —0VWVW0- —o/MWo—

2 4 V MINIMUM 15 d b . 2 TRANSMITTER 1-8 N E PE R . STANDARD T Y P E 229.

VOLUME INDICATOR

F ig . i .'—W orking Standard Test Circuit (“ SETAC ”).

(c) Subscribers’ Apparatus.—In addition to the transmitter and receiver of the type explained above, the following form part of the circuit : 1—2-microfarad condenser. 1—induction coil.

(d) Battery supply circuit.—The battery supply circuit includes : a non-inductive resistance of 300 ohms, simulating a subscriber’s line— 1—battery of 24 volts. 1—repeating coil. Addendum I, p. 48, contains the essential clauses of a specification for the supply of repeating coils. ■ (e) Artificial line.—Artificial lines used in the working standard must be non-reactive, and have a characteristic impedance of 600 ohms. The length of each of these lines, and the scales adopted therefor, are left to the discretion of each Administration. It is, however, advisable to employ variable lines adjustable in steps of 1 decibel, or o t neper.

3 2 In order to reduce reaction effects, the total attenuation of these lines between the transmitting and receiving system must be at least 15 decibels or i*8 nepers. This attenuation is considered a minimum for all tests made with the working standard.

Note.—This section gives the essential information for setting up a “ SETAC ” standard, the transmitters and receivers being bought from the laboratories of the “ SFERT ” ; the Engineer-in-Charge of the Laboratory of the “ SFERT” will give all supplementary information required. However, Administrations which prefer to obtain a complete “ SETAC ” standard can obtain the apparatus from the International Standard Electric Corporation, Connaught House, Aldwych, London, W.C.2; in this case the entire “ SETAC ” standard must be sent to the Laboratory of the “ SFERT ” in order that it may be calibrated officially with the “ SFERT.” Subsequently, it will be only necessary to send the transmitters and receivers for periodical calibration to the laboratory of the “ SFERT.”

WORKING STANDARD TRANSMITTING SYSTEM

F i g . 2.—Comparison of a " SETAC ” with, the “ SFERT ” for transmission.

B. COMPARISON OF THE ‘‘ SETAC ” WITH THE ‘ ‘ SFERT.”

This comparison is intended to define the transmission qualities of a SETAC ” component as compared with a corresponding component of the “ SFERT.” It indicates in transmission units (nepers or decibels) the respective inferiority or superiority of the transmitting or receiving system of the “ SETAC ” with respect to the transmitting or receiving system of the “ SFERT ” (inclusive of its attenuator).

(a) Testing Method.—The tests are carried out by telephonometric comparison (voice and ear tests), substituting the compared component to be tested (transmitting or receiving system) for the corresponding component of the “ SFERT ” with its attenuator. An adjustable artificial line, in series with the more efficient system, enables the equivalent efficiencies of the two systems to be obtained. 33 c When the transmitting system of the “ SETAC ” is compared with the “ SFERT/’ the transmitting system of the “ SFERT ” is provided with its attenuator and a comparative test is carried out with the receiving system of the “ SFERT ” without distortion.

F i g . 3.—Comparison of a /‘ SETAC ” with the “ SFERT ” for reception..

In the case when the receiving system of the “ SETAC ” is compared with the “ SFERT,” the receiving system of the ‘‘ SFERT ” is provided with its attenuator, and the receiving system of the “ SFERT ” is distortionless. Diagrams showing the general principles of these two tests are given in Figs. 2 and 3. (b) Reference Equivalents.—The transmission characteristics of transmitter and receiver working standards depend essentially on the circuit in which these instruments are connected ; their transmission properties are defined, by convention, by the reference equivalent of the “ SETAC ” working standard when these instruments are incorporated.

1. Reference Equivalent of a Transmitting System.—The reference equivalent of a transmitting system is the number of transmission units given by the whole of the adjustable artificial lines of the “ SFERT,” when these artificial lines have been adjusted direct the same intensity of sound is obtained at the receiving end of the “ SFERT ” when speaking alternatively with the normal voice intensity (see Appendix 3) into a transmitter of the “ SFERT ” and into a transmitter of the transmitting system under test, the two transmitting systems compared being switched over simultaneously.

2. Reference -Equivalent of a Receiving System.—The reference equivalent of a-receiving system is the number of transmission units indicated by the whole of the adjustable artificial lines of the “ SFERT,” when these have been adjusted to give the same mean sound intensity, on alternate listening tests, at the receiving ends of the receiving system under test and of the receiving system of the “ SFERT,” these systems being alternately connected to the distortionless transmitting system of the “ SFERT,” and the calling intensity being kept constant (see Appendix 3) at the common transmitting end (distortionless transmitting system of the “ SFERT ”).

3. Reference Equivalent of a complete System.—The reference equivalent of a complete system is the number of transmission units given by the whole of the adjustable artificial lines of the “ SFERT ” when these have been adjusted so that the same sound intensity is obtained at the receiving ends of the “ SFERT,” and of the system under test when the “ SFERT ” transmitter and the transmitter of the system under test are spoken into with normal calling intensity. 34 Note.—The reference equivalents so defined are obtained from the average of a number of telephonometric tests called “ elementary balance tests.” (c) Method of Comparing the SETAC with the SFERT.—The method of comparison employed in the Laboratory of the “ SFERT ” is based on elementary telephonometric tests by only two operators (one operator speaking and one listening) and the use of three distortionless attenuators with characteristic impedances of 600 ohms. The first attenuator is set to a value higher than 15 decibels (or i-8 nepers) in order— (1) to adjust the current intensity in the receiving systems to a value such that the best conditions for comparative listening tests are obtained; (2) to prevent reaction effects between the transmitting and receiving systems.

The second attenuator introduces a bias or “ unknown ” attenuation {affaiblissement “ secret ”) of which the value is unknown to the listening operator. The third attenuator, called a “ balancing line,” enables equality of sound to be obtained and is adjusted by the listening operator. A combination of three keys, C1; C2and C3 (see Figs. 2 and 3), adjustable simultaneously, provides for the necessary switching for the comparative tests. A volume indicator of the International Standard Electric Corporation's design enables the speaking operator to adjust the calling intensity to such a mean value that the indicator pointer shows a mean saving of 15 divisions (with up to 30 swings every 10 seconds, approximately). This “ normal calling intensity ” has been determined according to the method given in Section 3 of this Appendix.

(d) Preliminary Telephonometric Balance. 1. Tests on a Transmitting System (Fig. 2). Each preliminary telephonometric balance is carried out by two operators. The speaking operator (P). having adjusted the bias attenuation to a certain value (known only to himself) speaks conventional phrases alternately into each transmitter. By way of example, the following sentences, employed in the Laboratory of the “ SFERT,” are given :— Eins, zwei, drei, vier .... zehn ...... (German sentence) Joe took father’s shoe bench out (American sentence) She was waiting at my lawn (American sentence) One, two, three, four, five (English sentence) Paris, Bordeaux, Le Mans (French sentence).

The operator P endeavours to speak in a normal tone at a normal rate of speech, and to preserve a normal calling intensity. He adjusts the keys CJ, C2, C3 simultaneously so that the necessary connections are made according to the transmitter employed. The listening operator (EJ adjusts the balancing line, of which he has control, to obtain equality of sound intensity for the two positions of the keys.

2. Tests on a Receiving System (Fig. 3). Each preliminary telephonometric balance is made by two operators. The speaking operator (P) having adjusted the bias attenuation to a certain value (known only to himself) repeats, in a normal tone and at a normal rate of speech, while preserving the normal calling intensity, the conventional sentences into the transmitter of the “ SFERT” transmitting system (distortionless). He operates the keys CJ, C2, C3, putting the “ SFERT ” receiving system and the “ SETAC ” receiving system successively into circuit with the “ SFERT ” transmitting system. The operator (E) listens with the two receivers (“ SFERT” receiver and the receiver of the “ SETAC ” under test) successively, and adjusts the balancing line in order to obtain equality of sound intensity with each of the receivers.

3 5 c 2 (e) Number of preliminary balances required for each test.—Each series of telephonometric tests includes a certain amount of preliminary balancing tests. The number of balancing tests which makes up a series of tests is at least six; it is generally twelve, and can be increased when necessary. The test results are recorded on calibration sheets which are delivered to the various Administrations, and give the following indications :— 1. Number and specification of the tested instrument. 2. Date or dates of tests. 3. Value of the reference equivalent. 4. Mean quadratic deviation. 5. Quality of the sound with respect to the “ SFERT,” as indicated below. Note.—A copy of all these sheets is kept in a special file in the " SFERT ” Laboratory. (File of Transmission or Reception Tests.) See Addendum No. 2, p. 50. “ Sample calibration sheets.” (/) Quality tests.—When' sound balance has been obtained in a voice test, the listening operator compares the quality of the sound of the instrument under test with the quality of the sound of the Reference System. He records the result of this comparison in the column marked “ Remarks ” on the sheet. The scale of comparison is as follows :— Abbreviation entered in Comparison. the column marked “ Remarks.” Shrill (aigu)...... A Equal (egal)...... = Deep {grave) ...... G These remarks are recorded on the sheets sent to Administrations. • (g) Resistance tests.—A resistance test of the transmitter is carried out during the voice test by means of the voltmeter-ammeter method. The voltmeter and ammeter employed are of the damped type. Several observations are made while speaking into the transmitter under test, the number of observations necessary being indicated by experience. The resistance value is obtained from the mean results (mean readings) given by the testing instruments.

C. INSTRUCTIONS FOR THE USE OF A “SETAC.”

1 . First Method of comparison : Two-Operator and Bias-attenuation Method. General.—This method is similar to that normally used in the Laboratory of the “ SFERT” for comparative tests of working standards with the “ SFERT ” itself, which has already been described (Chapter B). The main differences arise in the details of switching. The method is based on the simultaneous use of two adjustable attenuators; one of these (balancing line) serves the purpose of equalising the sound intensities at the receiving end; the'second attenuator (bias attenuation) allows the adjustment at will, and unknown to the listening operator, of the apparent efficiency of one of the instruments compared. The results must be expressed as “ better ” (M) or “ worse ” (P) than the “ SFERT,” due consideration being given to the equivalent of the “ SETAC.” The particulars given below refer to installation details, and are given as examples (Fig. 4a and 5a.) They should be modified where an arrangement is used differing slightly in details of installation, but not of principle (Figs. 4 and 5). Comparison of two transmitters.—The necessary switching for these comparative tests is performed by four relays with multiple contacts A, D, E, F, shown in the schematic diagram, Fig. 4a, or by means of four groups of relays each having three contacts only—their supply circuits being controlled by a key. A key “ K ” enables the supply circuit of these relays 36 to be modified, and in consequence, changes the relative position of the two lines in the speech circuit (balancing line and bias attenuator). Preliminary Balancing Test.—An operator " A ” adjusts the bias attenuator to a certain value, then speaks alternately into the transmitter (i) and (2), repeating successively a con­ ventional phrase, (refer to the comparison between the working standard and the SFERT, paragraph B(^) ). He maintains the normal calling intensity and speaks into the transmitter in such a manner that his lips are approximately tangential to the plane of the circle enclosing the opening of the mouthpiece of the solid-back transmitter (see paragraph D (d)). He adjusts the key in a suitable manner to operate the key system, as explained above.*

F i g . 4.—Comparison of a Transmitter with a Transmitter Standard.

F i g . 4a.—Comparison of a Transmitter with a Transmitter Standard.

A second operator, “ B,” receives, in the same receiver, the currents from the two transmitters compared. He compares them by ear, and adjusts the artificial balancing line to obtain the same sound volume with the two key positions. In order to enable the listening operator to follow the respective positions of the key, it is advisable to use a lamp, the lighting circuit of which is controlled synchronously by the key. When glowing, it indicates that the balancing line is inserted in the listening circuit. When equilibrium is thus obtained, the test is completed, and it is sufficient to record the readings of the two attenuators,. and to interpret them according to the example given below. Comparison of two receivers.—The various circuit connections required for this comparison are obtained by means of four relays or a group of relays B, D, E, F, the circuits of which are controlled by one key. The circuit combinations obtained are the following (Fig. $a).

* The normal calling intensity is indicated by a volume indicator shunted across the output of the transmitting system, and calibrated by comparison with the volume indicator of the “ SFERT ’’ (see D (a), p. 43)- Key “ K ” controls the feeding circuit of these relays, and, as a result, changes the relative positions of the two lines (balancing line and attenuator) in the speech circuit.

Preliminary balancing test.—The first operator- “A” adjusts the bias attenuator to a certain value, then speaks into the standard transmitter (always the same one) repeating a conventional sentence at regular intervals and with normal calling intensity (see paragraph G (a) and (d)). He manipulates the key synchronously in order to obtain the appropriate circuit connections. The second operator “ B ” holds the two receivers in one hand, and places them alternately to his ear (in the most efficient position) in step with the switching of the key. He then adjusts the balancing attenuator until he obtains equality of sound from the two receivers. When necessary, he asks operator “ A ” (by means of any type of signalling system, as, for instance, a prearranged audible signal) to change the position of the key “ K ” which controls the positions of the biassing and balancing attenuators. A lamp, of which the circuit is controlled synchronously by the key, glows when the balancing line is inserted in the listening circuit, and also gives to operator " B ” the cadence of the switching.

VOLUME INDICATOR.

SUB'S SET.

TRANSM ITTER X !_< STANDARD. "T

1 ^ 1 SUB’S SET

SWITCHING CIRCUIT

F i g . 5 .—Comparison of a Receiver with a Receiver Standard.

Fig. 6 gives the schematic of the key circuits as used in the “ SFERT ” Laboratory. In order to ensure that the key contacts shall offer the least possible resistance, so that the feeding conditions and the apparent efficiencies of the sets are not affected, it is advisable to employ high quality spring blades for each contact.

3 8 Number of preliminary balances.—The reference equivalent cannot be obtained by only one test. It is obtained from the mean of a sufficiently large number of preliminary balancing tests made according to the method described above; the minimum number of tests is six, and 12 should, normally, be made. When three operators are available, they can be grouped in six different ways, and it will then be necessary to make only one, or preferably two, tests for each possible combination of operators.

FIXED ATTENUATOR. F i g . 6.—Typical Switching Arrangement for the various connections required for telephonometric te sts (see Fig. 4a) Results and recording of tests.—It is recommended that the test results be recorded on special sheets, which contain the values of the bias and balancing attenuation used during the preliminary tests, together with the final results which indicate the definite telephonometric balance values. The table below gives an example of such a test record for six preliminary balances :—

TEST OF TRANSMITTER X.

S t a n d a r d o f C o m p a r i s o n N o ......

O perators. Bias A tte n u a ­ B alance. R esult. tion. Speak. L isten.

A B 4 6 2 M B C 0 2-5 2 ■ 5 M C A 6 4 2 P A C 4 3 1 P C B 2 3-5 i *5M B A 3 3 0

Biassingv Attenuator in Mean overall result ...... 0-5M. series with standard. Reference Equivalent of standard . . 12 • o P. Reference Equivalent of instrum ent X, 11 • 5 P or + 11-5.

39 The reference equivalent of the working standard, including the transmitter or receiyer tested, is obtained in the following manner :—

The numbers entered as M are summed separately from those marked P ; let SM and SF be the respective totals. The difference between SM and SP is divided by the number of elementary balances, and the result so obtained is expressed as P 01 M, according to whether

TRANSMITTER STANDARD

TRANSMITTER f T E S T ^ f

F i g . 7 .— Comparison of a Transmitter with a Transmitter Standard.

F i g . 8 .— Comparison of a Subscriber’s Set with a Standard Subscriber’s Set.

STANDARD SYSTEM

RECEIVER STANDARD

SYSTEM UNDER TEST

F i g . q .— Comparison of a Standard Transmitting System with a Transmitting System;using a different battery supply. Note.—The three circuits above may also be realised in accordance with the principle of Fig. 4.

SP is greater or smaller than SM. It is then corrected for the value of the reference equivalent of the standard apparatus used.

Note.—The final result can be prefixed by the sign — or -(- instead of being followed by the letter M or P.

40 2 . Second Method of Telephonometric Comparison: Three-Operator, without Bias-attenuation, Method.

This method is normally used by the telephonometric departments of various Administra­ tions, and can be employed instead of the “ SFERT ” method, of which it is only a modification. It requires positions for three operators. (a) Transmitting position (b) Receiving position (where the telephonometric comparisons are made); (c) Adjusting, or controlling, position.

TRANSMITTER7 ^ - ' STANDARD I 7 ^

TRANSMITTER | 2. 1 ____ BALANCE ^

RELAY RELAY R — —| RELAY COMBINATION COMBINATION H combination % A- 0 . t h 1 ' - B f Q

K 1 RELAY ^ T F

1 — 1— iiiiiiij—1—

F i g . i o .—Comparison of a Transmitter with a Transmitter Standard.

The transmitting and receiving circuits are identical with those already described, and the only difference between the two methods is in the number and positions of the artificial lines (Figs. io and n). The method employing three operators, in effect, requires only one adjustable line, in addition to the fixed attenuator. This line is adjusted by operator “ C,” who occupies the controlling position, and receives signals from operator “ B ” at the receiving end. The bias attenuator is replaced by direct metallic connections between the normal positions of relays D and E.

.H RECEIVER i-| STANDARD

RECEIVER TEST.

F i g . i i .—Comparison of a Receiver with a Receiver Standard.

The mode of operation is then as follows :— Comparison of two transmitters (Fig. io).—Operator “ C ” adjusts .the artificial line to a preliminary value bx, and notes the position of key “ K ” ; he then signals by lamp, by buzzer, or verbally to the operator “ A ” that he may begin speaking. The latter repeats into the two transmitters alternately the conventional phrase adopted once for all, maintaining a normal calling intensity (see paragraph D(a)); he operates the switching system, synchronously, so that the transmitter spoken into is connected to the battery. Operator “ B ” receives, in a receiver standard, the currents emanating successively from’ the two transmitters. A 4i luminous indicator, controlled by the general switching system, indicates to him the transmitter in use at any instant (No. I or No. 2). If the sound intensity corresponding to transmitter 2 is less than the sound intensity corresponding to transmitter 1 (standard), “ B ” presses the signalling switch marked “ P ” (worse). A luminous signal (lamp on the cap of which is marked the letter P) together with, if necessary, a buzzer signal, indicates to operator “ C ” the preliminary test result. A signal of the same type is also used to inform operator “A” that he may stop talking. Operator “ C ” records immediately the test result in a table in the form bjP. The number bx can be entered in two columns. In the first, it indicates that the attenuation was introduced into the circuit at the same time as the standard, with the effect of attenuating the standard; inserted in the second column, it indicates that the attenuation was introduced into the circuit at the same time as the test apparatus, with the effect of increasing the attenuation of the latter. In the opposite case, if the sound intensity corresponding to transmitter No. 2 is greater than the sound intensity corresponding to transmitter No. 1 (standard), operator " B ” presses the signalling button marked “ M ” (better). A luminous signal (lighting of a lamp on the cap of which is marked the letter “ M ”) followed by a buzzer signal, if. necessary, then appears in front of the operator “ C.” If the test results correspond to an exact balance, operator “ B ” presses a third button controlling the circuit of a third lamp, which is reserved for signalling exact balance. The controlling operator “ C ” then gives a second value, b2, to the adjustable attenuator. He then signals to operator “A,” that he may resume speaking. The result of this measure­ ment will be a second statement, for instance, M, meaning that the transmitter compared appears to be better than the standard, when the latter is in series with an attenuation of b2 units; operator “ C ” records the corresponding remark : b2M. He then adjusts the attenuation, at his discretion, in order to diminish the interval between the two values for which the balancing results in changed signs. When successive intervals (forming a convergent series) have determined, failing the number corresponding to an exact equality of the sound impressions, at least two values b and bx differing at the most by one or two decibels, or by o-i or 0*2 neper, and for which one of the two instruments appears better or worse than the other, the test is considered as finished. Operator “ C ” at the control table signals the end of the test to the other two operators “ A ” and “ B,” and a new balance can then begin. Note.—A single determination of equality cannot be considered sufficient to denote balance, and must be confirmed'by at least two other balance conditions (M and P) enclosing it.

In order to facilitate the general inspection of the results, it is convenient to arrange the. individual test results in such a way that they show clearly the position of the balance attenuator on the one hand (standard or test side measured) and on the other hand the corresponding degree of balance given by the listening operator. The following table is an example of such an arrangement. The overall result of the balance is either the number corresponding to the exact balance of telephonometric estimations (when the exact balance has been obtainable, and confirmed'by enclosing values), or the mean of the two most adjacent numbers, one with the letter “ M ” (better) and the other with “ P ” (worse). The mean is then recorded, followed by the letter “ P ” or “ M ” according to whether the larger of the two numbers on either side of it is placed in the column marked “ standard ” or " instrument.” The overall test result for a series of six balances is the mean of the results of the six elementary balances. The net result of the test, or of a series of six balances, is equal to the overall result corrected for the reference equivalent of the standard. Note.—The final result, instead of being followed by the letter “ M ” or “ P,” can be prefixed by the sign — or + . 42 I

T E S T O F TRANSMITTER X.

S t a n d a r d o f C o m p a r i s o n No.

A B B C C A (speaks) (listens)

Attenuation. Attenuation. Attenuation.

'S ta n d a rd In s tru m e n t S tan d ard In stru m e n t S tan d ard In stru m e n t Side. Side. Side. Side. Side. Side.

6 M 1 P 1 M 0 P 5 M 3 P 3 M 3 M . 1 P 1 P \ 1 P \ 1 M \ 2 - M / 2 M / 0 P / 1 M M ean M ean M ean 1 )P 1 • 5 P O'. 5P

B — A C — B A — C

Attenuation. Attenuation. Attenuation.

S tan d ard In s tru m e n t S tan d ard In stru m e n t S tan d ard In stru m e n t Side. Side. Side. Side. Side. Side.

0 P 2 P 4 M 2 M 3 M 2 P 1 P \ 0 M \ 2 M 2 M / 1 P / 0 M \ 0 M 1 P / M ean M ean M ean 1 • > P . o -5 M 0 -5 M 1

Mean overall result ...... 0-7 P Reference equivalent of Standard ...... 5 *0 P Reference equivalent of the instrument X ...... 5*7 P, or -)-5 *7-

Comparison of two receivers (Fig. 11).—The operating method is similar to th at for comparing two transmitters : the only difference is, naturally, in the switching arrange­ ment, which ensures that the receiver, instead of the transmitter is switched into position. For the general arrangement of the results the same instructions should be followed.

D. GENERAL REMARKS CONCERNING THE CARRYING OUT OF THE TESTS. {a) Calling intensity to be used (Normal calling intensity). The calling intensity is of great importance in making tests, as the absolute and relative efficiencies of the apparatus are thereby influenced (especially in the case of carbon trans- 43- mitters). Tt must be normal, that is to say, neither too weak nor too strong, and " must approximate to the average calling intensity employed in telephone usage.' It must also correspond to the value used in the “ SFERT ” Laboratory, and must be obtained as described in Addendum 3 on p. 51. It is necessary to -control- this calling intensity by means of an indicator placed in front of the speaking operator, and connected to the input of the fixed artificial line. This apparatus is calibrated according-to the method given in Addendum No. 3. It is necessary to compare it with the volume indicator of the “ SFERT,” sending it to the “ SFERT ” Laboratory, together with the working standard, or to compare it with another volume. indicator of the same type which has. already been compared with the “ SFERT ” indicator.

(b) Packing effect. To prevent packing.of the carbon, it is recommended that the transmitter case.be tapped lightly before each test.

(c) Contact resistance. In order to.reduce to a minimum tie effect of contact resistances,pt is recommended that spring blades of good quality be used, exerting an appreciable contact pressure. The contact points will be made of a suitable metal, for example, silver and gold, or platinum, several leaves being in parallel when the contact points are made of silver and gold, in order, to ensure the same contact. It is, moreover, necessary frequently to verify the electrical contact qualities of the plugs and of the switching system, by measuring the transmission equivalent of the complete system at a given frequency, for instance, 1 000 -p.p.s., and with a very small current.

{d) Position of the lips with respect to the transmitter. In addition to the normal calling intensity, it is essential that the position of the lips with respect to the transmitter be rigorously defined. The operator, when speaking, must place his lips so that they are approximately tangential to the plane of the external opening of the transmitter, and maintain this position throughout the test. To assist in attaining this condition, a circular ring of 2 • 5 cm diameter may be fitted to the transmitter mouthpiece by means of light hooks, fixed so that the plane of the transmitter opening is tangential to the plane of the lips when the operator presses his lips on the ring. In all cases, the front of the transmitter must be inclined backwards, making an angle of 20° with the vertical.

(

45 for the value on the sheet for the primary working standard and issued by the " SFERT ” Laboratory). Choice of secondary “ SE T A C ” standards. Secondary standards may be selected from the solid-back type of commercial transmitters and from the Bell type commercial receivers. In this case, they will be selected by the tele­ phonometric service of each Administration. When making this choice, it is advisable to observe over a reasonable time (2 or 3 months) the deviations in relative efficiency of the various standards proposed. If the mean deviation is low (below 0’2 neper or 2 decibels) the instruments examined may be classified as secondary standards. (/) Testing of Commercial Instruments. The telephonometric tests of commercial instruments are carried out in the same way as the tests on secondary standards. It is, howevei, necessary to make three remaiks :— (1) The commercial instrument is a transmitter or receiver of the same type as the transmitter or receiver standards : the tests are carried out under the same conditions as those to which the standards themselves are subjected (see Fig. 7). (2) The commercial instrument is a subscriber’s set of the same type as the standard transmitting or receiving sets. It is fed in the same manner as the latter (24 volts, repeating coil, 300 ohms). The switching is performed on the two subscribers’ instruments as indicated pi Fig. 8 (case of transmitting instruments), or in the supply circuit. (3) The instrument is of a different type from the standard instrument, and is normally constructed to work with a supply system different from that of the “ SETAC.” The two instruments (standard instrument and instrument under test) are supplied according to their respective systems, and the switching is applied to both the transmitting and receiving systems (Fig. 9) in the case of a transmitting system, or a similar arrangement as shown in Fig. 4- ' Note.—The information given above is quite general. Later on, detailed information will be given especially concerning the precautions to be taken in tests of combined microtelephone instruments.

E. PERIODIC CALIBRATION OF THE STANDARD INSTRUMENTS BY THE “ SFERT ” LABORATORY. The reference equivalent of standard instruments, in particular of carbon transmitters, being susceptible to variation with tune, it is necessary to compare them periodically with the “ SFERT.” It is therefore recommended that Administrations possessing primary standards should send them to the “ SFERT ” laboratory every nine months, either in part or complete, so that they may be recalibrated by comparison with the “ SFERT.” In order that Administra­ tions may not be without any standard instruments during the period of recalibration, the Laboratory will send them, on receipt of the instruments to be calibrated, a similar number of standard instruments, calibrated by comparison with the “ SFERT,” which can be utilised as primary standards until a new exchange is made. These check tests can also be made whenever it is found necessary, as, for instance, when abnormal results are obtained, or when periodic check tests on the primary standards indicate a serious deviation in efficiency. Despatch of Instruments.—To protect instruments in transit during periodic exchanges, it is necessary to pack them specially to ensure maximum safety in transport. Fig. 12 (p. 45) shows a container for the solid-back type of transmitter, and also one for the Bell type receiver. These containers will be made of hard wood, oak or walnut. The interiors will be lined with 46 zinc or brass sheets, o *5 mm thick, soldered together to form a metallic box within the wooden container. The lid, also of hard wood, will be lined with a metal plate, which, when the lid is closedj will bear on a felt lining at the bottom of the recess for the lid. All surfaces on which instruments rest will be covered with felt. The interior of the container will be lined with felt, velvet or leather as desired. The boxes must be locked by means of safety locks. Each container will carry a metal plate giving, in French, the name of the Administration concerned (owner of the box). Cases can be provided to hold several of these containers, divided into compartments, each containing one box. * • It will be advisable to observe the following suggestions for despatch : (a) Choose an agent in the town of despatch and another in Paris. A list of agents willing to take charge of Customs’ formalities will be given on request by the Engineer-in-Charge of the “ SFERT ” Laboratory. (b) Label each package with the following information :—

“ X ” (name of agent in Paris) en douane, Paris. Appareils destines au Laboratoire du Systeme Fondamental Europeen de reference pour la transmission telephonique, 292, rue Saint-Martin, Paris (3®) Pour retour a l’expediteur apres etalonnage par la Laboratoire.

(c) Despatch “ en grande vitesse, port paye en transit international sur Paris.”

Before despatching, advice is sent to the Engineer-in-Charge of the Laboratory, giving him the name and address of the agent in Paris, a detailed description of the instruments sent, and a declaration of their exact value. The standard instruments will be returned by the Laboratory in the packing cases belonging to the respective Administrations, through the chosen agent in Paris, carriage forward. The general instructions given above concerning the despatch of primary instruments are equally applicable to the despatch of any instruments to be calibrated by the “ SFERT ” Laboratory. It will be necessary to give information as to whether the apparatus contains any precious metal, and to give the necessary information required by the various Customs authorities. When instruments are carried as hand luggage, the messenger must prevent their being subjected to violent shocks, and to prolonged exposure near heating systems in the carriages, so that their efficiency may not be impaired. The bearer should carry with him the full description of the instruments, as mentioned above. On arrival in Paris, he will leave the instruments with the Customs in exchange for a receipt;, they will be collected from the Customs by the “ SFERT ” Laboratory.

Note.—For any additional information application should be made to the Engineer-in- Charge of the “ SFERT ” Laboratory, at the Conservatoire National des Arts et Metiers, 292, rue Saint-Martin, Paris (3®). 47 ADDENDUM No. i to APPENDIX No. i.

Essential Clauses of a Specification for the supply of Repeating Coils (Toroidal Coils). The transformers used in working standard systems (“ SETAC ”) are of the type having four equal windings, giving, when connected two and two in series, a I to i transformer ratio. The four windings are connected to terminals marked respectively : 1-2, 3-4, 6-5 and 8-7. The transformers must satisfy the following conditions :

Insulation.-—The insulation resistance between any two parts, not electrically connected, must not be less than 100 megohms, the testing voltage being 250V.

Resistance.—The resistance of eaph winding must not be less than 18 ohms, or greater than 24 ohms, but'the relative resistances of the windings must satisfy the conditions given below.

Transformation Ratio (see Fig. 1).—This ratio will be measured with an alternating current of o> = 5 000 radians per second. The windings 2-1 -f- 6-5 and 4-3 -j- 8-7 are connected inductively in series and are arranged in adjacent arms of an alternating current bridge. A non-inductive slide wire resistance of 1 000 ohms may be used to form the two other arms of the bridge. The bridge is balanced

a

F ig . 1.—Transformation Ratio. by moving the sliding contact until silence is obtained in the receiver. Small auxiliary resistances rv r2 may be inserted in series with the windings, if necessary, in order to obtain a good balance. • The transformation ratio, i.e., the ratio P/Q, as obtained by the cursor position on the slide wire, must lie within the following limits :

Maximum: i -o i/ i . Minimum : o • 99/1.

BALANCED & SCREENED TRANSFORMER.

F ig . 2.—Impedance Balance.

48 Impedance Balance. (See Fig. 2),—The. variable condenser can. be shunted across each half of. the slide wire, and is adjusted, together with the cursor, until silence is obtained. With a slide wire of 100 ohms resistance, balance must be obtained for a position of the cursor such that the resistance between the cursor and the middle of the wire is not greater than 2*5 ohms, and with a capacity value less than 0-5 juF. The test is repeated with the windings 2-5 and 4-7 reversed.

Power Output. [See Fig. 3).—The power output is measured at a> = 5 000 radians per second. An alternating potential difference of one volt is applied to the terminals of the transformer connected to the bridge. The test is made several times under the two following conditions :— (1) Without direct current. (2) With direct current of 200mA in two windings (either in windings 2-1 -f- 6-5, or in windings 4-3 -|— 8-7).

The output can be calculated by measuring the impedance of the primary windings, and the alternating potential difference at the terminals of 'the primary and of the 500-ohm

F ig . 3.—Power Output. resistance. The potential difference can be measured by a Moullin voltmeter. The power output measured at each test must be not less than 0 • 8, and is obtained from the formula :

V2Z Power Output = ------a r 500 cos v where V is the voltage at the ends of the 500-ohm resistance, Z and 6 are the modulus and angle respectively of the primary impedance.

Crosstalk.—No crosstalk must exist between two adjacent coils.-

Heating Test.^-A coil should not suffer any damage when 24 volts are applied for one hour between the terminals of any of its four windings.

i

49 D ADDENDUM No. 2 to APPENDIX I.

Sample Calibration Sheet A. No. of the series of tests : Series of tests made on a transmitting system of a SETAC ” working standard using transmitter No...... Receiver No,

Specification of the No. of V Attenuation. p re­ “ S F E R T .” R esult R esist­ R em arks liminary- O perators. of ance in (q u ality ). balancing balance. use. T ran s­ Receiver. Bias. B alance. test. m itter.

Date : Reference equivalent: Mean quadratic deviation :

Sample Calibration Sheet B. No. of the series of tests : Series of tests made on a receiving system of a “ SETAC ” working standard using receiving No......

Specification of the No. of Attenuation. " S F E R T .” p re ­ R esult R esist­ R em arks lim inary O perators. of ance in (q u ality ). balancing T ran s­ balance. use. Receiver. Bias. Balance. test. m itter.

-

Date : Reference equivalent : Mean quadratic deviation : 50 ADDENDUM No. 3 to APPENDIX No. 1 .

EXPERIMENTS TO DETERMINE THE NORMAL CALLING INTENSITY TO BE USED IN PHONOMETRIC TESTS.

Definition of Normal Calling Intensity. Consider the circuit shown below, which corresponds to an average subscriber’s line* Let the volume indicator of the “ SFERT,” used in this circuit, be adjusted to — 15 decibels.*

1 m ile: or INDUCTION STANDARD CABLE. REPEATING

INDICATOR. When an operator speaks into the type-229 transmitter with a sound intensity such that the pointer of the volume indicator shows a mean reading of 15 divisions (with sv/ings up to 30 about every 10 seconds), he is said to speak with “ normal calling intensity.” This normal calling intensity, thus defined, must be,maintained in all the tests. Numerous experiments have shown that this value corresponds to the average of the calling intensities used in ordinary telephone communication.

APPENDIX II.

NOTE ON WORKING STANDARD SYSTEMS USING ELECTRO-MAGNETIC TRANSMITTERS (“ SETEM ” ). A. DESCRIPTION OF THE “ SETEM” WORKING STANDARD SYSTEM. (Fig. 1 , p. 5 2 .) The “ SETEM ” consists of a transmitter system, a set of artificial lines, and a receiver system. The various components of these systems are as follows -

(1a ) Transmitting System. The transmitting system consists of an electro magnetic transmitter, incorporating a separately excited magnet system, associated with a thermionic amplifier. Standard Transmitter.—The transmitter used is an electro-magnetic instrument comprising a system of electro-magnets for which the exciting current is provided by the 12-volt filament accumulator. The electro-magnets are energised so that normal variations of battery voltage ( ^ 20%) do not affect-the efficiency of the transmitter. The transmitter is fitted with a mouthpiece; it is mounted on a special support, slightly inclined with respect to a guard ring which defines the position of the operator’s mouth when speaking. This arrangement enables the transmitter to be tested to be placed at the side of the standard transmitter (Fig. 2, p. 52). It is thus possible to speak into both transmitters without moving the head.

* This adjustment of —15 decibels only defines the conditions of operation of the volume indicator, and has no absolute meaning.

5 1 D 2 Amplifiers of the Transmitter system. The circuit diagram of the transmitting system employed is shown in Fig. 3 (p. 53). It is a two-stage amplifier—BO-type valves—with mixed coupling (capacity, resistance, transformer). The voltages produced by the speech currents can be adjusted by means of two potentiometers W1} W2. The adjustable potentiometer W2 alone is employee! to adjust the amplifier during its intrinsic check.test.

Tw {a) Tx

(b) i ] v

BIASSING ATTENUTOR.

VD Tn (c) Tx BIASSING ATTENUATOR.

F ig . i.—Block Schematic for the comparison of two systems.

The other potentiometer W2 is used solely for the purpose of adjusting the reference level when comparing the “ SETEM ” with the “ SFERT. ” The amplifier comprises a distortion network in addition to its normal coupling elements. A peak indicator, connected to the output of the amplifier through the jack “Kf’, serves, at the same time, as an indicating voltmeter during amplification tests. Current from a testing

F ig . 2.—Position of Transmitters when comparing a transmitter with the " SETEM. vibrator is led to a fixed potentiometer via the same jack. A reversing switch, Uj, enables the voltage applied to the input and output of the amplifier to be compared. The voltages necessary for the working of the system are respectively 220V (plate voltage), 52 12V (filament battery current; filament current i *2A), and 6V (grid voltage). (6) Attenuators (Artificial Lines). Four artificial lines are used in the working standards; they are non-reactive, and have a characteristic impedance of 600 ohms. ' ' ' As described below, three of these lines are arranged together with the receiving system, forming a complete unit. The fourth is used as a bias attenuator, and is adjustable from 0 to 1 - o neper (8 *6 decibels) in steps of o -i neper (0*9 decibel, approximately).

IN PUT STANDARD. VOLTAGE. U 2 £ IN U3 U, £ t e s t . CIRCUIT. OUTPUT VOLTAGE.

F ig . 3.—Transmitting System.

(c) Receiving System. The receiving system consists of a fixed line L, a balancing line R, a compensating line D, the listener TN, and the amplifier Vst II, (Fig. 1) and the necessary switches. Line L has a characteristic impedance of 600 ohms, and a value of 2 nepers (17*2 decibels). Fig. 4 gives the circuit diagram of the apparatus. The balancing line R is divided into sections of o-i neper (i-o decibel, approximately), and has a total value of 6 nepers (52 decibels, approximately); its characteristic impedance is 600 ohms and, like the line L, it is an “ H ” network. The compensating line D has a fixed value of 2 nepers (approximately 17 decibels). The amplifier Vst II is a single-stage amplifier (BO-type valve) practically distortionless, giving an amplification of two nepers. The input voltage is adjusted by potentiometers Wj and W2 serving the same purpose as those of the transmitting system amplifier. Wx controls the zero of the receiving system, and W2 controls the amplifier during its intrinsic check test. This calibration is carried out in the same manner, with the aid of the potentiometer W3, the vibrator, the peak valve voltmeter and the switch Ur By means of the reversing switches marked “ Transmitter-Telephone ” and “ System ” the circuit connections indicated in Fig. 1 are obtained. A key is fitted on the instrument for operating the luminous signal situated in the transmitter stand. The electro-magnetic receiver TN is fed, like the transmitter, directly from the filament battery, the voltage variations of which are again without effect on its efficiency. The magnetic system consists of a central-cored coil. The diaphragm is not screwed down, and therefore the receiver, like the transmitter, is independent of temperature variation. 53 D 3 The necessary working voltages of the system are 200V (anode voltage), 12V (filament battery voltage; filament current i *2A) and 6V (grid voltage).

B. COMPARISON OF THE “ SETEM ” WITH THE “ SFERT. ” The telephonometric measurement of a working standard is intended to reduce the reference equivalent* of the working standard to zero, and to calibrate the volume indicator associated with the transmitting system. To this end, special regulating devices have been provided on the transmitting and receiving system, which are made use of only during calibration. When testing the receiving system of the working standard, an operator speaks continuously in front of the transmitting system of the working standard; when testing the transmitting system, an operator listens continuously at the output side of the distortionless receiving system of the “ SFERT.” In addition to the transmitting and receiving systems; the testing equipment includes three distortionless artificial lines having a characteristic impedance of 600 ohms. The first of these is the artificial line of the “ SFERT,” which is adjusted to a value exceeding 15 decibels or 1 *8 nepers : (1) in order to regulate the current in the receiving system to a suitable value for listening tests, and (2) in order to obviate any reaction between the transmitting and receiving ■ systems.

O N X RECEIVER US INPUT VOLTAGE U 3 I U,t Ui t o U+f X O N O TRANSMITTER IN o OUTPUT VOLTAGE CIRCUIT F ig . 4.—Receiving System. The second artificial line introduces a “ bias,” or unknown, attenuation, so called as its value is unknown to the listening operator. The third artificial line is controlled by the listening operator, and is used for obtaining a balance of sounds received. A set of three switches C2, C3 (see Figs. 5 and 6, pp. 5 5 and 5 6 ), operated simul­ taneously, provides the circuit changes necessary for the comparative tests. The listening operator specifies when the switches shall be operated.

* See definition in Appendix I, para. B. (d), p. 35.

5 4 .The volume indicator of the “ SFERT ” allows the speaking operator to adjust his calling intensity to a mean value such that the indicator pointer has a mean deflection of 15 divisions (with a maximum of 30 swings of the needle about every 20 seconds) in accordance with the information given in Addendum No. 4 of Appendix x.

PEAK VALUE INDICATOR.

F ig . 5.—Comparison of a " SETEM ” Transmitting System with the " SFERT.” Schematic Diagram of the Test Circuit.—The respective arrangements for testing, trans­ mitting and receiving systems are shown in Figs. 5 and 6. In Fig. 5, SL represents a pilot lamp, which is fixed on the support of the working standard transmitter, and which can be lit by means of a key controlled by the listening operator, as described below. Ij is one of the two indicating instruments which comprises the peak indicator, and I2 is the second instrument which is mounted on the support of the working standard transmitter.

1 . Preliminary Telephonometric Balance. (a) Test of Transmitting System.—Each preliminary telephonometric balance is obtained with a group of two operators : one speaking, and one listening operator. The complete test is carried out, in principle, with three persons associated successively in pairs, so as to obtain a sufficiently large number of preliminary balances. The speaking operator (P), having adjusted the bias attenuation to a certain value bs. known only to himself, speaks first into the “ SFERT ” transmitter, calling the numbers 1 to 10, or other conventional sentences, such as the phrases used in the “ SFERT ” laboratory. He endeavours to speak in a normal conversational tone, and to maintain the normal calling intensity. When the listening operator (E) thinks he has obtained a good impression of the sounds transmitted from the “ SFERT ” transmitter, he depresses the key of the working

5 5 m standard, and gives the speaking operator a signal to speak into the “ SFERT ” transmitter. At the same time he operates switches C1; C2 and C3 (or, as applicable, the switch relays) and adjusts the balancing line to obtain equality of sound intensities. When the lamp SL. is lit, operator (P) speaks into the “ SETEM ” transmitter, and when it is extinguished, into the “ SFERT ” transmitter. In both cases he maintains the same normal calling intensity. This is repeated as often as the listening operator requires. If be is the attenuation of the balancing line when equality of the sound intensities has been obtained, the difference between be and bs is a measure of the magnitude of the reference equivalent of the transmitting system of the working standard; this equivalent is to be reduced to zero. If be is different from bs, the listening operator adjusts, to a convenient value, the special instrument contained in the transmitting system of the working standard, which is only made use of for this calibration. The telephonometric tests are repeated until the difference be—bs'is reduced to zero.

F ig . 6 .— Comparison of a “ SETEM ” Receiving System .with the ‘‘ SFERT,”

(b) Test of Receiving System.—Each’preliminary telephonometric balance is obtained by the speaking and listening operators. It is desirable that the test be carried out by three persons associated in pairs, as for the comparative test of a transmitter system. The speaking operator (P), having adjusted the bias attenuation to a value bs, known only to himself, repeats in the regular manner, as before, the figures'! to io, or other conven­ tional sentences. He endeavours to speak in a normal conversational tone, and to maintain the normal calling intensity (as in the previous case). The listening operator (E) listens alternately with the two receivers (“ SFERT ” receiver and the working standard receiver under test). He operates the switches C1; C2 and C3 so as to connect alternately to the distortion­ less transmitting system of the “ SFERT,” the receiving system of the working standard, and the receiving system of the “ SFERT” with distortion. In addition, he adjusts the balancing line in order to obtain equality of sound intensity with the two receivers. If be be the value of the attenuation when this equality is obtained, the difference between be and bg is a measure of the reference equivalent which it is desired to reduce to zero. If be is different from bs, the listening operator adjusts, to a convenient value, the special instrument .contained in the receiving system of the working standard, which is only used for this calibra­ tion. The telephonometric tests are then repeated until the difference be—bs is reduced to zero. • . ■ ;

5 6 2 . Calibration of the Peak Indicator. The reference equivalent of the transmitting system of the working standard having been reduced to zero, as described in paragraph B. i (a), the calibration of the peak indicator connected to the output of the transmitting system of the working standard is' proceeded with. The tests are carried out in the same manner as for the calibration of the transmitting system, with the exception that the listening operator (E) notes only the movements of the needle of the instrument Ij, associated with the working standard. For this purpose he notes the mean value of the reading, and the extreme limits of the swing of the needle. The readings are taken for each of the conventional sentences, and observations of the corresponding readings of the peak indicator are taken over a sufficient length of time. The readings so obtained are also applicable to the second instrument I2, which is mounted on. the support of the working standard transmitter. As the operator speaks with normal calling intensity, the peak indicator will give similar indications to those of the volume indicator.

C. INSTRUCTIONS FOR USING A “ SETEM.” The “ SETEM ” being calibrated in the manner described (Chapter B), with respect to the European Fundamental Reference System, any apparatus compared with it can there­ fore be evaluated with reference to the “ SFERT.” The working standard thus enables the reference equivalent of subscribers’ sets to be determined with respect to the international standard. i. Purchase and Calibration of “ SETEM ” Standards. The “ SETEM ” standards, similar to those described above, can be obtained from Messrs. Siemens & Halske, Wernerwerke, Berlin—Siemensstadt. Administrations desiring to possess such a standard are requested, after purchase, to send it complete to the Laboratory of the “ SFERT ” for an initial official comparison with the “'SFERT.” Subsequent calibrations may be made either by comparison with any type of reference system calibrated periodically with the “ SFERT,” or in a laboratory where a primary system, calibrated with respect to the’ “ SFERT,” is available.

2 . Use of the “ SETEM.” The " SETEM ” can be used for measuring the transmission (or reference) equivalent of any receiving or transmitting system, particularly of systems normally employed in telephone service. In what follows, it will be understood that the transmitters and receivers compared with the “ SETEM ” will be placed in their normal service circuits, thus making a complete transmitting or receiving system. ■ . The method of comparison employed is the “ two-operator method with bias attenuation.” This method is analogous to that employed for comparing the “ SETEM ” with the “ SFERT,” which has been previously described (Chapter B). The modifications apply, mainly, to the switching details. The method is based on the use of two variable attenuators : one of these (balancing line) serves the purpose of equalising the sound intensities at the receiving end; the second line (bias attenuation) permits of modifying, at will, and unknown to the listening operator, the apparent value of the efficiency of one of the two. systems compared. (a) Comparison of two transmitters or two transmitting systems (Fig. ib, p. 52).—The transmitter to be tested and the standard transmitter are placed on the special support at the same distance from the guard ring, so that they are symmetrically placed with regard to the direction of speaking (Fig. 2). The key of the transmitting system marked “ Test-Calibration ” is thrown to the position marked “ Test.” The switch of the receiving system marked “ System ” is thrown to the position marked in red, and the key “ Transmitter- Receiver ” to the position “ Transmitter.” Any value unknown to the listening operator (E) 57 is given to the bias attenuator. By throwing the key “ N-X ” of the receiving system alternately one way and the other, the operator (E) compares the sound intensities received, and, by adjusting the balancing line, obtains a telephonometric balance between the reference transmitter and the transmitter under test. The adjusting device consists of two scales (graduated in nepers); one designated b is employed for the comparison of instruments less efficient than the working standard, the other s is employed for comparison of instruments more efficient than the working standard. As the bias attenuation is introduced in series with the instruments under test, the value read off on the scale must be subtracted from that of the bias attenuation. (b) Comparison of two receivers or receiving systems (Fig. i c, p. 52).—For testing two receivers or receiving systems, an operator speaks into the transmitter of the working standard transmitter system, and connects alternately to the latter (by means of the N-X key) the receiving system of the " SETEM ” and the system under test. The “ Transmitter-Receiver ” key is thrown into the position “ Receiver,” and the test is carried out in the same manner as for transmitters. In the course of these tests, the key of the volume indicator is placed in the position “ Test.” (c) Comparison of two complete systems (Fig. 1 a, p. 52).—In throwing the switch U3 into the position “ System ” the instruments connected to the terminals marked “ Mx ” and " Tx ” are made to form one complete system. An operator speaks simultaneously into the two transmitters, as in the case of transmitter tests; the sound intensities are compared in the same manner, by listening alternately to the one and the other of the systems compared. (d) Number of Preliminary Balances.—The determination of the reference equivalent cannot be obtained in a single test. It is obtained from the mean of a sufficiently large number of preliminary balances carried out according to the method described above. The number of tests must be at least six, and, in general, should be twelve. When three operators are available, and can be grouped in six different ways, it will then be necessary to carry out at least one, or preferably two, tests for each of the possible combinations of operators. (e) Results and recording of results.—It is recommended that the test results be recorded on special sheets on which are given the bias, and the balancing attenuation values respectively, observed during the preliminary tests, as well as the resultant values which give the final results of the telephonometric balance. These sheets can be of the same type as those used for “ SETAC ” standards.

TUNING FORK POTENTIOMETER VIBRATOR

PEAK VALUE VOLTMETER

F i g . 7.—Check Testing of Amplifiers.

( /) Check testing of Amplifiers (Fig. 7).—It is necessary to check the constancy of the transmission equivalent of the amplifiers employed in the “ SETEM ” standard. For this purpose, various controlling equipments have been provided, and must be used in the following manner I. Transmitting System Amplifier.—In throwing the key of the peak indicator marked ,J Test-Calibration ” into the position “ Calibration,” the instrument operates as a valve 58 voltmeter during the calibration. The testing voltage of a vibrator is applied to the input of the amplifier, by throwing the key of the transmitting system marked “ Test Calibration ” to the “ Calibration ” position. The valve voltmeter then gives, according to the position of the key “ Reference Voltage-Output Voltage,” either the voltage of comparison or the amplified output voltage. The output voltage is reduced to the value of the voltage of comparison by adjusting the regulating resistance provided for that purpose.,

II. Receiving System Amplifier.—After connecting the vibrator and the peak voltmeter by means of a plug, the amplifier is calibrated by a suitable adjustment of the key Ux and of the adjustable resistance W2 by inserting the plug into the jack, and is ready for test when the plug is withdrawn. The instrument is prepared automatically for calibration.

D. GENERAL REMARKS CONCERNING THE CARRYING OUT OF TESTS. (a) Speech intensity to be observed [normal calling intensity).—-The speech intensity is of great importance in the carrying out of these tests, as it influences the absolute and relative efficiencies of the instruments. It must be “ normal ” i.e. neither too weak nor too strong, and must be equal to the mean speech intensity used in practical telephony. It ■must correspond, moreover, to the speech intensity employed in the “ SFERT ” Laboratory, and must be determined as shown in Addendum 3 to Appendix I. For. this purpose, it is necessary to regulate the speech intensity according to the readings given by the peak indicator associated with the “ SETEM.” This peak indicator has been calibrated with reference to the volume indicator of the “ SFERT ” in the manner described in paragraph B 2.

(b) Position of the lips with regard to the transmitter. Like the normal speech intensity, the position of the lips with respect to the transmitter .must be rigorously defined. The operator, when speaking, must press the upper lip slightly against the guard ring mounted on the transmitter support, and maintain this position throughout the test.

(c) Effect of packing of the Carbon. When comparing commercial instruments, using carbon transmitters, with the “ SETEM,” it is necessary to tap the transmitter case lightly in order to'prevent packing of the carbon.

(d) Parasitic Contact Resistances. Particular care must be taken to inspect the switching contacts of the different parts of the working standard when carrying out telephonometric tests. Parasitic contact resistances can be of considerable magnitude and may falsify the results.

E. PERIODIC CALIBRATION OF STANDARD • INSTRUMENTS BY THE ‘‘ SFERT ’’ LABORATORY. It is necessary periodically to compare standard instruments with the international telephonometric base formed by the “ SFERT,” or with a standard itself calibrated with respect to the “ SFERT.” Taking into account, however, the construction of the transmitters and receivers ofthe “ SETEM ” these check tests could only be made every 18 months. These check tests could also be made when found necessary, as for instance, when abnormal results indicate a serious variation in the efficiency. When a check test is to be carried out specially at the Laboratory of the “ SFERT,” it is advisable to observe the following rules for despatching the instruments :—- 59 (a) Choose an agent in the town of despatch, and another in Paris. A list of agents willing to take charge of the Customs operations will be given, on request, by the Engineer-in- Charge of the “ SFERT ” Laboratory. (b) Label each package as follows : " X ” {name of agent in Paris) en douane, Paris. Appareils destines au Laboratoire du Systeme Fondamental Europeen de reference pour la transmission telephonique, 292, rue Saint-Martin, Paris (,3e) Pour retour a l’expediteur apres etalonnage par le Laboratoire.

(c) Despatch “ en grande vitesse, port paye en transit international sur Paris.” Before despatch, a notice will be sent to the Engineer-in-Charge of the Laboratory, giving the names and addresses of the agents, a detailed description of the instruments sent, and a declaration of their exact value. The standard instruments will be returned by the Laboratory, in the packing cases belonging to the Administration concerned, through the chosen agent in Paris, carriage forward. The general instructions above, concerning the despatch of primary standard instruments, are equally applicable to the despatch of any instruments to be calibrated by the “ SFERT ” Laboratory. It will be necessary to give all the information required by the various Customs authorities, stating, in particular, if certain parts of the instruments are of precious metals. When the instruments are carried as hand luggage, the messenger must avoid all violent shocks to the apparatus, and also leaving the instruments near the heating systems in carriages, etc, in order that their efficiency may not be impaired. The bearer can carry a full description of the instruments as mentioned above. On arrival in Paris, he will leave the instruments against a receipt, with the Customs, from whom they will be collected by the “ SFERT ” Laboratory. Note.—For any additional information, enquiry should be made direct to the Engineer- in-Charge of the “ SFERT ” Laboratory at the Conservatoire National des Arts et Metiers, 292 rue Saint-Martin, Paris (3e).

GENERAL METHOD TO BE EMPLOYED FOR TESTING SYLLABLE ARTICULATION. The International Consultative Committee— Having noted Technical Report No. 4 of the “ SFERT ” Laboratory relating to comparative articulation tests {see Appendix, p. 62); Considering, however, the difficulties in application of the various methods of articulation testing;

Unanimously advises :— That comparative tests of the methods of measuring articulation should be carried out by the “ SFERT” Laboratory.by varying either the transmission levels employed, or the frequency bands transmitted (use of filters) in the course of these tests. Note.—It is desirable to use successively during these tests the filters having characteristic impedances of 600 ohms as follows :— 1. Low-pass filters having cut-off frequencies respectively of 1500, 2000, 2 500 and 3 000 p.p.s. 2. High-pass filters having cut-off frequencies respectively of 400, 600, 800 p.p.s. 6 0 Various combinations of these filters will produce various band-pass filters. If the insertion of any of these filters introduces an additional attenuation, it will be advisable to compensate for this by diminishing the artificial line inserted between the trans­ mitter and receiving systems. Similarly, the attenuation' due to the series-parallel working of four receivers will be compensated for by increasing the transmission level of the receiving system.

The International Consultative Committee— Considering the interest which would be aroused by the preparation, for articulation tests, of lists of logatomes, together with their phonetic equivalents in other languages;

Considering again, That the preliminary tests carried out at the "SFERT” Laboratory (see Appendix, p. 62) have shown the possibility of compiling such lists, but that it is advisable, however, to eliminate systematic errors arising from the operators’ recollection :—

Unanimously advises :— 1. That lists of logatomes should be prepared from sounds most generally used in each language. Each logatome will be made up of the following sounds : I (a) An initial consonant, or a group of consonants, capable of being pronounced as a single vocal sound;

(b) A vowel or diphthong, also capable of being pronounced as a single vocal sound;

(c) A final consonant, or a group of consonants, capable of being pronounced as a single vocal sound.

The logatome consists of the combination of these three elements, and also must be susceptible of being pronounced as a single vocal sound. The frequency of repetition of sounds in any language will not be taken into account. It is suggested that a Sub-Committee of the 4th Commission of Assessors be formed, and entrusted with the preparation of these lists. This Sub-Committee could consult the experts on phonetics, and consider the possibility of adopting international phonetic symbols, illustrated by typical words giving the pronunciation of the symbols in each language. The Sub-Committee could also consider the use of phonograph records to standardise the pronunciation of phonetic symbols.

2. The Sub-Committee will study the methods to be employed to avoid the disadvantages arising from the operators’ recollection. Lastly, they will study the insertion of logatomes in typical sentences, in order to adjust the conditions of articulation tests to those of normal telephone conversation, particularly from the point of view of transient phenomena. The use of these typical sentences would also facilitate the measurement of the calling intensity. ' - '

3. A series of articulation tests will be made at the “ SFERT ” Laboratory with a large number of circuits containing distortion, and with several crews of experienced operators sent by different Administrations. 61 APPENDIX. COMPARATIVE ARTICULATION TESTS IN VARIOUS LANGUAGES. (T e c h n ic a l R e p o r t N o . 4 o f t h e “ SFERT ” L a b o r a t o r y .) As a result of the International Consultative Committee’s advice on long-distance telephone communications, comparative articulation tests in different languages and in accordance with the methods employed by various Administrations, have been made in the " SFERT ” Laboratory with the assistance of specialists of the German Administration, the British Post Office, and the Research and Investigation Service of the French Administration. These tests are divided into two principal parts. 1. Normal tests made by each crew according to its usual methods;

• 2. A preliminary international test consisting of preparing lists, with phonetic equivalents, of German, English and French words, and the transmission and reception of these lists by operators of different nationalities. The results of the two series of tests are given below :

I. Normal Articulation Tests. 1. A preliminary series of tests was made with the “ SFERT,” using the four following arrangements :— (a) Transmitting system and receiving system—both without distortion. (b) Transmitting system with distortion, and receiving' system without distortion. (c) Transmitting system without distortion, and receiving system with distortion. (d) Transmitting system and receiving system—both with distortion. 2. In a second series of tests the four combinations a, b, c, d were again employed, with the insertion, however, in the speech circuit immediately behind, the fixed artificial line of 24 decibels, of a low-pass filter with a cut-off frequency of 1 500 p.p.s., kindly lent by Messrs. Siemens & Halske. In order to allow several operators to listen simultaneously, the output of the “ SFERT ” was arranged with four electro-dynamic receivers, two pairs, of two in series, being placed in parallel. The result of this arrangement was that the impedance of the whole apparatus was equal to the impedance of one individual receiver, and that the working characteristics of the amplifiers remained unchanged. The intensities of the transmitter currents were halved, which corresponded to an increase of the overall transmission equivalent of the system of 0*7 neper or 6*o decibels. This increase also occurred in the working arrangements adopted by the different groups. The arrangements adopted were as follows : German Crew.—For each preliminary test, an operator (the same for all tests) called 100 logatomes; four operators, listening respectively with each of the four receivers, received transmitted logatomes; each average referred to four preliminary tests, i.e. 400 logatomes transmitted and 1600 received. English and French Crews.—Three operators working simultaneously. Each called 100 logatomes, the other two listening with two of the four receivers connected as indicated above (two receivers were therefore unused, but remained in circuit). As a result of permu­ tations of the operators, when the three speaking operators were replaced, 300 logatomes were called and 600 received. Results.—The test results are given in the charts on p. 64, which shows a sufficiently good agreement between the various figures obtained when no filter is inserted in the system. The maximum differences do not exceed 4 per cent, between the various groups. 62 If, however, the filter is inserted in the testing circuit, marked differences are apparent, which not only accentuate the differences between the crews, but also alter distinctly the speed of testing. It is apparent th at:— 1. All the results obtained by the ^English crew vary by about 10 per cent, with respect to those of the French crew. The general trend of the two curves relating to these two groups is, however, the same, and the systematic difference is constant (io per cent., except in the case of total distortion, where the deviation is 5 per cent.). 2. The results obtained by the German crew when the filter is inserted deviate appreciably from the other results, These results have been confirmed to within about 2 per cent, for two successive positions of the operators’ lips : first, at a distance of 10 cm, which is the distance normally used by this group, and then for the ordinary distance corresponding with the normal use of the “ SFERT.” The diagram of the results shows that the German results are between the French and English results with a distortionless system, (distortion other than that caused by the filter). They tend to be of the same order as those of the English crew when the transmitter system has its distortion network inserted; , but the curve again ascends rapidly and approaches that of the French crew when distortion is in the receiving system. Finally, when the distortion is complete, the German results are again below the other results. Conclusions.—It seems difficult to draw any definite and precise conclusions from these comparative tests of the methods employed for articulation measurement. The following facts may, however, be noted :— (a) Conformity of successive results obtained by one method under given conditions ' of electrical distortion; (b) Existence of a systematic deviation of one to three per cent, without filter, and of ten per cent., with filter, between the French and English results. This deviation for the case of the filter may be due to the existence of higher harmonics in the. English language, or to the difference of articulation; (c) Influence of the distortion of the transmitter system, in general more marked than that ,of the distortion of the receiving system. This may be explained by the general shape of the distortion curves, and by an attenuation due to the distortion, which is greater for the transmitting system than for the receiving system. This effect, however, is only slightly noticeable in the case of the French crew. (d) The results obtained by the French crew seem to indicate that the effect of the filter is approximately equivalent to 5 per cent, (for the French language and method), of that of one only of the two distortions, and that the filter added to the “ S F E R T ” equipped with its two distortion networks hardly modifies the reduction in articulation due to the two networks. This conclusion also holds good foi the English crew. For the German crew, however, the filter produces a relatively greater decrease in articulation for total distortion as compared with other distortion values. This may be explained by the increase in the total attenuation of the system to which the German operators appear very sensitive. Two tests carried out with the operators placing the lips at two different distances from the transmitter of the “ SFERT ” have shown a difference of two per cent, in the results, although the effect of reduction in efficiency with distance is only slightly apparent with the “ SFERT ” transmitter. It therefore seems that, in the tests which have been made at the “ SFERT ” Laboratory, the articulation measurements have been influenced by two factors simultaneously: one 01 these is the true distortion, the other .the reduction in the receiving intensity. It has not been possible, on account of lack of time and in view of the great number of tests to be made,

-6 3 to repeat the tests with different transmission levels. It will be desirable, in the near future and when the Master Reference System has been definitely adjusted, to ask the various Administrations to make tests by adjusting the ievels of their measuring systems to that of the reference value, then to other levels slightly greater and slightly smaller. When these preliminary results have been obtained, it will be advisable to repeat, at the “ SFERT ” Laboratory, a new series of comparative tests .which will allow of obtaining with maximum precision the “ articulation co-efficient” of the different languages, and the relative value of the testing systems normally employed. It will, moreover, be desirable to complete the information so obtained by experiments made with filters having various cut-off frequencies (high-pass filter, low-pass filter, and band-pass filter) which would allow of further defining the possible effect of the essential phonetic components of the languages compared.

II. International List Test.

In order to meet the requirements of articulation tests on international circuits, by operators of different nationalities, a list has been drawn up, in agreement with the representatives of the German and English Administrations who have been delegated to the “ SFERT ” Laboratory for comparative tests of articulation methods. This list includes 100 logatomes, and has been arranged by taking logatomes of each of the German, English and French lists successively in circular permutation. This list contains 34 German, 33 English, and 33 French words. It has been rearranged in three lists, “ a,” “ b,” and “ c,” intended respectively for the German, English and French operators, so that list “ a ” read by a German operator is equivalent, from the point of view of phonetics, to list “ b ” read by an English operator, and to list “ c ” read by a French operator.

------ENGLISH trench •GERMAN

WITH riLTER (CUT OFF FREQUENCY 1500 RRS)

1. COMPLETE SYSTEM -01STORTIONLESS. 3 .TRANSMITTING SYSTEM -DISTORTIONLESS. RECEIVING SYSTEM -W ITH DISTORTION. 2.TRANSMITTING SYSTEM-WITH DISTORTION. RECEIVING SYSTEM - DISTORTIONLESS. 4 . COMPLETE SYSTEM - WITH DISTORTION.

Comparative Articulation Tests.

64 FREQUENCY- PERIODS PER SECOND.

Siemens and Halske Filter used for the Articulation Tests (Jan.-Feb. 1929) Z = 600 ohms.

Thus, the first logatome has been taken from the list used in the German method for tests on articulation. It is written in list “ a ” ; in list “ b ” is given the phonetic equivalent of this logatome in English, and in list " c ” the phonetic equivalent in French. The second logatome is taken from the English language. It has been included as such in list “ b,” whereas in lists “ a ” and “ c ” the phonetic equivalents in German and French are recorded. The third logatome has been taken from a French list and placed in list “ c ” : it has been translated phonetically in lists " a ” and “ b.” The fourth logatome is German, and so on. These lists are reproduced on p. 66. In making up these lists, certain sounds peculiar to one language and non-existent in another have been eliminated, such as the sound “ t h ” in English, the sound “ ch ” in German and the sound “ je ” in French, etc. Conditions of Test.—The " SFERT ” was used with distortion for transmission and recep­ tion, and the attenuation introduced by the artificial cable was 24 decibels. The listening operators were drawn from the German crew specially trained for articulation tests. The speaker was, in turn a German, an Englishman, and a Frenchman. . In all cases the correction wras effected according to list “ a ” (phonetic German translation, read by a German corrector). The results were as follows :— Speakers. Listeners. German ...... German ...... 75 per cent. English ...... German 42 ,, French ...... German 48 „

The relatively short time available did not permit of further tests. It may henceforth be admitted that certain errors depend on the nationality of the operators. For example, confusion of the letters p and b by German operators when listening to an English or French operator, and of the sound “ ann ” with “ onn ” by French operators listening to a German or English operator, could not be regarded as errors, as they occur normally in the course of direct conversation, without the intervention of telephone instruments.

6 5 e In view of the small number of tests made, and of logatomes transmitted, no definite conclusions can be drawn from the test results. It will be desirable to resume these tests in the “ SFERT ” Laboratory at a later date, with lists prepared in sufficient numbers according to the principles given above. It is apparent that such tests with international lists are possible, and that their execution seems to be but a matter of arrangement.

German. English. French. List a. List b. List c. gets gates gettse sax sax saxe ur oor our mil meal millh schim shim chimm de day de fu foo fou dopt derft deupte pang pang fa n fruch frusch fruche taus towze ttahose wiw veev vive ba baa baa fut foot foute ong ong on bing bing binng neft neft nefte neb neb neb Jell yell yell sind sind cinnde tu too tou fen feign fene Jill yill yill itsch each itch elk elk ellk int int innte fa far fa

(A.a.2.) Recommendations of Principle. Practical Limits of Transmission Equivalents.*

The International Consultative Committee— • Unanimously advises:— (1) That it is desirable that the reference equivalent between two subscribers’ sets" involved in an international communication shall not exceed 3-3 nepers or 29 decibels. (2) That the reference equivalent of the international circuit, including the line transformers, shall not exceed 1-3 nepers or 11-3 decibels. (3) That the total losses occurring between the subscriber and the terminals of the input

* This text replaces that under the same heading on pp. 64—65 of the Green Book (C.C.I., Paris, 1928) ; English translation, 1928, p. 45. 66 transformer of the international circuit shall not ordinarily exceed i neper or 8-6 decibels, in order that any subscriber in one country may be connected to any subscriber in another country. The losses due to secondary long distance lines, intermediate offices, auxiliary apparatus connected in series or in shunt and the subscriber’s loop shall be included in the total losses occurring between the terminals of the subscribers’ set and the terminals of the input transformer of the international line. The above losses do not include battery supply losses.

N o t e .—When the Master Reference System which has been adopted is available, * it will be necessary to establish :— (a) The value of the overall reference equivalent of the complete connection between subscribers, as well as the reference equivalent of the connection between- two toll operators, or between a toll operator and each of the corresponding subscribers. (b) The value of the transmission equivalent of the connection between the subscriber and the terminals of the input transformer of the international circuit, including the current supply losses.

(4) That the maximum value allowable for transmission loss at a junction point on an international line caused by signalling or control apparatus (electro-magnets, resistances, condensers, keys, monitoring receivers and office cabling in the toll exchange) shall not exceed 0*2 neper or 1*7 decibels in the frequency range 300-2500 p.p.s., estimating the losses due to signalling apparatus at approximately 0-05 neper or 0-43 decibel, those due to control apparatus (silent listening position, i.e., transmitter out of circuit) at approximately 0 *09 neper or 0*77 decibel (see p. 75), and to office cabling in the toll exchange at approximately 0-06 neper or 0*51 decibel.

Transient Phenomena.* The International Consultative Committee— Unanimously advises :— that the duration of transient phenomena for any frequency in the frequency band to be transmitted (see Green Book, pp. 176 and 292, English translation, 1928, pp. 134 and 225) must not exceed 30 milliseconds for the complete connection between terminal exchanges.

Possibility of Standardisation of Long-Distance Telephone Systems.^ The International Consultative Committee— Considering :— That since the issue of the existing specifications, progress has been realised in the long­ distance telephone art which makes necessary a revision of these specifications. That it is desirable to improve, from the experience gained, the existing long-distance systems in Europe, by modifying the present characteristics which, determine the quality of transmission (cut-off frequency, frequency range transmitted, etc.). (a) That it is desirable to standardise the secondary electrical characteristics of the cables, i.e., the cut-off frequency, the frequency band to be transmitted and the attenuation

* This text replaces that relating to Transient Phenomena, p. 68 of the Green Book. English translation, 1928, p. 48. f This text replaces that on pages 74 to 171 of the Green Book relating to the Possibility of Standard­ isation of Long-distance Telephone Systems. English translation, 1928, pp 51 to 130. 6 7 E 2 between two successive repeater stations; it is, however, not necessary to standardise any further. .(b) That the values to be uniformly adopted for the cut-off frequency, the frequency band to be transmitted, and the attenuation between successive repeater stations, cannot be decided upon until the suggestions of the Administrations have been received. (c) That owing to the difficulties due to the existence, in certain countries, of large networks, and of the conditions which have to be met when planning new cable schemes, it is not practicable to standardise details of cable circuit characteristics such as loading coil spacing, diameter of conductors, etc. (d) That it is necessary to lay down, by way of example, detailed specifications for each of the systems la, lb, and II recommended by the C.C.I. At present, it is necessary to complete the detailed specification given for Systems la and lb, by detailed specifications relating to Method II.

The International Consultative Committee—

.Unanimously advises :— That in view of System II being adopted, the following corrections be made in the Green Book :— 1. Page 66. (English translation, 1928, p. 46.) Insert between the second and third paragraph in front of the words “ Four-wire circuits ” the following : “ When Loading System II is employed on two-wire circuits the frequency band to be transmitted must be from 300 to 2 400 p.p.s.” 2. Page 174. (English translation, 1928, p. 132.) Replace in the second paragraph the words “ Systems 1 and 2 ” by “ Systems la, lb and II.” 3. Page 176. (English translation, 1928, p. 134.) Between the 25th and 26th lines (English translation, 19th and 20th lines) insert the following new paragraph : “ These values hold for Systems la and 15. When System II is used, the frequency band to be transmitted must be 300 to 2 400 p.p.s. for both two-wire and four-wire circuits (medium-heavy loaded).” 4. Pages 233 and 234. (English translation, 1928, pp. 175 and 176.) (a) Add to the end of paragraph 2, “ Four-wire circuits,” page 233 (English transla­ tion, p. 176) : “ When System II is used, it is necessary, and sufficient, to make tests up to 2 400 p.p.s.” (b) Insert the same sentence on page 234 (English translation, 1928, p. 176) at the end of paragraph (a). 5. Page 292. (English translation, 1928, p. 225.) Add under 4 as the paragraph last but one : “ these values hold for systems la and 15. When System II is used, the frequency band for medium-heavy loading must be 300-2 400 p.p.s.” 6. Pages 321-326. (English translation, 1928, pp. 247-251.) In Appendix C.b.i, replace everywhere System 1 by System Ia\ System 2 by System 15; System 1 a, by System la, and System 2a by System 15. Add to the end of this appendix the following new paragraph : “ Where the circuits to be connected together have been installed according to loading systems la or 15 in the one case, and II in the other, it will be necessary for the installation of the repeater 68 section crossing the frontier to be left to one contractor who will apply, exclusively, either System II, I a or I b.

(A.b.) G eneral R ules concerning the C omposition of T ransmission S ystems. (A.b.2.) Carrier Current Telephony. Draft of a Model Questionnaire for Preliminary Information, in regard to existing Lines and Offices, to be obtained by Telephone Administrations wishing to establish Carrier Current Telephone Installations. The C.C.I. unanimously advises that the following questionnaire be used :— 1. What communication channels should be installed by means of high frequency carrier currents? 2. What lines are available for the installation of high frequency apparatus ? (a) The length of these lines. (b) Diameter, nature of conductois, distance between conductors. (c) Existing cable sections (situation, type and length of these cables). (d) Existing crosses and transpositions. (q) Among the lines available, are there two or more identical circuits which may be interchanged, and from which spare circuits can be obtained ? 3. Which intermediate localities are suitable for the installation of repeaters ? Where have low frequency repeaters already been inserted on lines which are to be equipped for high frequency ? 4. What aie the sites of radio stations likely to affect high frequency communication? What are the powers and frequencies used by these stations ? 5. Should the new high frequency channels be connected to other lines, either permanently 01 from time to time ? ' 6. As the replies to the above questions render possible the retention of. certain circuits and localities, Administrations should obtain the following information :— What are the results of the impedance and attenuation tests , made on each of the sections of line over the whole frequency range to be used ?

(A.b.3.) Radio-broadcast Transmission. Maximum and Minimum Transmission Levels to be adopted for Radio-broadcast Transmissions.* The International Consultative Committee— Considering :— That, as regards the maximum and minimum transmission levels to be adopted for the relaying of broadcast transmission, a distinction must be made between cable circuits and open wire lines, That, in fixing these values, consideration should be given to the technical qualities of the circuits involved, Unanimously advises:— (a) Cable Circuits. The maximum transmission level at any point on the line must not exceed 1 • 1 nepers

This passage replaces that on pp. 172-175 of the Green Book; English translation, 1928, p. 131-132. 6 9 E 3 or 9'5 decibels. In. ordinary cables the minimum transmission level should not be less than the limit allowed for ordinary telephony. In special cables, where the crosstalk is considerably reduced, this limit may be reduced by an amount corresponding to this reduction. For example, in the case of such special cables already in existence having crosstalk values of 12 nepers or 104 decibels, the transmission level may be fixed at — 5-5 nepers or — 47-7 decibels. (b) Open-wire lines. A limit of 4 milliwatts seems to be permissible for the maximum mean power, calculated for any interval of time of 10 milliseconds. No definite maximum level for the instantaneous power appears to be necessary, but the minimum value of this power must not be less than 1 • 6 milli-watts. If it is desired to use ordinary vacuum tubes, the mean value delivered to the long distance line and calculated for any interval of time of 10 milliseconds must not exceed 1 milliwatt. For the transmission of greater powers, it seems necessary to use special cables, equipped with proper vacuum tubes.

Conditions which Open-wire Lines must fulfil in order to be used for Radio­ broadcasting. The International Consultative Committee— Unanimously advises :— (a) That in all cases where parasitic noises or interference, due to mutual induction between the open-wire lines used for broadcasting and other circuits, do not enter into consideration, these open-wire telephone lines are in every respect suitable for broadcasting purposes. (b) That one should not forget that the necessary freedom from inductive interference . can only be obtained on circuits which are very carefully balanced and maintained. (c) That no serious distortion would be caused by the introduction of short, non-loaded cable lengths on open-wire lines, such as are used for railway and river crossings, etc. If long, loaded cables are inserted, the effects may be more serious. In the case of long cable lengths, the cut-off frequency must meet the conditions relating to the range of frequency to be transmitted for the various qualities of broadcast transmission. (Green Book, pp. 73 and 74; English translation, 1928, p. 51.) (d) That when amplification is necessary on open-wire lines used for broadcasting, it is desirable that the attenuation of the line between two successive repeater stations should not exceed 1 neper or 8-7 decibels. (e) That with respect to the value of the input power applied to the repeaters, vacuum tubes should be employed which are capable of dealing with 100 milliwatts without undue non-linear distortion. The repeaters to be used must have a very flat frequency characteristic curve over a range of 30 to 10 000 periods per second.

Alterations made in Cable Circuits in order that they may be suitable for Broadcast Transmission.* The International Consultative Committee— Having regard to the considerations laid down in the recommendation “ Frequency band to be transmitted for different qualities of broadcast transmission/' Unanimously advises :— (1) That cable circuits for radio-broadcasting require a different value of cut-off

.* This text replaces that under the same heading on pp. 174 and 175 of the Green Book; English tran slatio n , 1928, p. 132. 70 frequency. In medium-heavy loaded quads, the phantom circuits of which have a cut-off frequency of approximately 3 800 periods per second, these circuits can only be used for transmissions over which a range up to 3 000 periods per second is sufficient. For broad­ cast transmissions of a higher standard, extra-light loaded side and phantom-circuits are usable, with a preference for the phantom circuits. (2) In long-distance cables of the types specified by the C.C.I. (Systems 1 and 2 of the Typical Specification of Loading, contained in Appendix B.d.2, No. 3), when specially loaded circuits have been reserved for the relaying of broadcast transmission, it would be possible, both economically and technically, to prescribe for these circuits a cut-off frequency of approximately 10 000 periods per* second. (3) That, with respect to the repeaters, it is necessary that the frequency curve of amplification and the frequency curve of the circuit coincide. This coincidence should take place with a maximum allowable deviation of ffio-15 neper or ±1-3 decibel within the frequency ranges required for the different types of broadcast transmission. On the basis of the advice already given vacuum tubes may have to be used which are capable of dealing with a power of the order of 100 milliwatts in order to avoid non-linear distortion.

Electrical Conditions to be considered as a Criterion for the good condition of Lines for relaying Radio Broadcast Transmissions.

Equivalent and Distortion. The equivalent of a circuit relaying radio broadcast transmission (measured at a frequency of 800 p.p.s. and with a power of -I milliwatt into 600 ohms) between the ends of the circuit terminated by 600 ohms should be 0 neper. Variations of +0*3 neper or + 2-6 decibels are nevertheless admissible. The maximum variation between the values of transmission equivalents of the line must not exceed one neper or 8 • 7 decibels within the band of frequencies to be transmitted, in order that the line and the repeater shall ensure the desired transmission. (See Instructions for the drawing up of a specification for repeaters used for the relay of broadcast transmission, p. 126.) Transmission Level. The power level measured at the output of any repeater at 800 p-.p.s. shall not exceed -T i 'i nepers or -j- 9*5 decibels for cable lines and —}— o *5 neper or +4*3 decibels for open wires. The power level measured at the input of any repeater at 800 p.p.s. should not be less than — 3 - 5 nepers or — 30 *4 decibels for cable lines and — 1-3 nepers or — 11 *3 decibels for open-wire lines. These levels have been determined on the assumption that the sound intensity has been regulated in the studio in such a manner that the power does not exceed 50 milliwatts at any point of the line. Crosstalk. Crosstalk attenuation for the voice between two lines used for relaying radio broadcast transmission, or between one of these lines and a telephone line, should be at least 9 nepers or .78 decibels for cable lines and 7 nepers or 61 decibels foi open-wire lines. Where it is necessary to employ, for the relay of broadcast transmission, lines which have a crosstalk attenuation below the above values, it is necessary, in consequence, to reduce the maximum power applied at the input of these lines.

* The figures given here are only provisional. • f This text should be inserted on page 175 of the Green Book (English translation, 1928, p. 133), after the first paragraph, and immediately before “ A.c. Apparatus." 71 Absence of Noise. The noise level on the transmission line should be less than the maximum level used by at least 7 nepers or 61 decibels. A suitable value for the permissible limit of the noise voltage, measured at the end of the circuit (level zero) is 5 millivolts.

Non-Linear Distortion. The level of harmonics produced by non-linear distortion should be less than that of the fundamental wave by at least 2*3 nepers or 20 decibels for the maximum power and for any frequency comprised within the frequency band to be transmitted.

Transient Phenomena during the building up and decay of the current. The period of the building up and of the decay of the current shall not exceed 30 milli­ seconds for any frequency within the frequency band to be transmitted.

(A.b.4.) Picture Transmission.* Conditions relating to Picture Transmission over Telephone Circuits. 1. For the telegraphic transmission of pictures, it is only possible to use telephone circuits in which reaction coupling does not exceed the permissible value (see paragraph 4). On this basis, two-wire circuits cannot, therefore, be used in practice for the telegraphic transmission of pictures. With normal four-wire working, the circuit can only, be used each time for one-way transmission. In this case, it is generally necessary to make use of echo-suppressors, in order to eliminate coupling by reaction. If it is desired to transmit simultaneously in both directions, the terminals and the echo suppressors must be disconnected. 2. The conditions relating to the equivalent (of transmission) of four-wire circuits used for the telegraphic transmission of pictures are, in general, the same as when used for telephony. (a) Attenuation between terminating toll offices must not exceed 1 -3 nepers or 11 decibels. (b) Attenuation between photo-telegraph officesf shall not exceed 3*3 nepers or 29*0 decibels. (c) The attenuation distortion between photo-telegraph exchanges shall not exceed i*o neper or 9 decibels in the frequency band to be transmitted for picture telegraphy. As a distortion of 1 • o neper or 9 decibels is already allowed for the telephone circuit itself, it may therefore be necessary, eventually to compensate for the distortion of the lines connecting the photo-telegraph office to the toll exchange. (d) The equivalent must remain as constant as possible during the transmission of pictures. The effect of sudden variations of o-i neper or 1 decibel is already apparent on the pictures transmitted. It is, besides, necessary to avoid any interruption of the circuit, however short. For this reason it is necessary to give the greatest attention to tests taken on the repeaters and lines, and to the changing over of batteries. To avoid any disturbance it is desirable that the terminating toll exchanges should be placed out of circuit when the circuit is extended to the photo-telegraph exchanges. Special precautions should be taken to ensure that no modulation is caused in the carrier current, either by the line or by the lepeaters, even if this modulation is not audible. Such modulation can be caused in particular, either by variations in battery voltage or by infra­ acoustic telegraphy.

* This text should be inserted on page 175 of the Green Book (English translation, 1928, p. 133) immediately before chapter (A.c.) Apparatus. f By photo-telegraph office is meant any station for transmitting or receiving pictures.

7 2 . (e) The level (of transmission) at the outgoing side of the repeaters must be between -(-o*5 neper or -f- 4*5 decibels and -J- i*o neper or -f~ 9 decibels. The power of the photo­ telegraph transmitter must be calculated so that the power available for the transmission of a mark is from io to 20 milliwatts at the outgoing side of the repeaters.

3 . The difference in the times ot propagation of the various photo-telegraph frequencies, and the final width of the frequency band transmitted give rise to transient phenomena (during building up and decay) which limit the rapidity of transmission of the pictures. The frequency band chosen should be narrower—and, in consequence, the transmission speed slower—as the differences between the times of propagation in that band become greater.- The quality of the transmitted pictures depends on the separating network, and on the period of the transition phenomena which vary with the transmission qualities of the lines. The principal results of a large number of experiments obtained with a system of 5 marks per millimetre are given in the following paragraph by way of example. Medium-loaded lines were employed up to 600 km for a transmission period of six minutes for one square decimetre, and up to 300 km for a transmission period of three minutes for 100 square centimetres. For longer cables, it is necessary to eliminate the phase distortion by means of phase compensators. Long distance circuits with phase compensation and medium-heavy loading have already been used, with success, for photo-telegraph transmission over distances amounting to 1 800 km with a transmission period of three minutes per 100 cm2. Photo­ telegraph transmission can also be effected, without any phase compensation, on lightly loaded cable circuits over distances amounting to 1 800 km with a transmission period of three minutes per 100 cm2, and 3 600 km with six minutes per 100 cm2. 4. The troubles arising from crosstalk, noises due to heavy currents and reaction-coupling currents should be small enough to obtain a difference of at-least 4 nepers or 35 decibels between the level of the disturbing currents and the level of the photo-telegraph currents. The stability of the circuit should be at least 2 nepers or 17 decibels. If echo suppressors are used in the four-wire circuits, a stability of 0*5 neper or 4*5 decibels will be sufficient. 5.. It is desirable that circuits employed for picture transmission should be marked by a characteristic sign in the terminal exchanges and in the intermediate repeater stations, and, further, special instructions should be given to the personnel, in order that the latter shall not come in circuit when picture transmission is taking place.

(A .c.) A pparatus.

(A.c .i .) Subscribers’ Instruments.* Tests on Subscribers’ Instruments and Lines in Operation. The International Consultative Committee— Considering :— That, in order to obtain satisfactory transmission on international communications it is essential to have well-defined testing methods for subscribers’ instruments; Unanimously advises :— 1. That it is desirable that each subscriber’s station which is used in conjunction with international circuits shall be tested once a year,

2 . That, provisionally, Administrations may make use of the methods indicated in Appendices C.c.i, No. ia, C.c.j., No. ij3, C.c.i., No. iy , C.c.i, No. 2 , C.c.i, No. 3 , C.c.i, No. 4 .

* This text replaces that appearing under A.c. 1 on page 175 of the Green Book; English translation, 1928, p. 133. 73 (A.c.2.) Local Exchanges. General conditions which should be satisfied by the new Bourse-exchanges regarding the use of International Circuits. The International Consultative Committee— Considering :— That the practice of sending Bourse communications, during certain hours of the day, over direct connections terminating at the Bourse exchange, offers the advantage of eliminating certain intermediaries. Unanimously advises :— Where traffic justifies it, and especially when the calls are arranged according to a pre­ arranged system (list system), it is advantageous to use direct connections terminating in the Bourse exchange. Considering, however :— That where direct connections terminate in the Bourse exchange it is desirable to take all necessary steps to ensure that the transmission of ringing and speaking currents takes place under the best possible conditions. Unanimously advises 1. That the switching over of a circuit to the Bourse exchange should be effected at the toll office by means of metallic connection without the intervention of any other equipment. 2. That a source of ringing current having appropriate characteristics (namely a sufficiently large electromotive force and a frequency between 16 and 25 p.p.s.) be installed in the Bourse exchange.

Considering, finally :— That the Plenary Session of the C.C.I. in Paris, 1928, has laid down proposed regulations applicable to Bourse exchanges, (see Green Book, page 393, paragraph 3 (2), English translation, 1928, page 304, paragraph 3 (2)) providing for a broker asking, before receiving the final advice (avis definitif), for the call to be put through to an office situated outside the Bourse, but in the same local network. That, on account of the large attenuation resulting from the use of auxiliary lines and local exchanges of the local network, and of the inconvenience which would result in the nor mal working of the local services, it is undesirable, in such cases, to transfer a call, set up over the direct connection from the Bourse exchange to the office indicated by the broker.

Unanimously advises :— • That, when a broker, before receiving the final advice, asks for the call to be put through to another office of the same local network, it is desirable immediately to inform the originating station, which must take the necessary steps to ensure that the call is put through to the required office by means of a circuit of the general service, and not over the direct connection reserved for the Bourse exchange. In the case where calls to, or from, the Bourse exchange, are established over normal circuits (as, for instance, international calls from, or to, an ordinary subscriber), . The International Consultative Committee— Considering :— That the traffic from, or to, Bourse exchanges is very heavy, and must be dealt with in ' 7 4 a limited time, That the demand for corresponding connections always includes the names of persons. Unanimously advises :— . • 1. That it would be advantageous to connect Bourse exchanges to the calling positions of the toll office by means of special circuits. 2. That it might be advantageous for the calling indicators associated with the Bourse exchange to be specially marked.

N ote.’—It is to be noted that certain Administrations have found it advisable to establish Bourse exchange calls by means of direct circuits connecting the Bourse exchange to the toll office.

(A.c.3.) Toll Exchanges. Conditions to be satisfied by Cord Circuit Repeater Positions from the point of view of Facilities for regulation of the Repeater, as well as for supervision, and charging of Calls. The International Consultative Committee— Considering :— That it is desirable to standardise the system of operation to be followed in establishing, terminating and charging for international transit calls, cord circuit repeaters being employed or not. Unanimously advises :— 1. That the supervision and fixing of the chargeable period of a transit call using a repeater always devolves on the toll operator on the controlling circuit. 2. That it is desirable to suppress, if possible, or, in any case, to simplify as much as possible, the gain regulation of cord circuit repeaters. In this connection, it is" interesting to note the respective methods employed in Holland (disposition of circuits and installations, and use of auxiliary networks in order always to employ cord circuit repeaters set at the same gain; see Appendix A.c.3, No. 1) : in Great Britain and the United States of America (apparatus connected in the third wire of each long distance circuit, and intended to operate on the regulating devices of the cord circuit repeater in order to obtain the maximum gain for each combination of circuits, two at a time)—-{see Appendices A.c.3, No. 2 and A.c.3, No. 3). When one of these solutions is employed, it may be useful to arrange for any further gain regulation to be controlled by the toll operator operating the controlling circuit. 3. That the insertion of a cord circuit repeater in an international connection should depend on the judgment of the toll operator working the controlling circuit, and must be possible by rapid operation, either automatically or 'manually (the manual intermediary, if existing, taking no part in the operation). 4. That the signals sent over circuits when a call temporarily makes use of a repeater are still to be received by the toll operator operating the controlling circuit.

Conditions to be satisfied by International Positions, as regards the type of Operator’s Set and the Transmission Losses due to the Operator listening on the Line. The International Consultative Committee— Considering :— That the use of a breast transmitter and of an head-band receiver gives to operators 75 serving international positions, great freedom of movement, and allows them to be always ready to do their work. That light and efficient head-band receivers are now available.

Unanimously advises :—

That operators engaged on the international telephone service should be provided with head-band receivers and breast transmitters. Considering, however That disturbances caused by room noises, together with transmission losses due to the operators’ instruments, should be reduced as much as possible.

Unanimously advises :— 1. That the operator’s instruments used in the international telephone service should be provided with a device allowing the transmitter to be disconnected, this device being preferably a key. 2. That the loss due to an operator’s instrument, used in the international telephone service, must not exceed 0*9 neper or 0-77 decibel for any frequency between 300 and 2 500 p.p.s! in the silent listening position (transmitter out of circuit) (see above, p. 67), this limit being permitted provisionally; experiments should be made to determine whether it is possible to reduce this limit to a value, for instance, of 0-05 neper or 0*43 decibel (by increasing, as much as possible, the impedance of the operator’s instrument, maintaining at the same time satisfactory reception for the operator).

(A.c.4.) Repeater Stations. Compensation of the Effects due to Temperature Variations.* The International Consultative Committee— Considering :— That aerial cables are subjected to sudden, and underground cables to less sudden, temperature variations. Unanimously advises :— 1. That it is recommended to provide regulating devices, permanently associated with the repeaters, in cases where appreciable temperature variations frequently affect the transmission on cables, notably those containing long sections of aerial cable. In this case, the control stations, from the point of view of adjusting and distributing the amplification of the various repeaters, shall be the stations where such regulating devices are installed. 2. That it is recommended to take due note of slow temperature variations in underground cables, and set repeaters to a predetermined value in the cold winter months, to. another in the warm summer months, and to a mean value for other seasons; the measuring stations (control and sub-control) when making monthly tests of the equivalent, should first verify the setting of the repeaters corresponding to the time of year, and alter this setting if the temperature variations have been abnormal. On this basis, more frequent tests will have to be made than are prescribed for normal routine.

* This text replaces that on page 177 of the Green Book on “ Compensation of the effects due to rapid temperature variations English translation, 1928, p. 134. (A .d.) L in es. (A.d.i.) Open-wire Lines.*

Loading of Open-wire Lines. The International Consultative Committee— Considering :— That the loading of open-wire lines— (1) renders difficult the operation of these lines because of variations in the insulation resistance and magnetisation of the coils due to atmospheric discharges; (2) renders difficult the operation of these lines with repeaters; (3) is incompatible with carrier telephone operation on these lines; (4) varies excessively the transmission of the different speech frequencies, introduces distortion and consequently decreases the articulation of the conversation, Unanimously advises :— That open-wire telephone lines, operated with repeaters and used for long-distance international traffic, should not be loaded.

Setting up of Open-wire Lines.

The International Consultative Committee— Considering :— That the setting up of international telephone communications over long distances necessitates at present in certain countries the use of open-wire lines. That the greatest efficiency of these lines will be obtained if phantom circuits are used and, in addition, repeaters and also carrier systems. That in order to ensure satisfactory operation of these various arrangements as well as to avoid the introduction of losses due to reflection, it is essential that the circuits should be balanced and that the electrical constants should be uniformly distributed over the whole length of the lines between two repeater stations. That it is very important to construct the open-wire lines in such a way as to ensure continuity of service and satisfactory operation. That it is not possible to give general and permanent definitions of the geometric or mechanical constants of the lines, since the choice of these constants depends not only on the electrical characteristics, but also-on economic factors which may vary from time to time and from country to country.

Unanimously advises :— (a) Concerning the mechanical qualities of the open-wire lines : (1) That for the construction of long open-wire lines for international service, conductors of at least 3 mm diameter and having a sufficiently high mechanical resistance to reduce the chances of breaking to a minimum, shall be employed. (2) That the strength of the pole line shall be great enough to withstand with as great a margin of safety as possible the greatest load caused by wind, frost or snow.

* This text replaces that on pp. 178-180 of the Green Book; English translation, 1928, p. 135-136. 77 (b) Concerning the electrical qualities of the open-wire lines : (1) That the conductors shall be of copper or of an alloy of copper the conductivity of which shall not differ from that of high conductivity copper by more than io per cent., or of a metal or alloy which has the same advantages and satisfies the conditions mentioned below.

(2) That within a repeater section or between a repeater station and the neigh­ bouring terminal station, the metal of, the diameter of, and the distance between, the conductors of a long-distance telephone circuit shall remain the same in order to ensure a satisfactory degree of regularity. In order to ensure satisfactory regularity the deviation of the impedance (as a function of the frequency) from the mean curve shall not exceed 5 per cent. This deviation shall be calculated as indicated for “ Impedance Balance.”

(3) That all joints on an open-wire line shall be made in such a way as not to introduce variable resistance.

(4) That in any repeater section of open-wire line or in a section of line between a repeater station and the neighbouring terminal station, the resistance unbalance of the two wires of any pair, measured with direct current, shall not be greater than 2 ohms.

(5) That in order to avoid trouble due to crosstalk or interference from heavy current or high-tension power lines or from telegraph circuits, long-distance inter­ national telephone circuits shall have transpositions or rotations so made that the length over which neutralisation between any two of these circuits is complete shall be less than 100 km. In the case of carrier systems or interference from heavy current or high-tension power lines or parallels with telegraph circuits it may be advisable to reduce the length of the “ barrel.”

In order to protect aerial lines used for high frequency carrier currents from one another or from the disturbing influence of large broadcasting stations, it is advisable to provide the circuits with nearly similar lengths of “ barrel ” (if possible at each supporting point).

(6) That sp far as concerns dangers and operating troubles due to heavy current or high-tension power lines, the telephone circuits shall satisfy the conditions indicated in the “ Guiding Principles concerning measures to be taken in order to protect telephone lines against the disturbing influences of heavy current or high-tension power lines,” published by the C.C.I. (Paris, 1926).

(7) That the insulation resistance of each wire from earth shall not fall below the value of 1 megohm per km, which experience in several countries has shown to be a practicable value for normal conditions of humidity, the maintenance of this insulation resistance being possible by the use of double-shed insulators of suitable design. This value may be decreased in exceptionally damp districts.

(8) That the transmission equivalent of the line between two successive repeater stations or between a repeater station and the neighbouring terminal station shall not exceed i*6 nepers or 13-9 decibels.

(9) The circuits shall be brought out to testing points in accordance with the recommendations of the C.C.I. (“ Testing points on international circuits,” Green Book, p. 217; English translation, 1928, p. 165.) 78 (A.d.3.) Mixed Lines.

Rules for the Construction and Loading of Cables inserted in Open-wire Lines.*

The International Consultative Committee—

Unanimously advises :— (1) That any section of cable longer than 100 metres which is inserted in an open-wire line should be constructed specially to satisfy the following conditions :— Z — Z (2) That the difference 2 ^ ^ * between the impedance Z x of a section of mixed line between repeater stations or between a repeater station and the adjacent terminal station, and the impedance of a homogeneous open-wire section or of the balancing network, shall not exceed 5 per cent, (measured from the ends, of the ‘section) for any frequency between 300 and 2 500. p.p.s. This condition can be satisfied, according to the length and number of intermediate cables, by the use of Krarup cables or light loaded cables {see (4) below) or by medium loaded cables terminated by networks designed to adapt the impedances to each other {see (5) below). (3) That the electrical characteristics of a cable inserted in an open-wire line should be such that-— R L C = -j=- ~ where R x, L x and Cx represent the resistance, inductance and capacity of the cable, and R, L and C the corresponding values for the open-wire line. The leakance. is not considered, as its effect is very small and variable. (4) That for sections of cable there should be used— Either Krarup loaded cables—notably for one or more short sections of cable in the same circuit—whose electrical characteristics R, L and C conform to the conditions given in Section 3 ; Or cables loaded so that the electrical characteristics R, L and C conform to the conditions given in Section 3, and having a cut-off frequency such that the conditions given in Section 2 are met.

If there are several sections of cable in the same open-wire circuit, the cut-off frequency of the different cable sections shall be increased in order to fulfil the conditions given in Section 2. (5) That where very long cables are inserted in the line, economic consideration may be ' given to the use of medium loaded cable terminated at each end by a “ Supplementary Balancing Network,” designed to adapt the impedance of the cable to that of the open-wire line within the limits of the frequencies to be transmitted, with lower balance limits than allowed in paragraph (2) above. This proceeding will avoid difficulties in certain cases. (6) In the Appendices 2 and 3 details are given of two methods of calculating the data of Krarup loaded cables (or lump loaded cables) which may or may not be fitted with supple­ mentary balancing networks designed to adapt the cable and open-wire impedances in order to ensure that the conditions outlined above are met.

* This text replaces the similar text on pp. 182 and 183 of the Green Book; English translation, 1928, p p . 138- 140. . 79 7- On aerial lines used for high frequency carrier currents underground sections must be avoided as much as possible. If these sections are unavoidable the following advice must be followed. In certain cases it is possible and economical to reduce either the distortion or the high frequency equivalent of a repeater section in order that this equivalent remains below the prescribed limit of 5 nepers 01 43 decibels, by loading one or more sections of cable in the circuit. In this case a practical system of loading is the following: Loading spacing, 200 metres; coil inductance, 3 millihenries (specially prepared magnetic cored coils, coils devoid of magnetic material, the wire being in all cases divided); cut-off frequency, approximately 60 000 p.p.s.; characteristic impedance, 600 ohms. The first section must be completed in order to provide a half loading section (100 m). In any case the gauge of the intermediate cable must be such, that the relation RLC — = — = is satisfied (R, L, C being the constants per kilometre of the cable, and R v 1 1 1 L v Cv those of the aerial line). 8. To adapt the cable sections forming part of the existing open-wire lines the instructions given in Appendices II and III should be followed (see Green Book, pages 188-215, English translation, 1928, pp. 140-163).

N o t e .— The Appendices la, lb, Ic, Id, II and III shown on pages 184 to 216 of the Green Book, English translation, 1928, pp. 139 to 163, remain unaltered.

(A.e.) MAINTENANCE AND SUPERVISION. Advice of the International Consultative Committee regarding Maintenance and Supervision of Lines and Installations. Extract from the List of Periodical Tests for the Maintenance of International Circuits.*

II (4 ). Singing Point of a Circuit. The object of this test is to ascertain that no appreciable variation has taken place between the circuit and its balance. The test must be carried out with the repeater normally working in the circuit. To make the test a request should first be made to the stations in both the East and West directions to close the circuit to be tested by an impedance approximately that of the circuit. At terminal stations this should be done by means of a rheostat of the required value, unless a special impedance is provided. The test may also be made by reducing to zero the gains of the adjacent repeaters towards the repeater under test. Where the termination is made at a repeater station a repeater unit, in normal operating condition but with the gain regulating device set at zero gain, shall be used. Should it be desired to test the singing point on the direction East, a short-circuiting plug should be inserted in the West repeater balance jack. This converts the differential transformer in the direction West to an intervalve transformer, and the unit gives the improve­ ment of a two-way 2-valve repeater. The two potentiometers should be raised together until “ singing ” is heard when listening on the monitoring circuit, and then reduced alternately step by step until singing ceases. The test should be then repeated with the positions of the short circuiting and open circuit plugs interchanged. The singing point should then be taken as the sum of the gains represented by the positions of the potentiometers in whichever of the two tests gives the lower value. An

* Paragraphs under this heading on pp. 219-224 of the “ Green Book ” (English translation, 1928, pp. 166-170) remain without modification. Section II (4) on pp. 224-226 of the “ Green Book ” (English translation, 1928, p. 170), is replaced by the above. 80 allowance of 0*7 neper or 6 decibels should be added to allow for the fact that the West three-winding transformer acts as a simple inter-valve transformer and therefore acts with increased efficiency. • . The gains, represented by the sum of the potentiometer readings, should be taken from the records of test III (7), giving the calibration of the repeaters. In those cases where a specially prepared repeater unit is provided, a key is substituted for the plugs, but otherwise the method of test is exactly similar. A second method, described on a later page, may be used to determine the maximum gain which a repeater may give without “ singing.” The circuit in one direction and its balancing network are connected to the repeater in the normal way. The circuit in the opposite direction and its balancing network are replaced by two resistances, one of a fixed value (1 000 ohms) and the other by a variable resistance R. The gains of the two repeater elements are raised to their maximum value. The value of the resistance R is then decreased until “ singing ” occurs. The limiting value of the relation Rj 1 000, obtained in this manner, is a definite function of the maximum permissible gain. For this reason it is possible to calibrate the variable resistance R directly in terms of units of transmission. A record should be made of the result of these tests when the circuit is first formed and the variation from these figures on subsequent tests should not exceed 0-2 neper or 1-73 decibels. In the event of this figure being exceeded an impedance test should be made of the circuit and the balancing network. -

N o t e .— Repeater stations should be provided with instruments capable of indicating, rapidly and accurately, whether the singing of a repeater, under working conditions, is caused by insufficient agreement between the line and balancing network impedances. To check this, it is possible to use an apparatus known as “ Echomesser ” which is described by R. Feldkeller and H. Jacoby in an article in the “ T.F.T.” (March, 1928) (see Appendix I below, entitled “ Definition and Measurement of the Attenuation due to Echo ”), or an instrument known as a “ Singing Point Test Set ” described in an appendix presented by the British Administration. (See Appendix II, p. 84, entitled “ Impedance Unbalance Tests.”)

APPENDIX I.

DEFINITION AND MEASUREMENT OF ATTENUATION DUE TO ECHO (SINGING POINT). 1. The attenuation bE due to echo (or " Singing Point ”) of a two-wire circuit is defined as one-half of the natural logarithm of the input power N v sent into the line from an adjustable .generator, before the return of the echo, divided by the power of the reflected currents (power of the echo) N 2—produced by line irregularities and returning to the generator.

*>k = i loSe ^ ...... W 2 2. A simple relation exists between the singing point bE, the impedance ZE of a line free from echoes, and line impedance U when echoes are present. When a generator having an e.m.f. EQ and an internal impedance Z is connected, for example, to. the sending end of the line, the power taken by the line before the -arrival of the echo is N 1 = (2) 4Z After the echo has arrived, the impedance of the line changes from Z to U so that the

8 1 r received current, instead of the value

t — E o •(3) J l 2Z has the value E r ./2 = z + u •(4) The reflected current corresponds to the difference between the two currents :— 'Z — U' JiiJ = J2T - JlJ _ 2Z£o + UJ .. ■(5)

The power of the echo is therefore E 2 Z - U N 2 = — 1 ,(6) 2 4^ Z + £7 From the equation giving the singing point bE, this is related to the impedance by the expression :— Z + U log. z - u •(7)

3. Supposing that, in an ideally balanced line, the line with echo is reproduced by a line free from echoes : It is then possible to separate the ingoing line current from that which returns as echo. The loss between terminals 1 and 2 is obtained from the line impedance U, with echo, and the line impedance Z, without echo, from the formula : Z + U &1 2 = l0ge + log,2 (8) U or, conforming to equation (7)

h -> 2 = bE + loge2 •(9)

The characteristic impedance of the line free from echoes can be represented approximately by a balancing network. This simulation must be sufficiently exact in order that the error arising from simulating the line impedance by the network impedance is negligible as compared with the singing point.

LINE CONTAINING LINE FREE FROM REFLECTION OR REFLECTION OR ECHO CURRENTS. ECHO CURRENTS.

F ig . 1.—Balanced Circuit.

5. The stability of a circuit with terminating sets depends not only on the singing point bE of the line but also on the accuracy with which the impedance U of the network simulates the characteristic impedance of the line free from echoes. In the case of imperfect simulation (with Hoyt’s balancing networks for loaded circuits to within 2—3 per cent, approximately) 82 a line free from echoes can also give rise to loss between the terminals i and 2 of the hybrid coil. The singing point of the line appears then to be reduced by a certain value which depends on the accuracy of simulation of the balancing network employed. The value so obtained will be designated by the effective singing point, as it represents an important measure of service conditions of communication.

F ig . 2.—Echometer.

6. Method of Measurement.—Principle of the Echometer (see Fig. 2). The Echometer is made up of a terminating circuit, one side of which is connected to the line to be tested, and the other to the balancing network of that line, together with a repeater giving a constant amplification capable of accurate regulation between the limits of 300 and 2 000 or 2 400 p.p.s. The repeater is inserted between the terminals 1 and 2 of the hybrid coil (terminating circuit). The attenuation between these two points being bE + loge2 (see equation 9), singing will begin when the echo attenuation equals bE -J- loge2. The repeater comprises two normal B.O. valves connected in series, transformer-coupled; an arrangement generally used in telephone repeaters. To obtain a high amplification within the frequency range between 300 and 2 000 p.p.s., and a flat gain-frequency characteristic, a multiple-stage band filter is inserted. This filter gives, in addition, the advantage that the phase of the reaction circuit varies considerably with the frequency, the result being that oscillations will also be set up at frequencies where the reaction currents are in phase. The gain-frequency characteristic can be displaced by the potentiometer calibrated in steps of o • 1 neper; the amplification can thus be regulated between the limits of singing point of 0-5 and 4-5 nepers. The echometer can be calibrated accurately, by substituting for the line and balancing network connected to the measuring bridge, two resistances whose difference corresponds to a known singing point, say 3*0 nepers. By means of a special rheostat which is employed only for actual tests, the gain is varied until the echometer reaches the oscillation limit for this load on the bridge. When carrying out these tests the gain is gradually increased, starting at the lowest stop of the echometer, until continuous oscillations begin (or stop). The singing point can then be read off directly from the rheostat scale. The repeater can be calibrated by substituting for the line and its network two resistances whose difference corresponds to a known singing point as, for instance, 3 *o nepers.

8 3 f 2 APPENDIX II.

THE MEASUREMENT OF IMPEDANCE UNBALANCE.

Note by the International Standard Electric Corporation {June, 1929).

General Considerations. In order to ensure the stability and good quality of two-wire repeatered circuits under working conditions the following requirements must be met at all frequencies within the working range :— 1. The impedance balance between the line circuit and the simulating network associated with it must be good. This is ensured by the clause dealing with impedance unbalance in the C.C.I. requirements for repeater sections of loaded international cable (“ Green Book ” p. 283; English translation, 1928, p. 217) and by the monthly singing point tests prescribed as part of the routine maintenance tests to be made at repeater stations {“ Green Book," p. 224; English translation, 1928, p. 170). 2. There must be no serious impedance unbalance in the repeaters themselves. This is ensured by quarterly singing point tests on the repeaters. 3. There must be a sufficient margin of difference between the repeater gains and the singing points over the whole circuit to ensure that no repeater is operating at a gain so near the singing point as to cause distortion. This, is ensured by monthly stability tests {see, page 96, “ Suggested Instructions for Putting into Service and Maintaining International Telephone Circuits ”). . The second and third of these conditions can be ensured by tests made with the repeaters normally in use and, provided that their gains can be measured accurately, no special apparatus is required. To determine whether the first requirement has been met two kinds of tests are necessary, viz. :— {a) Acceptance tests to ensure that the repeater sections of cable meet the requirements specified for impedance regularity. {b) Maintenance tests to ensure that a sufficiently accurate balance is maintained between the lines and the simulating networks which are associated with them in practice. Such tests should be made monthly and whenever an abnormal unbalance between the lines and simulating networks has been detected by stability tests. For the acceptance tests, it is necessary to obtain an accurate and rapid measurement of the quality of the cable independently of any apparatus with which it may afterwards be associated. For the maintenance tests it is recommended that instruments should be provided in repeater stations, especially where repeaters designed to correct for line attenuation distortion are used, for checking rapidly and precisely whether singing under working conditions is due to unbalance between the line and network impedances. The International Standard Electric Corporation has recently developed an instrument, to be described below, which is suitable both for acceptance and maintenance tests. In both cases it is necessary to obtain a measure of the impedance balance, over the working range of frequencies, between the loaded line and a simulating network, the line being terminated by an impedance equal to its own characteristic impedance at all frequencies within the range. If the simulating network is suitably designed such a measure is a criterion of a regularity of the line and of the closeness with which its impedance characteristic approaches the standard form; any serious fault in loading regularity or capacity regularity or in the values- of the inductance, capacity, resistance or insulation of the circuit will therefore be detected by such a measurement.

8 4 : Theoretical Considerations. Suppose that the simulating network has an impedance ZN and that the line itself has an impedance ZL which, at any given frequency, differs from ZN by an amount which depends : i.. On the closeness with which the normal line impedance conforms to that for which the network was designed, and 2. On the amount by which the actual impedance as measured at the end of the line differs from the normal impedance which would be measured if the line were free from irregularities. If the impedance of the network is regarded as the internal impedance of a generator feeding into the impedance of the line, then there will be, in general, a difference between the current entering the line and that which would have entered it if its impedance had been equal to that of the generator. This difference may be regarded as reflected current returning from the line into the simulating network, and the ratio of this reflected current to the current which would have entered the line, if its impedance had been equal to that of the simulated network, gives a measure of the degree of unbalance. This ratio is conveniently expressed as an attenuation, which, for reasons which will appear later, is called the singing point between the line and simulating network, and is equal to the real part of—

Z ft-\-Z jj -v i i Z n T" 20 log10 —------— decibels or loge —------— nepers zN zL Z N ZL where ZN and ZL are, in general, complex quantities.

Z|

A o-'VWWWVWo— — o B

— ^kSiMSALP

F ig . i .

Now if the line and simulating network are connected to a differential transformer, as indicated in Fig. i, it can be shown that the attenuation which would be measured between the input terminals AB and the bridge terminals CD depends on the degree of impedance unbalance between the line and simulating network and also on the impedance Zj and Z2 across which the attenuation is measured. Assuming that the transformer is symmetrical and Z x and Z2 are correctly chosen so that in the balance condition no reflection losses occur at any of the terminals, the normal power developed in ZL will be half that in AB ; this corresponds to an attenuation of approximately 3-0 decibels. Now if, at any particular frequency, the impedance ZL is different from ZN the transformer is unbalanced and there is a reflected current equal to the current normally entering ZL attenuated by the loss in the' external part of the echo path (i.e., the singing point defined by the above expression). This reflected current may be considered as superimposed on the normal current; it re-enters the transformer from ZL and the power developed by it will be divided equally between A B and CD. This division corresponds to a further loss of 3-0 decibels. The total attenuation between AB and CD, provided that the impedances Z v Z 2 and ZN have their normal values, is therefore 6 decibels, plus the singing point expressed in decibels, plus o-6 decibel, corre-

85 . ' ' F 3 sponding to the iron and copper losses occurring in commercial transformers. The singing point can therefore be expressed as the attenuation measured across the differential transformer minus 6*6 decibels. Now a two-way one-element repeater cannot sing unless the gain of the amplifying element is at least equal to the attenuation across the differential transformer. The gain of the amplying element is equal to the gain as measured at the line terminals of the repeater plus the loss of 6-6 decibels occurring in the transformer during the measurement. Hence singing cannot take place unless the measured gain is at least equal to the attenuation across the differential transformer minus 6 • 6 decibels, that is to the singing point between the lines on the two sides of the repeater. Similarly a two-way t.wo-element repeater cannot sing unless the sum of the measured gains in the two directions is at least equal to the sum of the singing points between the lines and networks on the two sides. If one transformer is completely unbalanced by short-circuiting the line terminals and open circuiting the simulating network terminals, or vice versa, the division of the power by four at this transformer no longer takes place and it acts merely as a repeating coil with a loss of about o-6.decibel; if the gain of the repeater is then varied until the repeater is on the point of singing the sum of the measured gains is equal to the singing point at the other differential transformer minus 6*o decibels. The singing point may then be defined as the sum of the measured gains plus 6-0 decibels. Hence from the fundamental definition of singing point as the real part of Z -j- Z 20 log10 ----- decibels two practical definitions are deducible, viz. :— Z N Z L 1. The singing point of two impedances connected to a differential transformer as described above is the transmission loss, minus approximately 6*6 decibels or 0*76 neper, measured between the input terminals and bridge terminals of such a transformer. 2. The singing point of two impedances connected to one differential transformer in a two-way two-element repeater, the other differential transformer being completely unbalanced as described above, is the sum of the measured gains of the repeater elements when the circuit is on the point of singing, plus approximately 6 *o decibels or 0 *7 neper. This is the definition adopted by the C.C.I. for the singing point of a repeater on a circuit (“ Green Book," p. 225; English translation, 1928, p. 170). In addition to these two definitions, there is a third which has been adopted by the C.C.I. for the impedance unbalance of a line. This is defined as the vector difference between the line impedance and that of a simulating network designed to match the impedance deduced from the measured mean circuit constants, this difference being expressed as a percentage of the network impedance (“ Green Book,” p. 283; English translation, 1928, p. 217). Since the impedance of the line may be greater or less than that of the simulating network, there are, in general, two values of this percentage for any value of singing point as given by the expression deduced above, which is symmetrical with regard to the line and simulating network impedances.

Practical Considerations. Corresponding to these three definitions of impedance unbalance, or singing point, three methods have hitherto been available for its measurement, viz. :— 1. A method based on the first practical definition of singing point given above; an instrument is used which measures directly the attenuation loss across a differential transformer to which the line and simulating network are connected. 2. A method based on the second practical definition of singing point given above; a repeater or improved type of amplifier is used, the gains or losses in which can be varied until the overall gain neutralises the loss between the input and bridge terminals of a differential transformer to which the line and network are connected. At this point, provided that the correct phase relations hold, the amplifier sings. 86 3. Direct measurement of the line and simulating network impedance over the working range of frequencies. The third method is long and laborious because many closely spaced frequencies must be measured on each circuit and subsequent calculation is necessary to obtain a figure for the minimum singing point or maximum unbalance. The second has been employed in two ways. In one of these the gain of the amplifier is varied until the amplifier is on the point of singing. A portable set working on this principle was designed and used by the International Standard Electric Corporation, but has since been replaced by an improved type of instrument to be described later. In the second application of this method the gain of the amplifier remains constant and an additional variable loss is introduced into the circuit, which is similar to that of a two-way two-element repeater, by connecting a fixed resistance across one side of the second output transformer and a variable resistance across the other side. The degree of balance between these resistances at the point where singing just stops gives an indication of the singing point being measured, provided that the remaining gains and losses in the circuit are known. Both applications of this second method give an indication of the probable behaviour of a circuit when associated with a repeater having the same characteristics as the amplifier used in the measuring instrument. They do not, however, give a reliable or absolute measure of the impedance regularity of the line itself, for the following reasons :— It can be shown* that, in order that an amplifier may sing, two conditions must be satisfied, viz. :— (a) The gain round the singing path must at least equal the loss round the same path. (b) The total phase rotation round the singing path must be equal to 2nrr radians, where “ n ” is any integer. Hence it follows that an amplifier will not necessarily sing at the frequency corresponding to the maximum unbalance between the line and its associated network, since, although condition (a) may be satisfied at this frequency, condition (b) will not necessarily hold. The actual magnitude of the singing point indicated by the instrument corresponds to the maximum unbalance at the frequencies at which both conditions (a) and (b) are satisfied simultaneously, and it is independent of the unbalance at any other frequency. Hence a bad unbalance at one frequency will not cause the amplifier to indicate a low singing point unless the conditions (a) and (6) happen both to be satisfied at this frequency. The frequencies at which condition (b) is satisfied are spaced at intervals depending on the phase constant of the line and the distance of the irregularity, and variations of singing point up to 5 decibels or more may occur between them. It has been found in practice that errors of this magnitude do occur with this type of instrument. Furthermore, it is necessary to design the filter circuit in the amplifier to pass a definite range of frequencies so that it will not indicate any unbalances which occur outside this range. This reduces the scope of the instrument, since, unless provision is made for changing the filter, it cannot be used to measure unbalances outside the range for which it was designed or to indicate the performance of the line when associated with a repeater having a filter circuit of different characteristics from that in the instrument. Also this type of test set does not give any indication of the singing point at frequencies other than that at which the minimum measured singing point occurs. This is a disadvantage in detecting faults, since an unbalance at a low frequency may indicate a more serious fault than a similar unbalance at a higher frequency. When measuring any circuit having an impedance different from that for which the set was designed there will be a slight error due to the reflection loss at the simulating network terminals unless special precautions are taken.

* See “ Vacuum Tube Oscillators,” J. W. Horton, “ Bell System Technical Journal,” Vol. iii, 1924, p. 508, and also Appendix to the present note, 87 F 4 The first method of measurement can be made to obviate the disadvantages of the other two, and an instrument working on this principle was in use by the International Standard Electric Corporation for some years and was described in a paper published in 1924.* This instrument, while giving a more reliable indication of the regularity of the line impedance than could be obtained by the second method, had certain drawbacks. It was necessary to use rectifier tubes of very nearly identical characteristics, because any difference in their rectifying properties caused an error in the reading. This was especially disadvantageous for field transmission measurements when specially selected tubes were not readily available. As in the case of the second method a slight error was introduced when measuring a line of an impedance different from that for which the set was designed. This instrument also shared with those designed according to the second method the disadvantage that the dial from which the reading was taken was variable in coarse steps of 1 decibel so that an accurate comparison of two slightly different unbalances was not possible.

L I N E R 3

F i g . 2 .—Circuit Diagram o f a p p a ra tu s fo r the measurement o f Impedance Unbalance (Singing Point Test Set).

New Impedance Unbalance Measuring Set. All the above-mentioned disadvantages have been overcome in a new type of impedance unbalance set recently' developed by the International Standard Electric Corporation. A simplified diagram of the circuit of this instrument is given in Fig. 2. The set works on a null system in which the current depending on the quantity being measured is compared, by means of a galvanometer, with another curren t from the same source which flows in a reference circuit. Alternating current from an oscillator is applied through a transformer A to the two resistances R x and R 2 in series. These resistances feed into the calibrating and measuring circuits respectively. The voltage across R 2 gives rise to a current passing into the input winding of the differential transformer B. In the “ measuring ” position the line and simulating network terminals of this transformer are connected through the contacts of the calibrating key to the line ana- simulating network terminals of the instrument.

* J.I.E.E., Vol. 62, p. 653, German translation in “ TechnischeMitteilungen,” Vol. IV, p. 133, Vol. V, P- 15- Three sets of line and simulating network terminals are provided on the differential transformer, and these can be selected to suit the impedances of new types of circuit by throwing the appropriate line impedance key. The bridge terminals of the transformer are replaced by an output winding which feeds into a transformer C. The output of this transformer passes through a network T giving a loss of 20 decibels, to the potentiometer controlled by the measuring dial, which is graduated in decibels. The voltage tapped off from this potentiometer is applied to the grid circuit of the amplifying tube V v The output voltage from this amplifier is applied to the grid of the rectifier V 3 and the resulting change in the anode current of this rectifier produces a change in the potential across the high resistance R 5 (17 000 ohms). The voltage across R produces a current in the potentiometer associated with the calibrating dial and the voltage drop in this potentiometer is applied to the transformer D. The voltage from the secondary of this transformer is applied to the grid of the rectifier V 2. This causes a change in the anode current of V 2 which produces a change in the potential across R 6 which is a resistance similar to R b. The voltage-drops in R 5 and R e are opposed through the galvanometer G which stands at zero when the anode currents of the two rectifying tubes are equal. When the calibrating key is thrown to the “ calibrating ” position the potentiometer controlled by the measuring dial is replaced by an “ L ” network which gives a loss of 20 decibels. The resistances R 3 and are connected to the line and network terminals of the differential transformer B in place of the line and simulating network terminals of the set. These resistances each have three different values, one associated with each of the three positions of the line impedance key mentioned above. These values are so chosen that, when the resistances are connected to the line and simulating network terminals, the loss measured across the differential transformer including the copper and iron losses in the transformer is 6*6 decibels. The total loss in the measuring circuit is then 20 + 20 + 6 -6 = 46*6 decibels. The calibrating dial is then adjusted until there is no deflection on the galvanometer. Provided that the two rectifiers are exactly similar, this will occur when the total loss in the calibrating circuit is equal to the total loss in the measuring circuit, viz., 46 *6 decibels. During calibration the measuring potentiometer is not in circuit so that its reading does not affect the calibration of the set. If the calibrating key is now thrown to “ Measure " the “ L ” network L is replaced by the measuring potentiometer, and the reading of the latter is adjusted until the galvanometer deflection returns to zero. The total loss in the measuring circuit is then again 46-6 decibels. This is made up of the loss of 6-6 decibels across the transformer, the loss of 20 decibels in the “ T ” network T and the loss corresponding to the reading of the measuring dial. This dial can therefore be graduated so as to read singing points up to 20 decibels directly in decibels. For singing points greater than this a third position of the calibrating key is provided which cuts out the “ T ” network from the circuit. The singing point is then 20 decibels plus the reading of the measuring dial; the total range of the instrument is therefore 0-40 decibels. It will be seen that the accuracy of the set depends on the equality of the anode current of the two rectifying tubes for equal grid potentials. In order to avoid the necessity of using two precisely similar tubes, which has been found to detract from the usefulness of previous types of set operating on this principle, a device is used for controlling the grid bias on the rectifier V 3. This is the bias dial which is so arranged that with no A.C. input the grid bias on V 3 can be adjusted until the galvanometer reading is zero. The plate currents of the two rectifiers are then equal, and, provided that the characteristics of the two tubes are approxi­ mately similar and the input voltages small, they will have very nearly the same rectifying efficiency. The value of the resistance R v which acts as a shunt across the calibrating circuit, is so chosen that under these conditions the set will measure the impedance unbalance with the required degree of accuracy. The above is a brief description of the principles underlying the operation of this set.

8 9 In practice the differential transformer actually consists of two repeating coils specially wound to secure a high degree of balance, and each having three sets of line and simulating network tappings; the primary of one corresponds to the input winding, and the secondary of the other to the bridge terminals of the differential transformer. The amplifying circuit has been arranged so as to give a good overall frequency characteristic, so that a frequency curve can be made without the necessity of recalibrating during the run. A reflecting galvanometer

1200 1300 1*00 1500 1600 1700 1800 1900 2 0 0 0 2100 2200

FREQUENCY - PERIODS PER SECOND.

F ig . 3.—Singing Point—Frequency Curve for a medium-loaded side circuit.

is used to facilitate the rapid and accurate determination of the minimum singing point occurring over a range of frequencies. The use of a single continuously variable measuring dial also facilitates rapid and accurate measurement and enables small differences between, or improvements in, singing points to be accurately determined, a change of o-i decibel being easily perceptible. In operating the set the impedance key is set to the value nearest to the mean impedance of the line over the frequency range under consideration. After the calibration has been performed at any convenient frequency, the whole frequency range can be covered without further calibration. To determine the minimum singing point over a range of frequencies it is then merely necessary to observe the galvanometer spot as the frequency is changed. At the frequency where the deflection reaches its extreme position towards the left hand end of the scale the spot is brought back to zero by means ot the measuring dial, and this dial then indicates the minimum singing point over the range. The same batteries may be used as for the oscillator.

Auxiliary Apparatus. While the impedance unbalance set can be used with any oscillator capable of giving an output of 5-10 mA, which is approximately constant at all frequencies, it has been found desirable to develop a new type of tuning unit to facilitate rapid changes of frequency. Such a tuning unit which can be used in conjunction with a portable oscillator is also a great advantage in making frequency runs of impedance, crosstalk and attenuation, and whenever it is required to cover a number of different frequencies quickly and with approximately the same current output. It gives a practically constant output from 200 to 3 000 p.p.s. The frequency is variable in steps of 20 p.p.s. by the manipulation of a 40-point switch and four keys. Each key position is associated with a capacity value and feedback resistance designed to give the same output for each frequency range. The 40-point switch is associated with a retard coil having 40 tapping points. » Thus for any given frequency range designated on the 9 0 keys, the coil, together with- the condenser corresponding to the selected frequency range, •forms the oscillatory circuit of the oscillator to which the unit is connected, and replaces the oscillatory circuit in the oscillator. Laboratory tests showed that with this tuning unit, used in conjunction with an oscillator, any frequency corresponding to steps of 20 p.p.s. from 200 to 3 000 p.p.s. could be obtained within ^ o;4 per cent. The output, with the oscillator potentiometer set at the “ maximum ” position, when feeding into 600 ohms varied between the limits 30*0 and 39*0 m.A over the same range of frequencies. The fact that a whole range of frequencies can be covered by the rotation of one dial is very convenient when measuring the minimum singing-points over such ranges. Test Results. The new impedance unbalance set, when tested by connecting resistances to the line and simulating network terminals so chosen as to give calculated singing points from 19 to 40 decibels and to represent the impedances of lines corresponding to each of the impedance settings, is accurate within 0-5 decibel at all frequencies within the C.C.I. range (300- 2 200 p.p.s.). When the output from the oscillator is between 8 and 10 mA the sensitivity of the set is about 1 division for 0*5 decibel. Under these conditions readings can easily be made to o*i decibel.

FREQUENCY - PERIODS PER SECOND.

F ig . 3#.—Impedance-Frequency Curve for a medium-loaded side circuit.

The new impedance unbalance set, in conjunction with the new tuning unit, has been used in actual tests on cables in Holland and in Switzerland. It was found that the difference between the measured values and those calculated from impedance-frequency curves was never greater than o *8 decibel at any frequency between 200 and 2 800 p.p.s., and was usually 9i less than 0*5 decibel. Curves showing the results of such measurements are shown in Figs. 3 and 4, the impedance curves for the same circuits and those for the simulating networks . being shown in Figs. 3a and 4a (pp. 91 and 93). '

FREQUENCY - PERIODS PER SECOND.

F ig . 4.—Singing Point-Frequency Curve for a medium-loaded phantom circuit.

A singing point-frequency run can be made under these conditions in about 5 minutes. In practice it is usually not necessary to make complete frequency runs of singing points, but merely to find the minimum singing point over the bands of frequency covering the C.C.I. range. This can be done in about 1 minute for each circuit, with the accuracy indicated by the following table, which summarises the results obtained on the circuits for which the curves are given.

Minimum Singing Points Measured on Typical Cable Circuits.

Medium-Heavy Medium-Heavy Side Circuit. Phantom Circuit.

Minimum S.P. measured over range 300-2 200 p.p.s. 30-2 28-4 decibels Frequency for lowest S.P...... 2 120 I 800 p.p.s. S.P. given by calculation from impedance curves . 30-3 27 • 9 decibels

There is no appreciable change in the value of the singing point when the testing current- is varied between 5 and 10 mA.

Conclusions. The new type of impedance unbalance set, when used in conjunction with the new type of tuning unit and the usual oscillator, enables rapid measurements of singing paint to be made to an accuracy of 0*5 decibel. These tests can be made by a single operator if necessary. The results give a definite and reliable measure of the impedance regularity of the line as compared with a standard simulating network, and also indicate the minimum singing point which could be expected under the most unfavourable working conditions. These instruments therefore fulfil all the requirements for rapid and accurate measurement of singing point set forth at the beginning of this note as being necessary for both acceptance and maintenance measurements. 92 Note.—Limitations of Singing Point Tests. The measurement of the singing point constitutes a simple and rapid method of checking the balance between a line and its associated simulating network. The usual practice is to connect the line and simulating network, under test to one side of a two-wire repeater, and on the other side, to open and short-circuit the line and simulating network terminals respec­ tively, or vice versa. The repeater used may be that associated with the particular line in practice, or a special repeater employed.for'the purpose. The gain of the repeater is increased until singing begins, and then decreased until it stops. The gain at which singing absolutely stops is taken as a basis for obtaining the value of the singing point between the line and simulating network. Although this test may be considered as an excellent method of discovering the existence of defects, it is fundamentally wrong to suppose that the value thus obtained or that which would be obtained by any test using the same principle, gives the minimum singing point of the line associated with the simulating network over the range of frequencies effectively covered by the repeater. Singing can occur only at a point where the phase rotation around the singing path is equal to 2mr radians, where n is an integer; the measured singing point corresponds to the impedance unbalance at this point.

F ig . 4a.—Impedance-Frequency Curve for a medium-loaded phantom circuits

There may be several similar points in the range transmitted, and singing will occur at the one at which the unbalance is a maximum. The test described below was made to demonstrate as clearly as possible that the preceding statements are borne out in practice. A singing point measurement was made with a resistance 93 of 600 ohms connected to the simulating network terminals of the repeater and with a network designed to produce a considerable unbalance at 1 700 p.p.s. connected to the line terminals. The network consisted of a resistance of 600 ohms in series with a circuit resonating at 1 700 p.p.s. (parallel resonance). The following table gives the impedance and the theoretical singing point against a 6oo-ohm network, the singing point being defined by :—

Singing point (decibels) = 20 log10 Z . N TA- 7 L . V

In this case ZL represents the network impedance and ZN the 6oo-ohm resistance.

O 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 FREQUENCY - PERIODS PER SECOND.

F ig . 5.

94 F requency. Line Impedance. Approximate Singing Point in Decibels.

600 602 / 4-2° 28-8

1 000 605 / 7-6° 23-6

1 200 614 /12-0° 19-.5 1 400 645 /2 1 •6° 14-2

1 500 749 /29'4° io -6

1 600 1 152 [42 - 6 ° 5-9 1 700 2 400 /30•90 4-o

1 800 995 /4 1 ’5° 6-3 2 000 670 /23-2° 13-6

2 200 6 3 0 l l 5 ' 3° 17-1 2 400 620 /12-6° i9 ’0

Figure 5 shows the line and simulating network impedances and the theoretical singing point of the line against the simulating network over the frequency range. It should be observed that the maximum unbalance occurs at about 1 700 p.p.s. and corresponds to a singing point of 4 ‘O decibels.

LINE 600*

600 O -M A /W V ——i 105 JL 8-35 NETWORK /iF. m H . O------

FREQUENCY - PERIODS PER SECOND.

F i g . 6 . In the actual test made under the conditions described, however, the repeater sang at 2 150 p.p.s. and the singing point measured was 16 decibels, which agrees very closely with the theoretical singing point for this frequency. The phase relations for the singing path have been calculated and are shown in Fig. 6. It will be seen that at 1 700 p.p.s. the phase rotation is about 190° and that singing was then impossible. At 2 150 p.p.s. the phase rotation was zero (or equal to some multiple of 2-n) and in that case the repeater could sing when the gain was equal to the total loss in the singing path. This example shows in a striking way the error which may be made in assuming that a singing point test gives the minimum line-simulating network singing point. Of. course, this example is purposely exaggerated in order to make this fact clear, and errors of such a magnitude would not actually occur in measuring a toll cable. In cables, the phase rotation varies rapidly with frequency so that there are several points in the transmitted band at which the phase is the same. Moreover, a reversal of the connections can be made during the singing point test so as to give a phase rotation of 180°. However, taking all these points into consideration, it is seen that the point of maximum unbalance does not necessarily correspond with a point where the phase angle is zero so that the singing point test applied to the measurement of maximum unbalance is definitely unreliable. In actual tests differences of 5 decibels have been observed between the true calculated values and those measured by singing point tests. • To sum up, the following statement agrees with both theory and practice-:— Any method by which it is proposed to determine the maximum unbalance between a line and simulating network, on the assumption that oscillations are necessarily produced in the singing path at this point, is inherently false.

SUGGESTED INSTRUCTIONS FOR PUTTING' INTO SERVICE AND MAINTAINING INTERNATIONAL TELEPHONE CIRCUITS. * t A. Setting up and Putting into Service International Circuits. 1 . General. When the Administrations have decided to bring a circuit into service, the technical department of one of the countries in whose territory the circuit terminates shall get into touch with the other technical departments involved in order to appoint a Control Station. After the Control Station has been chosen, the technical departments of those countries in whose territory the Control Station is not situated shall each appoint a Sub-control Station. The technical department to which the Control Station reports shall arrange for correspondence to take place between the different technical departments in order to decide on the type of circuit to be established (two-wire or four-wire), diameter of conductors, type of loading, length of uniform sections, numbers of the pairs of the frontier section, position of stations, transmission equivalent of sections,J limiting gains of repeaters and location of echo suppressors if used. If a new cable is to be put into service, the technical departments concerned shall interchange copies of the circuit assignment charts and circuit diagrams dealt with in Appendices 2, 2a and 2b (pp. 104-106), as well as all other documents which they may consider necessary.

* This text replaces that on pages 232-254 of the “ Green Book ” (English translation, 1928, pp. 175- 195)- f The recommendations given on circuit maintenance are very wide in character; exceptions arise, particularly in the case of very long circuits, when it will be necessary to regulate the repeater gains and the equivalent more frequently than specified. The frequency of regulation should be fixed, when necessary, by the respective technical departments. Similarly, for short circuits having only one repeater, the tests indicated in these instructions should be carried out only once a year. J The mean value of this equivalent shall be given, if possible, as well as the mean yearly correction. 96 It is recommended that different procedures be followed for the putting into service of two-wire and four-wire circuits, on account of the difficulties generally experienced with the former.

2 . Four-wire Circuits. Each technical department shall send to the other technical departments concerned the partly filled-in circuit and level charts, drawn up in accordance with the attached forms, Appendices I , I a and 3, (pp. 102, 103 & 107), for its own territory. These charts will be sent * in duplicate, one for the Control Station (or Sub-control Station) and the other for the technical department. Any modifications to either of these two charts shall be notified in duplicate to the technical departments concerned. In order to facilitate the preparation of the various level diagrams, it is agreed that the power level on the output side (towards the foreign country) of repeaters at frontier stations shall have a uniform value for all circuits of the same type. In principle, this value is fixed at +0-5 neper, and each technical department shall draw up its section of the level diagram accordingly. Each technical department shall, within its own territory, give instructions that :— (a) The repeater gains shall have the prescribed values. (b) The differences of level between the stations at the ends of that part of the circuit which concerns the department shall have the correct value.* This part of the circuit will then be ready for over-all tests. The frontier stations will receive orders to verify that the repeater section which crosses the frontier is in good order. The various technical departments shall notify the technical department to which the Control Station reports as soon as their parts of the circuit are ready. As soon as the various sections of the circuit are ready, the Control Station, in con­ junction with the other stations concerned, shall start the final adjustment of the circuit; it shall arrange for final adjustments to be made with a view to assuring the best possible transmission. In particular, the equivalent of the circuit shall be measured at least at the following frequencies : 300, 500, 800, 1 400 and 2 000 p.p.s. (and 2 400 p.p.s. for light-loaded circuits); measurements a t. the following additional frequencies are desirable : 400, 600, 1 000, 1 200 and 1 600 p.p.s. (and 2 800 p.p.s. for light-loaded circuits). Measurements at other frequencies may be made by agreement between the technical departments. The tests shall be continued until the levels at the intermediate stations have the correct value.*

3 . Two-wire Circuits. The technical department to which the Control Station reports shall draw up the level diagram of the circuit (following the model in Appendix Ilia, p. 108) in accordance with information received from the other technical departments concerned; copies of the diagram shall be sent in duplicate to the other technical departments for verification and approval. The following rules are recommended for drawing up the diagram (a) The gain " S ” of the various repeaters, starting from a terminal station, shall be determined as follows :— Let the circuit consist of five sections. „ bv b2, b3, 64 and b5 represent the respective attenuations of the various sections. ,, S4 represent the gain of the first repeater. - . 7 , ,, S2 and S3 represent the gains of the intermediate, repeaters. ,, S4 represent the gain of the final repeater—

* By " correct value ” is meant the prescribed value z t 0-2 neper, 97 G Then—

S n = ^ b n + ^ b n+1 ( n = 2 or 3;

S4 = b5 -f — 0-65 neper

The value 0-65 neper is one half the maximum value (1-3) recommended by the C.C.I. for the total equivalent of the circuit. The technical departments shall give the necessary instructions in their territory to ensure that the circuit is adjusted to give the correct levels; tests shall be made to find the best networks for the two directions of the repeaters; when these tests are made the gains of the repeaters adjacent to the repeater under test shall be set at zero; in the case of terminating repeaters the repeating coil on the office side of the repeater shall be closed by a resistance equal to the nominal value of the office impedance. As soon as all stations have determined the singing point or the degree of balance on each side of the repeaters, the information shall‘be communicated to the Control or Sub-control Station. ’ ■ The Control Station. shall, in collaboration with the Sub-control and other stations on the circuit, then proceed with the final adjustments in order to obtain as good transmission as possible. In particular :— (a) The equivalent of the circuit shall be measured at least at the following frequencies, 300, 500, 800, 1 400 and 2 000 p.p.s. (also 2 400 p.p.s. for light-loaded circuits); measurements at the following additional frequencies are desirable : 400, 600, 1 000, 1 200 and 1 600 p.p.s. (also 2 800 p.p.s. for light-loaded circuits). Other frequencies may be used by mutual agreement. (1b) The stability of the circuit shall be tested as described in section B. 3 (b) below.

4 . Organisation of Routine Tests. The technical department to whom the Control Station reports shall arrange with the other technical departments the dates and routine to be followed for the periodic maintenance tests. The form given in Appendix IV shall be used for this purpose (p. 109).

B. Routine Tests to be made in order to ensure Satisfactory Operation of the Circuits.

1 . Daily Tests. (a) Each morning the operators at terminal stations shall make talking tests on all circuits in order to satisfy themselves that they are in every way suitable for commercial speech. If a fault is observed, the tests described in Section 3 (a) (Monthly Tests) shall be made. (b) The voltage and current of all repeaters on the circuits shall be checked. (c) Ringing Tests.—In order to check the signalling apparatus the operators shall exchange rings whilst making the talking tests. If the ringing signals are not received correctly, the procedure described in Section 8 (Localisation of faults) shall be applied.

2 . Weekly Tests. The gains of all repeaters in service, at a frequency of 800 p.p..s. (co = 5000), shall be measured in both directions and the results noted. These tests shall be made in such a way 45 not to interfere with the traffic; if a spare repeater is available, it shall be substituted 98 for the repeater to be tested and shall previously be adjusted to give approximately the gain required. If no spare repeater is available, the time chosen for the tests shall be such that a short interruption of the circuit does not interfere with the service. This time shall be chosen by mutual arrangement between the terminating stations. The filament current at stations at which no automatic voltage or current regulation is available shall be regulated, before the gain tests are made, to its nominal mean value.

3 . Monthly Tests.

(a) Attenuation Test.—This test shall be made on all. circuits at a frequency of 800 p.p.s. ((0 = 5 000), and the results noted. It shall be considered that a fault exists if the results vary by more than o • 2 neper or 1 • 7 decibels from the normal value. The normal values of attenuation are given in Appendix IV, together with the Control Stations, Sub-control Stations and the date of the tests. For localisation of faults see section 8. (b) Determination of the Stability of a Two-wire Circuit equipped with Several Repeaters.— The stability (stabilite-Pfeifsicherheit) of two-wire circuits is determined as follows :— Let the equivalent for which singing in a circuit will cease be called the singing-equivalent, the operators at the terminating exchanges being in circuit. A circuit is made to sing by increasing the gains of one or more repeaters. When the plugs are not in the jacks at the terminal stations the circuit must not sing. The gains of one or more repeaters are increased simultaneously in both directions, and the gain is then reduced progressively until singing ceases. It is recommended that the gains of the repeaters in the middle of the circuit be increased and decreased first, as these repeaters contribute most to singing. Transmission in one direction is suppressed; the equivalent ex in the other direction is measured at 800 p.p-s. If e% is the normal equivalent of the circuit in the other direction, and e the average of the equivalents in the two directions, then the stability a is given by—

2 The stability of a two-wire circuit should not be less than 0-4 neper or 3*4 decibels.

(c ) Determination of Singing Point (or of Degree of Balance) of a Two-wire Repeater.— This test shall be made by one of the methods recommended on pages 224 to 227 of the “ Green Book ” (English translation, 1928, pp. 170 and 171). It is proposed to try certain methods as soon as the opportunity presents itself. Until then it is not possible to recommend any method applicable to all cases. (d) Determination of the Stability of a Four-Wire Circuit.—The stability of a four-wire circuit is determined by increasing the gains of one or more repeaters simultaneously in the two directions, until the singing begins, and by decreasing the gains until the singing ceases. After suppressing the transmission in one direction which is not necessary for circuits furnished with echo-suppressors, the equivalent is measured in the other direction, and vice versa. The stability a is calculated by means of the results ex and e2 of these tests, in accordance with paragraph (b). It is recommended that the stability be tested with the terminal exchanges under service conditions and the operators in circuit. The stability of the circuit should not be less than 1 neper or 8 *7 decibels. With the plugs not in the circuit jacks, the circuit should not sing. Under these conditions the repeater stations should verify whether or not singing takes place. (e) Where the circuit is composed of two- and four-wire circuits, the method and the figure given for the two-wire circuits hold good. 99 - 62 (/) Line Insulation Resistance. (g) Conductor Resistance.—These tests shall be carried out as described on page 220 of the " Green Book ” (English translation, 1928, p. 167), but the results need not be communi­ cated to the control or sub-control stations. The results shall be noted and kept at the repeater station at which the tests are made (h) Ringing Apparatus,—The ringing apparatus shall be tested every month, the repeater station concerned measuring and noting the voltage necessary to operate them.

4 . Quarterly Tests. Measurements of level at 800 p.p.s. (a> — 5 000) shall be made at all stations shown in Appendix No. TV (p. .109) at the same time as the monthly over-all transmission tests are being made. Note shall be made of the normal and measured values of level. Following these tests, the over-all attenuation on all circuits shall be measured at the frequencies given in Appendix No. IV. The normal values are shown in this Appendix.

5 . Half-yearly Tests.

(a) Measurement of Gain given by the repeaters within the frequency range which the circuit is to transmit efficiently.

(b) Calibration of Repeaters.—These tests shall be carried out as recommended on page 99, but the results need not be communicated to the control or sub-control stations. The results shall be noted and kept at the repeater station at which the tests are made.

6 . Yearly Tests.

(a) Impedance Tests (if desired). (b) Transmission Tests on sections of the circuit (including repeating coils). These tests shall be carried out as recommended on page 224 of the “ Green Book ” (English translation, 1928, p. 169), but the results need not be communicated to the control or sub­ control stations. The results shall be noted and kept at the repeater station at which the tests are made. (c) Determination of Singing Point of Repeaters.—These tests shall be carried out as recommended on page 224 of the “ Green Book ” (English translation, 1928, p. 170).

7 . Sundry Tests. (a) Crosstalk Tests.—The method of making these tests will be described after the experiments mentioned in Appendix No. Ill (p. 107) have been made. (b) Measurement of Line Noises.—If “ frying ” noises are noticed on the line, the fault shall be localised as described in Section 8.

8 . Localisation of Faults. (a) Defective Transmission.—-If a fault, is noticed when the monthly tests of (transmission) equivalent are being made, the level shall be measured at the repeater station which is nearest to the frontier, in order to determine in which country the fault has developed. The normal values of level are set down in Appendices III and II la by the Administrations concerned. The control or sub-control stations are responsible for the clearing of the fault; they shall inform the terminal stations of the. nature of the fault and shall advise them when it has been cleared. The terminal stations shall, if requested, take part in the location and clearing of the fault by assisting in the tests made in either country. If a fault is noticed when the quarterly' tests of transmission equivalent at various frequencies are being made, the stations mentioned above shall make level measurements at these same frequencies. The results shall be sent to the central technical department by the control and sub-control stations. ' 100 (b) Bad Transmission of Ringing Signals.—If the ringing signals are not received satisfactorily, the local apparatus shall be verified first; if it appears to be normal, tests of transmission level shall be made in the same way as for a case of defective transmission, except that the frequency shall be 500. p.p.s. (c) “ Frying” Circuit.—If “ frying” noises are heard on the circuit, the fault shall be localised by starting from the terminal stations and putting out of circuit one repeater after the other.. The defective section of the circuit will be found by noting at which terminal station the noise is heard whilst successive repeaters are put out of circuit. To determine the country in which the fault exists, the repeaters which are nearest to the frontier shall be put out of circuit one after the other; the echo suppressors shall be out of circuit during the whole period of these tests. (d) Crosstalk.—If service is interfered with by crosstalk, the tests described in Addendum I shall be made, first of all between terminal stations. In order to find in which country the fault exists, the tests shall be repeated with the repeater . stations nearest , to the frontier, taking them one after the other and making the tests in both directions from the terminal stations. The tests described above in (a) to (d) shall be made every time a fault occurs, even if they have already been made on the same day. If a circuit sings, the determination of the singing point should be made in each repeater station on the circuit. In cases where the singing can be suppressed by a slight increase of the equivalent, this should be done in order that the circuit may remain in operation during hours of heavy traffic. In this event, it is recommended that the removal of the fault should be left until another time.

List of Appendices and Addenda to the Instructions for putting into Service and maintaining International Circuits. < Appendices I and I a ...... Circuit Chart. ,, II, II a and IU •• •• .. •• Assignment Chart. ,; III and Ilia ...... Level Diagrams. Appendix IV ...... J. Programme of Routine Tests. Addendum I ...... Crosstalk Tests.

Application of the Instructions for putting into Service and maintaining International Telephone Circuits. The International Consultative Committee— Considering :— That it is essential, to ensure a regular Operation of the international telephone service, that different Administrations employ the same methods for putting into service and main­ taining international telephone circuits. , ■ . . . Unanimously advises :— 1. That all Administrations strictly apply the instructions laid down by the C.C.I. regarding putting into service and maintaining of international circuits. 2. That the phrases in the booklet published by the C.C.I. under the title “ List of usual Phrases to be employed in dealing with faults and tests and in repeater stations; for the Maintenance of International Telephone Communications ” shall be used by the personnel concerned of all Administrations. 3. That a permanent sub-commission (consisting of a representative from each of the following Administrations : Germany, France, Great Britain and Holland) should be-com­ missioned to solve all urgent questions dealing with the application of the recommendations of the C.C,I. regarding the putting into service and the maintenance of international telephone circuits. “ :

101 C 3' 16 R em arks. neper. 3- 5—28. 0-2 t 500/20 500/25 C urrent. T ype of R inging W e set.W e p.p.s. r4 800 800 Card issued 800 p.p.s. : i -o ± 1 -2 1 13 800 distortion. with or without Line Attenuator, w ith w ith o u t (2-wire) : stability at (4-wire) : echo suppressor at Equivalent at 41 1-37 2-49 2-63 2-13 2-20 2-41 2-31 ‘ 2 2-28 coils. o-5 o-5 including rep eatin g of Section - - 2-42 Equivalent

960 1 1 000 London Berlin {Front). .Rotterdam oo p.p.s. 8 A verage Im pedance a t 920 without/with 1 1 770 repeating coils. Sub-control Sub-control C ontrol Sub-control 400 400 F re ­ 5 3 Cut-off

quency.

CIRCUIT CHART t 1 A. t 79 73 87 73 73 122 t No. P a ir I I I ■v I 135 51 59 80 45 45 101 101 f Lnd. Bln. 1, Lnd. Bln. 1, F k. 9950, 0-9 No. No. No. D ia­ No. m eter

102 CIRCUIT CHART -{Back).

Adjustment of Direction A to B. Direction B to A. Singing Point. T ype Gain. Fixed or O rder S tatio n s. Adjustable R em arks. No. of R epeater. E qualiser. G ain a t Gross G ain a t Gross Max. Min. Side A. Side B. 8oo p.p.s. Level. 800 p.p.s. Level.

i 2 3 4 5 6 7 8 9

t B erlin 4 SI. ■2-5 2 • O fixed 2 -O o -7 2 • 2 0-75

2 F riesack 2 • 2 o • 8 2-2 0-7

3 Perleberg ) i 2 • 2 o -8 2-4 0-7

4 V ellahn ) > 2-4 o -8 2-3 0 -7

5 H am b u rg i ) 2*3 o -75 2-4 0-7

6 R o tenburg i > 2-4 o -75 2-4 o -75

7 B assum ) ) 2-4 o -75 2-4 o -75

8 B ohm te 2-3 o -75 2-4 0-65

9 M unster 2-4 0*65 2-5 0 -7

ro W esel 4 RhS 2-8 2-4 2-68 0-7 2-7 o-8 ” . la Appendix Cable Circuits—“ Germany—Belgium.” a. Four-wire Connection : Conductor diameter o-gmm. Heavy Loading.

HAMBOURG BASSUM MUNSTER (W) COLOGNE AIX.LA. CH. BRUXELLES 149*4- km. 147 * 4 km. 149 • 1 km. 74 km. 139 km. i—o------o------— - o ------o—M------—o ------o—i o -fo= 2700 ,------4 ------f0= 3200— 4 - — f0- 2700 f 0 = 2 9 0 0 ------0 1 x 658*9 krn. —cp- -9 - ■9- -9 - -@ —9 - -9 - ^ b = 2 - 6 3 I 2 6 2 6 4 1 3 2*57 I I I ANVERS — d>- ■o J) |CF 0.9% 52.km. 0 — © 1x710*9 km. b=M 3 -6- 0 9 Q- '—o o -o -o—i / 177m H \ Uo = 2 9 0 0 / Telephone Exchange.

Two-wire Repeater.

Four-wire Repeater.

- J - Four-wire Termination.

—Q ~ Artificial Line Pad. b. Four-wire Connection : Conductor diameter o-gmm. Light Loading.

BERLIN FRIESACK. 'PERLEBERG. VELLAHN. HAMBOURG. ROTTENBOURG. BASSUM. BOHMTE. MUN5TER(W). COLOGNE. AIX-LA-CH. BRUXELLES. _ 65 *5 km. 67-6 km. 74-6km. 77*3 km. 74-5 km. 74-9km. 70*4km. 77. km. 149-7km. 74. km. 139. km. -f0= 5400 ------F-fo=3ZOoH*fo=5400-H-£)=5700- 1 x943-9 km.

b= 2 03 , 2 31 I 2-4 2-31 2-57 | I 1 I I -4------4------1X995-9 kr b= M4 I (,p44mH>) I \Xo= 5700/ A MARKT- VIENNE. ST.POLTEN. AMSTETTEN. LINZ. PASSAU. 5TRAUBING. HEMAU. NUREMBERG.NPHOFEN. HEIOENFELO. F.FT.S/u. GIESSEN. SIEGEN. LUDENSCHEIO. G5-Bkm. 62-7km. 58-7 km. 89-3km'. 77*9 km. 72-8 kmA 74-£ km. 72'8km . 58*4 km. 84*7km. G1-5km. 74-4 km. 70*2 km. l42-5km.j

h fo= 5400- --4*fo=3200*i 1x1279 -3 km. o Ut b.2'04 I 194 I182 ] 2 -77 ] 2-41 I 2-26 | 2-31 T 2-26 1 X- 81 i 2 -63 T 1-91 [> 2 3 I 218 I 2-53 | ! ! i ! ! ! ! ! ! ! ! ! ! ! , I LA PANNE. TO LONDRES ~A>____ Q-i

I b= 2-83 I / 44 mH \ l(fo= 5700/ ' Telephone Exchange. r- ® FRA NCFOR T ©— ■*------fo= 5400' 1 x 561-6 km Two-wire Repeater, S/M A IN . (oij—o—4— > j Four-wire Repeater.

Four-wire Termination. O r 4 3 - Artificial Line Pad. pedx I la. Appendix Appendix Jib.

c. Two-wire Connection : Conductor diameter { aS^C h.-B r^l^A ^t^rp : 1,5 mm.

AIX-LA-CH. BRUXELLES km ______7 4 .k m . r —1— 1 1 139.1 3 9 .k km. m . x—. COLOGNE 0 ------Q - g ------0 Phantom 1 x 213*0 [ b = o-67 I b=i 36 ; fo = 3500 fo= 3800 1 COLOGNE Side X 213-0

139 km ! fo= 2900 Side 2 x 307-1 DUSSELDORF 0 - ;115'8km' EjglA - ® T b = 1-04 — T b=1 33 1 fo = 2700 fo= 2900 Side 2 x 255■ DUSSELDORF (° -£IK>- I 1 I I 37- 8 km 1 1 116 • 8 km. Side 2 X 345-6 DUISBOURG + - © b= 0 3 b= 1 0 4 ■p- p - H— fo=3000— *4 Fo= 2700 I DUISBOURG Side I X 293-7

I AIX- Side 2 X 191-0 LA-CHAPELLE. P- ■€>

MANHEIM FRANCFT S/M ANDERNACH I I 8o 9a .k m . ,—1— 1| _ 145-Skm. 14-: !45-7km. ------Side 2 x 571•2 0 - - © T b= 0-79 1 •29 1 - 2 9 P- fo= 2700 -•

AIX-LA-CH 4> BRUXELLES. Side 2 x 139-0

Side AIX-LA-CH LIEGE 2 x 39-0 ■<§>

7 4 . k m . COLOGNE Side 2 X 113-0 66 ! f0= 2700

k m = 2 2 COLOGNE VERVIERS/. Side 1 .x ~g6-o b= ~0-21•21 T 0 Telephone Exchange. ! fo = 2900 Side 2 X-^22-0 —O Two-wire Repeater. AIX-LA-CH (°> 4 )

Four-wire Repeater.

= 5 - Four-wire Termination.

Artificial Line Pad.

106 BERLIN. FRIESACK. PERLEBERG. VELLAHN. HAMBURG. ROTENBERG. BASSUM. BOHMTE. MUNSTER. WESEL. (ARNHEM. > ► ► ►- - £ = 5 4 0 0 - £=3400— z|— ► TO-B"

DISTANCE. 1 65-6 | 67-6 | 74-6 | 71-3 | 74 6 | 75 0 | 70-4 | 770 | 1438 69-6

LOSS OR GAIN. N E PE R S - 1 0 1-0-5 +3-0 -2-13 +2-2 -2 -2 +2-2 -2-41 + 2-4 -2-31 +2-3 -2-41 +2-4 -2 -4 2 +2-4. - 2 2 8 +2-3 -2-4-9 +2-4 -2 -6 3 +2-68 — (1-37+ l-2 ) POWER LEVEL. 0-5 0-57 0-57 0-56 0-55 0-54 0-52 0-54 0-45 0-5 VOLTAGE LEVEL. » 0-72 0-79 0-79 0-78 0-77 0-76 0-74 0-76 0 -64 0-69 ■O

■B'TO'A". pedx I. I I Appendix LOSS OR GAIN. NEPERS. -1 -0 (-0-5 +2-2 -2 -1 3 + 2-2 -2 -2 + 2-4 -2-41 +2-3 -2-31 +2-4 -2-41 + 2-4 + 2-42 + 2-4 - 2 -2 8 + 2-4 - 2 - 4 9 + 2-5 -2 -6 3 + 2-7 -(1 -3 7 + 1-2', POWER LEVEL . 0 -5 5 0-48 0 -48 0-49 0-5 0-51 0-53 0-41 0 -5 0-63 0-5 VOLTAGE LEVEL. 0-75 0 -7 0 - 7 0-71 0-72 0-73 0-75 0 -6 ^ 0-72 0-82

CONVENTIONS.. DENOTES 4--WIRE REPEATER •—C .. CIRCUIT TERMINATION. Ho) „ ARTIFICIAL LINE. NEPERS = I Level Diagram of the Circuit. Berlin—London i (Fk. 9950) German Section HAMBURG- BASSUM. MUNSTER (w) WESEL. . ARNHEM. AMSTERDAM. . a i l I x i d n e p p A -A”*------MEED----H — ------•B”

IPISTANCE. KM-1 149-4 | 147-4 1 143*6 1 69-8 | 104-5 ~1

+ | . :------

2

LOSS OR GAIN. NEPERS. - 1 - 4 + 1*6 -(I-4+0-2") +1-5 - 0 - 2 + O - 2 ) + 1-4- -C0-7+ 0-6) + 1*2 - 1 - 2 POWER LEVEL 0 2 0 1 O-I 0 VOLTAGE LEVEL. „ 0 - 7 0 - 6 0 - 3 0 - 2 M O 0O (f) +1

-2

LOSS OR GAIN. NEPERS - 1 -4 + r- 6 -C l-4 + 0-2") + 1-5 -(I-2 + 0 -2 " ) + 1-4 - C 0 - 7 + 0 - 6 ) + 1-2 -1-2 POWER LEVEL. 1. 0 - 2 0 - 2 O-I O VOLTAGE LEVEL. 11 0 - 7 0 - 7 0 - 3 0 - 2

CONVENTIONS. ■ DENOTES 2-WIRE REPEATER. • ------n CIRCUIT TERMINATION mi - ARTIFICIAL LINE. NEPERS = 0*2. Level Diagram of the Circuit. Hamburg—Amsterdam 2 (Fk. 1045). P r o g r a m m e o f R o u t in e T e s t s .

Circuits between...... and......

Months, Days and Hours of Circuit d Normal Values. o Routine Tests. d ■ No. .2 0! d m Voltage Level C/5 Equivalent at output of No. of 'o Equivalent R em arks. from to O E q u iv alen t E q u iv alen t a t 500, repeater at 800 p.p. s . (h d at 500, 800, C ircuit. d O a t S tability. a t 1 400, 2 000, S tab ility . o 1 400, 2 000, A B M 8oo p.p.s. 800 p.p.s. an d 2 400 D irec­ D irec­ O d 2 400 p.p.s. c/5 p.p.s. S tatio n . tio n tio n A to B. B to A.

i 2 3 4 5 6- 7 ' 8 9 10 11 12 13 14 15 16

oH neper decibel nep er

_

> ■ pedx V. IV Appendix | | j decibel ADDENDUM I.

C r o s s t a l k T e s t s .

The method of measuring crosstalk is as follows :— The crosstalk at the receiving 'end is considered to be equal to n + n ', where n' is the total attenuation of the line, and n is the attenuation of the variable artificial line, when the volume of. sound in the telephone receiver is the same for the two positions of the switch. The crosstalk at the transmitting end is measured in the same way, the receiver, artificial line and switch being at the same end of the circuit.

n o Maintenance of Circuits used for the Relaying of Broadcast Transmission.

Maintenance Tests. The International Consultative Committee— Unanimously advises :— (a) That for the maintenance of lines used for broadcast purposes similar measurements are necessary to those used for long-distance telephone traffic, i.e., (1) Periodic measurements on the cable lines themselves for verifying the con­ dition of insulation, resistance and the attenuation of the various repeater sections. (2) Periodic measurements of the repeaters in order to determine whether the frequency curve of amplification is satisfactory. For this purpose it is necessary to test with four frequencies within the transmission range. (3) Periodic measurements of the line used throughout its whole length in order to determine the total transmission loss and the transmission level at the various repeater stations; for this purpose it is usually sufficient, in accordance with long­ distance telephone practice, to make tests with a frequency of about 800 periods per second.

(b) That volume measurements appear to be necessary only at the input end of the line; the various Administrations are invited to ascertain what devices can best be used for these tests as outlined in Appendices C.e., No. 1 and No. 2, “ Green Book,” pp. 334-337 (English translation, 1928, pp. 261-265).

Division of Responsibility between Telephone Administrations and Radio-broadcast Services (State or Private) regarding the Maintenance of Circuits used for the Relaying of Broadcast Transmissions. The International Consultative Committee— Unanimously advises :— (a) That the limit of responsibility of supervision between Telephone Administrations on the one hand, and the Broadcasting Authorities on the other, should be the protectors which are inserted at the broadcasting stations in the leads to the telephone exchanges at both ends of the line. (b) That when there is a broadcasting circuit in a long-distance telephone cable, the role of the control station should be the same as it is in ordinary telephone communication.

Technical Responsibility in Connection with the Renting of International Telephone Circuits to Broadcasting Authorities. The International Consultative Committee— Unanimously advises :— The Broadcasting Authorities should be responsible for the supply of broadcasting energy at the requisite level, while the control station of the Telephone Administration should control the transmission over the telephone circuits as in the Case of ordinary telephone connections.

HI Instructions to Broadcasting Organisations and to terminal exchanges or repeater stations of Telephone Administrations, for putting into operation a connection to be used for broadcast transmission, and for the re-establishment of this connection in its normal service. (1) The instructions given by the C.C.I. regarding the maintenance of telephone lines used for long-distance traffic are also suitable for the maintenance of lines used for the relay of broadcast transmission. They involve the establishment and exchange of circuit charts, and of level diagrams for all lines in regular service, the measurement of equivalents and levels at regular intervals of time and at frequencies which have been fixed for every line by the different technical departments concerned. In addition, the gain of the repeaters used for broadcasting must be measured at one or more frequencies, and it is necessary to designate control and sub-control stations, etc. (2) The lines used for the relay of broadcast transmission should be ready half-an-hour before the beginning of a radio transmission. The terminal exchange and the repeater stations must previously regulate the gain of the repeater to be connected to the value given on the circuit chart, and, by means of a test at a frequency of 800 p.p.s., it must be verified that the gain really has this value. The results are communicated to the control station and to the sub-control station on demand. The two terminal exchanges will then test the equivalent at a frequency of 800 p.p.s.; different repeater stations simultaneously test the level. If it is necessary to modify the levels, the control station shall decide what is to be done, in con­ junction with the sub-control station. The control station is always to be the terminal exchange in the direction of the transmission, because it is only this station which can correctly assess the transmission. As soon as the attentuation test shows that the line is in good condition, . the line is transferred to the broadcasting organisations at its two extremities. (3) In addition to the transmission line, Broadcasting Organisations may employ a line for conversation. It is desirable, where possible, that this line should serve several telephone instruments in the different control posts of the Broadcasting Organisations concerned. (4) After the Broadcasting Organisations have taken possession of the lines connected, they will make tests on the whole connection serving the broadcasting transmission, from the studio to the transmitting station, in the whole transmission interval (frequency band to be transmitted) by means of self-recording apparatus (level recorders), which enable more rapid tests to be made. These devices must be designed so that they permit of simultaneous testing (at a frequency of 800 p.p.s.) of the levels at the intermediate stations. (5) Broadcasting Organisations should never exceed the limit selected by Telephone Administrations concerned for the maximum power supplied to the transmission line. As regards supervision of the broadcast transmission, it is recommended that the Broadcasting Organisations (at the studio, at the outgoing side of the repeater, and at the transmitting station, after the final low frequency amplifier) as well as the two terminal stations, volume indicators capable of giving, in each test the maximum value of acoustic power integrated during 20 milliseconds at most (e.g., an apparatus described in the " Green Book," pp. 334 to 337, (English translation, 1928, pp. 261-265, Appendices C.e., Nos. 1 and 2). Regarding intermediate repeaters, it is recommended that volume indicators of this type should also be held in readiness, in order that it ma}^ be possible rapidly to localise any faults which may arise. In this case, the studio supplies to the line a fixed and constant power (transmission of a dash—“ emission d’un trait ’’). (6) As soon as the Broadcasting Organisation announces to the control or the sub-control station that the broadcast transmission is finished, the latter will switch off the repeaters, and, when long-distance telephone lines to be employed with other repeaters are concerned, the control station replaces the repeaters used for broadcasting by repeaters normally used for telephony. (7) The terminals of the last lines put into operation form points dividing the responsibility between the Broadcasting Organisation and the Administrations whose duty it is to put, 112 these lines in working order. As regards testing the circuits, the Telephone Administrations use, for the preliminary test, the apparatus connecting the lines to the studio. These tests are not extended to the operating rooms of the Broadcasting Organisations unless the tests between the terminal exchanges of the line show that the fault is situated between the terminal exchange and the repeater rooms of the Broadcast Organisations. (8) It is desirable to identify, by means of a special mark in exchanges and repeater stations, the circuits and apparatus to be used for the relay of broadcast transmission, and to instruct the personnel never to come in on the circuits unless necessary for service reasons.

APPENDIX TO THE QUESTIONS CONCERNING SUPERVISION AND MAINTENANCE OF INTERNATIONAL TELEPHONE LINES. Description of Apparatus for making Transmission Measurements. The descriptions below show a typical device for making the transmission tests referred to above (pp. 96-113). At the end of this description will be found circuit diagrams of special instruments used in different countries to measure the over-all transmission equivalent of a telephone circuit between test boards in the central offices. Fig. 1 shows the general arrangement of the apparatus. An oscillator G producing currents of audible frequencies is connected through a regulating resistance P, a screened and balanced transformer T and a milliammeter A to a section of artificial cable C2. The functions of this cable are : (1) to make the impedance of the sending end approximately equal to that of the line; (2) to reduce the current in some convenient ratio so that the milliammeter A may measure a current larger than that entering the line under test. By this means it is possible to use a robust type of instrument for measuring the current and at the same time obtain more accurate measurements of the current entering the line under test than would be the case if the latter current were measured directly. A convenient ratio of reduction is found to be 5 to 1. A switch 5 provides for the connection of the oscillator and measuring instrument to one extremity of an artificial cable Cv or, alternatively, to one extremity of the circuit under test. Each circuit is normally closed through a resistance Z 0, approximately equal to the characteristic impedance of the line. The voltmeter should be of the recognised thermionic valve type having an impedance high compared with that of the line. Connection is made to the line under test by means of the jacks shown. Fig. 2 shows the method of applying this set to “ Gain ” measurement. The telephone repeater R is connected between fixed sections of artificial cable. The two ends of circuit thus formed are connected by means of plugs to the “ send ” and “ receive ” jacks, respectively. The current entering the circuit is adjusted to a suitable value. The length of the cable Cx is adjusted until the deflection on the voltmeter is the same in either position of the switch. The transmission equivalent of the circuit consisting of the repeater R and the sections of artificial cable is then equal to the indicated length of the cable Cv The gain of the repeater is then easily deduced. Fig. 3 shows the application of the apparatus to over-all measurements. At the sending end the switch is left in the position shown and the current adjusted to an agreed value. At the receiving end the line under test is connected to the “ receive ” jack. The current into the artificial cable C2 is adjusted to the same agreed value as that at the sending end. A balance is then made as before by manipulating the switch and adjusting the length of the cable Cx. The resultant length of Cx then indicates the transmission equivalent of the circuit under test. Fig. 4 shows the application of the apparatus to “ transmission level ” measurements. The sending and receiving ends are similar to Fig. 3 and the measurements are made in the same way. At intermediate stations the line is connected to the “ intermediate” jack as shown.

1 1 3 H H 55 W W co < W o u

O £

A balance is made in the same way as at the receiving station. The indicated value of the cable Ci then gives the “ transmission level ” required. The voltage corresponding to this “ transmission level” may be-greater than that at the sending end. To provide for this condition cable Cx is set at zero and the Cable C2 is made adjustable and is so calibrated that it indicates directly the transmission units (or absolute units) by which the transmission level exceeds that at the sending end of the circuit. 114 - H 2 F ig . 4 . Transmission Level Measurement. 1 1 6 It will be understood from the above description that it is essential that all circuits should be brought to approximately the same impedance in order that this system of measurement should give accurate results.

Various Special Instruments used for Measuring Over-all Transmission between two Offices.

(i) Method used by the British Post Office.

T 20J

(2) Method used by the International Standard Electric Corporation.

117 H 3 (3) Method used by the German Administration and Messrs. Siemens <£ Halske.

GENERATOR

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D ia g r a m o f t h e L e v e l M e t e r .

i i 8 CO-EXISTENCE OF TELEPHONE AND TELEGRAPH CIRCUITS IN THE SAME CABLE.*

The International Consultative Committee— Considering :— That technical arrangements already exist which permit telephone and telegraph service in the same cable, either over separate conductors or even over common conductors; that with these arrangements, and by taking the precautions stated below, the telephone circuits, including phantoms, are practically not influenced by the telegraphs, either from an electrical or from a traffic standpoint; That even when the cable is subject to influence by power systems (in particular, rail­ roads using A.C.), it is possible to obtain a telephone and telegraph service free from interference troubles by using devices which have already proved satisfactory in practice; That, furthermore, the simultaneous use of long-distance cables for telephony and telegraphy is recommended for economical reasons;

Unanimously advises :—■ That the simultaneous exploitation of international telephone and telegraph circuits in the same cables be forthwith accepted in principle, either over separate conductors or common conductors, on condition that all measures be taken to ensure that the telegraph does not interfere with present and future telephone traffic; The provisory conditions which, in the present state of the technique, shall be met by simultaneous or co-existent telegraph and telephone installations, are as follows —

I.—SIMULTANEOUS TELEGRAPHY AND TELEPHONY (OVER THE SAME CONDUCTORS) OR INFRA-ACOUSTIC TELEGRAPHY.

In order not to prejudice the transmission quality of telephone circuits the following requirements must be met :— 1. The E.M.F. produced in the line circuit by the telegraph transmitter must not exceed 50 volts. 2. When the terminals of the telegraph transmitter are closed through a resistance of 30 ohms substituted for the line, the current through this resistance must not exceed 50 mA, This limit is increased to 100 mA if the cable is equipped with coils having cores of compressed iron dust. 3. The increase in the attenuation of the telephone line due to infra-acoustic telegraph installations must not exceed 0-06 neper or 0*52 decibel for a repeater section, and over the frequency range between 300 p.p.s. and the maximum frequency transmitted. 4. Over four-wire circuits the variation of line impedance produced by infra-acoustic telegraph installations must not exceed 10 per cent, in the frequency range indicated. As regards two-wire circuits, infra-acoustic telegraph installations must not exceed the values prescribed by the Telephone C.C.I. for the exact simulation of the impedance of the line by balancing networks. (See p. 135, Impedance Balance.) 5. Interference noise produced in telephone circuits by telegraph apparatus must not exceed a value which corresponds to a noise voltage of o-i mV for a transmission level

* This text replaces that under the same heading on pp. 255-262 of the " Green Book ” (English trans­ lation, 1928, pp. 196-201).

1 1 9 H 4 of — i neper or — 8*7 decibels and an impedance of 600 ohms.* 6. The increase in crosstalk produced by infra-acoustic telegraph installations shall be determined as follows :— The cable quads are replaced by artificial lines free from crosstalk and reproducing within the closest possible limits, the impedances of the circuits (terminal apparatus for quads). Under these conditions the attenuation corresponding to the crosstalk measured from the telephone office side must not be inferior to the following values :— (a) For four-wire circuits: 7*5'nepers or 65 decibels for the crosstalk between any two speech circuits in the same quad; (b) For two-wire circuits: 8*5 nepers or 74 decibels for the crosstalk between any two speech circuits in the same quad; (c) For four-wire and two-wire circuits : 10 nepers or 87 decibels for the crosstalk between two speech circuits in different quads. 7. After infra-acoustic telegraph systems are connected into a circuit, the unbalance to earth of the telephone circuits must not exceed the value prescribed by the C.C.I. . 8. The circuits employed for infra-acoustic telegraphy must not be used for relaying broadcast transmissions, as the low frequencies are useful for a good reproduction of music.

II.—CO-EXISTENT TELEGRAPHY AND TELEPHONY (OVER SEPARATE CONDUCTORS). 1. Where the telegraph uses loaded conductors which may later be used for telephony, the conditions stated under heading I, Nos. 1, 2 and 5 must be fulfilled. 2. Where the telegraph uses non-loaded conductors, paragraph 5 of heading I, need only be fulfilled.

III.—VOICE FREQUENCY TELEGRAPHY. The total power of the telegraph currents corresponding to the frequencies employed simultaneously on the same circuit must not exceed 5 milliwatts at zero level.f

(A .g.) " CO-ORDINATION OF RADIO TELEPHONY AND TELEPHONE SYSTEMS. J

The International Consultative Committee— Considering :— That the use of a radio link in a long-distance telephone circuit involves certain special conditions with consequent particular difficulties which are not encountered when using wire circuits exclusively.

* The definition of noise voltage, the measurement of its magnitude and the limit to be placed on interference noise from all sources, form part of the study, and are the subject of experiments, by the International Mixed Commission dealing with the protection of underground cables and lines for tele­ communication. •f The text of the Green Book,” pp. 257-262 (English translation, 1928, pp. 197-201), relating to the selection of carrier frequencies, is deleted, together with the Appendix thereto. J This text replaces that under the same heading on p. 263 of the " Green Book ” (English translation, 1928, p. 202). • 120 A radio telephone circuit differs from a metallic circuit in the following respects— (1) A radio telephone circuit is subject to variations of attenuation, with the particular difficulty of “ fading,” which is characteristic of transmission with very high radio frequencies. (2) A radio telephone circuit suffers from the noise of “ atmospherics,” varying in intensity from a negligible quantity to a strength of the same order as the signal it is desired to receive. (3) Special precautions are necessary in the design and maintenance of a radio telephone circuit in order to avoid, at the radio receiving station, interference from the radio transmitter used for other services; in other words, abnormal ‘‘singing ” and ‘'crosstalk” conditions must be avoided or corrected. (4) In order to maintain the radio link at the best standard of transmission* it is necessary to provide special means for ensuring that the radio transmitter is fully loaded, as far as possible, whatever the nature and attenuation of the extension connected to the radio telephone circuit. (5) The band of voice frequencies which can be transmitted by the radio link may be limited by one or more of the following conditions :— (a) The necessity for economy in the frequency spectrum used for radio trans­ mission. (b) The use of a low radio frequency. (c) The necessitjT- for electrical filters in connection with the particular system of transmission used. (6) A radio telephone circuit is usually a long-distance inter-continental circuit providing a telephone service between two extensive networks, and this fact is of great importance from two points of view— (a) It is desirable that the standards of transmission aimed at for such a radio telephone circuit should be higher than those at present laid down for long-distance metallic circuits. (b) In the present state of the art, a valuable service should not be denied to members of the public under the pretext that it does not at all times reach the standard of excellence desirable for long-distance communications. Unanimously advises :— (1) That the band of frequencies transmitted by a radio telephone circuit should not be less than that recommended by the C.C.I. for long-distance international telephone circuits, i.e., 300 to 2 500 p.p.s., but it is desirable, if possible, to provide a wider frequency band than this, and, where practicable, the radio telephone circuit should be designed for a frequency band of not less than 200 to 3 000'p.p.s. Note.—In the present state of the art, it might be desirable to use provisional frequency bands differing from those specified above, if improved transmission results therefrom, e.g., on account of a reduction in the volume of interference. (2) That the normal attenuation of a radio telephone circuit should not be greater than the limit recommended for long-distance ciicuits, viz., 1-3 nepers or 11*3 decibels, but wheie practicable, a radio telephone circuit should be designed to have less than this attenuation under favourable radio conditions; that, as, in the present state of development, it is not practicable to maintain rigidly a radio telephone circuit below the limit of 1*3 nepers or n*3 decibels, a certain amount of latitude should be permitted under unfavourable radio conditions, rather than that a valuable long-distance service should be denied to subscribers. It must be recognised that, under unfavourable radio conditions, it might be necessary to do without the extensions normally possible by a radio link through the medium of wire connections. (3) That every endeavour should be made to minimise the noise level relative to speech, by the use of such radio devices as directive antennae, etc. That it is, however, necessary 121 to tolerate wide variations in the noise level on a radio telephone circuit. . Further, that in the present state of the art, neither a limiting ratio of noise to speech, nor a method of measuring noise, can, as yet, be recommended. That, provisionally, the following values can be taken as a general guide for the noise level on a radio telephone circuit ::— (a) Under average radio conditions, a mean noise voltage of 25 mV in 600 ohms at zero level, corresponding to a mean rectified power of o-ooi milliwatt, may be expected. (b) Under unfavourable radio conditions, a mean noise voltage as high as 200 mV in 600 ohms at zero level may be tolerated, if the extension circuits, including the subscribers’ circuits, are of sufficiently high grade (this noise voltage corresponds to a mean rectified power of 0*067 milliwatt). It must be ascertained that the noise voltage is not sufficient to affect the echo suppressors with which the extension circuits may be supplied. (4) That the extension circuits connected to a radio telephone circuit should conform to the various recommendations of the C.C.I. for normal metallic circuits in regard to the transmission equivalent, distortion, noise, echoes, transient phenomena, etc., in particular, the following :— (a) The attenuation between a subscriber and the terminals of the radio telephone circuit should not exceed 1-3 -j- i-o — 2-3 nepers or 20 decibels. The attenuation from subscriber to subscriber, including the radio telephone circuit and occasionally cord circuit amplifiers, should not exceed 3-3 nepers or 30 decibels (“ Green Book,” page 64, English translation, 1928, p. 45). (b) The noise voltage should not exceed the provisional value of 5 mV in 600 ohms at the transmission level of — 1 neper. (c) The echo effects should not be greater than the limits indicated by the curves and recommendations of the C.C.I., on pages 66 to 68 of the “ Green Book ” (English translation, 1928, pp. 46, 47). (d) The duration of transient phenomena in extension circuits should be such that, for any frequency within the band transmitted and for the complete circuit between subscribers (including the radio telephone circuit and both extension circuits), the total duration of a transient phenomenon shall not exceed 30 milliseconds. (5) That, in cases where a radio telephone circuit utilises a fairly low frequency band, making it necessary, on account of the congestion of radio services in the frequency spectrum, to use the same frequency band for transmission in both directions, a voice-operated switching device should be incorporated in the radio telephone circuit in order to avoid “ singing,” or interference from a radio transmitter on the receiving station. Although it is not always essential, from the technical point of view, to use a voice- operated switching device where the same frequency band is not used for radio transmission in both directions (as is the present practice with very high radio frequencies), it is desirable that such devices should be fitted, in order that the radio telephone circuit can be used, (a) with a low attenuation, and (b) for the inter-connection of two long-distance extension circuits which, in the absence of such devices, would constitute a circuit with excessive echo effects. 6. That, in the present state of the art, and in order to maintain the necessary-speech levels, a radio telephone circuit should be under the continuous observation of a technical operator at a position equipped with suitable instruments for indicating speech volumes and the mean noise voltage, and that this operator should be able to adjust the speech volume so as to load the radio transmitter fully, and also to make any necessary adjustment of the circuit conditions (including any voice-operated devices) to meet the varying conditions of speech volume and noise in respect of the transmission on the radio telephone circuit. 122 7. That when utilising very high radio, frequencies, an automatic gain control should be fitted to the radio telephone circuit to compensate automatically and as far as practicable for the radio phenomenon of “ fading.” 8. That the radio circuit should be terminated in such a manner that it can be connected to any other type of circuit in the normal way.

B. ESSENTIAL CLAUSES OF TYPICAL SPECIFICATIONS.

APPENDIX B.b.2, No. i.*

INSTRUCTIONS FOR DRAWING UP A TYPICAL SPECIFICATION FOR THE SUPPLY OF A MULTIPLE TELEPHONE INSTALLATION USING HIGH FREQUENCY CARRIER CURRENTS FOR INTERNATIONAL SERVICE.f

1. Multiple telephony by high frequency carrier currents can be used either on open- wire lines or on special cables. 2. The distribution of frequencies can be, for example, the following :— Up to 300 p.p.s.—infra-acoustic telegraphy. From 300 to 3 000 p.p.s.—low frequency telephony. Above 3 000 p.p.s.—high frequency telegraphy and telephony. If low frequency telephony is used for the relay of radio-broadcast transmissions, a frequency band larger than the above frequency band, e.g., from 50 to 10 000 p.p.s., should be reserved for this. 3. A high frequency telephone communication can be realised, either by using the same frequency band on the outgoing transmission and on the incoming transmission, or by using different frequency bands for the incoming and outgoing transmissions. 4. It is to be recommended that only one side band of the modulated carrier current should be transmitted along high frequency channels. In the case of speech transmission, this side band should correspond to a low-frequenc}^ interval of, at least, from 300 to 2 000 p.p.s. In this case, the carrier current can be either suppressed or transmitted at the same time as the side band. In the case of a suppressed carrier current system, the oscillators used at ends of the same channel should be either supplied with a s3mchronisation device, or should show a sufficient frequency stability not to require too frequent adjustments (e.g., more than once a week). 5. A system providing a complete high-frequency telephone communication comprises :— (а) Two terminating sets for connection with a toll line, or with a subscriber’s line. (б) Two transmitters. (c) Two receivers. (d) Filters for separating the various frequency bands, and duplex apparatus in the case where the same frequency band is used for both directions. (e) Devices foi signalling, monitoring and control. (/) Intermediate repeaters, if necessary. Half of the system is installed at each terminal high frequency station, i.e., a terminating set, a transmitter, and a receiver, as well as the associated filters and monitoring devices. Filters, devices for monitoring and control, and duplex apparatus if it is desired to use

* This appendix is to be inserted on p. 266 of the "Green Book ” (English translation, 1928, p. 204) in front of Appendix B.C.3, No. 1. f The figures given in these instructions correspond to the present position of the technique, and should be considered as provisional. 123 the same range of frequencies in both directions, are installed at each repeater station. 6. The levels of the complete connection—toll exchange, high frequency station, open- wire line, high frequency station, toll exchange—should be fixed so th a t: (a) The equivalent measured at 800 p.p.s. between two toll offices does not exceed i*3 nepers or 11*3 decibels. • (b) In certain cases (through traffic, mixed circuits comprising long cable sections) it is desirable to be able to attain a resultant gain of 1 *3 nepers or 11 -3 decibels between high frequency stations. (c) The high frequency level* at the origin of the open-wire line shall not exceed -j-2 nepers or 17-4 decibels. (d) The high frequency level at.the end of an open-wire line shall not be less than — 4 nepers or 35 decibels. Where the line connecting the toll exchange to the high frequency station has an attenuation - of 1 *3 nepers, or 11 *3 decibels, the diagram showing the levels is, for example, the following :—

H igh H igh Toll O pen-W ire Toll F req u en cy F req u en cy E xchange. Line. E xchange. S tation. Station.

Low frequency level measured at 0 - i '3 —■ 0 - i -3 800 p.p.s. nepers nepers or or —11 ’ 3 —11' 3 decibels. decibels. High frequency level + 2 —4 nepers or + 17-4 - 3 5 decibels.

7. The range of a high frequency communication should be in agreement with the range of the. low frequency communications on the same open-wire line. With normal equivalents, the ranges obtained for low frequency communications are as follows :— Open-wire lines of copper or copper alloy, the conductivity of which does not vary by more than 10 per cent, from that of high conductivity copper— Diameter ...... 2 mm 3 mm 4 mm Range ...... 150 km 300 km 500 km On any carrier communication channel, the attenuation of the line is then not more than 5 nepers or 43 decibels. Intermediate repeaters are necessary to obtain greater ranges. The attenuation characteristic of a repeater section should be as regular as possible. In the case of a duplex system, the impedance for any frequency should not differ from the mean impedance curve by more than 20 per cent. 8. In regard to near and far end crosstalk, and to the absence of disturbing noises, the different high frequency channels should satisfy the conditions which hold good for the use of low frequency.

* By “ high frequency level ” is meant the level of the side band transmitted. A normal low-frequency generator (frequency n, power 1 milliwatt into 600 ohms) placed at the end of the line (toll station) produces, at the near end of the open-wire line, the side band frequency of h — n o r h -f n. From the amplitude V of this frequency, the level of the high frequency voltage p is deduced by the equation V = V 0 eP (where Vo = o-755 voit). 124 Crosstalk attenuation (near or far end) measured at low frequency at the toll station between two high frequency channels, or between a high frequency channel and the low frequency channel on the same circuit, should exceed a value provisionally fixed at 7-5 nepers or 65 decibels; the noise voltage, measured at the circuit terminals in the toll exchange, should be less than 5 millivolts.* 9. The supervisory device must include : (а) Testing instruments for voltages of the filament, plate and grid batteries. (б) Apparatus for the measurement of the carrier current at the near end. (c) Apparatus for the measurement of the carrier current at the far end. (d) Installations for the control of low and high frequency repeaters. (e) A device for signalling, listening and speaking. (/) An alarm device arranged to function when the reception level deviates above or below the normal level by a certain amount (for example, +0*2 neper or + 1*7 decibels). Items (b) and (c) also serve for verifying the line attenuation. In suppressed carrier current systems, an auxiliary frequency is transmitted to permit of controlling the line attenuation: in this case, the measuring apparatus (b) and (c) should be suitable for this auxiliary frequency. 10. Receiving apparatus should comprise a regulating device, enabling the low frequency transmission equivalent on each channel to be adjusted in accordance with the indications given by the control apparatus. 11. The supplementary attenuation produced in ordinary low frequency conversation by the whole equipment of the line, in view of the use of high frequency, should not exceed 0*15 neper or 1-3 decibel for any frequency between 300 and 2 000 p.p.s. when, there are no high frequency repeaters on the line. 12. When a. circuit equipped for carrier current telephony is combined with another circuit, the presence of high frequency installations must not disturb the operation of the combined circuit. For this reason, the same line filters should be reproduced on the other side ciicuit. 13. The installation should take into consideration the transmission of the ringing current (16 to 25 p.p.s. or 20/500 p.p.s.). It should enable signals to be transmitted direct from toll station to toll station with intermediate calling of the two high frequency stations. 14. It is necessary to interconnect high frequency circuits in such a manner that— (a) No additional echo is produced. (b) The levels in each circuit do nor vary by more than plus or minus 0*2 neper or plus or minus 1 *7 decibels.

APPENDIX B.b.2, No. 2(|).

INSTRUCTIONS FOR DRAWING UP A SPECIFICATION FOR THE SUPPLY OF A HIGH FREQUENCY REPEATER STATION. J 1. The range of high frequency communication can be increased by means of intermediate repeaters. It is desirable to instal high frequency repeaters at the same spacing as low frequency repeaters, i.e., at intervals of 250 to 500 km.

* This figure is provisional; its definite determination will depend on the joint deliberations of the 3rd Commission of Assessors and of the 6th Sub-Committee of the C.M.I. (International Mixed Commission). 4 This text'is to be inserted on p. 266 of the “ Green Book” (English translation, 1928, p. 204), between Appendices B.b.2, No. 1 and (B.c.3) No. 1. J The figures given in these instructions correspond to the present state of the technique, and should be considered as being provisional. 125 2. The maximum gain of an intermediate repeater must amount to, at least, 3 nepers or 26 decibels. 3. The incoming level must not fall below — 4 nepers or 35 decibels. The outgoing level must not exceed + 2 nepers or + 17*4 decibels. 4. It should be possible to regulate the gain, either in accordance with the prescribed value for amplified carrier current, or in accordance with the amplitude of the auxiliary frequency transmitted (in the case where the carrier current is suppressed). Where the same repeaters serve simultaneously for all the channels, they should be supplied, for each direction, with an equaliser or correcting device to ensure the same transmission equivalent on all these channels. 5. The repeater should comprise, in addition to the measuring instruments supplied for the purpose of verifying the operating voltages, a device to show the value of the amplified carrier current (or of the auxiliary frequency current). It is further desirable that a listening device should be provided. 6. The effects of parasitic modulation, between currents of one band, or between currents of two different bands amplified simultaneously, being of such a nature as to cause noise or crosstalk between the channels of the same system, the high frequency repeaters should be so constructed that these parasitic modulation phenomena are systematically eliminated. 7. Supplementary attenuation produced in ordinary low frequency conversation by the insertion of a complete high frequency repeater, should not exceed 0 • 15 neper or 1 *3 decibels for any frequency between 300 and 2 000 p.p.s. 8. If, at the points where the high frequency repeaters could be installed, there are already low frequency repeaters, the balancing networks of these low frequency repeaters should be modified during the installation of this new equipment.

APPENDIX (B.b.), No. 3(*).

ESSENTIAL CLAUSES OF A TYPICAL SPECIFICATION FOR THE SUPPLY OF REPEATERS AND SPECIAL CORRECTORS FOR THE RELAY OF RADIO BROADCAST TRANSMISSIONS-!

General.—The present specification governs the principal conditions which must be fulfilled, from an electrical standpoint, 'by repeaters when they are taken over in the factory. It does not, however, govern the corresponding conditions after installation. Type.—The repeater should be equipped with vacuum tubes and give one-way amplification, with a transmission quality maintained within the frequency band to be transmitted, which band, in accordance with the recommendations of the C.C.I. (“ Green Book," page 74, English translation, 1928, p. 51) must extend, at least, from a frequency of 50 p.p.s. up to a frequency equal to 0*7 of the cut-off frequency, but in all cases less than 10 000 p.p.s. for a loaded line; for open-wire lines the repeater should be capable of transmitting frequencies up to 10 000 p.p.s. Amplification;—The repeater, with all its auxiliary apparatus, should amplify in such a manner as to compensate, as much as possible for the calculated attenuation of the preceding repeater section, communicated beforehand to the contractor. In the frequency band to be transmitted, therefore, the amplification should increase with the frequency in such a way as to suppress the distortion produced on the line. For frequencies still lower or still higher, the amplification must not exceed the values given by the amplification curve, values which produce a sufficient distortion correction.

* This text is to be inserted on p. 266 of the “ Green Book ” (English translation, 1928, p. 204) between Appendix B.b.2, No. 2, and Appendix B.c.3, No. 1. ■j" The values given hereafter must be considered as provisional. 126 It is necessary to provide for the regulation of the amplification in steps of o*i neper or 0*87 decibel, as a maximum. The amplification curves for the whole frequency band to be transmitted (giving amplification in terms of frequency) must be parallel for all settings of the regulating device. The variations in voltage at the terminals of the repeater, with a regularly maintained source of current, should give rise to a maximum variation in amplification oh 0*03 neper or 0-26 decibel. Impedance.—Values of the repeater impedance, measured at the, input and output terminals, are to be adapted as well as possible to the values of the impedance of the lines which will be connected to them.. Listening Device.—A listening device must be provided, enabling the radio transmission to be monitored before and after the repeater. This device should have a sufficiently high impedance as not to cause a diminution in the gain (increase in attenuation) of more than 0-03 neper or 0-26 decibel. Crosstalk.—Crosstalk attenuation measured under operating conditions at the output terminals should be equivalent to at least 10 nepers or 87 decibels between two repeaters used for broadcasting, or between one of these repeaters and a repeater to be used for ordinary telephony. When tests are made, the repeaters should be closed by impedances corresponding to those of the lines to which they will be connected. Output Power.—The maximum power given out from the repeater and transmitted to the line without distortion should amount to approximately 50 milliwatts. The music or speech volume will be chosen so that it may be possible to use all this power when the laigest possible quantities of energy are being transmitted. The gain should not vary by more than o*i neper or 0-87 decibel in the whole frequency band to be transmitted, when the output power varies from 1 to 50 milliwatts. Absence of Noise.—The noise level should be less than the maximum level used by at least 9 nepers or 78 decibels, which corresponds to a noise voltage of approximately "s cmTct Part °f the maximum voltage used. Non-linear Distortion.—The level of the harmonics produced must be less than that of the fundamental wave by a minimum of 3 '2 nepers or 28 decibels for the maximum power and for any frequency in the frequency band to be transmitted.

APPENDIX B.C.4, No. i.* ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION FOR THE SUPPLY OF TWO-WIRE TELEPHONE REPEATERS. General.—This specification covers the more important electrical requirements concerning the essential qualities of the repeater units as supplied by the factory. It does not cover the requirements for installed repeaters. Type.—It shall be a two-valve vacuum tube repeater, generally equipped with filters, and using balancing networks. It shall give two-way amplified transmission without introducing appreciable distortion for all frequencies within the efficient speech ranges of the cable circuits and for the maximum inputs occurring in practice. Balance.—The repeater shall not “ sing,” i.e., it shall not generate oscillations which cause singing at maximum gain, when the circuit and network terminals on either side

* This text replaces that of Appendices B.’c.4, Nos. x and 2 on pp. 268-271 of the “ Green Book’ (English translation, 1928, pp. 205-207). 127 are closed through non-reactive resistances, equal to the input impedance specified for the repeater; whilst the circuit and network terminals on the other side are open and . short circuited, respectively, or vice versa. Amplification.—The amplification produced by the repeaters shall vary with frequency within the frequency range efficiently transmitted by the circuit so as to compensate suffi­ ciently for the distortion introduced by the line. For the higher frequencies, the amplifica­ tion shall be decreased so as to be entirely suppressed in the region of the cut-off frequency of the circuit; for the lower frequencies, the amplification shall not exceed the values of an amplification curve which would produce an exact compensation. Means shall be provided for regulating the gain of the telephone repeater, preferably by .steps not exceeding o • i neper or I decibel. The gain-frequency curves shall be parallel in the band of frequencies for which the cable transmits efficiently for all repeater settings. The repeater circuit and apparatus shall be so designed that, with normal maintenance conditions of the power supply, variations in the supply voltage and current shall not produce a maximum variation in the gain of the repeater in service greater than o-o5 neper or 0’43 decibel. The maximum gain variation of a repeater inserted in very long lines (equipped with more than twelve repeaters) must not exceed 0*03 neper or 0*26 decibel. To this end, it is recommended that automatic control be provided for the filament and plate voltages. Impedance.—The impedance of the repeater, including the line transformers, shall be approximately equal to that of the circuit upon which the repeater is placed in service so that : z — w 2 - Z + W shall be a maximum.of o-q for the whole band of frequencies efficiently transmitted by the repeater, 2 being the characteristic impedance of the fine, w the impedance of the repeater measured as follows :— The impedance of the repeater is measured under working conditions using the networks but suppressing reaction effects, e.g., to measure the impedance of side “ X ” of the repeater, the circuit of side “ Y ” is replaced by a balancing network : the balancing network of side “ X ” shall reproduce the circuit of side “ X ” which is replaced by the measuring set; the potentiometer of the direction X —Y shall remain on the normal service position and the transmission is suppressed in the direction Y—X. Monitoring.—Means should be provided so that it is possible to monitor on the circuits in either or both directions with an operator’s telephone set and to talk on the circuits when necessary. - When'monitoring on a through connection, the losses caused bj' the monitoring device shall not exceed 0*03 neper or 0-26 decibel.' Crosstalk.—When repeater units, mounted either side by side or one over the other, are operated by batteries, as in practice, the crosstalk between the units measured on the output side shall not be less than 8 nepers or 70 decibels, on the understanding that when these measurements are being carried out the repeaters will be joined to impedances having a value equal to that of the uniform impedance fixed for international circuits.

APPENDIX B.C.4, No. 2. ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION FOR THE SUPPLY OF FOUR-WIRE TELEPHONE REPEATERS. General.—This specification covers the most important electrical requirements concerning the essential questions pertaining to telephone repeater units as supplied by the factory. 128 It does not cover the requirements for installed repeaters. Type.—It shall be a vacuum tube repeater and shall give one-way amplified transmission without appreciable distortion for all frequencies within the efficient speech range of the cable circuits with which it is associated and for the maximum inputs occurring in practice. Amplification.—The amplification produced by the repeaters shall vary with frequency within the frequency range efficiently transmitted by the cable so as to compensate suffi­ ciently for the distortion introduced by the line. For the lower and higher frequencies, the amplification shall not exceed the values of an amplification curve which would produce an exact compensation. Means shall be provided for regulating the gain of the telephone repeater, preferably by steps not exceeding o-i neper or I decibel. In the case of very long circuits, it may be necessary to provide an adjustment by steps not exceeding o-03 neper or o-26 decibel. The. gain-frequency curves shall be parallel in the band of frequencies for which the circuit transmits efficiently for all repeater settings. The repeater circuit and apparatus shall be so designed that, with normal maintenance conditions of the power supply, variations in the supply voltage and current shall not produce a maximum variation in the gain of the repeater in service greater than o-o5 neper or o -43 decibel. The maximum gain variation of a repeater inserted in very long lines (equipped with more than twelve lepeaters) must not exceed 0*03 neper or 0*26 decibel. To this end, it is recommended that automatic control be provided for the filament and plate voltages. Impedance.—-The input and output impedances of the repeater, not including the line transformers, shall in general, lie between 600 ohms and 950 ohms when measured at a frequency of 800 p.p.s. Monitoring.—Means shall be provided so that it is possible to monitor on the lines in either or both directions with an operator’s telephone set and to talk on the circuit when necessary. When monitoring on a through connection the losses, caused by monitoring shall not exceed 0-03 neper or 0-26 decibel. Crosstalk.—With repeater units mounted either side by side or one over the other and operated by batteries, as in practice, the crosstalk, between units, measured between the outgoing terminals, shall not be less than 8 nepers or 70 decibels, on the understanding that, when these measurements are being carried out, the repeaters will be joined to impedances having a value equal to that of the uniform impedance fixed for international circuits.

APPENDIX B.d.2, No. 1.* ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION GENERALLY APPLYING TO FACTORY LENGTHS OF INTERNATIONAL TELEPHONE CABLES OF THE QUADDED' TYPE. General. This specification covers the electrical requirements which must be fulfilled by factory lengths of air-space paper-insulated lead-covered cables for long distance telephone circuits. These requirements are specified in order to ensure that the cables will be suitable for :— (1) Phantom working. (2) Loading of pair and phantom circuits. (3) Efficient long-distance working in conjunction with repeaters.

* This text replaces that of Appendix B.d.2, No. 1, pp. 273-278 of the “ Green Book” (English translation, 1928, pp. 209-213).

1 2 9 These requirements do not apply :— (1) To cables in which the conductors are smaller than eight-tenths (o-8) of a millimetre (approximately 16 lb. per mile). (2) To groups of one gauge of conductors of less than ten (10) quads. (3) When the total number of circuits of each gauge specified is such that the lay-up of the cable is necessarily unsymmetrical, or such that conductors of different gauges are required to be in the same layer. Some of the more important raw material requirements are also specified.

Raw Materials. Copper Conductors. Each conductor shall consist of a wire of pure, annealed copper, smoothly drawn, cylindrical, uniform in quality, and resistance, free from scales or other defects and having a conductivity at least equal to that specified by the International Electro-technical Com­ mission (Berlin, 1913), th at is, one fifty-eighth (■£%) of an ohm for the resistance of a wire of standard annealed copper one (1) metre in length and of a uniform section of one (1) square millimetre at a temperature of twenty (20) degrees Centigrade. When correcting for temperature, the temperature coefficient specified by the same Com­ mission will be admitted—that is, at a temperature of twenty (20) degrees Centigrade, the constant mass ” temperature coefficient of resistance of standard annealed copper is 0-00393 per degree Centigrade. The diameter of the wires used shall not vary by more than one and a half (1-5) per cent, above or below the nominal diameter.

Factory Joints. When it is necessary to join conductors in the factory, the joint shall be made by a method which meets the following requirements :— The tensile strength of a section of a conductor which includes the joint shall be at least ninety (90) per cent, of the tensile strength of an adjacent section of the conductor of equal length without joint. The resistance of a section of the conductor not exceeding fifteen (15) centimetres (approximately 6 inches) in length, which includes the joint, shall not exceed by more than five (5) per cent, the resistance of an adjacent section of the conductor of equal length without joint. No twist joints shall be used. The material used for the joints must not contain acid. The joints shall be brazed with silver solder.

Insulating Paper. The paper used for insulating the conductors shall be uniform in texture and thickness, long-fibred and free from metallic particles or other deleterious substances. A sample of paper, taken from the finished cable and subjected to exposure to the atmosphere for one hour, shall have a tensile strength of not less than 4 kilometres (approxi­ mately 2-5 miles) length of paper of the same dimensions and the same quality.

Sheathing and Armouring Material. The requirements for these materials shall be specified separately for each individual cable. Electrical Characteristics. Conductor Resistance. The direct current resistance of any wire in a finished manufacturing length shall not exceed by more than four (4) per cent, the value calculated for a straight wire of the nominal

1 3 0 size of the conductor considered. The average resistance of all the wires in a group of one gauge shall not exceed the nominal value, as defined above, by more than one (i) per cent. For the maximum and for the average value an additional allowance, for the increase in length due to the stranding, shall be made in accordance with the table below

Over-all diameter of Allowance for the outer layer containing the increase in length due to gauge considered (in stranding. millimetres).

Below 30 1 -o per cent. 30-40 i- 6 40-50 2-5 50-60 3-7 60-70 5 -o 70-80 7 -o

In any length of cable the difference between the direct current resistances of the two conductors of a pair shall not exceed one (i) per cent, of the loop resistance of that pair. The difference in direct current resistance between the two pairs of a single quad, the conductors of each pair being taken in parallel in any length of cable, shall not exceed by more than 2 per cent, the loop resistance of the two pairs, the conductors of each pair being taken in parallel.

Insulation Resistance. In a length of cable each conductor, when measured for insulation against all other conductors and the sheath connected to earth, shall have an insulation resistance equivalent to not less than ten thousand (10 000) megohms per kilometre of cable (approximately 6 200 megohms per mile), the potential difference employed being at least 100 volts and not more than six hundred (600) volts. The reading shall be taken after an electrification of one (1) minute, at a temperature of not less than fifteen (15) degrees Centigrade (approximately 6o° F.).

Dielectric Strength. When specially called for, the cables shall-be designed so-that the insulation on every length of cable shall be capable of withstanding for two (2) seconds without rupture a fifty (50) period alternating current potential of the R.M.S. value specified in each particular case but not exceeding two thousand (2 000) volts, when applied between all conductors of the cable connected together and the cable sheath earthed. The maximum value of the testing voltage shall not differ by more than ten (10) per cent, from that of a true sine wave of the same R.M.S. value.

Mutual Capacity (Alternating Current). The mutual capacity of a pair is the capacity measured between the two conductors of the pair when all the other conductors in the cable are connected to the lead sheath. The mutual capacity of a phantom circuit is the capacity measured between the two pairs of a quad with each of the pairs short-circuited, and all other conductors in the cable connected to the lead sheath. The test shall be made with alternating current at room temperature. No correction for temperature shall be applied. In case of dispute, the results obtained with an alternating current of 800 p.p.s. (a> = .5 000) at not less than fifteen (15) degrees Centigrade (approxi­ mately 6o° F.) will be taken as final. . In each length of cable the average mutual capacity of all the pairs of each gauge, taken separately, shall be as specified by the Administration concerned; a tolerance of plus or minus five (4- 5) per cent, on ninety (90) per cent, of all factory lengths, and a tolerance of plus or minus eight (+ 8) per cent, on one hundred (100) per cent, of all factory lengths shall be allowed. In each length of cable the average mutual capacity of phantom circuits of each group of one gauge shall not differ by more than plus or minus five (dr 5) per cent, from the value which shall be determined by multiplying the average pair-capacity of that group by the factor 1-62. The mutual capacity of every pair and every phantom circuit shall be measured on not less than ten (10) per cent, of the total number of factory lengths. In any length of cable the capacity deviation of the pair or phantom circuits, respectively, of a group of one gauge shall not exceed the following values :—

Average, 4 per cent. Maximum, 12^ per cent.

By “ capacity deviation ” is meant the difference of the capacity of any circuit of a group from the average capacity of all similar circuits of that group in the same factory length.. This difference shall be expressed as a percentage of this average value.

Measures to be taken with a view to Equalising, as far as possible, the Capacities of the Loading Sections between Successive Repeaters. For each group of physical and phantom circuits of the cable the average capacities of the various loading sections between repeater stations should not differ by more than dr 2 per cent, from the average value of the capacity of the group of circuits in question throughout the whole of the loading sections. Where such regularity could not be obtained directly by manufacturing processes, if there are deviations greater than the limits indicated, it is recommended that the factory lengths be distributed in each loading section in such a manner that the capacities of the various loading sections shall fulfil the condition men­ tioned above.

Leakance• Constant. The average leakance of the pair and phantom circuits shall be determined on a small percentage of factory lengths, with an alternating current of 800 p.p.s. (a> = 5 000). The average leakance constant for each type of circuit for any length tested shall not exceed twenty-five (25).. This constant shall be taken as being equal to the ratio of the average leakance and the average mutual capacity measured with alternating current. This value may also be expressed as the ratio : G/coC — Leakance/Susceptance, which must not exceed 0-005.

Capacity Unbalance. In a cable two hundred and thirty (230) metres (approximately 750 ft.) in length, the capacity unbalances, measured with alternating current of approximately 800 p.p.s. (5 000 radians per second), shall not exceed the value given in the following table, each gauge being considered separately:— 132 - Limits for Capacity Unbalance in micro-microfarads per 230 metre lengths.

A verage. M axim um .

C Side to Side ...... 40 150 -r, . , 1 Phantom to Side ... 375 .Between circuits m the same quad < o-i , t- ,, 75 ■ ] Side to Earth 150 600 * Phantom to Earth ... 300 1 200 Between circuits in adjacent quads in') ^pajr 60 225 the same layer or between circuits I , , A • . J , , . ... > ^Phantom to Pair ... 60 225 m the centre quad and in a quad in | ™ , Phantom to Phantom 60 225 the first layer. J

* Owing to the large number of measurements that would be involved in making.complete tests, it is desirable to limit the measurements marked with an asterisk in the above table to 2 per cent, of the factory lengths of an order, with a minimum of two lengths. In exceptional cases the Administrations concerned may demand a greater number of lengths to be tested. The cable lengths on which these tests are to be made shall be indicated by the Administrations. If the capacity unbalances in a cable length exceed the limits specified above, only that length shall be rejected, but the Administration may demand measurements on other'cable lengths. In cables intended for four-wire operation, the average capacity unbalance between circuits in one. direction and similar circuits in the other direction shall be measured on one or more factory lengths and the average unbalance for a factory length of 230 metres shall not exceed 3 micro-microfarads. In each manufacturing length of cable having a length other than 230 metres, the capacity unbalance tested with alternating current for the different conductor diameters, shall not exceed the values obtained when the following rules are applied :— (a) Between the circuits—• Side to side Pair to pair =Average values. Phantom to pair Phantom to phantom Multiply the values given in the above table, applying to lengths of 230 metres, by the square root of the ratio between the length in question and 230 metres. (b) Between the circuits— Side to side h Pair to pair ' . , r,, . >Maximum values. Phantom to pair f Phantom to phan tom J Phantom to side h Side to earth Average and Maximum values. Phantom to earth J Multiply the values given in the preceding table by the ratio between the length in question and 230 metres. This correction shall not apply to lengths of cables less than one hundred (100) metres (approximately 330 feet). For such lengths the limits for a one hundred (100) metre length shall apply, computed in accordance with the preceding rules.

1 3 3 13 The limits here specified are based on the following definitions for the capacity unbalances. The capacity unbalance between the side circuits of a quad is the unbalance which would be produced or corrected, as the case may be, by the insertion of a capacity between one wire of one pair and one wire of the other pair of the quad. The capacity unbalance between a phantom circuit and either of its side circuits is the capacity unbalance which would be produced or corrected, as the case may be, by the insertion of a capacity between one wire of a pair and a wire of the other pair. The capacity unbalance to earth of a side circuit is the difference between the direct capacities of the two wires of the pair to the conductors of all other quads in the cable connected together and to the sheath, which shall be earthed. The capacity unbalance to earth of a phantom circuit is the. difference between the direct capacities of the two pairs of the quad to the other quads of the cable connected together and to the sheath, which shall be earthed. The capacity unbalance between two pairs of different quads is the unbalance which would be produced or corrected, as the case may be, by the introduction of a capacity between one of the wires of one pair and one of the wires of the other pair. The capacity unbalance between a phantom circuit and either of the two pairs of another quad is the unbalance which would be produced or corrected, as the case may be, by the introduction of a capacity between one of the pairs of the phantom circuit and one of the wires of the pair in question. The capacity unbalance between two phantom circuits is the unbalance which would be produced or corrected, as the case may be, by the insertion of a capacity between one of the pairs of one quad and one of the pairs of the other quad.

APPENDIX B.d.2, No. 3.* ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION FOR REPEATER SECTIONS OF LOADED INTERNATIONAL TELEPHONE CABLE. General. This specification covers the chief electrical requirements of installed repeater section lengths of loaded cable, where the factory lengths of cable and the loading coils are in accordance with their corresponding specifications. The clauses of this specification are drawn up so as to ensure that the cable shall be suitable for phantom working and for efficient long-distance performance in conjunction with two-wire or four-wire repeaters. The clauses below apply equally well to two-wire or four-wire circuits, except when otherwise indicated in the text.

Resistance Unbalance. In any cable section between telephone repeaters, the difference between the direct current resistance of the two conductors of any pair shall not exceed six (6) ohms for conductors of 1 mm maximum diameter, or four (4) ohms for conductors larger than this.

Insulation Resistance. The insulation resistance, between any wire and all other wires together with the sheath connected to earth, measured from the terminals of the cable, and not including the internal office wiring, shall not be less than five thousand (5 000) meghoms per kilometre of cable, this insulation resistance being measured with a difference of potential of at least 100 volts and not more than 600 volts, the readings to be taken after one minute's electrification.

* This text replaces that of Appendix B.d.2, No. 3, pp. 283-290 of the “ Green Book ” (English translation, 1928, pp. 217-223). 134 Impedance Balance. The balance between the impedance Zct of any side or phantom circuit and the corre­ sponding network impedance Zeq, calculated from the measured average constants of the circuit, shall satisfy the following requirements : after determination, by direct measurement, of the real and imaginary components of the impedance Zct and Zcq, the difference between the real components and the difference of the imaginary components, will be expressed in percentages, de and db of the impedance Zea of the balancing network, and if de and di are taken as the Cartesian co-ordinates of a point, this point should be situated within a circle having a radius of for all the circuits and for any frequency between 300 and 2,200 periods per second. Further, for 90 per cent, of the circuits and for all the frequencies indicated above, the corresponding point should fall within a circle having a radius of yoV

System of Loading and Cut-off Frequency. By way of example, two systems are described below under the titles : System No. I and System No. II, the former comprising two alternatives, Nos. Ia and lb. Both systems are equally' satisfactory from an international point of view. Administrations are invited to study the possible methods of application of System II to their internal systems, and to inform the C.C.I. of their observations and proposals on this subject.

System No. la. (i) Loading Coil Spacing. In any cable section between successive telephone repeaters the average loading coil spacing shall be eighteen hundred and thirty (1 830) metres within limits of plus or minus two 2) per cent. The actual length of any loading section, measured along any cable section between two successive repeaters, may vary as a maximum, plus or minus ten (10) metres from the normal spacing.

(ii) Loading Coil Inductances. For circuits which are planned not to exceed seven hundred (700) kilometres in length the units of loading shall have nominal inductance values of one hundred and seventy-seven (177) millihenrys for side circuits and sixty-three (63) millihenrys for phantom circuits (alternatively, one hundred and seven (107) millihenrys may be used for phantom circuit inductance). The limit of seven hundred kilometres may be extended to one thousand (1 000) km for four-wire circuits, provided that no disturbing echo currents are produced. For circuits which are planned to exceed seven hundred (700) kilometres in length, with the exception stated in the preceding paragraph, the units of loading shall have nominal inductance values of forty-four (44) millihenrys for side circuits and twenty-five (25) millihenrys for phantom circuits.

(iii) Cut-off Frequency. The cut-off point for the various systems of loading for both side and phantom circuits shall be calculated by the formula :

" s = T l c where cos = cut-off point, expressed in radians per second. L — inductance per coil, in henrys. C -- mutual capacity of the circuit between loading coils, in farads. 135 14 The cut-off point has approximately the nominal values given in the following table :—

Side. P h an to m .

Periods per Periods per R adians. R adians. Second. Second.

Circuits less than 700 km in length. With 177 mH side, 63 mH phantom 18 000 2 900 23 600 3 600 With 177 mH side, 107 mH phantom 18 000 2 900 18 000 2 900

Circuits over 700 km in length. With 44 mH side, 25 mH phantom 36 000 5 800 37 4°° 6 000

(iv) Impedance. The characteristic impedance of side and phantom circuits, loaded in accordance with the foregoing systems of loading, is calculated from the formula :

Z0 = A/L/C

(where Z 0 = the characteristic impedance, L and C being the constants referred to in paragraph on “ Cut-off Frequency ”) and has the values given in the following table :—-

' Ohms Impedance.

Side. P h an to m .

Circuits less than 700 km in length. • With 177 mH side, 63 mH phantom 1 590 740 With 177 mH side, 107 mH phantom 1 590 970

Circuits over 700 km in length. With 44 mH side, 25 mH phantom 790 470

(v) Attenuation Constant. The average attenuation constant for all circuits of one type, in any section between successive repeaters, loaded in accordance with the foregoing rules of loading, shall not exceed the values quoted in the following tables. The attenuation constants shall be measured on the cable sections between telephone repeaters, including exact half value terminating loading sections. In cases where exact half value terminating loading sections do not exist, these terminating sections shall be built out to half value by artificial cable and suitable corrections made to the measurements taken. The following table gives the values of the attenuation constants for circuits loaded with 177 mH side circuit coils and 63 mH phantom circuit coils on t 830 m nominal spacing. 136 Mean mutual capacity of cable : side circuit 0 *0385 /zF per km, phantom circuit 0*0625 /zF per km.

M a x im u m A v e r a g e A t t e n u a t io n p e r km a t 80 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 • 9 m m 0-0217 0 • 0228

1 • 3 m m 0-0121 0-0125

M a x im u m A v e r a g e A t t e n u a t io n p e r k m a t i 900 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 • 9 m m .. .. 0-0250 o •0245

1 • 3 m m 0-0164 0-0147

The following table gives the values of the attenuation constants for circuits loaded with 177 mH side circuit coils and 107 mH phantom circuit coils at 1 830 m spacing. Mean mutual capacity of cable : side circuit 0*0385 /zF per km, phantom circuit 0*0625 /zF per km.

Maximum Average Attenuation per km at 800 periods per second.

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 • 9 m m 0-0214 0-0177

1 • 3 m m .. 0-0119 0-0099

M a x im u m A v e r a g e A t t e n u a t io n p e r k m a t i 900 p e r io d s p e r s e c o n d .

Diameter of Conductors. Sid.e C ircuit. Phantom Circuit.

P P 0 • 9 m m 0-0251 0-0202

1 • 3 m m 0-0159 0-0127

_

1 3 7 The following table gives the values of the attenuation for circuits loaded with 44 mH side circuit coils and 25 mH phantom circuit coils on 1 830 m spacing. Mean mutual capacity of cable : side circuit 0-0385 [iF per km, phantom circuit 0-0625 [xF per km.

M a x im u m A v e r a g e A t t e n u a t io n p e r km a t 800 p e r io d s p e r s e c o n d .

Diameter of Conductors.. Side Circuit. Phantom Circuit.

P ■ P 0 • 9 m m 0-0390 0-0328

M a x im u m A v e r a g e A t t e n u a t io n p e r k m a t i 90 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit. •

P P 0 • 9 m m 0-0410 0-0339

System No. Ib.

(vi) Loading Coil Spacing. For cables with wires 0-9 mm diameter (having a mean mutual capacity of 0-0335 microfarad per kilometre for the side circuit and 0-054 microfarad per kilometre for the phantom circuit) and for those with wires 1-4 mm diameter (having a mutual capacity of 0-0355 microfarad per kilometre for the side circuit and 0-057 f°r the phantom circuit) the nominal loading coil spacing shall be two thousand (2 000) metres ^ 2 per cent. In any cable section between two successive telephone repeaters the actual length of any loading section (measured along the cable) shall not vary from the nominal spacing by more than plus or minus ten (^ 10) metres.

(vii) Loading Coil Inductances. For circuits which are planned not to exceed seven hundred (700) kilometres in length, the units of loading shall have nominal inductance values, for wires of 0-9 mm diameter, of 200 mH for side circuits and 70 mH for phantom circuits; for the wires of 1-4 mm diameter, 190 mH for side circuits and 70 mH for phantom circuits. The limit of seven hundred (700) kilometres may be extended to one thousand (1 000) kilometres in the case of four-wire circuits, provided always that this does not give rise to disturbing echo currents. For circuits which exceed 700 kilometres in length, excepting as provided in the preceding paragraph, the units of loading shall have nominal inductance values of fifty (50) mH for the phantom circuits.

(viii) Cut-off Frequency. The cut-off points, calculated by the previously mentioned formula, will have the approxi­ mate values given in the following table :— 138 Side. P h an to m .

R adians. Periods. R adians. Periods.

Circuits less than 700 km in length. Wires of 0-9 mm diameter (200 mH side, 70 mH phantom) 17 300 2 7 5 0 23 000 3 670 Wires of 1-4 mm diameter (190 mH side, ‘ 70 mH phantom) 17 200 2 740 22 100 3 520 Circuits over 700 km in length. Wires of 0-9 mm diameter (50 mH side, 20 mH phantom) 33 500 5 34° 43 000 6 840

(ix) Impedance. Calculated by the previously mentioned formula, the characteristic impedance shall have the values given in the following table :—

Ohms Impedance.

Side. P h an to m .

Circuits less than 700 km in length. Wires of o- 9 mm diameter (200 mH side, 70 mH phantom) 1 730 805 Wires 1-4 mm diameter (190 mH side, 70 mH phantom) x 630 775 Circuits over 700 km in length. Wires of 0-9 mm diameter (50 mH side, 20 mH phantom) 355 440

(x) Attenuation. The table below gives the values of the attenuation for circuits of :— (1) 0 -9 mm diameter (loaded with 200 mH side circuit coils and 70 mH phantom circuit coils, with 2 000 metre spacing, and mean m utual capacities of cable :—side circuit 0-0335 microfarad per kilometre, phantom circuit 0-054 microfarad per kilometre); (2) for circuits of 1-4 mm diameter (loaded with 190 mH side circuit coils and . 70 mH phantom circuit coils with 2 000 metre spacing, with a mean mutual capacity of cable:—side circuit 0-0355 microfarad per kilometre, phantom circuit 0-0585 microfarad per kilometre).

M a x im u m A v e r a g e A t t e n u a t io n p e r km a t 80 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 • 9 m m 0-0197 0-0210

1 • 4 m m . . . . 0-0097 O-OIOI

139 M a x i m u m A v e r a g e A t t e n u a t i o n p e r k m a t i 9 0 0 p e r i o d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 -9 m m 0-0236 0-0234

1 -4 m m 0-0133 0-0131

The following table gives the values of the attenuation for circuits of 0-9 mm diameter, loaded with 50 mH coils on the side circuits and 2 0 mH coils on the phantom circuits, the normal spacing being 2 0 0 0 metres and the mean mutual capacity 0-0335 jaF per km side circuit, and 0 -0 5 4 Per km phantom circuit.

Maximum Average Attenuation per k m at 800 periods per second.

Diameter of Conductors. Side Circuit. Phantom Circuit.

' • P P 0 • 9 m m 0-0307 0-0350

M a x im u m A v e r a g e A t t e n u a t io n p e r k m a t i 90 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side Circuit. Phantom Circuit.

P P 0 • 9 m m 0-0308 0-0353

Crosstalk. . The following tables state the maximum crosstalk allowable between any circuits as specified above and measured on any repeater section of cable between two successive repeaters. The values are those which would be measured from the terminals of the cable and include only crosstalk contributed by the cable and loading coils. They do not include crosstalk introduced by arrestors, terminal transformers, repeater station cabling and other equipment located in the repeater or terminal buildings. The crosstalk values shall be determined by means of a talking test or by tone approxi­ mating, in energy distribution; to speech (in cases of dispute, speech tests shall be taken as final). The measuring circuits employed shall be such that both the disturbing and disturbed circuits are closed at both ends through impedances which conform to the impedance of the disturbing and disturbed circuits, respectively.

1 4 0 The limiting value of attenuation corresponding to the crosstalk expressed in units of transmission shall be at least equal to the values quoted below :— Near End and Far End Crosstalk, Two-wire Circuits. Side to Side of same quad Phantom to Side of same quad .. Phantom to Phantom 78 nepers or 69-5 decibels. Phantom to Pair of different quads Pair to Pair of different quads .. Near End Crosstalk, Four-wire Circuits between Opposite-going pour-wire Groups. Pair to Pair...... Phantom to Pair ...... >9 nepers or 78 decibels. Phantom to Phantom ...... I Far End Crosstalk, Four-wire Circuits between Circuits Transmitting in the same Direction. Side to Side...... • • 1 Phantom to Side of same quad .. Phantom to Phantom U. 5 nepers or 74 decibels. Phantom to Pair of different quads Pair to Pair of different quads ..

System No. II. (xi) Loading Coil Spacing. For cables consisting of wires of o *9 mm diameter (and having an average mutual capacity of 0-0335 microfarad per kilometre for side circuits and 0-054 microfarad per kilometre for phantom circuits) and for cables consisting of wires of 1 - 4 mm diameter (having a mutual capacity of 0-0355 microfarad per kilometre for side circuits and 0 -057 microfarad for phantom circuits) the nominal loading coil spacing shall be seventeen hundred (1 700) metres (within 2 per cent.). In a repeater section of cable, the actual loading coil spacing (measured along the length of the cable) must not vary from the nominal loading coil spacing by more than plus or minus ten (^ 10) metres.

(xii) Loading Coil Inductances. The loading units employed on side circuits shall have a nominal inductance of 140 milli­ henrys, and those employed on phantom circuits of 56 millihenrys.

(xiii) Cut-off Frequency. The values of the cut-off frequency calculated from the formula coQ = 2 are given, approximately, in the following table :—

Side. P h an to m .

R a d ia n s. Periods. R adians. Periods.

Conductor diameter 0-9 mm (140 mH side, 56 mH phantom) 22 500 3 5oo 28 000 4 400 Conductor diameter 1-4 mm (140 mH side, 56 mH phantom) 21 700 3 400 27 000 4 300

141 (xiv) Impedance. The characteristic impedance, calculated from the formula Z0 = -y/ L/C shall have the values given in the following table :—

Ohms Impedance.

Side. P h an to m .

Conductor diameter 0-9 mm (140 mH side, and 56 mH phantom) ...... 1 570 780 Conductor diameter 1 -4 mm (140 mH side, and 56 mH phantom) ...... — 1 520 760

(xv) Attenuation. The following table gives the attenuation values for :— (1) A circuit having a diameter of 9/roths (0*9) mm loaded with coils of 140 millihenrys for the side circuit and 56 mH for the phantom circuit, spaced at a distance of 1700 metres, and having an average mutual capacity of 0-0335 microfarad per kilometre for the side circuit and 0*054 microfarad per kilometre for the phantom circuit; (2) A circuit having a diameter of 14/ioths (1*4) mm loaded with coils of 140 millihenrys for the side circuit and 56 millihenrys for the phantom circuit, spaced at a distance of 1 700 metres, and having an average mutual capacity of 0 *0355 microfarad per kilometre for the side circuit and 0*0585 microfarad per kilometre for the phantom circuit.

M a x im u m A v e r a g e A t t e n u a t io n p e r km a t 8 0 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side. P h an to m .

j8 J3 0-9 m m 0-0195 0-0190 1 • 4 m m 0-0095 0-0095 .

M a x im u m V a l u e o f A v e r a g e A t t e n u a t io n p e r km a t 2 20 0 p e r io d s p e r s e c o n d .

Diameter of Conductors. Side. P h an to m .

]8 0 0 • 9 m m 0-0225 0-0205 1 • 4 m m 0-0125 0-0115

(xvil Phase Compensation. Circuits likely to be used for long-distance international communication must be supplied with phase compensators. 142 (xvii) Crosstalk. The tables below give the maximum crosstalk permissible between any circuits corresponding to the above specifications and measured within a repeater section of a cable. These values are those measured at the ends of the cable and apply only to crosstalk arising from the cable and from the loading coils. These figures do not take into account crosstalk arising from the protectors, terminal transformers, cabling and supplemental y equipment in the repeater'station or the building where the cables terminate. The crosstalk values will be determined by a voice test,, or by using a complex tone in which the distribution of energy approaches that of speech (in the event of dispute, voice tests shall be considered as final). For these tests, the disturbing and disturbed circuits will be terminated by impedances which correspond to their respective characteristic impedances. The limiting attenuation values corresponding to the crosstalk values expressed in units of transmission shall be at least equal to the following values. Near End or Far End Crosstalk, Two-wire Circuits. Side to Side of same quad Phantom to Side of the same quad ... Phantom to Phantom . >8 nepers or 70 decibels. Phantom to Pair of different quads

Pair to Pair of different quads... ’ J Near End Crosstalk, between Opposite-going Four-wire Circuits. Side to Side ...... % ...... ") Phantom to Side ...... nepers or 78 decibels. Phantom to Phantom ...... J Far End Crosstalk, between Four-wire Circuits transmitting in the same Direction. Side to Side Phantom to Side of the same quad Phantom to Phantom 8*5 nepers or 74 decibels. Phantom, to Pair of different quads Pair to Pair of different quads...

APPENDIX B.d.2, No. 5.*

ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION OF GENERAL APPLICATION TO LOADING COILS FOR INTERNATIONAL TELEPHONE CABLES. The loading coils shall be suitable for loading both side and phantom circuits. The coils employed shall be assembled to form a unit of loading, so that when this unit is inserted in any quad, both side and phantom circuits shall be loaded. The electrical requirements hereinafter specified apply to the side and phantom circuits of such a unit of loading. The magnetic material employed shall be of the compressed iron dust type or other approved material having equally satisfactory characteristics.

Housing. The coils shall be encased in suitable protective cases which shall be hermetically sealed. The cases shall be waterproof and able to withstand being buried in damp ground without deterioration. Means shall be provided for easily connecting the loading units to the main cable.

* This text replaces that of Appendix B.d.2, No. 5, pp. 301-303 of the " Green Book” (English translation, 1928, pp. 232-234).

1 4 3 Magnetic Stability. The magnetic stability of the core material shall be such that the inductance of a coil shall not vary by more than dr two and one half (24) per cent, after direct current of any value between zero (o) and two (2) amps, has been allowed to pass through one line winding. This test shall be made five (5) minutes after the cessation of the direct current. This is a destructive test and should be applied only to sample coils.

Inductance. The inductance measured with a current of one (1) mA at 1 800 periods per second (more exactly, at co — 11 000) shall be equal to the values stated for side and phantom circuits, with a tolerance of -j- (2) per cent.

Effective Resistance. The effective resistance of the side or phantom circuit measured with a current of one (1) mA at 1 800 periods per second (more exactly, at o> =11 000) shall not exceed one hundred and fifty (150) ohms per henry of the specified inductance.

Crosstalk. The crosstalk in potted loading coils shall be measured with an alternating current of not less than five (5) milliamperes at 800 p.p.s. (more exactly £0 = 5 000) or with speech, under the following conditions :— The side circuits of medium-heavy units shall be terminated by non-reactive resistances of about 1 600 ohms. The phantom circuits of medium-heavy units shall be terminated by non-reactive resistances of about 800 ohms. The side circuits of light-loaded units shall be terminated by non-reactive resistances of about 800 ohms. The phantom circuits of light-loaded units shall be terminated by non-reactive resistances of about 400 ohms. The input terminals of the circuit under test and the input terminals of the apparatus used for comparison shall be joined in parallel and to the source of current. In the correcting formula corresponding to this arrangement 1 600, 800 or 400 ohms will be taken for Z x and Z2, as the case may be. In cases of dispute, speech tests shall be taken as final. The values of attenuation corresponding to the crosstalk between any side circuit and side circuit, side circuit and phantom, and phantom and phantom in any loading coil case shall not be less, in any case, than 9-5 nepers or 83 decibels. Between side circuit and side circuit in a coil unit 9 nepers or 78 decibels. Between side circuit and phantom circuit in a coil unit.. 8 nepers or 70 decibels. Between phantom circuit and phantom circuit 9 nepers or 78 decibels.

Insulation Resistance. The insulation resistance of any line winding of a loading coil unit against all other line windings (both in the same unit and in all other loading-coil units) and the case shall not be less than ten thousand (10 000) megohms. This test shall be made with a potential difference not less than one hundred (100) volts and n*ot more than five hundred (500) volts, at a temperature of not less than fifteen (15) degrees Centigrade (approximately 6o° F.).

Dielectric Strength. The insulating material between any two line windings shall withstand, without rupture, a difference of potential with a R.M.S. value not exceeding five hundred (500) volts. This .144 test shall be made with an alternating current of a frequency not less than fifty (50) periods per second, the voltage being applied instantaneously. The insulation between any line winding and the case, shall withstand, without rupture, a difference of potential of any effective value not exceeding two thousand (2 000) volts, applied during two (2) minutes. The maximum value of the testing voltage shall not differ by more than ten (10).per cent, from that of a true sine wave of the same R.M.S. value. Unbalances to Earth. The difference in the capacity to earth of loading coils of the two pairs ol the same quad shall not exceed a value provisionally fixed at 100 {x/xF. Variation in Inductance. The difference of inductance of loading coils of the two pairs of the same quad, tested in phantom circuit, shall not exceed a value provisionally fixed at 0*25 per cent, of the phantom circuit inductance. Variation in Resistance. The difference in the direct curient resistance of loading coils of the two pairs of the same . quad, tested in phantom circuit, shall not exceed a value provisionally fixed at 0*20 ohm.

C. APPENDICES.

List of Appendices on Transmission Questions. A.c.3, No. 1—Cord Circuit Repeaters used at Amsterdam, operating always at the same gain. A.c.3, No. 2—System of Cord Circuit Repeaters used in Great Britain. A.c.3, No. 3—Automatic Gain Regulation of Cord Circuit Repeaters. (Note by the International Standard Electric Corporation.) C.c.i, No. ia —British Post Office method of measuring the transmission efficiency of a subscriber’s installation from the central office.

C.c.i, No. - i / 3 —British Post Office method for measuring the efficiency of a subscriber’s station from the central office by means of alternating current. • C.c.i, No. iy—A method of measuring, by speech test, the sending and receiving efficiency of a subscriber’s installation in situ (alternative to the method described in Appendix C.c.i, No. 1/3). C.c.i, No. 2—Methods adopted by the French Telephone Administration for testing subscriber’s installations in operation. C.c.i, No. 3—Method used by the German Administration for testing a complete subscriber’s installation from the local telephone exchange. C.c.i, No. 4— Information concerning methods utilised in the United States of America for testing subscribers’ instruments and lines in operation.

APPENDIX A.c.3, No. i.

CORD CIRCUIT REPEATERS USED AT AMSTERDAM, OPERATING ALWAYS AT THE SAME GAIN. It is desiiable that, by means of a suitable arrangement of telephone lines and installations, and by use of supplementary networks placed in series with those lines having the lowest transmission loss, cord circuit repeaters used with such lines and installations shall require no gain regulation when operating in international telephone service. This result has been obtained, notably in Amsterdam, by the following methods :— The cord- circuit repeaters are mounted on a table, with two operating positions, six repeaters being available at each position. The conduct and control of calls is in charge of the operator dealing with the toll or international circuits. Contrary to the procedure adopted with former cord circuit repeater installations, the gain is not regulated for each call, but is fixed once and for all, and for all the repeaters, at a constant value of i ‘2 nepers.. This method tends considerably to simplify the service, and to avoid those faults which of ten arise fiom the adjustment of the potentiometer by operators. Thus, the B operator who distributes the repeaters is able to operate a greater number. This arrangement has, been made possible by ensuring that the degree of simulation of each line by a balancing network . exceeds a certain minimum. In order to accomplish this, -a supplementary artificial line, of which the attenuation is dependent upon the shape of the impedance curve of the circuit and on its attenuation, is added to the circuit where necessary. This artificial line is automatically introduced into the circuit by means of relays directly the repeater begins to function. The operator supervising the call has at her disposal normal cord circuits, by means of which she can listen-in, speak, call or cut-off, as circumstances may require. She can listen-in while a repeater is in operation; during the other operations, the repeater is disconnected. If the listening key is switched into the listening position, the circuits are connected to the cord circuit in the usual way without the B operator being given any indication that the repeater had ceased to function. The completion of the call is only signalled to the B operator when the through connection is cut off. The installation is used in Amsterdam principally for international traffic. A similar arrangement is being installed at Utrecht*

APPENDIX A.c.3, No. 2.

SYSTEM OF CORD CIRCUIT REPEATERS USED IN GREAT BRITAIN. This cord circuit repeater system is designed to give control of the call, on which a cord circuit repeater is used, to the toll operator who would normally control the call if a repeater were not used. This is effected by connecting each toll line, which may require the use of a cord circuit repeater, through a switching relay to its normal position. The cord circuit repeaters are wired to a special position, and, by means of the circuits, from the switching relays referred to above, terminating on jacks at the cord circuit lepeater position, a repeater may be inserted between any two toll circuits. At the same time, monitoring facilities are afforded to the toll operator on whose position one of the connected toll lines appears. The insertion of the repeater is done by an operator at the repeater position, who exercises no control over the calls, but merely sets up connections as requested by toll operators, over an order wire, and clears these connections on receipt of clearing signals. The gain of the cord circuit repeater is automatically adjusted to the requirements of the two lines connected together, and neither the toll operator nor the repeater operator has any control over this. Normally, the toll operator can monitor on the cord circuit repeater, but when she requires-to speak on the toll lines after a repeater has been inserted, she does so by plugging into a special jack which causes the repeater to be removed from the through circuit, and speaks directly on either toll line without giving a clearing signal to the cord circuit repeater operator. - The plugs and cords associated with the repeaters are fitted on a position known as the “ Repeater Position.” The plug shelf of this position is 4 ft, 6 ins. long, and accommodates 146 To face p. 147.]

TRUNK LINE

TO RELAY TO RELAY CONTROLLING CONTROLLING ARTIFICIAL ARTIFICIAL L IN E S IN L IN E S IN 4 - WIRE 4 - WIRE TERMINATION TERMINATION

TO , BALANCING \ NETWORK 1

__ 1----- A A——1 _ TRUNK CORD CIRCUIT -9

D ia g r a m T L . 1 2 9 7 B .— Cord Circuit Repeater operated from the ordinary toll position. Circuit of Repeater and its equipment. the plugs and cords for 20 repeaters, two plugs and cords being used for each repeater. Each plug consists of three three-way plugs, mounted in an ebonite holder, which permits of a certain amount of individual movement of the component plugs. The jacks are arranged in strips on the repeater position. A complete jack strip which accommodates ten toll lines, consists of 30 type-B Gauge Jacks arranged in three horizontal rows of ten. A designation strip is fitted above each complete jack strip. Two lamps are associated with each cord circuit. The green lamp lights when a connection is set up, and indicates that the repeater is functioning correctly. The white lamp gives a clearing signal. Diagram T.L. 1297B (opposite) shows, in schematic form, the cord circuit repeater connections and those of two toll lines. Each toll line is connected, via the armatures and back contacts of a relay (OB or ON), to a jack on an ordinary toll position. The front contacts of the relay (OB or ON) are connected, via signalling unit A to a jack on the repeater position. A second jack on the repeater position is connected, via a signalling unit B, to the back contacts of the relay (OB or ON), and a third jack is connected to an impedance balance for the toll line. The first, second and third jacks are mounted in the same vertical plane, so that connection can be made simultaneously by means of a triple plug. The method of operation is as follows :— The toll operator sets up the connection between the two circuits concerned via a cord circuit on the ordinary toll position in the usual manner, i.e., by means of a transfer circuit. The toll operator then requests the repeater operator, over an order wire, to insert a repeater between the two circuits. The relay operation is as follows :— On insertion of the plugs by the toll operator, relays CO operate. On insertion of the plugs by the repeater operator (assuming that the " X ” plug is inserted first) relays LB, XB, LN, and XN, in the sleeve circuits of the line plugs, operate, causing the operation of relays OB and SB through the contacts of LB and LN. OB switches the toll circuit through to the X side of the repeater. SB operates SN which, in turn, operates ON, which switches the other toll line through to the Y side of the repeater. The contacts of relay SN complete the input circuits of the repeater, those of SB complete the monitoring circuit from the repeater to the monitor jacks on both X and Y sides, and also disconnect the clearing relay circuit. The contacts of relays XB and XN disconnect the clearing lamp circuit and cause the operation of relay FS. The contacts of FS complete the filament circuit. If the valves are functioning correctly, the relays in the plate circuits operate, disconnecting the earth from relay GL, the contacts of which in the unoperated position complete the circuit for the green lamp, which lights. The toll circuits are therefore connected to each other via the cord circuit repeater, and the toll operator is able to listen to the conversation via the monitoring windings of the repeater. If the toll operator wishes to speak on the toll circuits, she inserts the Repeater Cut-out Plug (of which one is provided per toll position) into the special jack which is provided for each toll circuit. This causes relay TB to operate, thus inserting resistance in the circuit of relays LB and XB. This resistance is sufficient to cause LB to release whilst XB remains operated. The release of LB (or LN) releases SB which, in turn, releases SN; the monitoring circuit and the input ciicuits of the repeater are disconnected, relays OB and ON are released, and the toll operator speaks direct on the toll circuits. No clearing signal is given to the repeater operator, as although relay CL is operated, the circuit of the clearing lamp is not complete, since relays XB and XN remain operated. Also, FS remains operated and the green lamp remains alight. ■The series of relay operations is similar if the “ Y ” plug is inserted first. At the end of the conversation, clearing signals are received, via Units A and B, by the toll operator, who then withdraws the plugs on the toll position.

147 k 2 A clearing signal is given to the repeater position on the withdrawal of the plug by the toll operator at the controlling position, or by the operator who disconnects the second, or borrowed toll line, on receipt of a clearing signal over the transfer circuit. The clearing signal is therefore given on the first disconnection. This is effected by the release of relays LB and XB, or LN and XN, or all of them, the result being the breaking of the circuit of relay SB and the operation of relay CL.. This relay is a high resistance relay, and operates through the resistance of relay ON with a current which permits the release of the latter relay. Relay CL, on operating, completes a battery circuit through the clearing lamp and the armature and back contact of relays XB or XN, or both in parallel to earth. The release of relay SB releases SN, and the repeater inputs are disconnected. Relay FS releases when both XB and XN release, i.e., when both toll plugs are withdrawn, the filament circuit is broken and the green lamp goes out. The repeater operator clears on receipt of the clearing signal on the white lamp, whether the green lamp is alight or not. The following details are given of portions of circuit or equipment not mentioned in the foregoing method of operation. The usual jacks are provided on the repeater equipment for testing the operation of the repeater. In order to avoid the necessity of connections at the repeater position when testing a repeater from the repeater rack, two test keys A and B are provided on the repeater rack for each repeater. When the test key A is thrown, relays LB, XB, LN and XN are operated in the same way as when two toll circuits are connected to the repeater position, and the operation of relays SB, SN and FS follow, completing the input circuits of the repeater, and the filament circuits. Test key B completes the circuit to earth of the relays governing the gain control networks, and the operation of these relays may be tested by varying the resistance between test key B and earth. Gain Control.—All repeater units at an exchange are set to have the same basic gain (usually about 12 decibels) by means of potentiometers associated with each repeater unit. The variation in the control of the gain given by the. cord circuit repeater is effected by means of networks introducing attenuation in the input circuits of the repeater. The attenuation of these networks is controlled by a selective relay system, the selection being obtained by associating spools of different resistances with the sleeve of the balance jack. The lines are classified into four different groups according to the singing points obtained between the lines and their balances. Resistances are fitted in the sleeve circuit of the network jack of the following values. Type. Resistance. 1 20 ohms. 2 350 „ 3 1 000 4 2 600 When the plug is inserted, the resistance is part of a circuit containing also three relays of 100 ohms, 20 ohms and 5 ohms respectively (see Diagram T.L. 1317, p. 149), the operation of which is determined by the resistance. Thus, if the 20-ohm resistance is used in the sleeve circuit, all the relays Xi, X2, X3, or Yi, Y2, Y3 operate; with 350 ohms in the sleeve circuit, Xi, X2, or Yi, Y2 operate; with 1 000 ohms in the sleeve circuit, X i or Yi operate, and with 2 600 ohms in the sleeve circuit, no relays operate. . ' 148 In the input circuits of the repeater, i.e., between the terminals of the output transformers and the potentiometer, are networks the attenuation of which can be varied from nothing to 6 decibels, in steps of 2 decibels, by the operation of relays 2X and 2Y, 3X and 3Y, 4X and 4Y, respectively. The relay controlling a particular attenuation in the input of the “ Up ” repeater is in series with the relay controlling the same attenuation in the input of the “ Down ” repeater. When none of the attenuation control relays is operated, the full attenuation, viz. : 6 decibels, is introduced. The operation of relays 2X and 2Y reduces the attenuation to 4 decibels. 3X and 3Y „ „ „ 2 ,, ,, 4X and 4Y „ ,, „ zero. (See Table on P- I 50-)

TO 21*5 VOLT T O S L E E V E RELAY BATTERY o r P L U G X. VIA RELAY CONTACT.

D iagram TL. 1317. Cord Circuit Repeater. Relay connections for Automatic Gain Regulation.

TRIPLE JACK ON ‘REPEATER" POSITION.

D iagram TL. 1318. Cord Circuit Repeater. Diagram showing connection of Four-wire Circuit.

The Connection of Four-Wire Circuits.—A compromise balance is provided to balance the termination during the time that the toll operator is speaking from the termination. When a four-wire circuit is connected to a cord circuit repeater, the compromise balance is disconnected, and the balance terminals of the hybrid transformers are connected, via K 3 1 4 9 X CORD Y CORD Gain. Selective Relays Control Relays in Line of in Line of Repeater Gain less O perated. O perated. T ype— T ype— Attenuation of— ■ .

1 1 X i, X2, X 3 2X, 2 Y -3 X Zero Y i , Y2, Y3 3y , - 4x , 4y 1 2 X i , X2, X3 2X, 2Y.--3X, 3Y 2 decibels Y i, Y2 2 2 X i , X2 2X, 2Y-3X, 3Y 2 ,, Y i, Y2 2 3 X i , X2 2X , 2Y • 4 Y i 3 2 Y i , Y2 2X, 2Y 4 X i 3 3 X i 2X, 2Y 4 Y i 3 4 X i ---, 6 4 3 Y i --- 6 4 4 — -- 6 1 3 X i, X 2, X3 2X, 2Y-3X, 3Y 2 Y i 3 1 X i Y i , Y2, Y3 2X, 2Y,-3X, 3Y 2 1 4 .Xi, X2, X3 2X, 2 Y 4 4 1 ■ Y i, Y2, Y3 2X, 2Y 4 2 4 X i, X2 2X , 2Y 4 4 2 Y i, Y2 2X , 2Y 4 ' >.

an artificial line, balance jack and plug, to the balance terminals of the cord circuit repeater output transformer. At the same time, an artificial line is inserted between the line terminals of the hybrid transformer and the line jack. The change fiom terminal condition to through condition is effected by relay OB (or ON), the action of which, as regards the cord circuit repeater, has already been described. Diagram TL. 1318 (p. 149) shows the connections from the hybrid transformer of the four-wire circuit to the jacks on the repeater and the toll positions.

APPENDIX A.c.3, No. 3.

AUTOMATIC GAIN REGULATION OF CORD CIRCUIT REPEATERS.

(Note by the International Standard Electric Corporation.)

1. Gain Control of Cord Circuit Repeaters.—The type of two-wire repeater used as a cord circuit repeater is of the same type as the ordinary “ Standard ” type of repeater. Certain additional appaiatus is, of course, necessary for cord circuit operation. The gain of such a repeater must be regulated in order to be suitable for the various types of circuits to which it is to be connected. This is performed either manually or ' automatically. For these two methods of regulation a n-shaped balanced pad is inserted in front of the potentiometer in each direction of transmission. The position of these pads in the repeater is shown in Fig. 1. The losses introduced by the pads are as follows :— 150 Stop i ...... Loss = 5'7 decibels. 2 „ = 3*8 „ 3 ••• - = i '9 » 4 ••• „ = o » ' The pads being regulated simultaneously cause the same loss in both directions of transmission. The regulation of the pads is effected by means of six relays, iA, 2A, 3A, iB, 2B, 3B (Fig. 2, p. 152.) The relays act in the following manner :—

Series S hunt Loss in Gain. R elay. Resistance. Resistance. Decibels.

_ 1 106 . 950 5-7 2 iA , iB 68 1 400 3-8 3 iA, iB, 2A, 2B 33 2 750 1-9 4 iA, iB, 2A, 2B 0 Infinity 0 3A, 3B,

These relays can be controlled manually by means of a contro] key, or automatically by a selective system. . • 2. Automatic Gain Regulation.—In this system, a definite gain is determined for each circuit. The cord circuit repeater, gain is set to the average value of the gains of the two circuits to which it is connected by means of the automatic circuit controlling the gain.

NORMAL POTENTIOMETER

< k OOP P— oGRftTo—1

FRONT BACK LINE LINE NORMAL ^_Q0Q_i> —Q. QOQ P- ■WiQQQ.Pf - ^QQol POTENTIOMETER d'OW'11

LOSS s2 DECIBELS s, 1 • 9 3 3 w 2750“ 3 <£ 00 3 - 8 1 4 -0 0 ° 5 • 7 1 0 6 “ 9 S 0 U

F ig . 1.

The sleeves of the balancing network jacks are earthed through resistances, the values of which depend on the gain assigned to the circuit. - The resistances of all the calling and answering lines are marked Rx and R2 in Fig. 2. The following are the resistance values of the sleeve circuits for the four gain positions :— :— positions gain four the for circuits sleeve the of

TO 2 -WIRE REPEATER CIRCUIT. an Position.Gain 4 4 3 2 1 ......

...... 152 lee ici Resistance. CircuitSleeve . 2 o ohms. 6oo 2 ...... ooo i 0 5 3 20

„

& O 01 The relays F2, F3, F4, B2, B3, B4 in Fig. 2 are marginal relays, and their operation therefore depends on the resistance inserted in their battery circuit. The following table gives the order of operation of the relays and the corresponding repeater gain. Two differential relays, SA and' SB, are used in the circuit; they are inoperative when the current flows in their primary and secondary windings.

Notation. O = Operative. P = Primary Winding. NO = Non-operative. S = Secondary Winding.

Position Position of G ain Relays Operated. of Gain D esired. E m ployed.

Ans. Call. F2 f 3 f 4 B‘2 b 3 b 4 SA . SB iA 2A 3A iB 2B 3B

1 1 NO NO NO NO NO NO NO NO NO 1 1 2 NO NO NO 0 NO NO •— s NO NO NO 1 1 3 NO NO NO O O NO S s O NO NO 2 1 4 NO NO NO O O O s s O NO NO 2 2 1 O NO NO NO NO NO — p NO NO NO 1 2 2 O NO NO O NO NO — P & s O NO NO 2 2 3 O NO NO O O NO s P & s O NO . NO 2 2 4 O NO NO O O O s P & s O O NO 3 3 1 O O NO NO . NO NO p p O NO NO 2 3' 2 O O NO O NO NO p P & s O NO NO 2 3 3 0 O NO O O NO P & s P & s O O NO 3 3 4 O O NO O O O P & s P & s 0 O NO 3 4 1 O O O NO NO NO p p O NO NO 2 4 2 O O O O NO NO p P & s O O NO 3 4 3 O O O O O NO P & s P & s O 0 NO 3 4 4 O O O O O O P & s P & s O O O 4

3. Gain Reduction Key.—By means of this key the operator can reduce the repeater gain in steps, but the key does not permit of-the gain being increased beyond the value determined by the controlling circuit.

The relay RG operates and earths the set of relays, thereby giving a gain equivalent to that obtained on the lowest stop. The table below indicates the operation.

R.G. R.G. Non-operative. O perative.

Relays Earthed. Relays Earthed.

iA, iB, 2A, 2B, 3A, 3B iA, iB, 2A, 2B iA, iB, 2A, 2B iA , iB xA, iB

153 4- Automatic Cut-off Jack for Automatic Gain Regulation.—When a short-circuiting plug is inserted into this jack, the six relays iA, iB, 2A, 2B, 3A, 3B operate, and isolate the gain controlling device; this arrangement permits of regular repeater tests. 5. Gain-control Jacks for Testing Purposes.—A set of three jacks is provided, together with the necessary resistances connected between sleeves and earth, to enable the automatic gain regulation to be checked.

APPENDIX C.c.i, No. ia.

BRITISH POST OFFICE METHOD OF MEASURING THE TRANSMISSION EFFICIENCY OF A SUBSCRIBER’S INSTALLATION FROM THE CENTRAL OFFICE.

General. The testing set described was designed to measure the over-all sending efficiency from a subscriber’s office. A condition laid down was that the test should be made from the exchange. The set was the outcome of a desire to obtain, in a simple manner, information as to the efficiency of telephone apparatus in commercial use. To obtain all the necessary information about the transmission of the instrument, it is obviously necessary to measure both sending and receiving efficiency, but as for the latter it will be essential, either to visit the subscriber’s office, or to secure his co-operation, preliminary efforts were concentrated upon the sending efficiency. Experience shows that the transmitter is liable to far more variation and deterioration than the receiver, so that the sending test is the more important of the two. Details are given in Appendix C.c.i, No. 1 of a proposed transmission set, which is actually in course of design, to measure the receiver efficiency.

Transmission Testing Set for Measuring Sending Efficiency of Subscriber’s Installation. This set is based upon the measurement at the local exchange of the voltage induced there by the subscriber speaking on a normal telephone call. It will be noted that the test includes both the telephone apparatus and the subscriber himself. This is of great importance, as faulty speaking on the part of the subscriber is likely to be far more harmful than faults due to apparatus. The two can be separated in any individual case, when required, by instructing the subscriber to speak correctly, or by sending an officer to do so. The subscriber’s line is tapped by means of a high impedance transformer and the voltage amplified by means of a valve and passed thence to a special valve rectifier. This consists of a normal type grid leak rectifier except that the leak is caused to be put into circuit by the incoming speech currents from the subscriber and is normally not in circuit. This is effected by a standard type-B relay of high resistance which is operated by the amplified and rectified speech currents in a second circuit connected with the first as shown in the diagram (Fig. 1, p. 155). This subsidiary circuit is adjusted so that the relay operates with the faintest speech which the set is arranged to test. The rectifier in this second circuit operates by anode rectification. A high resistance microammeter is inserted in the plate circuit of the first rectifying valve, the normal plate current being biassed out as shown.

The operation of the circuit is as follows :— Incoming speech currents cause the B relay to operate, hence putting the grid leak into circuit; the speech current voltage, amplified in valve 1, is rectified in 2, and causes a proportionate deflection on the microammeter. Should the speech cease, the grid leak is immediately open circuited on the relay, leaving the grid of valve B negatively charged. With a high valve and condenser insulation this voltage is only very slowly dissipated, and 154 hence the microammeter reading remains at what it was immediately prior to the opening of, the grid leak circuit. Should the speech become fainter, the grid leak remains in circuit but the rectifier grid voltage reduces proportionately and hence also the microammeter reading. By suitable setting of the condenser and grid leak resistances it is possible to adjust the conditions so that with steady incoming speech the microammeter gives a steady reading in a few seconds. It will be seen, therefore, that provided the incoming speech is constant for this time, what is indicated on the instrument is the average maximum incoming voltage. The microammeter is calibrated directly in standard miles. The average voltage impressed upon the line, using an instrument with zero allowance, zero local line resistance and with average speakers talking in a standard manner, was measured and gives the zero of the scale. The rest is obtained by adding the appropriate lengths of standard cable. An explanatory diagram of connections is shown in Fig. I.

TRANSMISSION TESTING SET, FOR .MEASURING THE OUTPUT FROM SUBSCRIBER'S TELEPHONE.

F ig . i .

Results. Tests have been made on working lines on two exchanges. It was found that, after making all due allowances for all apparatus and lines in circuit, the sending efficiency in the one exchange is 0-67 neper or 5*8 decibels below its nominal value, and in the case of the other, o*6 neper or 5*2 decibels worse. These two exchanges were central battery exchanges, and central battery transmitters are accepted 0-37 neper or 3-2 decibels below standard, so that these figures may reasonably be reduced to 0-29 neper or 2-5 decibels and o • 23 neper or i-g decibels, respectively. Several examples of very poor transmission were met with. ,

155 APPENDIX C.ci, No. ij8.

BRITISH POST OFFICE METHOD FOR MEASURING THE EFFICIENCY OF A SUBSCRIBER’S STATION FROM THE CENTRAL OFFICE BY MEANS OF ALTERNATING CURRENT. 1. General Method of Test. The procedure is briefly as follows :— A small portable valve oscillator set operates a special receiver to form an acoustic generator. This apparatus is taken to the subscriber’s office and applied in turn to the trans­ mitter and receiver, and finally to a standardised receiver which is temporarily substituted for the subscriber’s receiver. The voltages generated are transmitted to the exchange, and, after amplification and rectification, produce deflections upon a direct current needle instru­ ment. These deflections are reduced to equality by means of a potentiometer, calibrated in nepers, decibels or S.M., and from these readings the efficiency of the set, both for sending and receiving, is obtained in terms of the efficiency of the standardised receiver.

2 . Apparatus Details. The oscillator is of normal type, except that the tuning inductance is built on iron stampings in order to obtain such a value of inductance that an air condenser with a maximum capacity of o • 001 /uF will be sufficient for tuning. The condenser is continuously driven by clockwork at about 120 r.p.m., with the result that the oscillator output varies in frequency from 600 to 1 500 periods per second. Over this range the voltage output does not vary 10 per cent. This range of frequencies covers the fundamental resonances of normal pattern receivers and transmitters. This appears to be an essential condition. The actual sound is produced by a receiver operated from the oscillator. In the receiver the space behind the diaphragm is nearly filled, so as to raise the natural frequency above that of the oscillator. To this receiver is attached an arrangement for coupling it to either the receiver or transmitter under test, the coupling device being so designed as to put an acoustic load on the apparatus under test of the same order as would be obtained in normal use. The measuring set used at the exchange contains two amplifying valves and one anode rectifier, all transformer-coupled. Two potentiometers (arranged to give o to 20 S.M. in five S.M. steps and o to 5 S.M. in S.M. steps), control the input. The measuring instrument is arranged as a fixed deflection instrument, i.e., the input is altered by means of the potentio­ meters until a given deflection is obtained on the instrument. The position of the potentiometers is then taken as the reading. A switch is provided to arrange for the difference between the output from transmitters and receivers. The part of the apparatus which is taken to the subscriber’s premises is a little complicated and heavy. It is therefore proposed to simplify the design and investigate its suitability. The new apparatus will comprise a direct acoustic source rather than a rhythmic oscillator. Further details of this research with the results obtained will be communicated.

3. Results. A test of 45 receivers by means of this apparatus has given the following results :— The maximum variation in efficiency between this and a speech test was 0*4 neper or 3*4 decibels and the mean variation, neglecting signs, 0-14 neper or i'2 decibels. Tests of 73 C.B. transm itters gave the following results :— The maximum variation in efficiency between this and a speech test was o • 71 neper or 6-1 decibels and the mean variation, neglecting signs, 0-22 neper or 1-9 decibels. Sixty-three per cent, of the transmitters tested were within 0*15 neper or 1-3 decibels of their true value, 85 per cent, within 0-3 neper or 2*6 decibels of their true value. These results include, of course, the natural variations which are to be expected in such

1 5 6 apparatus and are quite accurate enough for the commercial testing under consideration. The general assembly of the apparatus is shown in Fig. i, while Fig. 2 (p. 158) shows the circuit of the oscillator and Fig. 3 (p. 159) shows the voltmeter circuit.

The frequency of a vacuum tube oscillator which operates a special receiver is varied rhythmically between 600 and 1 500 p.p.s. at 150 revolutions per minute. The acoustic output of this receiver is applied by means of a special coupling unit either to the transmitter or receiver which is being tested. The resulting output voltage is measured at the central office by means of a special vacuum tube voltmeter and the efficiency of the transmitter or receiver is determined by comparison with a standard receiver.

ALTERNATING CURRENT TEST OF THE TRANSMITTING AND RECEIVING EFFICIENCY OF A SUBSCRIBER’S SET.

FIG . 1.

APPENDIX C.c.i, No. iy.

A METHOD OF MEASURING, BY SPEECH TEST, THE SENDING AND RECEIVING EFFICIENCY OF A SUBSCRIBER’S INSTALLATION IN SITU. (ALTERNATIVE TO THE METHOD DESCRIBED IN APPENDIX C.c.i, No.'ijS.)

The method described in Appendix C.c.i^ No. i/3 of testing the sending and receiving efficiency of a subscriber’s equipment necessitates the transport of a comparatively bulky testing set, which could not conveniently be carried by the lineman in addition to the normal tool kit. As the test involves a comparison with the output of a standard receiver, the employment of the voice of the tester, applied in turn to the standard and test receivers and to the transmitter, in place of the rhythmic oscillator, was suggested with a view to reducing the amount of testing equipment required. A method of test has been developed giving sufficient accuracy for the purpose, and requiring the conveyance to the subscriber’s office of only one case 7-5 cm diameter and 10 cm long. The method of test is similar to that described in Research Reports No. 4080 and 4208 of the British Post Office, except that speech is used in all tests. Details are given of the accuracy to be expected. General.—The method of testing subscriber’s apparatus in situ described in this report is a modification of that described in Appendix C.c.i., No. i/3. That method employs a rhythmic oscillator, which must be carried to the subscriber’s premises by the operator making the test. The new method substitutes the human voice for the oscillator, with the result that very much less apparatus is required at the subscriber’s premises. The general principle is the same, i.e., the receiver has attached to it, for test purposes, an acoustic coupler, which is arranged to provide the same acoustical loading as a human ear. 157 RHYTHMIC OSCILLATOR.

APPARATUS TAKEN TO SUBSCRIBER’S OFFICE.

DRIVEN VARIABLE OUTPUT 1-38 V. AT 600 ~/SEC. TO 1-5 V. AT 1475 ~/SEC. AIR CONDENSER. ON BELL RECEIVER (2000 OHMS). SPEED OF CONDENSER 200 R.P.M.

FIG. 2 158 THREE-VALVE MEASURING SET FOR A.C. TESTS ON SUBSCRIBER’S APPARATUS.

APPARATUS IN TEST ROOM.

1 0 0 V. 6 V. + - - +

2 0 15 IO 5 o O 5 IO 15 2 0 OvVWVNAAAA/VWVWVo

O IN P U T O

FIG. 3.

I 59 This coupler has attached to it a mouthpiece of standard size, and this enables the lineman to talk into it conveniently. The output from the subscriber’s telephone is compared with that obtained from a standardised receiver of special design, by means of a valve voltmeter situated at the exchange.

N o te.—An experimental testing set has been installed at the Research Station of the British Post Office. It will be operated by the exchange staff, which will enable the method to be given an extended practical trial, and modifications, if any, which may be necessary in arrangement and procedure, to be determined. The information given in this report refers to the methods so far tested, and to the results obtained using the semi-portable apparatus built for the specific purpose of investigating complaints in one area. Apparatus Required.—The only apparatus required at the subscriber’s office will be the acoustic coupler, with mouthpiece, and a standardised receiver. The output from the subscriber’s, instrument is measured at the exchange by means of a three valve valve-voltmeter. The measurement is made by altering potentiometers at the input to the set until a given deflection is obtained on the valve voltmeter. As it is required to measure speech currents, leaky grid rectification, employing a 1-5 pF grid condenser, is used. The operation will be described later. The actual arrangement of a set of this kind for routine testing will depend on the method of use. The best method would appear to be to make the set in two parts, one containing the potentiometers, the instrument and controls, while the other consists solely of an amplifier. This method eliminates the troubles which arise in practice, with a combined set, due to the action of the valve switches on the microphone. Four or five electrode valves can be used in the amplifier, so as to be able to work with the minimum value of plate voltage. It is realised that the maintenance, in exchanges, of small secondary cells for high tension purposes, presents a difficult problem, but some form of high tension supply is necessary. It may be possible to use the high tension, or part of it, for supplying current to the line under test. A battery completely free from noise is essential for this purpose. The valve filaments can conveniently be run off the exchange battery. Method of Use.—(1) After a clear connection between the instrument to be tested and the test set is established,, the lineman connects the line receiver to the line terminals of the instrument and takes up the test receiver. The test clerk at the exchange then adjusts the line current to 51 milliamperes (22 volts, repeating coil 4003A, relay 39J, 300-ohm local line, and 6o-ohm electro-magnetic line receiver). When the line resistance is greater than 300 ohms, the battery voltage is increased sufficiently to bring the line current to 51 milliamperes, thus obviating troublesome corrections. (2) The lineman listens on the line receiver until he receives the order to begin talking, when he applies the acoustic coupler to the receiver and counts, “ one, two, three, four, five ” several times, pauses and then counts again. He then listens on the line receiver. The .test clerk, having set the potentiometer to some given value depending upon the efficiency of the standardised receiver used, notes the mean deflections obtained, and if they are in good agreement with the figures given for the particular line receiver in use, continues the test. (3) The lineman then talks into the transmitter with the same volume as before. The test clerk measures the corresponding voltage by adjusting the potentiometers until the line receiver deflection is obtained. (4) The lineman then shakes up the transmitter, and repeats. (5) The lineman then cuts out the transmitter, either by short circuiting it in the case of a central-battery circuit, or by disconnecting the cells in a local battery circuit, applies the acoustic coupler to the test receiver and speaks into the attached mouthpiece with the same volume. The test clerk measures the corresponding voltage by adjusting the potentiometers. The whole test takes about three or four minutes.

1 6 0 Three potentiometer readings are obtained. Let the line leceiver reading be represented by A. „ „ test receiver „ ,, „ „B. „ „ transm itter „ ,, ,, ,, C. In addition, two calibration values are required. (1) The efficiency of the line receiver in terms of the standard receiver of the Department; let this be D worse. (2) The efficiency of the line receiver and artificial ear together, in terms of the standard transmitter of the Department; let this be E worse.

The efficiency of the test receiver will then be . . . A + D — B, and the efficiency of the transm itter . . . A -\- E — C. A -f- D and A -\- E will be constants for any particular line receiver and artificial ear, so that the calculations required are a minimum. A, D and E are given by measurements with the receiver and artificial ear.

Circuit Arrangements.—It has been found possible to work over an area covered by several exchanges by installing the valve voltmeter at a central exchange, and* using junctions to connect to subscribers outside that exchange area. The junctions used should not have a greater transmission equivalent than 5-3 decibels. The normal test desk equipment is of considerable help in tracing faults. Faults have frequently been found which had not been reported. In the case of an extension instrument on a. private branch exchange, a double-ended cord will generally be used to connect the extension directly to the exchange, in order to ensure that no apparatus is connected across the line. In the case of the old pattern (ex National Telephone) boards, which have a 400 or 6oo-ohm holding coil associated with the day jack, the test should be made using the night jack. The loss in the private branch exchange itself may be found by speaking into the line receiver, fust on the extension side, and then on the exchange side, of the apparatus using the normal cords of the private branch exchange. The loss will be the difference between the two readings, no correction being necessary. The general piinciple to be followed when special cases occur, is that there must not be any direct current shunt, but that indicators may be connected in series and alternating current shunts do not affect the test.

Results of Tests at Various Exchanges.—The test has been employed in making special investigations into the general efficiency of subscribers’ apparatus in various exchange areas. A consideiable amount of experience in the working of the test has been gained, and several modifications in the original scheme, as outlined in the advance copy of this report, have been made. One cause of trouble in the earlier tests was the unreliability of the line receivers and acoustic couplers that were being used. An all-metal receiver, and an acoustic coupler with a marble case, were substituted with considerable success. Tests on the receiver (which has a brass case) have shown that the variations in efficiency with temperature are small. One receiver over a temperature range of 19 degrees Centigrade showed an efficiency range of 1-6 decibels, while another similar one with a temperature range of more than 37 degrees Centigrade showed an efficiency range of 3-2 decibels. Further experiments are being made v with a receiver haying a soft iron case, and even better results are expected. The acoustic coupler is still not entirely satisfactory, but it is expected that an improved type will shortly be produced, which will be more reliable and more sensitive. In carrying out the tests at exchanges, the line receivers and acoustic couplers were calibrated, against standard receivers and transmitters, every morning before the lineman set. out. This occupied an appreciable time, and would be impracticable for maintenance purposes. •. • 161 L It is evident that the line receivers and acoustic couplers must be made sufficiently reliable so that calibration will only be needed once a month. • Tests of Accuracy .Attainable.—Preliminary tests were made on several receivers whose speech efficiencies were known. The receivers were connected to a standard central battery circuit with the transmitter replaced by a 50-ohm resistance. The standard receiver was spoken into once for every six receivers. The output current was measured directly in decibels by means of the speech measuring set described in Research Report No. 3920 of the British Post Office, with the addition of an extra stage of amplification, the proper set not being available at the time. These tests gave an average error of 1 • o decibel, neglecting signs, with a maximum of 2*8 decibels. Further tests were made by a crew of four operators on a group of 39 receivers, so as to include as many variables as possible. The test was modified, in that, for each receiver, first the test receiver, and then the standard, was spoken into. In 89 per cent, of the cases the error was less than 3*2 decibels; the aveiage error was i-6 decibels. A large number of transmitters were tested in the same manner, with similar results. The voice of one of the operators gave very much greater errors than the others, and his readings were very .much higher than the average of the rest. It is known that; whereas the output sound pressure from a receiver is practically proportional to the input voltage, a similar relationship does not apply for a transmitter. Tests were made to determine the extent of the error which is introduced by speaking at widely differing levels of volume. It was found that three observers, speaking at volumes varying between 16 to 21*5 decibels, gave an aveiage error with six transmitters of 4-3 decibels. This range of volume is greater than 'would be experienced with trained observers, but indicates the necessity of working to a definite speech volume. This is obtained as already explained. . . In testing further transmitters, special care was taken to keep the volume within about — 2*15 decibels of the mean, and all three speakers then give about the same order of errors. The average error for this last batch of transmitters is 1*7 decibels, and 84 per cent, have an error less than 3-2 decibels. The average error is 1*6 decibels for all the transmitters tested (98 in number with 265 observations) and 88 per cent, are within 3*2 decibels. Conclusions.—A method of testing subscribers’ . apparatus in situ has been developed, which is capable of giving a reasonably high order of accuracy. The apparatus required to be carried to the subscriber’s office has been reduced to the minimum. The test can be made to include every part of the subscriber’s equipment. A semi-portable set has been constructed and used with considerable success at several exchanges. No diagram of the circuit arrangements has been given, as the arrangements will depend on the method adopted for the test, and may be different, for every case, from those of the existing set. Further research is in progress, with a view to producing a receiver and an artificial ear sufficiently reliable to be used without frequent recalibration.

APPENDIX C.c.i, No. 2.

METHODS ADOPTED BY THE FRENCH TELEPHONE ADMINISTRATION FOR TESTING SUBSCRIBERS’ INSTALLATIONS IN OPERATION. .

The French Telephone Administration has adopted a method for measuring the efficiency of subsciibers’ installations in operation (referred to hereafter as “ Method A ”). In addition, the Investigation and Technical Research Section of the Fiench Administration is studying a new method (referred to later as “ Method B ”) for measuring the efficiency of a subscriber’s transmitter under normal service conditions. 162 Method A. This is a simple method of telephonometric testing, by voice and ear, consisting of two different tests :— (1) A rapid talking test, between an operator at the central office and the sub­ scriber himself, over an artificial line of attenuation 3 nepers, by which it was hoped to measure approximately tthe transmission efficiency of the complete arrangement of subscriber, subscriber’s line and set: this test is interesting, as the subscriber himself is included, the results obtained depending on the subscriber’s voice and his manner of using the instrument; fuither, this test requires no displacement of apparatus, and, therefore, can be made very rapidly. (2) A complete telephonometric test, carried out by two operators, one of whom speaks from the subscriber’s residence, using a calibrated subscriber’s set; this test enables both the receiving and sending efficiencies. of the subscriber’s set to be measured. The method employed for each type of test, and the results obtained, will now be examined. I .— Rapid Test. (1) Method of Operation.—The first practical tests made showed that it was impossible for the operator to estimate, even approximately, the intensity of sound received when listening to a subscriber over a line in which an artificial line is inserted; his duty is to maintain conversation with the subscriber, whilst sound intensities can only be judged when no account is taken of the meaning of the words heard; thus, it was found necessary to employ two operators.

F i g . i . On the other hand, it has, however, been found impossible for the operator to judge the sound intensity, with any degree of accuracy, without referring from time to time to a standard source of sound, as far as possible of the same type. The local effect in the auxiliary receiver of the type-1924 subscriber’s set of the French Telephone Administration has been chosen for this purpose. According to the circuit diagram given in Fig. 1, the sound intensity obtained by the local effect in this watch receiver was regulated, in the first place, so that it was equal to that obtained in the receiver of a standard instrument connected j as shown in the diagram of the standard circuit, to an artificial line having a characteristic impedance of 600 ohms and an attenuation of 3 nepers, when speaking, at the other end of the line, into the transmitter of the standard instrument connected to the artificial line, as shown in the same circuit diagram. The sound intensity obtained with the local effect is, in general, greater than the sound intensity obtained with a standard ieceiver; a balance is obtained by adjusting the two resistances R2 and R2; Rx is approximately 2 000 ohms and R2 about 200 ohms. 1 6 3 --L2 The test is then carried out in the following manner. The first operator equipped with the apparatus “ A ” (Fig. 2) connects to the subscriber’s multiple jack, and enters into conversation. A second operator, equipped with the apparatus ■“ B,” situated, so far as possible, in a quiet place, listens in the auxiliary receiver. Key C being depressed when the first operator speaks, he receives the sound intensity of his standard; the key being released when the subscriber speaks, he hears him over the artificial line D. It is possible for him rapidly to adjust the artificial line D to reduce the two sound intensities to approximately the same value. If the transmission equivalent of the watch receiver is n nepers (positive if the receiver is worse than the standard) and if the adjustment reduces the attenuation of the line D to N nepers, the transmission equivalent at the output of the combination formed by the subscriber, his instrument and line will then be 3 — n — N.

s u b s c r i b e r ’s LIN E J A C K .

(2) Tests and Results.—By agreement with the Administration of the Paris telephone services, tests have been made according to this method on 143 subscribers’ sets in the “ Segur ” area, some of which were of a very old type and have been in use for several years. In these 143 tests, 70 have a negative, or zero, transmission equivalent; 9 have an equivalent lying between 0 and 0-5 neper; 32 have an equivalent greater than, or equal to, 0*5 and smaller than i*o; and 32 have an equivalent greater than, or equal to, i*o. As already stated, the interest in these tests lies in that the subscriber himself speaks on the line, and that they can be rapidly effected; in practice, at least 100 subscribers’ instruments can be tested in this manner in a day by a crew of two operators. This test is, however, incomplete. On the one hand, as in all methods where the operator does not visit the subscriber, it cannot give any indication of the receiving efficiency of the subscribei’s set; the subscriber’s declaration on this point must, therefore, be accepted. On the other hand, if the test results show that the combination of subscriber, subscriber’s set and line has too large a transmission equivalent, this can be due to various causes. It can be due to the length of the subscribei’s line, which introduces its own attenuation and reduces the current supply. Knowing the construction of the line, it is possible to ascertain whether, the equivalent obtained is abnormal, from curves, giving transmission equivalents of a subscriber’s set at the end of lines of various types as a function of the line resistances. A second cause may be the bad state of the subscriber’s line; the existence of a fault on the line may be immediately ascertained by the ordinary tests. 164 There now remains the subscriber’s set, and the subscriber himself, who may have a voice of weak intensity or may use his instrument incorrectly. To ascertain if the subscriber’s set is inefficient, and if it is necessary to change it, it is therefore necessary to send an operator to the subscriber, and to make a complete test.

11.—-Complete Test. i. Method of Operation.—The principle of the testing method is to substitute, at the subscriber’s premises, a standard instrument for the instrument to be tested, as shown in Fig. 3, by means of a switching device.

To measure the receiving efficiency of the instrument, it is convenient to use a shunt on the receiver of the standard instrument. This shunt has been calibrated with the set and the standard receiver to be used in the tests according to the method indicated in Fig. 4. The values of the shunt r, corresponding to the attenuation values introduced in the artificial line E of 0-2, 0*4, o-6, o-8, ro , 1*5 and 2-0 nepers, have been thus obtained. Switching Device —This device is contained in a box used for transporting the standard subscriber’s set; the schematic diagram is given in Fig. 5. It consists of :— (a) A long four-conductor cord K, terminated at one end by a double plug F, and at the other by means of a piece of ebonite G, which can replace the fuse plug on the subscriber’s installation; where this fuse plug is inaccessible, a block H has been provided, with four terminals, which allow of easy connection to the con­ necting strip or plug. (b) Two double jacks A and B arranged on the left hand side of the panel of the apparatus, which allow of easy reversal of the connections. (c) A milliammeter (0 to 100 mA), put into action by depressing the push button L ; this milliammeter enables a measurement to be made of the feeding current of the subscriber’s set, and also of that of the standard instrument; the plug F is inserted in the double jack A or B, corresponding to a deflection of the milliammeter in a convenient direction.

Z n * 6 0 0 I b VARIABLE

| pyWAf<^ ^ Z n * 6 0 0 JP STANDARD SET I b « 3

F i g . 4 .

(d) A switching key Cp which allows of inserting into the line, without discon­ nection, the instrument under test or the standard instrument. (e) Finally, the shunt r, which enables, as already stated, the receiving efficiency of the instrument to be measured. 165 r 3 As soon as this apparatus has been installed at the subscriber’s premises, the operator demands that number of the “ Segur ” exchange, which corresponds to a special line having no local jack and leading to the telephonometric laboratory, where it is terminated as shown in Fig. 6. The plug of the two-way plug-in switch B being in the normal position a, ringing current operates the bell S; the second operator replies by moving the plug of the switch B from a to b, which has the effect of looping the line. The two operators are then connected, and begin the transmission efficiency tests of the instrument by operating their switches simultaneously.

rfc— 4 -i-o d bo i I1 H I j Qc{ C 9 I j r — |

T-bof- "1 SUBSCRIBER’S ) EXCHANQE SID E I SIDE -1 -0 c l_____ a ° H h

bi d|

a c

To test the leceiving efficiency, the operator at the telephonometric laboratory speaks into his instrument, and the operator at the subscriber’s end, by operating the switch Cj, adjusts the shunt r to obtain approximately the same sound intensity in the receiver of the instrument under test and in the receiver of the standard instrument. 2. Tests and Results.—After a preliminary rapid test, 49 subscribers’ instruments were thus tested. Among these, 22 had been found better than the standard in the rapid test. Of these 22 sets, 19 were found to be better than, or approximately equivalent to, the standard, in the complete test; one was found to be worse by 0*7 and two worse by i*o neper; it must, however, be mentioned that, for these last two instruments, the feeding current in the standard instrument exceeded 100 milliamperes, whereas in the standard circuit it was only 55 milliamperes; short lines are, therefore, involved, and it is not surprising that the first test gives a better result than the second. Of the 27 sets found to be worse than the standard under the rapid test, only 7 have been found to have an efficiency greater than, or equivalent to, the standard. - In the case of 14 of these sets, the difference in the absolute value between the first and the second test results was smaller than 0/3 neper, and for 10 of the remaining 13 the second test gave a result better than the first, which seems to prove that the subscribers use their instruments under unfavourable conditions.

166 The interest of this complete test lies in the possibility of testing the reception, which seems very useful; in fact, of 49 instruments tested, only 10 had a receiving efficiency greater than, or equivalent to, that of the standard tiansmission equivalent (negative or zero); 17 had an equivalent lying between o and 0-5 neper; 5 had an equivalent greater than, or equivalent to, 0 -5 and smaller than 1 *o neper; 16 had an equivalent greater than, or equal to, 1 - o neper and were, in consequence, very bad, although the subscribers, when consulted as to the quality of audition at the time of the rapid test, did not complain.

F ig . 6 . Conclusion. The two alternatives of Test Method A, which does not pretend to be an actual measuring method, but rather a means of estimating the quality of subscriber’s instruments, are capable of application as such. The Administration of the Paris telephone services has adopted the rapid test method, despite the difficulties arising from the differences of quality which are possible between the two sound intensities which are to be compared and which require an experienced operator. Method B. Principle.—This method relies on electrometric recording (by a condenser and a kenotron valve) of potential differences produced between two conductors of a circuit by microphonic currents. The electrometer is connected across the condenser and is graduated directly in units of transmission (decinepers) by reference to a standard voltage E (see Fig. 7). The capacity must have a convenient value, and be sufficiently large so that the system does not register extreme values of voltage (a capacity of 0*2 /xF has been found particularly suitable). A difference of potential U measured by this arrangement can be expressed as : 10 log ^ E decinepers. The reference voltage E corresponds to the mean voltage recorded in the course of the normal telephonometric tests. Under these conditions, the relative efficiency of a transmitter supplied with current according to a definite circuit and which is spoken into with a normal voice intensity, can also be measured by the number n — 10 log where U is the voltage between the terminals of the transmitter (or between two agreed points in the feeding circuit).

electrometerO-IO OECINEPERS

F i g . 7.—Rectifier Voltmeter arrangement for telephonometric measurements.

Two transmitters may also be compared, in a similar manner, by carrying out the former . test on each of the transmitters in turn, and taking the difference of the two results n1 and n2 given by the special voltmeter. The number %— measures the relative efficiency of 167 r 4 transmitter No. 2 (with respect to transmitter No. 1 taken as reference). This figure must correspond exactly to the numbers obtained by the telephonometric tests (voice tests) which, until now, alone have been used. Numerous comparative tests have confirmed that this is so, and that the values given by the two methods agree very satisfactorily provided that the operator who speaks maintains the same voice intensity during the two consecutive tests. The electrometer is graduated from o to 10 decinepers, but a variable graduated line (5, 10 decinepers) allows of adding or subtracting 10 decinepers to the value given by the electrometer. One or two amplifying valves are placed between the kenotron and the input terminals of the instrument; they provide a greater sensitivity for the instrument and also a definite input impedance which is independent of the magnitude of the measured voltage. Method of Use.—The system can be used in two ways : (a) It enables the telephonometric transmission equivalent of a subscriber’s set to be determined with respect to the standard E. For this, it is sufficient to measure the voltages (expressed in decinepers) due to the microphonia currents during a conversation utilising this set. This test is only,a preliminary check, which enables the complete arrangement (set—user) to be given a definite equivalent b. If this figure is sufficiently small, it is not necessary, as a rule, to carry the test any further. (b) If, however, this figure is greater than a limiting value n (taking into consideration, by means of special tables, the unavoidable diminutions of efficiency due to the length of a subscriber’s line) a check will be carried out by sending an expert operator to the subscriber’s station. This operator speaking with the “ normal calling intensify,” the voltmeter instrument gives readings closer to those which correspond to the true efficiency of the transmitter. (c) Finally, in the third case where it is essential to obtain precise information, the operator takes a standard transmitter which can be substituted for the transmitter of the instrument under test. The difference of the telephonometric voltages corresponding to the two transmitters compared (the transmitter of the subscriber’s set and the standard transmitter) gives the required transmission or reference equivalent.

N otes.— (1) A method for measuring the efficiency of a receiver, based on a similar principle to the preceding, at the present moment forms the subject of research. (2) Where two transmitters are compared directly, it is possible to use a system allowing of simultaneous speaking in front of the two transmitters. Two amplifiers and two complete, condenser-kenotron equipments are then necessary; the electrometer can be used to measure successively either the tension at the terminals of the two condensers, giving, as before, the relative efficiency, or as a zero instrument to adjust a potentiometer graduated in nepers, equalising the potential differences of the terminals of the two condensers. The relative efficiency is then given by the graduation read from the potentiometer.

APPENDIX C.c.i., No. 3.

METHOD USED BY THE GERMAN ADMINISTRATION FOR TESTING A COMPLETE SUBSCRIBER’S INSTALLATION FROM THE LOCAL TELEPHONE EXCHANGE.

The tests described below are for the sole purpose of ascertaining whether the subscriber’s station as a whole is in good condition, or otherwise. As shown in the diagram on p. 169, the test set, comprising the transmitter M and the receiver T, is connected to the subscriber’s station A through (1) an artificial line B, which is adjustable in four steps :■ 2; 2-5; 3; 3-5 nepers, or 17; 21-7; 26; 30-4 decibels, and 168 (2) a repeating coil Tr, the secondary winding of which obtains its current supply from the central battery of the exchange. The tests are carried out between one -tester, operating the above described test set, and another tester who is stationed at the subscriber’s set under test. All the subscribers’ instruments are tested, in turn, once a year, unless there are reasons for special tests. The two testers carry out a speaking test, while the attenuation of the circuit is being gradually increased. Up to a distance of 4 to 5 km' of subscriber’s loop, satisfactory transmission should be obtained with a maximum value of 5*5 nepers or 47*7 decibels in the artificial line; for longer loops the corresponding maximum value should be 3 nepers or 26 decibels. If these values are not obtained, special tests are made in order to locate the fault.

Although this method depends a good deal on personal factors, it has given very satisfactory results. Since the tests are carried out by men who are capable of judging the grade of transmission and since the attenuation artificially introduced is of considerable magnitude, it is hardly possible that a defect in the line, or the apparatus will escape notice. This method has the great advantage that it does not require special apparatus nor lengthy preparation. For other purposes, for example, tests on various types of transmitters and receivers, more exact testing methods are, of course, to be recommended. -

APPENDIX C.c.i, No. 4.

INFORMATION CONCERNING METHODS UTILISED IN THE UNITED STATES OF AMERICA FOR TESTING SUBSCRIBERS’ INSTRUMENTS AND LINES IN OPERATION. The experience of the American Telephone and Telegraph Company continues to show that, in addition to the efficiency tests made at the factory on subscribers’ sets, and on new subscribers’ lines before the installation of new sets, it is necessary to make efficiency tests on the completed installations, and to complement these initial tests b}^ others carried out at close intervals. As shown in the previous communication of the American Telephone and Telegraph Company, these tests are carried out between a person at the subscriber’s premises and a test board at the central office which permits of checking signalling and transmission conditions. These test boards allow of various types of tests, such as : insulation resistance, loop resistance, dielectric breakdown at 200 volts (in cases of calling by ringing machines), operation of line relay ringing, operation of automatic calling dial (where applicable), and a conversation test between operator and subscriber. This last test requires the insertion of an artificial line of about 20 decibels in the loop of the subscriber’s line on the test boaid; the available margin from the transmission standpoint is, therefore, reduced and the conditions of the talking test can then be compared with those obtaining over a long toll circuit. The test board also provides means for regulating the current supply in the subscriber’s loop, which is essential in order to obtain uniform transmission over subscribers’ loops of various lengths. Past experience has shown that, if these tests are carefully carried out, they allow of removing and eliminating troubles in the loop and subscriber’s set which may seriously affect the service and transmission. 169 D.—BIBLIOGRAPHY.

ABBREVIATIONS.

(a) German Publications.

E. F.D. Europaischer Fernsprechdienst. u . E. N .T . .. Elektrische Nachrichtentechnik. 5 . Z. Siemens Zeitschrift. T. u. F. r . .. Telegraphen- und Fernsprechtechnik. W. V. S. K. Wissenschaftliche Veroffentlichungen aus dem Siemens- konzern.

(b) English Publications.

B. repr.- . Bell Reprint. B. 5 . T. J ... . Bell System Technical Journal. B. T.Q. . Bell Telephone Quarterly. Elec. The Electrician. El. Com. .. . Electrical Communication. El. Rev. .. Electrical Review. El. W. Electrical World. Eng. . Engineering. t. P. O. E. E. Institution of Post Office Electrical Engineers. J. A. I. E. E. Journal of the American Institute of Electrical Engineers. J. Fr. I. . Journal of the Franklin Institute. J. I. E. E. Journal of the Institution of Electrical Engineers. P. 0 . E. E. J The Post Office Electrical Engineers’ Journal. Pr. I. R. E. . Proceedings of the Institute of Radio Engineers. W. P. . World Power. W. W. & R: R. . Wireless World and Radio Review.

(c) French Publications.

A . P. T. T. . Annales des Postes, Telegraphes et Telephones. B. S. F..E. Bulletin de la Societe frangaise des Electriciens. Onde Elec. Onde Electrique. R. G.E. .• Revue generale de l’Electricite. T. S. F. mod. T. S. F. moderne.

(a) GERMAN PUBLICATIONS. tiber den Einfluss des Phasenmasses und der Dampfung bei der Ubertragung von modulierten Wellen, H. Bartels, W. V. S. K., Vol. VII. No. i, 1928, p. 260. Uber logarithmische Masse von Verhaltnissen gleichartiger Grossen und liber die Frage ihrer Stellung zum absoluten Masssystem, F. Breisig, E. F. D., Sonderheft “ Como,” 1927, p. 5. Uber die Theorie der Anlaufvorgange, F. Breisig, E. N. T., 1928, p. 214. - Dampfungsentzerrung und Phasenverzerrung, H. Decker, E. N. T., 1928, p. 163. Der Einfluss der Schwankungen des Kabelwellenwiderstandes auf die. Rest dampfung einer Femsprechleitung ohne Rfickkopplungsverzerrung, H. Decker, T. u. F. T 1929, p. 102. Uber die Bedeutung der Hysterese bei Pupinspulen, W. Deutschmann, E. N. T., 1929, p. 80. Funkbild-Ubertragung im Anschluss an Rundfunk-Gerat, M. Dieckmann, E. N. T., 1926, p. 201. 170 • Uber den Kapazitatsausgleich in Fernsprechkabein ohne Phantombenutzung, K. Dohmen und G. Pleuger, T. u. F. T., 1928, p. 178. Uber die Wirkung des Pressdrucks auf die Eigenschaften von Massekernen fur Pupinspulen, W. Ehlers und F. Falkenberg, E. N. T., 1926, p. 281. ' Eine Kompensationsmethode zur genauen vektoriellen Bestimmung von Wechselspannungen, K. Eppelein, E. N. T., 1927, p. 211. Uber die kleinste Riickkopplungsverzerrung bei einer Zweidrahtverbindung mit Zweidraht- Zwischenverstarkern, R. Feldtkeller, T. u. F. T., 1926, p. 97. Uber die Bemessung von Ubertragem und Entzerrern fur Fernsprechzwischenverstarker, R. Feldtkeller und H. Bartels, W. V. S. K., Vol. VI., No. 1, 1927, p. 65. Uber rechteckige Verstarkungskurven, R. Feldtkeller, W. V. S. K., Vol. VI., No. 1, 1927, p. 81. Uber die Betriebsdampfung symmetrischer Vierpole, R. Feldtkeller, W. V. S. K., Vol. VI., No. 2, 1927, p. 106. Uber ein Endnetzwerk fur homogene Fermeldeleitungen, R. Feldtkeller, T. u. F. T., 1927, p. 91. Uber einige Endnetzwerke von Kettenleitern, R. Feldtkeller, E. N. T., 1927, p. 253. Uber die Nachbildung des Scheinwiderstandes von Pupinleitungen unter Beriicksichtigung der Amtsschaltungen, R. Feldtkeller, und F. Strecker, E. N. T., 1927, p. 125. Zur Konstruktion des Eingangswiderstandes symmetrischer Vierpole, R. Feldtkeller, W. V. S. K., Vol. VII., No. 1, 1928, p. 254 Uber die Messung der Echodampfung, R. Feldtkeller, und H. Jacoby, T. u. F. T., 1928, p. 6i. Scheinwiderstand und Betriebsdampfung von Ringubertragern, R. Feldtkeller, und V. Gandtner, T. u. F. T., 1928, p. 375. Uber das Verhalten symmetrischer, verlustfreier Kettenleiter zwischen ohmschenWiderstanden, R. Feldtkeller, E. N. T., 1928, p. 145. Uber das Verhalten von Ubertragern zwischen ohmschen Widerstanden, R. Feldtkeller, und H. Bartels, E. N. T., 1928, p. 247. Vorubertrager verzerrungsfreier Verstarker, R. Feldtkeller und H. Bartels, E. N. T., 1929, p. 87. Doppelsternkabel, Kuno Fischer, E. F. D., No. 11, 1929, p. 50. Diagramme zur Berechnung von .Vierpolen konstanten Wellenwiderstandes, V. Gandtner und G. Wohlgemuth, W. V. S. K., Vol. VII., No. 2, 1928, p. 67. Der Messschrank fur Fernkabelleitungen, W. Gebhardt und P. Richter, T. u. F. T., 1928, No. 11, Sonderbeilage. Der modulierte Tonfrequenzanruf in Fernkabelleitungen mit Verstarkern, G. Grimsen, T. u. F. T., 1929/p. 104. Eine Messeinrichtung fur betriebsmassige Verstarkungsmessungen bei Verstarkeramtern, „ G.' Grimsen, T. u. F. T., 1927, p. 49. Uber den Klirrfaktor langer Fernkabelleitungen, M. Griitzmacher, T. u. F. T., 1929, p 143. Uber Materialen mit hoher Anfangspermeabilitat, E. Gumlich, W. Steinhaus, A. Kussmann und B. Scharnow, E. N. T., 1928, p. 83. Ein neuer Ruckkopplungssperrer, W. Hahn und H. Warncke, E. N. T., 1928, p. 522. Uber die Verbindung von Vierdrahtleitungen untereinander, K. Hopfner, T. u. F. T., 1927, p. 166. Die Technik der Betriebsausnutzung der Fernkabel, K. Hopfner, E. F. D., Sonderheft “ Como,” 1927, p. 31. Fernsprechverkehr zwischen Deutschland und Nordamerika, K. Hopfner, T. u. F.'T., 1928, P- 98- Ergebnisse der Versuche mit einem neuen Pupinisierungssystem mit erhohter Grenzfrequenz und mit Phasenausgleich im Fernkabel Hannover-Wiedenbriick, K. Hopfner, T. it. F. T., 1929, p. 148 und E. F. D., No. 12/13, 1929. p. 118. Bildtelegraphie, G. Kette und W. Kiel, T. it. F. T., 1927, p. 31. Die Bildtelegraphie und das Problem des elektrischen Fernsehens, A. Korn, E. F. D., Sonder­ heft “ Como,” 1927, p. 51. 171 ' Wellengleichung und. Telegraphengleichung, A. Korn, E. N. T., 1927, p. 90. Uber Einschwingvorgange in Pupinleitungen und ihre Verminderung, K. Kiipfmiiller und H. F. Mayer, W. V. S. K., Vol. V., No. .1, 1926, p. 51. Die Ubertragungseigenschaften von Fernkabelverbindungen, K. Kiipfmiiller, E. F. D., No. 5, 1927, p. 19. fiber Pupinseekabel, K. Kupfmiiller, E. N. T., 1927, p. 359. Uber Beziehungen zwischen Frequenzcharakteristiken und Ausgleichsvorgangen in linearen Systemen, K. Kiipfmiiller, E. N. T., 1928, p. 18, and E. F. D., Sonderheft “ Como,” 1927, p. 25. fiber die Dynamik der selbsttatigen Verstarkungsregler, K. Kiipfmiiller, E. N. T., 1928, p. 459. fiber das Nebensprechen und andere damit zusammenhangende Erscheinungen, T. Laurent, E. N. T., 1928, p. 179. fiber die Wahl der Tragerfrequenzen fur die Tonfrequenztelegraphie, F. Liischen und K. Kiipfmuller, E. N. T., 1927, p. 165. fiber die zweckmassigste Pupinisierungsart von Fernkabeln, F. Liischen und K. Kiipfmiiller, E. F. D., No. 4, 1927, p. 10. Ausgewahlte Kapitel aus der Elektroakustik, F. Liischen, T. u. F. T., 1928, p. 125 and p. 163. Das neue Pupinisierungssystem fur Femsprechleitungen mit erhohter Grenzfrequenz und Phasenausgleich, F. Luschen und H. F. Mayer, E. N. T ., 1929, p. 139. Echosperrer fur Fernverbindungen, H. F. Mayer und H. Nottebrock, T. u. F. T., 1926, p. 353 and S. Z., 1926, p. 446. Das Dampfungsmass der Pupinleitung, H. F. Mayer, T. u. F. T., 1927, p. 163. Der Pegelzeiger, H. F. Mayer, E. N. T., 1927, p. 379. Uber automatische Amplitudenbegrenzer, H. F. Mayer, E. N. T., 1928, p. 468. Die Betriebssicherheit in Fernkabelanlagen, A. Mentz, E. F. D., No. 12-13, 1929, p. 128. Berechnung der Sprechfrequenzverluste in Schnurstromkreisen mit in Briicke liegenden Scheinwiderstanden, M. Merker, E. N. T.y 1926/p. 172. Neue Erfahrungen mit Instandsetzungen und mit der Lebensdauer von Fernsprecb-Seeblei- kabeln, E. Muller, E. F. D., No. 5, 1927, p. 47. ■ Die Messung des Nebensprechens, U. Meyer, T. u. F . T., 1926, p. 1. . Die Dampfung von Leitungen, deren Widerstand und Selbstinduktion Stromabhangig ist., U. Meyer, E. N. T., 1926, p. 33. Die neuere Entwicklung der Schnurverstarkertechnik, E. Neumann, T. u. F. T., 1929, p. 129. Die Entwicklung dei Fernsprechverstarker im Jahre 1927 und die Grundlagen des Einheitsver- starkers, H. Nottebrock und R. Feldtkeller, T. u. F. T., 1927, p. 307. „ fiber die Benutzung verzerrungsfreier Verlangdrungsleitungen im Zweidrahtverstarkerbetrieb, P. Oehlen, T. u. F .T ., 1929, p. 140. Fernkabelleitungen und ihre tiberwachung, W. Rabanus, T. u. F. T ., 1928, p. 1. fiber die Nachbildung langer Seekabel, H. Salinger, und H. Stahl, E. N . T., 1926, p. 296. Wodurch wird die Telegraphiergeschwindigkeit bestimmt? H. Salinger, E. F. D., Sonderheft “ Como,” 1927, p. 46. Der Bildfunk nach dem System Lorenz-Korn, W. Scheppmann und A. Eulenhofer, E. N. T., 1928, p. 373. Drahtlose Bildtelegraphie, F. Schroter, E. N. T., 1926, p. 41. Die neuesten Fortschritte des Bildtelegraphiesystems Telefunken-Karolus-Siemens, F. Schroter, E. F. D., Sonderheft “ Como,” 1927, p. 62. Fortschritte in der Bildtelegraphie, F. Schroter, E. N. T., 1928, p. 449. Welches Ubertragungsmass ist zum Gebrauch in der Ferntelephonie zweckmassig, und wie wird es gemessen? H. Schulz, T. u. F. T., 1926, p. 161, 265 and 370. Die Betriebsdampfung, H. Schulz, E. N. T., 1928, p. 449. Die Ausnutzungsmoglichkeiten einer Fernkabelader fur Telegraphie, H. Stahl, T. u. F. T., 1929, p. 95. !72 Ubei die Nachbildung des Wellenwiderstandes homogener Leitungen, F. Strecker, W. V. S. K., Vol. VI., No. i, 1927, p. 88. Uber die Ortskurven der Scheinwiderstande elektrischer Netzwerke in Abhangigkeit von der Frequenz, F. Strecker, W. V. S. K., Vol. VI., No. 2, 1927, p. 67. Uber Schaltungen zur Verbindung von homogenen und pupinisierten Leitungen, F. Strecker, und R. Feldtkeller, W. V. S. K., Vol. VI., No. 2, 1927, p. 127. Uber Anpassung und Nachbildung von Kettenleitem, F. Strecker und R. Feldtkeller, W. V. S. K., Vol. V., No. 3, 1927, p. 128. t)ber die Nachbildung einer verlustbehafteten Pupinleitung, F. Strecker und R. Feldtkeller, W. V. S. K., Vol. V., No. 3, 1927, p. 134. Eine Naherungskonstruktion fur eine Nachbildung homogener Leitungen, F. Strecker, T. u. F. T., 1928, p. 329. Kettenleiter und Wellensiebe, K. W. Wagner, E. N. T., 1928, p. 1 und E. F. D.} Sonderheft “ Como,” 1927, p. 8. Papierbleikabel fiir transozeanische Fernsprechverbindungen, K. W. Wagner und U. Meyer, E. F. D., No. 11, 1929, p. 10. Transozeanische Fernsprechkabel, K. W. Wagner, E. N. T., 1929, p. 125. Ein neues System fur Wechselstrommehrfachtelegraphie, M. Wald, E. N. T., 1928, p. 391. Das AEG-Vielfachtragerstromtelegraphie-System mit Sprachfrequenzen fur Fernsprechkabel, K. Wedler, T. u. F. T., 1929, p. 159. Uber Nachbildungen von Fernsprechkabelleitungen, W. Weinitschke, T. u. F. T., 1927, p. 40. Ergebnisse neuerer Untersuchungen an Zweidrahtverstarkerleitungen, W. Weinitschke, T. u. F. T., 1928, p. 135. Verfahren zum Messen von Betriebsdampfungen und-Verstarkungen, W. Weinitschke, T. u. F. T., 1928, p. 359. Vor der Einfiihrung des Tonfrequenzrufverfahrens fiir Zweidrahtverstarkerleitungen bei der Deutschen Reichspost, W. Weinitschke, T.,u. F. P ., 1929, p. 61. Die Fernsprechverbindung zwischen Europa und Amerika, E. Wollner, E. N. T., 1928, p. 489. Fernsprechverstarkeramter neuer Bauart, R. Ziihlke, T. u. F. T., 1927, p. 9.

(b) ENGLISH PUBLICATIONS. Telephone Cable Development, Mercer; W. P., March, 1928. Compressed Powdered Permalloy, Shackleton and Barber, J. A. I. E. E., June, 1928. Harmonic Production in Ferromagnetic Materials at Low Frequencies and Low Flux Densities, Petersen; B. S. T. J., October, 1928. Telephone Line Disturbance and Cable Balancing, Engelhardt, El. Rev., December 21, 1928. Cables (paper-core, twin, local, 1800 pairs), Rhodes, B. T. Q., January, 1929. Air-space, Paper-core, Telephone Cables of the Twin, Multiple-twin and Quad Types, Morris, P. 0 . E. E. J., October, 1927. Transformation Operators for use in Cable Balancing, Morris; P. 0 . E. E. J., January, 1928. Some Aspects of the Electric Capacity of Telephone Cables, Morris; P. 0 . E. E. J., April, 1927. Developments in the Manufacture of Paper-core Telephone Cables, Hart; B. S. T. /./April, 1928. Irregularities in Continuously Loaded Cables, Rosen; J. I. P. P., Vol. 65, No. 371. Quad Telephone Cables, Morris; Elec., July 29, 1927. Telephone Circuit Unbalances, Ferris and McCurdy; B. repr., B. 134. The Anglo-French Cable (1926), P. 0 . E. E. J., July, 1927. Submarine Insulation with special reference to the use of Rubber, Williams and Kemp; J. Fr. I., January, 1927. ' Long-distance Cable Telephony, Erikson; Elec., 1928, pp. 178 and 242. Science in the Cable Industry, Dunsheath; El. Rev., March 26, 1926. Recent Developments in Submarine Cable Design, Hughes; J. I. E. P., No. 373, 1928.

1 7 3 The Submarine Link in International Telephony, Robinson; I. P. 0 . E. E., Paper No. 117. Phase Distortion and Phase Distortion Correction, Mead; B. S. T. J ., April, 1928. Loading Coil Cores and their Magnetic Stability, Shida; El. Com., January, 1928. Distortion in Irregularly Loaded Lines, Warren; J. I. E. E., June, 1928. Carrier Telephone Systems in Australia, Partington; P. 0 . E. E. J., October, 1928. Single Side-band Carrier on Power Lines, Wilkins and Lawson;, El. W ., November 3, 1928. Carrier Current Telephone System for Short Toll Circuits, Black, Almquist and Ilgenfritz; J. A. I. E. A., January, 1929. Carrier Current Telephony, Timmis; P. O. E. E. J., January, 1929. Carrier Current Communication on Submarine Cables, Hitchcock; J. A. I. E. E.,October, 1926. High-frequency Measurements of Communication Lines, Affel and O’Leary; B. repr., B. 317. - Carrier Telephony on High-voltage Power Lines, Wolfe; B. repr., B. 116. The C-2-F Carrier System, Jammer; El. Com., July, 1928. Carrier Current Telephony on Power Lines in Southern California, Ashbrook and Henry ; El. Rev., May 18, 1928. Composited Telegraph and Telephone Working, Owen and Martin; P. 0 . E. E. J., July, 1929. Voice-frequency Telegraphs, Cruickshank; I. P. 0 . E. E., Paper No. 113. Telephone Repeaters (Cord-ciicuit) at New Delhi, P. 0 . E. E. J., January, 1929. The Fultograph, Haynes; W. W. and R. R., October 24, 1928. Transmission of Pictures ovei Telephone Lines, Ives, Horton, Parker and Clark; B. S. T. J., April, 1925. Some Photographic Problems in the Transmission of Pictures by Electricity, Ives; B. repr., B. 190. Photo Telegraphy, T h o rn Baker; El. Rev., August 17, 1928. Picture Telegraphy, Ritter; P. 0 . E. E. / . , ‘October, 1928. The Wireless Transmission of Pictures, Eng., April 30, 1926. Picture Reception, W. W. and R. R., May 23, 1928. Telephone Standards and Testing Technique for Microphones and Receivers, Cohen; J. I. E. E., Vol. 66 and El. Rev., December 2, 1927. Testing of Telephone Circuits and Appaiatus with Alternating Currents, Ritter and Milton; I. P. 0 . E. E., Paper No: no. Calibration of Wente Condenser Transmitter, Aldridge; P. 0 . E. E. J., October, 1928. Articulation and Intelligibility of a Telephone Circuit, Collard; El. Com., January, 1929. Routine Transmission Testing of Subscribers’ Instruments at the Exchange and at the Subscriber’s Office, Hudson; P. 0 . E. E. J., January, 1929. Transatlantic Telephony; the Cupar Receiving Station, Eng., August 24, 1928. Transatlantic Telephony, Jewett; B. repr., E. 166. Transatlantic Radio-Telephony, Bown; B. S. T. J., April, 1927. The London-New York Telephone Circuit, Hansford; P. 0 . E. E. J., April, 1927. Power Amplifiers in Transatlantic Telephony, Oswald and Schelleng; B. repr., B. 130-1. Production of Single Side-band for Transatlantic Radio-telephony, Heising; B. repr., B. 131 and Pr. I. R. E., June, 1925. Transatlantic Radio Telephone Transmission, Espenschied, Anderson and Bailley; B. S. T. J., Vol. IV., No. 3, July, 1925. Transatlantic Telephony: the P.O. Differential Voice-operated Anti-singing Equipment, Beer and Evans; P. 0 . E. E. J., April, 1927. Transmission Features of Transcontinental Telephony, H. H. Nance and O. B. Jacobs; J. A. I. E. E., 1926, p. 1061. Frequency Measurements with the Cathode Ray Oscillograph, F. J. Rasmussen; J. A. I. E. E., 1927, p. 3. Location of Opens in Toll Telephone Cables, P. G. Edwards and H. W. Herrington; B. S. T. J., 1927, p. 27. J74 Fatigue Studies of Telephone Cable Sheath Alloys, J. R. Townsend; Testing Materials (2nd part), 1927, p. 153. Application of the Theory of Probability to Telephone Trunking Problems, E. C. Molina; B. S. T. J., 1927, p. 461. Symposium on Television from the Bell Telephone Laboratories, B. S. T. J., 1927, p. 551. Radio Transmission System for Television, E. L. Nelson; B. S. T. J., 1927, p. 633. Power Plants for Telephone Offices, R. L. Young; B. S. T. J., 1927, p. 702. The New Yoik-London Telephone Circuit, S. B. Wright and H. C. Silent; B. S. T. J., 1927, P- 736. Advance Planning of the Telephone Toll Plant, J. N. Chamberlain; J. A. I. E. E., 1927, p. 994. Rigorous and Approximate Theories of Electrical Transmission, J. R. Carson; B. S. T. J.. 1928, p. 11. Tandem System for Short Haul Toll Calls, E. C. Wheelock and E. Jacobsen; J. A. I. E. E., 1928, p. 20. Telephone Toll Plant in the Chicago Region, G. B. West; J. A. I. E. E., 1928, p. 43. Electrical Measurement of Communication Apparatus, W. J. Shackleton and J. G.Ferguson; • B. S. T. J., 1928, p. 70. Transatlantic Telephony': the technical problem, O. B. Blackwell; J. A. I. E. E., May, 1928 and B. S. T. J., 1928, p. 168. Transatlantic Telephony : service and operating features, K. W. Waterson; J. A. I. E. E., April 1928 and B. S. T. J., 1928, p. 187. Present Status of Wire Transmission Theory and some of its Outstanding Problems, J. R. Carson; B. S. T. J., 1928, p. 268. Recent Developments in the Process of Manufacturing Lead Covered Telephone Cable, • C. D. Hart; B. S. T. J., 1928, p. 321. Measurement of Capacitance in terms of Resistance and Frequency, J. G. Ferguson and B. W. Bartlett; B. S. T. J., 1928, p. 420. Distortion Correction in Electrical Circuits with Constant Resistance Recurrent Networks, Otto J. Zobel; B. S. T. J., 1928, p. 438. Transmission of Information, R. V. L. Hartley; B. S. T. J., 1928, p. 535- Carrier Systems on Long-distance Telephone Lines, H. A. Affel, C. S. Demarest and C. W. Green; J. A. I. E. E., January, 1929 and B. S. T. J., 1928, p. 564. Relation between Transmission Line Insulation and Transformer Insulation, W. W. Lewis; J. A. I. E. E., 1928, p. 637. Rationalization of Transmission System Insulation Strength, P h i l i p Sporn; J. A.. I. E. E., 1928, p. 641. Power Line Carrier Telephony, L. F. Fuller and W. A. Tolson; J. A. I. E. E., 1928, p. 711. Problems in Power Line Carrier Telephony, W. V. Wolfe and J. D. Sarros; J. A. I. E. E., 1928, p. 727. Carrier Telephone System for Short Toll Circuits, H. S. Black, M. L. Almquist and L. M. Ilgenfritz; J. A. I. E. E., 1929, p. 15. The Transmission of High Frequency Currents for Communication over Existing Power Networks, C. A. Boddie and R. C. Curtis; J. A. I. E. E., 1929, p. 37. The Graphic Solution of A. C. Transmission Line Problems, F. M. Denton; J. A. I. E. E., 1929, p. 49- Losses in Armoured Single Conductor Lead-covered A. C. Cables, O. R. Schurig, H. P. Kuehni, F. H. Buller; J. A. I. E. E., 1929, p. 206. Decibel— the Name for the Transmission Unit, W. H. Martin; J . A. I. E. E., 1929* P- 223 and B. S. T. J., January, 1929. The Receiving System for Long Wave Transatlantic Radio Telephony, A u s t in Bailey, S. W. Dean, W. T. Wintringham; Pr. I. R. E., December, 1928, and B. S. T. J., 1929. p. 309.

1 7 5 (c) FRENCH PUBLICATIONS. La lutte contre la corrosion par les traitements electro-chimiques, M. Cournot; B. S. F. E., 1928. Emploi d’un plan de jonction pour la localisation des derangements dans les cables, Prache; A. P. T. T., April, 1929. . Note sur l’elimination des perturbations causees par leslignes exploitees au Baudot, Boyer; A. P. T. T., October, 1928. Sur les constantes du quadripole passit, Telligen; R. G. E., August 11, 1928. Ligne artificielle d’equilibre pour ligne pupinisee, J. B. Pomey; R. G. E., October 20, 1928. Sur les amplificateurs a resistances, J. B. Pomey, A. P. T. T., October, 1928. • Les ondes electro-motrices, Aguillon; A. P. T. T., October, 1928 and February, 1929. Sur une expression de 1’energie transmise par un quadripole neutre, J. B. Pomey; R. G. E., March 31, 1928. ' Sur la distorsion telephonique et sa mesuie, David; A. P. T. T., April, 1928. Sur une methode pour la mesure des affaiblissements, Chavasse, A. P. T. T., January, 1928. Sur une proposition fondamentale de la theorie des filtres electriques, J. B. Pomey; R. G. E., February 21, 1928. Addition des affaiblissements effectifs, P. Mocquard; A. P. T. T., August, 1928. Le systeme fondamental de reference pour la transmission telephonique, P. Chavasse; A. P. P. T., November, 1928. Influence des emissions secondaires des metaux sur le fonctionnement des lampes a trois electrodes, Le Boiteux; R. G. E., June 2, 1928. Determination de la condition d'entretien et de la periode d’oscillation d’un oscillateur triode, Abeles; R. G. E., 21 April, 1928. Mesure des frequences, Bedbade and de Mare; T. S. F. Mod., August, 1928. Dispositif antiparasite (de Bellecisze); Onde Elec., March, 1927. Quelques procedes d’amplification des courants photoelectriques et applications a l’emission des belinogrammes, Toulon; Onde Elec., February, 1928. Derniers progres de la transmission belinographique en France, Ogloblinsky; Onde Elec., August, 1928. Installations executees par la Societe d’Etudes pour liaisons telephoniques et. telegraphiques a longue distance, Cahen; A. P. T. T., June, 1927. L’adaptation du reseau frangais au service telephonique universel, H. Milon; A. P. T. T., January, 1928. Les essais telephonometriques des appareils d’abonnes, P. Chavasse; B. S. F. E., March, 1928. Remarque sur les mesures de desequilibre de capacite des cables telephoniques, R. Dunand; R. G. E., July 20, 1929. Transmission en ondes courtes, H. Chiriex; Onde Elec., June, 1926. Liaisons radio tel ephoniques a grande distance par ondes courtes projetees, H. Chiriex; B. S. F. E., July, 1928. Systemes frangais d’aeriens projecteurs pour emissions sur ondes courtes, H. Chiriex; B. S. F. E., May, 1929. Compensation des courants induits entre antennes emettrices voisines, Villem; R. G. E., March 24, 1928. La transmission radiotelepbonique par ondes courtes dirigees et la station d'essai de communica­ tion Paris-Alger, Villem; R. G. E., June 16, 1928. Liaison radiotelephonique Paris-Buenos Ayres par ondes courtes projetees, Villem; B. S. F. E., October, 1929. ' Note sur la modulation dans les appareils recepteurs, H. de Bellecisze; Onde Elec., April, 1926. Dispositif alternant les effets du “ fading.” Application et consequences, H. de Bellecisze; Onde Elec., March, 1927. Etablissement du courant dans une serie de circuits resonnants couples entre eux par l’intermediaire de lampes triodes, G. Fayard, Bulletin de la S. F. R., October, 1928. Etude sur un filtre, G. Fayard; Bulletin de la S. F. R., June, 1929. 176 V.—QUESTIONS OF TRAFFIC, OPERATION AND TARIFFS.

A.—General. B.—Various Classes of Calls and Facilities available to the Public.. C.—Methods of Operation. D.— Rates and Tariffs. E.—Proposed Typical Form of Agreement between Administrations for International Telephone Service. F.—Traffic Statistics.

A.—GENERAL. RECOMMENDATION No. 4a.*

Establishment of the Nomenclature, of the International Circuits and the Schematic Plan of the Cables.

I. Form under which the Nomenclature of the International Circuits should be arranged."j* # The International Consultative Committee in agreement with the International Bureau of the Telegraph Union— Unanimously advises :— That, in future, the nomenclature of existing and projected international circuits, kept up to date and published by the International Bureau of the Telegraph Union, should be arranged in accordance with the following indications : The nomenclature of the international telephone circuits, which will form the subject matter of a new edition dated March ist, 1929, should be presented in the form of the following table comprising 11 columns (page 179).

* This recommendation replaces that appearing under the same heading on pages 354 to 360 of the “ Green Book ” (English translation, pages 278 to 282). j" The International Consultative Committee recommends that each terminal exchange to which are connected international circuits, other than frontier circuits, should be provided with a nomenclature of international circuits. . ’ . 177 M This nomenclature should be arranged in such a manner that a complete idea of the composition of each international circuit maybe obtained without having to consult different pages of the nomenclature for the same circuit. All the international circuits (excluding circuits connecting frontier towns) are arranged in alphabetical order according to their official des’gnation. Column i —"Designation of the Circuits. ” Each international circuit is designated by the names of the two terminal exchanges followed by the number of the circuit, the names of the exchanges included in the designation of the circuit being those which figure on the official plans of their respective countries, the two names being placed in alphabetical order, e.g., Berlin-London 3. Column 2— ‘ ‘ Countries. ’ ’ Column 2 should include the names of the countries on whose territory the different sections of the circuit lie, in the order in which the circuit crosses them going from one terminal exchange to the other terminal exchange, in geographical order : e.g., for circuit Berlin- London 3 : Germany-Holland-Great Britain. Column 3— “ Length of Successive Homogeneous Sections in each Country (km).” Column 3 should include the length of each homogeneous section of the circuit expressed in kilometres.

Column 4— “ Type of Construction.” The type of construction of each section of the circuit should be shown as follows :— Open-wire line ...... la Underground cable...... st Aerial cable ...... ca Submarine cable ...... sm

Column 5—-“ Nature of Circuits.” The nature of the different sections of the circuit should be shown as follows :—■ Two-wire side (or physical) circuit ...... 2f. Two-wire phantom circuit ...... 2f. comb. Four-wire side (or physical) circuit ...... 4f- Four-wire phantom circuit ...... 4L comb.

Column 6— “ Diameter of Conductors (mm).” The diameter of the conductors should be expressed in millimetres for each section of the circuit.

Column 7— ‘ ‘ Coil Loading or Continuous Loading. ’ ’ This column should include concise information on the type of coil loading or continuous loading of each section of the circuit. If the coil loading conforms to the recommendations of the International Consultative Committee, it is sufficient to show the method chosen in the following way : “ Method 1 ” or “ Method 2.” If the methods of coil loading differ from the International Consultative Committee’s recommendations, the inductance per kilometre and the coil spacings should be shown :— 103 mH/km {D = 1 • 66 km In the case of continuously loaded cables the inductance per kilometre followed by the word " Krarup ” should be included, e.g., 13 mH/km Krarup. If a section of the circuit is neither coil loaded nor continuously loaded, this should be indicated in Column 7 by “ Non-loaded.” 178 APPENDIX i

FORM OF TABLE FOR ESTABLISHING THE NOMENCLATURE OF THE INTERNATIONAL CIRCUITS.

L ength of Equivalent D esigna­ successive T ype of N atu re D iam eter at 8oo p.p.s, N am es of Coil loading or Cut-off tio n of homogeneous Con­ of of Con­ Intermediate and Countries. continuous fre­ R em arks. the. Sections in stru c ­ Cir­ ductors, Terminal Repeater loading. quency. C ircuits. each Country, tion. cuits. (mm) S tations. nepers. decibels (km) p.p.s.

3- 5- 6. 7- Q.

B e rlin -' G erm any 4 st 2f 2 ‘O Non-loaded Berlin, Friesack, 2f 2f 4f C.C. rep. L ondon 3. 582 s t 4 0-9 M ethod 2 5 4 0 0 Perleberg, Vellahn, 2f 4f 4f Hambg., Rotenbg,, T93 st 4* 0-9 [*103 m H /k m Bassum, Bohmte, 3 3 0 0 Munster, Wesel. H olland 20 s t 4 0-9 |_D = i- 66 km

30 m H /k m A rnhem 119 st I • 29 5 7 0 0 4 { D = 1 •’ 65 km R o tte rd a m Z25 m H /km D om burg. s t 1-23 5 7oo 8-7 65 4 D = 1 • 84 km 100 m H /k m 2 790 s t 1-8 93 4 D = 1 • 761km 13 m H /k m I53 2f 2-0 .. f K rarup A ldeburgh 2f 2f 4f C.C. rep. — — — Gt. Britain ^ M arks T e y . F 2f 4f 4f 50 m H /km 3 9 2 0 s t 0-9 73 4 D = 1 • 83 km 65 m H /km 2 340 82 s t 1-27 4 D = 2*72 km

1 384 Column 8—" Cut-off Frequency (p.p.s.).” In this column the cut-off frequency (or frequency limit) should be expressed in periods per second for each loading section of the circuit. Column 9-—“ Equivalent (at 800 p.p.s.).” This column is divided into two parts. On the left the transmission equivalent at 800 periods per second is shown in nepers, and on the right this equivalent is shown in decibels. For each circuit the nomenclature must give both the number of nepers and the number of.decibels. Column 10— “ Names of Intermediate and Terminal Repeater Stations.” The names of intermediate or terminal repeater stations shown in this column should be grouped together by countries. Column 11-—“ Remarks.” It is desirable to include in this column, for each of the terminal exchanges, reference t° the use of cord circuit repeaters for connecting two-wire—two-wire, two-wire—four-wire and four-wire—four-wire as follows 2f 2f 4'f Cord circuit repeaters ^

The nomenclature of the international telephone circuits should be set up in future in accordance with the table shown in Appendix No. 1 (p. 179). After the list of circuits in alphabetical order there should be given a general summary showing for connections between two certain countries, the number of circuits existing in each direction, including the circuits connecting the neighbouring networks of the frontier, as shown in Appendix No. 2 below. Finally, following this, a list should be given (by countries and in each country by alphabetical order) of the terminal exchanges of the international circuits which hav£ several designations in their own countries. The form of this list is shown in Appendix No. 3 (p. 181). The first nomenclature of circuits made up in accordance with the above will be issued by March ist, 1929. It will include all the circuits which were in service on December 31st, 1928. On March ist, 1930, a supplement to this nomenclature will be issued showing the modifications and additions made during the year 1929. > ■ These publications will be renewed every two years.

APPENDIX 2.

Form of the General Summary of the International Circuits to be attached to the Nomenclature of the International Circuits.

Telephone Connections between Germany and other Countries.

I. Connections Germany-Belgium. Exchanges in direct Connection. No. of Ccts. Aix-la-Chapelle-Liege .. 2 . Aix-la-Chapelle-Verviers • • 3 Berlin-Antwerp ...... 1 Berlin-Brussels .. ... 1 etc. ■ ' ...... * ' ”180 2. Connections Germany-Denmark. Berlin-Copenhagen ' ...... • • 3 Hamburg-Copenhagen . ’ ...... ■ .. 4 etc.

Telephone Connections between Belgium and other Countries. 1. Connections Belgium-Germany. Exchanges in direct connection. No. of Ccts.

Antwerp-Aix-la-Chapelle .. 1 Antwerp-Berlin .. 1 Brussels-Berlin 1 Brussels-Frankfurt (Main) 1 Liege-Aix-la-Chapelle .. .. 2

Liege-Cologne .. . . 1 - etc.

2. Connections Belgium-Austria. etc.

APPENDIX 3.

Form of List of Terminal Exchanges having several designations to be attached to the Nomenclature of International Circuits.

Official Designation Unofficial Designations Name of Country. of the Exchanges. of the Exchanges.

Belgium Kortryck Courtrai

Switzerland Geneve Genf, Ginevra

II. Form under which the Schematic Plan of the Cables should be drawn up.

The International Consultative Committee in agreement with the International Bureau of the Telegraph Union— Unanimously advises That, in future, the plan showing the existing and projected cables, kept up to date and published by the International Bureau of the Telegraph Union, should be set up in accordance with the following :— In view of the rapid development of the European network of telephone cables, the plan should be re-edited at least every two years. On one plan there should only be shown the cables already in service or those which it is known definitely will be in service before a new publication of the plan. The distinction between a central exchange with a repeater station and a repeater station only is of little interest and should not be shown. '

l 8 l M 3 On the other hand, on each line representing a cable a reference number should be shown. The reference number of a cable should correspond to a similar number on a list attached to the plan, on which should be indicated :— The type of cabling: D.M. (Dieselhorst-Martin) or Quadded Cable. E. Star Quadded Cable. P.E. Four-pair Star Quadded Cable,

also for each type of quad; the number of quads, the diameter of the conductors and the type of loading. These indications should be given in the following form :—

Different Classes of Loaded Quads. Type of Cabling, total Reference Number of Quads, loaded No. of the or non-loaded for the R em arks. No. of Quads D iam eter T ype Cable. different homogeneous of the class of th e of sections of the cable. concerned. Conductors. L oading.

i. 2. 3- 4- 5- 6.

4 Paris—Selestat Paris—Nancy D.M. 94 12 i ’3 non-loaded A lum inium 16 i -3 177/107-1830 screened. 24 0-9 44/25-1830 42 0-9 177/107-1830

Nancy—Selestat D.M. 94 12 i -3 non-loaded A lum inium 16 i -3 177/107-1830 screened. 18 0-9 44/25-1830 .46 0 9 177/107-1830

8 Boulogne—-Canterbury E- 7 7 ‘ 2 K raru p m H /k m P h an to m circuits used.

i i Arnhem—Utrecht E. 117 82 I -29 155-1630 P h an to m 22 1-29 50-1630 circuits *3 I • 67 155-1630 n o t used.

RECOMMENDATION No. 6A.

Emergency Lines.

The International Consultative Committee;— Considering :— That it is desirable to take steps so that, in case of interruption of an international channel, the traffic normally carried by that channel may be maintained; That the use of emergency lines in exceptional cases should not modify the charges for calls, Unanimously advises :— That Administrations concerned should come to an understanding as to the line or lines to be used as emergency lines in case of interruption of the normal service, and that emergency lines should be chosen from those which cross countries not normally used; That the list of such lines should be revised each year at the Plenary Session of the C.C.I.; That the rates to be charged when these lines are utilised should be the same as for normal lines; That the rates allotted to each Administration should be divided as follows : Total rate obtained by adding the rates appertaining to the first zone in each terminating country and, where necessary, to parts of the countries traversed.* The total rate is then divided between the respective Administrations in the following manner :— Each terminating Administration receives a proportional part corresponding to its share of the first zone with consideration of the emergency line. Each transit Administration receives a proportional part of the rates to which it is normally entitled for conversations using normal service circuits ; That the Administrations give instructions with regard to the constitution of the direct emergency lines when the network layout allows it, and when impossible the Head of the terminal exchange will endeavour to deal with the traffic in such a manner that the maximum waiting time as laid down by the C.C.I. is not exceeded (Recommendation No. 2, " Green Book,” page 352, English translation, 1928, p. 277).

Method of Use of Emergency Line. Considering the line Glasgow (third English Zone) — Zurich, the normal line is made up of a direct circuit London-Zurich passing through France. In case of inteiruption, the auxiliary lines crossing the same countries, i.e., first of all lines connecting Great. Britain and Switzerland via France directly, but, should these also be interrupted, the circuits London- Paris, and Paris-Switzerland, should be considered. In these two cases the division of rates between the Administrations is not changed If the auxiliary lines are also interrupted, an emergency line (lines crossing countries which are not used for the normal line nor the auxiliary lines) for instance, one made up of circuits London-Frankfurt (crossing Belgium) and Frankfurt- Ziirich should be employed. The rate of distribution of the charges will be obtained by adding— (a) The terminating section of the British first zone for the connection Great Britain-Switzerland.| (.b) The terminating Swiss portion (for the Swiss portion consists of only one zone), lor the connection Great Britain-Switzerland. (c) The French transit portion for the connection Great Britain-Switzerland. This amount will be divided as follows : Great Britain’s share will be proportional to its first zone for the connection Great Br it ain-G ermany. Belgium’s share will be proportional to its transit portion in the connection Great Britain- Germany. Germany’s share will be proportional to the amount received normally for London- Frankfurt and Fiankfuit-Zurich connections. Switzerland’s share will be proportional to the terminating portion in the. connection Germany-Switzerland.

* It is understood that the amount of the terminal charge beyond the first zone charge is still payable to the terminal Administration concerned. f Great Britain will retain (or receive, in the case of incoming calls) the difference between its third and first zone charges for the connection Glasgow-Zurich. 183 M 4 RECOMMENDATION No. 7a. Recommendations concerning the establishment of Telephone Directories and the conditions under which these may be purchased by the public. The International Consultative Committee— Considering :— That it is advisable to facilitate the sale, to subscribers of each country, of telephone directories of other countries, and to provide facilities for their use by subscribers and Administrations, That in accordance with the International Regulations (Section C, paragraph 1, section 1) subscribers and public officers must be classified according to districts, Unanimously advises (1) That the Administrations conform to the following rules : Subscribers desiring to have a foreign telephone directory should address their enquiry to the Administration of their own country; the latter will place the order with the foreign Administration, which will then despatch the directories to the Administration which has ordered them, giving the price in gold francs (the retail price plus postage). The home Administration will then deliver the directories to its subscribers against payment. At the end of each year, each Administration which has supplied directories to another Administration will send in a special account (independent of the account for telephone conversations) showing the amount due. (2) That it is desirable that the districts shown in the directories should be classified alphabetically.* If this classification is not observed the method adopted should be indicated in each volume. (3) That the directories published in a language other than German, English or French, and sent abroad (either to a private person or to. Administrations for use in the service) should contain a translation, in one of the three above-mentioned languages, of the information relative to the method of using these directories.

. B —VARIOUS CLASSES OF CONVERSATIONS AND FACILITIES AVAILABLE TO THE PUBLIC. RECOMMENDATION No. 9a. Fixed-time Calls by Subscription during the heavy traffic period (except during the hours of maximum traffic). The International Consultative Committee— Considering :— . That it is advisable when traffic conditions permit, to develop the service of calls by subscription, Unanimously advises :— That during heavy traffic periods, except during the hours of maximum traffic (to be determined by the Heads of the terminal exchanges concerned) subscription calls should be allowed without a time limitation at the ordinary call rates, provided : (a) That the circuits are available, (b) That the average delay at the time fixed for the call does not exceed, or does not appear likely to exceed the following, according to the terms of the subscription — 15 minutes for circuits under 500 km, 30 ,, ,, ,, between 500 and 1000 km. 45 „ ,, „ exceeding 1000 km. 184 That subscription calls allotted during heavy traffic periods when the above-mentioned conditions are not fulfilled should be charged at three times the normal rate. There is no necessity to modify the conditions already laid down for subscription calls during periods of light traffic. RECOMMENDATION No. ioa. Establishment of a Subscription Call with or from Telephone Stations other than those indicated in the Subscriber’s Agreement. The International Consultative Committee— Considering :— ' ✓ That as, according to the International Regulations, Article 71, Section H, Paragraph 2 (1), subscription calls should take place daily between the same stations ; That owing to unforeseen circumstances subscribers are sometimes unable to conform to these rules : • Unanimously advises :— . That the holder of an international subscription should be able in exceptional cases, provided be applies in writing twenty-four hours in advance, to change his call to or from a station other than the one indicated in his subscription call agreement, but forming part of the same local network. RECOMMENDATION No. 14a. Calls demanded by Aeroplane Pilots in Cases of Forced Landings. The International Consultative Committee— Considering :— That as, according to the terms of Article 33, paragraph 2 of the International Regulations appended to the St. Petersburg Convention (Paris Revision, 1925) absolute priority is given to international telegrams relating to security of human life in marine or aerial navigation, Similar priority seems justifiable in the case of international telephone calls asked for in cases of forced landings in aerial navigation. That special guarantees should be enforced in order to prevent misuse. Unanimously advises :— (1) That in the case of a forced landing the pilot (or his deputy) should be able, on production of Licence B (Licence for public transport), to obtain priority for a telephone call to his base or with one of the aerodromes in the vicinity of the place of landing. (2) That these calls should have priority over ordinary private calls, urgent private calls, and, in cases where urgent State calls are admitted, over ordinary State calls. (3) That the calls so obtained in these circumstances should be announced by the words “ Urgent avion ” and that they should be rated at three times the ordinary rate for international calls where urgent private calls are allowed.

C.-METHODS OF OPERATION. RECOMMENDATION No. 18a * Method of Establishing Calls with Preavis or Avis d’appel. The International Consultative Committee— Considering : — That the International Regulation (Paris Revision, 1925) does not contain sufficient detailed information concerning the establishment of calls with preavis or avis d’appel.

* This Recommendation replaces Recommendations Nos. 18 to 20 which appear on pages 385 to 390 of the “ Green Book ” (English translation, 1928, pages 299-302). 185 That it would be advisable in the public interest to give increased facilities for preavis calls, especially on the long distance international service. That while telegrams could replace preavis calls and are more economical on long distance calls, the avis d’appel is of public utility in frontier communications and in districts wheie the telephone network is not highly developed. Unanimously advises* :— i. That Section N of Article r of the International Regulation (Paris Revision, 1925) should be revised and. completed as described later, the arrangements for preavis and avis d’appel being kept separate for simplicity under the new arrangements outlined later. That these arrangements should be applied in the international service as from October ist, 1929. SECTION N. I.—Calls with Avis d’appel. §1.—(1) The request for a call can be accompanied by avis d’appel. (2) An avis d’appel has for object the calling of a person or somebody living in the same house in order to answer a call at a public call office. (3) Avis d’appel are set up by special arrangement between the Administrations concerned. §2.—(1) An avis d’appel is charged at one-third of the charge applicable to an ordinary call of three minutes, made during the same period as the call requested by the avis d’appel, with a minimum charge of 50 centimes (0.50 fr.). (2) If an avis d’appel does not result in the establishment of a telephone call the charge will be one-third of the rate applicable to an ordinary call of three minutes’ duration taken during the chargeable period in which the avis d’appel has been transmitted. (3) Charges for avis d’appel are divided between the Administrations concerned in the same proportions as the charges for ordinary calls. §3.—An avis d’appel only gives the following information ' (1) The name of the caller and, if necessary, his telephone number; (2) The name of the called party and, if necessary, his substitute and their full address. (3) If necessary, the time after which the request for the call should be cancelled (R.I. Section L, paragraph 8) or the period during which the call must not be made. This information is transmitted as quickly as possible from one exchange to the other! and is prefixed by the words “ Avis d’appel ”J; the exchange of destination records them on forms for delivery to the called party. The avis d’appel are delivered in the same manner as telegrams. When the called party lives outside the free delivery area for telegrams the avis d’appel will be surcharged an amount equal to that applying to an international express telegram in accordance with the publications of the International Bureau at Berne. This surcharge is always charged to the caller; it forms part of the international accounts and is handed over to the Administration of the exchange of destination. If the caller intimates, when originating his call with avis d’appel, that the called person - lives outside the free delivery area and that the caller is paying the express fee, the transmission of the avis d’appel is preceded by the words “ expres paye.” When the caller does not possess any information as to the manner in which the avis d’appel is to be delivered, he is informed by the originating exchange that he may be charged

* This Recommendation replaces Recommendations Nos. 18 to 20 which appear on pages 385-390 of the " Green Book ” (English translation,. 1928, pp. 299-302). t The same applies to all other service information relating to avis d’appel. J If necessary the words “ avis d’appel, expres paye ” (see following paragraphs). 186 a fee for expressing his avis d’appel. The caller is also informed that although the Administra­ tion will do all in its power to make timely delivery of the avis d’appel, it cannot undertake any responsibility for this if the called party lives outside the free delivery area for telegrams. When an exchange receives for distribution • an avis d’appel which is not marked " expres paye,” and addressed to a party living outside the free delivery area, the exchange of origin is advised of this. If the caller refuses to pay the surcharge, the call is cancelled but the special charge for the avis d’appel is made.

§4.—Calls with avis d’appel are subject to all the rules of international telephone communi­ cation, with the following reservations :— §5.—Calls with avis d’appel are only established in their order when the controlling exchange (terminal exchange, originating end, in case of direct calls, transit exchange in the case of transit calls) has been informed that the called party is ready to receive the call. §6.—To establish a call with avis d’appel the procedure is as follows :— (a) The controlling operator in transmitting the avis d’appel must give the approximate time at' which the call should be established. (b) As soon as the called party (or his substitute) appears at the call office or announces that he is ready to receive the call at a subscriber’s station which he indicates, the terminal exchange immediately advises the controlling exchange. The latter establishes the call in its turn.* (c) When the terminal exchange is informed that the called party (or bis substitute) can be reached at a public call office or at a subscriber’s station of another net work, the caller is informed of this and the original call is cancelled. If the caller asks for a call in another network it is treated as a new application. If the terminal exchange is informed that the called party (or his substitute) cannot or does not wish to receive the call, the caller is informed at once and the call is cancelled. (d) If the terminal exchange is informed that the called party (or his substitute- cannot answer the call at the approximate time arranged, the caller should be imme diately advised. As soon as the terminal exchange can give the time from which the called party (or his substitute) will be able to receive the call, the caller will be notified of this. (e) If at the time at which the called party is ready to receive the call the turn for setting up this call has not yet arrived, the call shall retain its normal sequence. If its turn has already passed, the request shall take its place in the normal sequence of its category, following calls already in preparation at that time.

§7.—If, after calling at the public call office, the called party (or his substitute) makes known before the call is established (see §10) that he can await the call no longer, the calling party is advised and the demand for the call is cancelled.

§8.—An application for a call with avis d’appel is valid until the closing hour of the exchanges concerned. If all the exchanges in question give a twenty-four hours’ service, applications for calls with avis d’appel received before 10 p.m. are cancelled at midnight, except in cases where the exchanges have been informed that a call can take place between midnight and 8 a.-m.; applications for calls with avis d’appel received between 10 p.m. and midnight are cancelled the next morning at 8 o’clock.

§9.—If for any reason an avis d’appel cannot be delivered, the caller is informed thereof and the demand for the call cancelled.

* When a person is to receive a call at a subscriber’s station, the arrangements relating to preavis will apply. §io.—At the beginning of the call which immediately precedes the call with avis d’appel, the exchange of origin and of destination will inform the caller and the called party that the call with avis d’appel will be established in a few minutes, and will ask the persons concerned to keep themselves in readiness to receive the call (warning call) §n.—The special charges appertaining to avis d’appel and also to express delivery are not demanded in the following two cases :—- (a) When, through defective service, the transmission of the avis d’appel has not been effected. ' (b) When, after the receipt of an avis d’appel, the calf cannot take place through faults happening on the line or in the installation. If the caller cancels his application for a call with avis d’appel after transmission of the avis d’appel has begun he will be charged with the avis d’appel charge; the terminal exchange is informed of the cancellation. This cancellation is notified to the called party if present at the public call office, or if he calls there later. If the caller wishes the called party to be informed of the cancellation at his house, a further charge corresponding to that for the avis d’appel is applied, possibly with the addition of an express surcharge. If, before the departure of the messenger taking the avis d’appel with the extra fee “ expres paye,” the terminal exchange is informed of the cancellation of the call, the express charge will not be made.

SECTION N.

.II.—Calls with Preavis. §i.—(i) An application for a call can be accompanied by preavis. (2) The object of preavis is to advise the subscriber’s station that the caller wishes to speak to a certain person or to an indicated supplementary station. (3) The caller is allowed to ask for a substitute in case the person he wishes to speak to is absent. If he does not name a substitute he has the privilege of asking for a second station, where the wanted person may be found. (4) The preavis are accepted by special arrangements between the Administrations concerned. §2.—(1) A preavis is subjected to a charge of one-third of the ordinary rate applied to the normal three minutes’ conversation, held for the same chargeable period as the conversation with preavis, with a minimum charge of 50 centimes (0.50 fr.). (2) If a preavis is not followed by a call it is subjected to a charge of one-third of that applicable to a normal conversation of three minutes, held over the chargeable period during which the preavis was transmitted. (3) The charges for preavis are divided between the respective Administrations in the same proportions as charges for calls. §3.—(1) A preavis contains only the following information :— (1) The caller’s name, and, if necessary, his telephone number; (2) The proper designation of the called party, and, if necessary, his substitute or the supplementary station required; (3) If necessary, the hour after which the demand for the call is to- be cancelled (R.I. Section L, §8) or the period during which the call should not be made. (2) This information should be sent as soon as possible from exchange to exchange* through to the terminal exchange, and is preceded by the word “ preavis ” : however, the caller’s name or number or both will only be transmitted at the caller’s lequest.

*. This applies to all service information relating to preavis. §4.—Calls which take place as the result of the preavis are subject to the international telephone regulations, subject to the following comments :— §5.—Calls with preavis are established in their proper sequence only if the controlling exchange (terminal exchange—originating end—in case of direct calls; transit exchange in case of transit calls), has been informed that the called party is ready to receive the call.

§6.—To establish a call with preavis, the procedure is as follows :— (a) The controlling operator when transmitting the preavis to the terminal exchange must give the approximate time from which the call can be established. (b) As soon as it has received the preavis, the terminal exchange should enquire of the station or stations concerned whether the called party or his substitute, or the supplementary station asked for, is ready to accept the call, and should at the same time state the approximate time at which the call will be made. (c) If on receipt of the preavis, the called station declares that the called party or his substitute or the supplementary station asked for is ready to answer the call, the terminal exchange should advise the controlling exchange immediately; the controlling exchange will then establish the call in its proper sequence. (d) If the terminal exchange is informed that the called person or his substitute can be found at a different station of the same local network, the call is put through as if the application had been for that particular station. If the terminal exchange is informed that the called person or his substitute can be found at a certain station of another network, the caller is advised and the application for the original call is cancelled unless the caller decides to accept the call with the original station in spite of the absence of the called party. If the caller applies for a call to the other network for the desired person this is treated as a new application. If the terminal exchange is informed that the called party or supplementary station asked for cannot or does not wish to receive the call, the caller is notified immediately and the application for the call cancelled. (e) If the called station intimates that the person or the supplementary station required cannot receive the call at the approximate time arranged for its establishment, this information is sent to the caller immediately. Further, if the called station at the request of the terminal exchange has been able to give the time from which the required person or supplementary station can receive the call, the information is to be sent to the caller immediately. If no information can be given as to the time when the called party can be reached the terminal exchange should enquire at least once every hour (night service excepted) as to the possible time of return of the required person. As soon as the terminal exchange has received the necessary information the caller is informed immediately. (/) If at the time when the called party is ready to answer the call, its turn has not been reached, the call will keep its normal sequence. • If its turn has been passed, the call will follow according to its category at the end of the calls in preparation at that time.

§7.—If the called party, having declared his readiness to answer the call, intimates before receipt of the warning call (see §10) that be can no longer wait for the call or that the call must be adjourned, the procedure will be as indicated in §6 (d), last paragraph, 01 6 (e).

§8.—An application for a call with preavis is valid until the closing times of the exchanges concerned. If the exchanges in question give a twenty-four hour service, applications for calls with preavis received before 10 p.m. are cancelled at midnight unless the exchanges have been informed that the conversation can take place between midnight and 8 a.m.; applications for calls with preavis received between 10 p.m. and midnight are cancelled the next morning at 8 o’clock. .

,1 8 9 §9-—In case of no reply at the time of transmitting the preavis to the called station another attempt should be made at the end of a few minutes; if this is unanswered a third call should be made half an hour after the first. If this last attempt fails, the caller should be informed. If the caller does not then cancel his call the latter will remain valid for the period specified in §8; during these delay periods the terminal exchange calls the required station repeatedly. When a reply is obtained the regulations given in §6 are applicable. §io.—From the beginning of the call which immediately precedes the call with preavis the exchanges of origin and destination advise the calling and called stations respectively that the call with preavis can be established in a few minutes, and that the persons interested should stand by to receive the call. If at this time, or even at the moment of the actual call the called station is unable to accept the call because the called party is not immediately available, the application for the call is cancelled, the caller is informed, and the preavis rate only is charged. If at the time of the preliminary warning call, the called station declares its readiness to accept the call, the subscriber’s line serving this station and that of the caller remains connected respectively to the originating exchange and to the terminal exchange (warning call); the call is established in the usual manner, and is charged as if it were a call without preavis. (R.I. 1925, Section L, §§2 and 3.) §11.—The special charge for preavis is not applicable to the following two cases :— (a) When, through defective service, the transmission of the preavis has not been effected. (b) When, after the receipt of a preavis, the call does not take place through faults occurring on the line or in the installation. If the caller cancels his application for a call with preavis, after the transmission of the preavis has been commenced, the preavis charge is applied. In this case the terminal exchange is informed of the cancellation, and the latter advises the called station.

RECOMMENDATION No. 21a.*

Bourse Calls.

The International Consultative Committee— Considering :— That §io of Section L of article 71 of -the International Regulation (Paris Revision, 1925) concerning conversations originating from, or destined for Bourses (commercial, financial, etc.), should be clearly specified. That it is necessary to treat separately the case where the Bourse contains public call offices accessible to all brokers and served by the Telephone Administration, Unanimously advises :— That -the arrangements indicated in the following proposed regulations should be applied in this case. Considering, on the other hand :— That Bourses, having public call offices accessible to all brokers and not served by the Telephone Administration (Bourses with private exchanges), should be treated as subscribers,

* This recommendation replaces that under the same title on pages 390 and 391 of the “ Green Book ” (English translation, 1928^. 303).

1 9 0 Unanimously advises :— 1. That calls originating from, or destined for, such Bourses should be subject to the ordinary regulations of the international telephone service. 2. That the charge period for these conversations commences from the moment when the private exchange has replied (International Regulations, Section L, § £-5). 3. That persons who request calls for Bourses be advised to include a preavis with their demands.

Considering finally :— That the special arrangements provided in the following proposed regulations constitute a breach in the regulations of the international telephone service, and that it is desirable to restrict, as much as possible, the number of cases of such breach,

Unanimously advises That, in all institutions similar to Bourses (fairs, periodical exhibitions, etc.) the telephone installation should, as far as possible, be a private exchange. The International Consultative Committee— Considering :— That it is desirable in future to standardise the Bourse exchanges,

Unanimously advises :— That the C.C.I. recommendations relating to new Bourse exchange installations with regard to the exploitation of international circuits should be applied (see A.c.2. Local Exchanges, p. 74).

Proposed Regulations for Calls originating from or destined to Bourses.

§ 1.—(1) The arrangements below apply to calls, originating from or destined for public call offices in a Bourse, accessible to all the brokers and operated by the Telephone Administration. All these call offices and the switch boards which serve them, if such exist, constitute what is called a Bourse-exchange (“ bureau-bourse ”). Calls originating from, or destined for, public call offices in a Bourse, accessible to all brokers, but not operated by the Telephone Administration, are subject to the general regulations of the international telephone service. (2) Administrations concerned should communicate the official names of the Bourses having a ‘ ‘ bureau-bourse ’ ’ and if they think necessary, the days and the times during which these ‘ ‘ bureaux-bourses ’ ’ are in use.

§ 2.—(1) For a request for a call originating at, or destined for, a “ bureau-bourse,’’ the name of the Bourse and the name of the broker, calling or called, should be given. Examples.— (a) Amsterdam commercial Bourse—P. Jansen requests Paris Littre 24-30. (b) Paris Littre 18-93 requests Amsterdam commercial Bourse Dunlop & Co. (c) Amsterdam commercial Bourse—P. Jansen requests Paris financial Bourse, Lebrun, Banque Nationale Credit.

Requests for calls destined for a “ bureau-bourse ” cannot be accompanied by a preavis or avis d’appel. 191 (2) The transmission of a request originating from a “ bureau-bourse ” conforms to the regulations [International Regulations, Art. 71, Section O, § 2 (1) and (4)], but should include, as well as the ordinary indications, the name of the originating Bourse. (3) Requests destined for a ‘ ‘ bureau-bourse ’ ’ during the operating times of this exchange, should be transmitted as rapidly as possible to the ‘ * bureau-bourse. ’ ’ Outside this period the transmission should be made according to agreement between the exchanges concerned. (4) After the receipt of a request the receiving “ bureau-bourse ” should ascertain (several times if necessary) if the broker called is present and should advise him that he has been called (Avis prealable—warning call). If this person accepts the call he should be advised definitely when his turn arrives (avis definitif). If the warning call has not reached the required broker after a reasonable time, or if he does not accept the call, the controlling exchange should be informed. In the first case the establishment of the call should be. put back; in the second case the request for a call should be cancelled. § 3 .—-(1) Before the beginning of the conversation preceding that with the “ bureau- bourse ” the toll exchange should advise the “ bureau-bourse ” that the call is about to be established. The “ bureau-bourse ” should advise the broker, calling or called, as quickly as possible that his turn is about to arrive, and should indicate to him the call office to be used for his conversation. (2) Before receiving the final advice (avis definitif) the broker can ask for the call to be established with another station of the same local network. § 4.—(1) The charge for the conversation should be made from the moment that the call is given to the broker. However, if the preceding conversation has lasted less than 3 minutes and if the broker is not present to take his call at the expiration of these 3 minutes, the charge only begins at the end of these 3 minutes. . (2) If the broker does not arrive to time or does not appear at all, the call will be held for him during 3 minutes. A caller, however, may request that a call be held during a maximum period of 6 minutes. §5.—(1) Calls destined for a “ bureau-bourse” are liable to the ordinary fee, which can, by arrangement between the Administrations concerned, be increased by a surcharge fixed at one-third of the unit charge. (2) This surcharge should be made for each request transmitted to a “ bureau-bourse ” ; it forms part of the international accounts. In cases where the call is refused at the time of the warning cah, the surcharge should then be levied. (3) When, through a fault in the telephone service, the conversation cannot take place, the surcharge should not be levied. ■ (4) In cases where the call is refused at the time of the final advice, the charge for a conversation of 3 minutes of the particular category of the call requested should be made.

RECOMMENDATION No. 23a. Enunciation of Subscriber’s Numbers. The International Consultative Committee- Considering :— That when an operator speaks in a foreign language, it is easier for her to give figures rather than numbers.

1 1 9 2 Unanimously advises :— • That, on international circuits, subscriber’s call numbers should be given by successively enunciating the figures.

RECOMMENDATION No. 24a.

General Principles for equalising Waiting Times in both directions.*

The International Consultative Committee— Considering :— ( That efforts made to equalise waiting times in both directions have had good results, Unanimously advises :— That when the waiting time on a direct international route exceeds the maximum limits provided for by the International Consultative Committee, or those fixed by arrangement between the Administrations concerned, efforts should be made— 0 (1) To equalise the waiting times in the two directions in accordance with the following principles; (2) If this attempt is not successful, or does not appear likely to be successful, to utilise concurrently with the normal route one or several auxiliary routes with less traffic.

Principles.—If the Waiting time on a directj international route exceeds the maximum at one of the terminal exchanges on this route, and if this exchange has reason to believe that the difference of the delay in both directions will exceed 30 minutes, it should enquire from the corresponding terminal exchange thp length of the delay at this latter exchange. If the difference of the delays in both directions is greater than half an hour, the exchange where the delay is greatest decides, in agreement with the corresponding exchange :— (a) In the case of circuits operated alternately, to pass two or three outgoing calls for one incoming call until the delay is almost the same in the two directions; (b) In the case of circuits used in one direction, to operate one of the incoming circuits as an outgoing circuit until the waiting time is almost equal in both directions.

A terminal exchange must give the duration of the delay to the corresponding exchange requiring this information and should also indicate its own waiting time. • For this purpose the following phrases are used :— Here the delay is x minutes. What is yours? Modification of the alternate use of circuits— Two outgoing for one incoming, or, Three outgoing for one incoming. Modification of the use of a circuit— Circuit number...... outgoing from ......

* This recommendation replaces that under the same heading on pages 395 and 396 of the " Green Book ” (English translation, 1929, page 306). . f Only delays in connection with calls between two countries in direct communication with each other are to be considered. 193 N D.—RATES AND TARIFFS. RECOMMENDATION No. 35a.

Rates applicable between Primary Zones of two Contiguous Countries. The International Consultative Committee— Considering :— That the number of circuits handled by one operator on short distance calls is larger than for other calls, and that the costs of operation are, therefore, lower, Unanimously advises :— That, for calls between networks in the respective first zones between two contiguous countries, it is desirable to adopt a basic charge of o-6o franc, instead of o’8o franc, for deteimining the terminal portion to be allocated to each Administration for the operating costs of the terminal exchange.

RECOMMENDATION No. 35b.

Rates applicable to Calls originating from, or. to be completed at, a Public Call Box. The International Consultative Committee— Considering:— ' . That the amount of the unit charge is determined by arrangement between the Administrations concerned (Section K, Paragraph 1 (2), International Regulation, Paris Revision, 1925). That the setting up of a call originating from, or to be completed at, a public telephone box entails special expenses, but that these are negligible in comparison with the other expenses involved in the establishment of an international call. Unanimously advises :— That it is preferable not to make an additional charge for the use of a public call box for an international call, but that Administrations who make an additional charge for their local services may apply it to international calls, provided it does not appear in the international accounts.

* RECOMMENDATION No. 35c.

Rates applicable to Press Calls. The International Consultative Committee— Considering :— On the one hand that, as the international telephone rates are at present very nearly equal to the working costs and that any reduction favouring certain classes of subscribers would force the Administration to increase the general rates; On the other hand that, as the operators are unable to follow the conversations between subscribers, the Administrations are unable to lay down tariffs varying according to the type of communication, and that, as regards calls between newspaper reporters and their offices, it would be impossible to ascertain whether the conversation consists of the transmission of material intended for publication, or was of a different nature. Unanimously advises : That there is no reason why a reduction in international telephone rates should be made for press calls. RECOMMENDATION No. 37a.

Picture Transmission between Correspondents over General Service Circuits (conditions relating to acceptance and tariffs).

The International Consultative Committee— Considering :— That most of the Administrations have little experience of picture transmission by means of instruments operated by Administrations, Unanimously advises : That it is premature to fix the rates for picture transmission between exchanges.

Considering :— That the experience of some Administrations with respect to picture transmission, carried out and maintained by the interested parties by means of their own instruments and over international telephone circuits provided by the Administrations, shows that these transmissions involve special expenses to the Administrations, but that these can be compen­ sated for if it ensures the use of the circuits during periods of light traffic. Unanimously advises : That the transmission of pictures effected directly between the interested parties should conform to the following rules : They shall be allowed without limitation of time : (a) During periods of light traffic; (b) During -periods of heavy traffic, except during periods of maximum traffic (to be decided, when necessary, by agreement between the terminal exchanges concerned), provided that— either (1) the circuits are available; or (2) the waiting time for ordinary calls at the time stipulated for the transmission of pictures does not exceed, or does not appear likely to exceed, by reason of this transmission, the following delays :— 15 minutes for circuits less than 500 km in length. 30 ,, ,, ,, between 500 and 1000 km in length. 45 „ „ ,,. exceeding 1000 km in length.

Provisionally, the following rates shall apply :— (a) During the heavy traffic period :— The ordinary telephone call rate. (b) During the light traffic period (1) In the case of transmission by subscription, or for a transmission for a period of at least 1 hour, one-half the rate stipulated in {a). (2) In other cases, three-fifths of the rate stipulated in (a).

Note.—Transit Administrations are advised to facilitate transmission tests requested by terminal Administrations, provided that the above rates be applied to these tests.

Considering :— That cases may exist where picture transmission between two countries will be carried out by connecting, over a telephone circuit, an instrument belonging to, and maintained by

1 9 5 x 2 a user, to an instrument belonging to the Administration of another country and situated in an exchange in that country. Unanimously advises :— That, in these cases, the use of the international circuit for.picture transmission be subjected to the same conditions and rates (with respect to the international circuit) as those above -relating to two private instruments, the Administration operating the exchange instrument making a supplementary charge for its use, the. amount of which is not to appear in the international accounts.

RECOMMENDATION No. 40a.

Recording the Chargeable Duration of Calls.

The International Consultative Committee— Considering :■— That it is desirable to avoid any complication of the service; That according to the terms of the International Regulations, the chargeable duration of a call must be fixed by agreement between the two terminal exchanges, and that, in consequence, it is necessary to avoid one of these' exchanges being connected, by a given warning signal, to the subscriber of its network for the duration of The call. Unanimously advises : (a) That it is not necessary to inform the calling party on an international call of the commencement of the chargeable period. (b) That an Administration should refrain from giving to its operators instructions to warn subscribers of the expiration of every 3-minute or 6-minute period, without having come to an arrangement with the Administrations concerned. (c) That it is desirable to inform the subscriber of the expiration of each 3-minute period by means of an audible signal, which does not interfere with the conversation, provided that no excessive expenses are entailed thereby, and also that this signal be considered as a warning which does not involve the Administration as regards charges. (d) That, although many international terminal exchanges use counting clocks to check the duration of calls, which have given satisfactory results, it seems unnecessary to generalise this system, provided that all necessary precautions have been taken that counting devices operate regularly and do not show differences among themselves. (e) That it is not absolutely necessary to indicate the time of commencement and end of a call on the record slips by means of a costly printing instrument, provided that the recording of these times in manuscript is not inconvenient.

RECOMMENDATION No. 40b.

Maximum Duration of a Call.

The International Consultative Committee— Considering : — That the prolongation of the maximum duration of calls is likely to increase the traffic on circuits, Advises :— That the maximum duration of a private call, provided for in Paragraph 8 of Section 0 of the International Regulations (Paris Revision, 1925) be increased, as an experiment, from 6 to 12 minutes; that these arrangements be put into force in the international service as from October ist, 1929.

RECOMMENDATION No. 41a.

Checking the Number of Minutes of Conversation between Terminal Exchanges on International Lines.*

The International Consultative Committee—

Considering :—

That the test results obtained do not justify the general recommendation of the cancellation of daily checking (International Regulations, Section O, Paragraph 9 (4) ). That many difficulties would be avoided if sufficient time were allowed to the services concerned for the preparation of this checking,

Unanimously advises :— That the following arrangements be applied :— (1) At the end of each call, the operators confer to agree upon the chargeable period, thus : three minutes, for calls of three minutes or less; and in other cases, four minutes or seven minutes, or five minutes (difficult conversation actually lasting 8 minutes); in addition, the type of call will be indicated, except in the case of an ordinary call, for example : urgent or lightning, or with preavis or avis d’afipel. In the case of a preavis or avis d’appel not followed by a conversation, the following indication is transmitted as soon as the exchanges concerned have advised each other that the call cannot take place : Preavis to be charged, or preavis not to be charged. Avis d’appel to be charged, or avis d’appel not to be charged. Each operator informs her colleague of the moment of passing from a period of heavy traffic to a period of light traffic, or vice versa. (2) The checking should be carried out by the accounting departments of each of the two terminal exchanges, after checking the service records, it being understood that this checking must be completed on the second day after the day considered, at the latest by the time when all circuits are required for traffic. (3) With respect to monthly accounts, it is advisable to arrange them in such a manner that the number of minutes, chargeable in each category, is’ given for each circuit, or group oft circuits, between two terminal exchanges.

E - TYPICAL FORM OF AGREEMENT BETWEEN ADMINISTRATIONS FOR INTERNATIONAL TELEPHONE SERVICE. (See " Green Book,” pages 417-424, English translation, 1928, pp. 322-326.)

* This recommendation replaces Recommendation No. 41 of the “ Green Book,” p. 416 (English translation, 1928, p. 321). 197 F.—TRAFFIC STATISTICS. RECOMMENDATION No. 43a.

Supervision of International Telephone Traffic.* The International Consultative Committee— Considering :— That it is essential that international telephone traffic on the principal circuits be controlled simultaneously from both ends of the circuit, in order to ascertain that the circuits and the installations are in good condition, to supervise the work of operators, to ascertain to what degree subscribers collaborate with Administrations, and eventually to improve the conditions of working of the service. Unanimously advises - 1. That the principal international circuits should be subjected to periodical supervision, as, for instance, once every month during one of the busy hours, this supervision being effected by means of a high-impedance instrument unknown to the operators under supervision, so as to observe what happens on the line and at the operators’ positions. 2. That the Heads of exchanges concerned should arrange, by telegram or letter, that this supervision is made simultaneously at the two ends of the circuit, the exchange which is first in alphabetical order initiating the arrangement. 3. That in order to record the results of this supervision a uniform table be used. Pro­ visionally, the form given on pages 426 and 427 of the “Green Book ” (English translation, 1928, pp. 328, 329) will be used. If an Administration does not use this form of table, it is desirable that it should communicate its service instructions, together with the form of report which it uses for international telephone traffic control, to the other Administrations with which it is working. 4. That the Heads of exchanges should inform each other at the beginning of each month of the outstanding results of this supervision, adopting provisionally the following form of report :•— Form of Report to be used by Exchanges.

Summary of observations made on circuit A-B by Exchange A on {date) from {X o’clock to Y o’clock). (a) Total number of calls supervised. Calls from A to B ...... „ B to A ...... ?...... (b) Mean delay before re-entering circuit A -B , after the end of a call.. Minutes. Seconds. 1. For operator at A ...... ,, ,, ,, B ...... (c) Mean delay occurring between the end of a call and the moment when the next subscriber is connected. 1. At Exchange A ...... 2. At Exchange B ...... (d) Mean duration of calls......

* This recommendation replaces Part II of Recommendation No. 43, on the supervision of International Telephone Traffic (" Green Book,” p. 428; English translation, 1928, p. 329). 198 (e) Mean duration of lost time due to service faults (for example, subscriber cut-off in error, wrong number, etc.) ...... (f) Various irregularities observed, for example, wrong number, false cut-off, a third subscriber on the line, lack of attention by the controlling operator, use of service phrases other than those contained in the list laid down by the C.C.I. :— 1. Attributed to Exchange A ...... 2. Attributed to Exchange B ...... Irregularities attributed to Exchange B must be indicated precisely, in order to facilitate investigation. .

1 9 9 VI.—QUESTIONS CONCERNING THE PROTECTION OF LINES.

Modifications to be made to the “ Guiding Principles concerning measures to be taken in order to protect telephone lines against the disturbing influences of heavy-current or high-tension power lines ” (1926 Edition).

How can the disturbing effect of harmonics from direct current traction installations be defined ? The International Consultative Committee— Considering :— That there does not yet exist a precise definition for the disturbing effect of harmonics due to power installations, Unanimously advises :— 1. That the following definitions be adopted provisionally :— (a) The " Disturbing Voltage Equivalent ” is the voltage, at a frequency of ‘ 800 p.p.s., which, when applied to a power line, would induce in a neighbouring telephone line the same disturbance as that induced by the normal voltage of the power line with all its harmonics. (b) The “ Disturbing Current Equivalent ” is the current at a frequency of 800 p.p.s., which, when flowing in a power line, would induce in a neighbouring telephone line the same disturbance as that induced by the normal current of the power line with all its harmonics. The " Disturbing Current Equivalent ” is, therefore, the quotient of the “ disturbing voltage equivalent ” by the impedance of the power line under service conditions, for the frequency of 800 p.p.s. (c) The “ Telephone Interference Factor of the Wave Form of the Voltage ” is the ratio of the disturbing voltage equivalent to the normal voltage. (d) The “ Telephone Interference Factor of the Wave Form of the Current ” is the ratio of the disturbing current equivalent to the normal current. These definitions are applicable to power installations of any kind, either direct or alternating current.

2. That these definitions be inserted in the text of the “ Guiding Principles ” by the Editing Committee of the First Commission of Assessors. Note.—The preceding definitions are translated in the French and German languages as follows :— Disturbing Voltage Equivalent. Tension Perturbatrice Equivalente. Storspannung. 200 r Disturbing Current Equivalent. ' (6) f Courant Perturbateur Equivalent. l^Storstrom. Telephone Interference Factor of the Wave Form of the Voltage. Facteur Telephonique de Forme de la Tension. Fernsprechformfaktor der Spannung {formerly : Spannungsgiite). Telephone Interference Factor of the Wave Form of the Current. Facteur Telephonique de Forme du Courant. Fernsprechformfaktor des Stromes (formerly : Stromgute)..

Steps to be taken in the case of parallelism between international telephone lines and direct current traction lines. The International Consultative Committee- Considering that parellelism between international open-wire telephone lines and direct current traction lines supplied from rectifiers may give rise to serious disturbances on these telephone lines, Considering that these disturbances can be very effectively attenuated in telephone lines affected by such induction by mounting on the rectifier a suitable absorbing device (as, for example : induction coil and resonant shunts), Unanimously advises :— 1. That the " Guiding Principles ” should mention, for cases of parallelism between inter- - national open-wire telephone lines and direct current traction lines supplied from rectifiers, the advantages which ensue, in the present state of the technique, from mounting on the rectifiers suitable absorbing devices (as, for example : induction coil and resonant shunts). 2. That the insertion of this recommendation in the text of the •“ Guiding Principles ” be entrusted to the Editing Committee of the First Commission of Assessors.

Permissible Limits for Induced Noise on Open-wire Circuits and on Cable Circuits. The International Consultative Committee— Considering that it is necessary to define induced noise, and considering that it is now possible to lay down the principle on which this definition will be based, Advises :— 1. That it is desirable to define induced noise by an equality of audible impression between the real noise and a noise artifically produced and recorded, under conditions to be defined, by an instrument of which the components are well standardised. 2. That this equivalent should be expressed, in millivolts, by a voltage known as “ noise voltage ”, read directly from this instrument.

How can the disposition of the conductors of a two-wire single-phase line, and of a three- phase line, be taken into account in the calculation of the noise voltage on a neighbouring telephone line ? The International Consultative Committee- Considering that it does not appear possible to obtain a practical and accurate formula for the calculation of noise voltage for all possible dispositions of a power line and a telephone line; ' Considering, however, that an approximate formula gives satisfaction, 201 Unanimously advises :— 1. That, except in the particular cases given m paragraph 2 of the present recommendation, the following formula be employed, which is applicable to two-wire single-phase lines and to three-phase lines : _ 22-5 X io -3 . 1. 8 . E 6 “ a2 + 62 + c2 where :

Ub — the noise voitage expressed in millivolts. I = the length over which the lines are parallel, expressed in-kilometres. 8 — the spacing of the power line conductors, expressed in metres( in the case of unequal spacing, as for a three-phase line with conductors in a plane, the geometric mean of the three lengths is taken). E = the normal voltage of the high-tension line expressed in volts. a = the distance between the two lines, expressed in metres. b — the mean height above ground of the conductors of .the high-tension line, expressed in metres. c = the mean height above ground of the conductors of the telephone circuit, expressed in metres.

2. That, where the distance between the. power line and the telephone line exceeds 100 metres, and where the conductors of the power line lie in a horizontal plane, the two following expressions should be used :— (a) For single-phase lines : ^2 _ A2 r 2 Ub = 22-5 X IO -3 . Z . 8 . E a (a2 + b2 + c2)2 (b) For three-pha*se lines : 2 ab Ub = — 36 x io-3 . I . 8 . E {a* + 62 + c2)2 where the symbols have the same meanings as in the formula given in Paragraph 1.

3. That the insertion of these formulae in the text of the “ Guiding Principles ” be left to the Editing Committee of the First Commission of Assessors.

Considering, on the other hand, that the foimulae, already given in the “Guiding Principles,” for the case of earthing the power line can give rise to a new and clear development;

Unanimously advises :—

That a new development be incorporated in the text of the “ Guiding Principles ” by the Editing Committee of the First Commision of Assessors.

Note on the Method of Calculation leading to the above FormulcB.

The calculations should be made in the same manner as those in the “ Guiding Principles.” Formulae 10 and 11 are the fundamentals (see page 32 of the “ Guiding Principles,” English translation, p. 34). The simplification of the determinants must be carried out differently, as the simplified formulae, at present given in the “ Guiding Principles,” only apply to lines of which one phase is earthed. (On p. 44, English translation, p. 46, it has been assumed th at dI4 = d24 = d34, etc. . . .; the differences in the spacing between the conductors of

2 0 2 •different phases and the telephone circuit have thus been neglected.) The calculation gives the following results :— A—Double Single-phase Lines. In the case of double single-phase lines, the general formula which gives the current in a looped telephone line will be, instead of formula 16, page 34 of the “ Guiding Principles ” (English translation, p. 35).

t _ j o i l E , (^14 ^15) (^24 ^25)

, y . i o 6 ^12) • (^44 ^45) If du be replaced by its series, according to the formula (17), and if the numerator is obtained by differentiation with respect to the distance a and heights b and c (where 8 is the width of the loop of the power line, and a is that of the telephone circuit) and if dn — d12 = 5*9, and ^44 — di5 = 5*o are placed in the denominator, the following values are obtained for the four principal arrangements. (1) 8 vertical, a vertical:— x J45 = 0 ’94

(2) 8 vertical, a horizontal

(3) 8 horizontal, a vertical:—

145 ■ j. - (4) 8 horizontal, a horizontal : ibcfea2 — b2 J45 = o •94a)^E8

Let a = 0*4 m, be the width of the loop; also, according to the " Guiding Principles,” let o*02E be the value of the distmbing voltage corresponding to co = 5 000; if, further, it is assumed that half the current J45 flows through each receiver, and if the noise voltage be calculated by multiplying the current in the receiver by the impedance of the circuit “ line + receiver ” (= twice the characteristic impedance = 1 200 ohms), the following noise voltages, expressed in millivolts, are obtained for the four cases :— 8 vertical ai ~ &4 “ c4 + 6&2c2 tt- Gs„ = 22*5 x 10 318E • , „ 4 7„ —sro— mV. cr vertrcal sp J [a2 + b2 _j_ c2)3

, . f 8 vertical _ 2ac{^b2 — a2 — c2) <2> V horizontal G» = aa-5 x 10 »HE • (g2 + b, + g2)3 "V. rs horizontal = I0-3ffiE . ~ ~ f) mV. vertrcal sp J {a2 + b2 + c2)3 . . f 8 horizontal ~ 2bc{^a2 — b2 — c2) <4> \« horizontal G-P = **-S X i«>-*JKE • (fll + p + c2)3 “ V.

If the loop of the telephone circuit is arranged in an oblique plane, its components in the vertical and horizontal planes must be calculated separately and added vectorially. The same procedure must be applied if the power line loop lies in an oblique plane. If the terms of higher

2 0 3 orders are neglected, simplified formulae are obtained for the case where the telephone circuit loop occupies an unfavourable position. a 2 - b2 + c2 (5) 8 vertical Gsp = 22-5 x icr3 ISE (^ T- ^ , ^ mV. {a2 + b2 + c2)2 2 ab (6) 8 horizontal Gs/) = -22-5 X 10 3 IBE m , ^2 , ^2X2 mV- • [a2 +~P“+ c2)2 By further simplification from the formula for the case where the power line loop is vertical, the telephone circuit lying in the unfavourable position, the formula (B. 10) given below is obtained. B— Three-phase Lines. For three-phase lines, several other cases have to be considered, and, therefore, only the results of calculations for an unfavourable disposition of a telephone circuit will be given. Let 8 be the geometric mean of the spacings of the three phases (in a triangular arrangement, 8 then represents the distance between two phases; if arranged in a plane 8 = 1-26 times the distance between two adjacent phases). Then— (7) If the conductors of different phases are arranged in a triangle, arranged in any manner— r „ r V (a2 — b2 + c2)2 + 4a2b2 = 22-5XIO »«E- (a2 + i2 + cy mV.

(8) If the conductors of different phases are arranged in a vertical plane :

a 2 _ b 2 _j_ C 2 G„ = 36 X 1 0 - ISE ■ , ^ ..T -s-, mV. (a 2 + b2 + c2y (9) If the conductors of the different phases are arranged in a horizontal plane : 2 ab G»rsp = - ^36 x 10 8 ™is e ■ ^2+^ 62 + c2)2 mv.

(10) The approximate formula obtained by simplification,mp using the same notation, is- 22*5 X 10~3 £SE &sp a 2 -I- b2 + c2 mV-

C.— Conclusions. It can be seen that a rigorous examination of the positions of the loops leads to detailed formulae. It cannot be stated, in a general way, that where the power line loop is horizontal, the disturbance is always less than in the case of its being vertical. On the contrary, when the distances apart are small, the horizontal arrangement is less favourable; the disturbance created in the case of .a vertical arrangement decreases to zero for a certain distance and then changes sign. From the point of view of disturbance, the difference between the two arrangements is only appreciable for distances greater than about 100 metres, for which the disturbances, in absolute value, are small.

Should consideration be given to the danger caused by a double accidental earth on a three-phase line with neutral point insulated ? The International Consultative Committee— Considering, that, except for certain exceptional lines specially maintained and inspected according to methods to be defined, the possibility of double accidental earthing should be considered,

2 0 4 Unanimously advises :— 1. That it is advisable to make the calculation of proximity for three-phase lines, where the above-mentioned exception is not applicable, as if the neutral point were earthed; 2. That, when the calculations have been made in this manner,- it is not necessary to consider the case of double earthing of the power line; 3. That it is then possible, as regards exposure to danger, to earth the neutral point directly for all cases where this arrangement has been specially authorised; 4. That the modifications to the “ Guiding Principles ”, involved by paragraphs 1 and 2 of the present recommendation, be entrusted to the Editing Committee of the First Commission of Assessors. Considering, on the other hand, that the above-mentioned exception concerning lines specially maintained and inspected, should allow railway companies to install, within their territories, lines of moderate voltage on which calculations made according to the “ Guiding Principles ” would lead to their exclusion from the railways, had they been installed with the neutral point earthed. : Unanimously advises :— That the International Union of Railways be asked to give its opinion on the special conditions of maintenance and inspection allowing such lines to benefit by this exception.

Comparative study of various protective devices against acoustic shocks, by means of exchange of apparatus between interested Administrations.

The International Consultative Committee— Considering, That certain devices against acoustic shocks have given satisfactory results with certain telephone Administrations : as for example, coherers, valve installations, Boye circuit breaker, apparatus of the Allgemeine Elektrizitats Gesellschaft, Considering, on the other hand that these devices do not give absolute security, but provide, in general, effective protection, Unanimously advises :— 1. That the use of these devices is advisable for all telephone Circuits particularly exposed to danger from power lines or atmospheric discharges. 2. That this recommendation be inserted in the “ Guiding Principles ” by the Editing Committee of the First Commission of Assessors, together with an Appendix giving descriptions and methods of installation of these instruments, and indicating their practical applications and maintenance conditions.

Determination of the Coefficient of Mutual Induction.

The International Consultative Committee- Considering that the study of the determination of the co-efficient of mutual induction has given rise to tests which have been confirmed by the Eighth Committee of Research dealing with this work and attached to the C.M.I. (Mixed International Committee for experi­ ments concerning the protection of telecommunication lines and underground channels), and that the conclusions arrived at by this Research Committee have been confirmed by the C.M.I, at its Plenary Meeting in Paris (April 3rd-8th, 1929), ' 205

\ Unanimously advises :— 1. That it is advisable that the “ Guiding Principles ” should employ, fundamentally, only the Pollaczek formula; 2. That it is advisable provisionally to use for calculations "the formula : K a ~ v 7 where a is the apparent conductivity of the earth expressed in C.G.S. units, / is the frequency and K is the empirical constant expressed in C.G.S. units. 3. That for plains and temperate climates, as specially met with in Germany and France, the value for the constant K should be :— E = 1 *5 x io -12 C.G.S. 4. That it is desirable for the “ Guiding Principles ” to give new curves showing the value of the coefficient of mutual induction as a function of the spacing for frequencies of 16-2/3, 50 and 800, and obtained according to the Pollaczek formula and the empirical law recommended in Paragraph 2. 5. That the Guiding Principles should also give a general curve giving the value of M as a function of the theoretical parameter : 2a 7T's/2ai where a represents the spacing of the lines ^ Expressed a „ „ apparent conductivity of the ground in C.G.S. / ,, „ frequency J units. . 6. That all modifications and additions to the “ Guiding Principles ” recommended in para­ graphs 1, 2, 3, 4, and 5 should be entrusted to the Editing Committee of the First Commission of Assessors.

Replying to a question by the International Union of Railways concerning the length of telephone circuits to be used in the calculation of noise voltage.

The International Consultative Committee— Considering the request of the International Union of Railways on the subject of the length of parallelism to be considered in the calculation of noise voltage, Unanimously advises :— That the “ Guiding Principles ” (page 12, para. 2, English translation, p. 13) be modified as follows :— Replace the third paragraph by the following text :—- " The length of line to be included in the calculation must be the effective length of parallelism; if, however, the telephone line includes rotations or transpositions, the length to be considered is only that for which the inductive effects on the most exposed telephone circuit have not been compensated for by transpositions. This length depends on the type of installation in each country. In any case, it must not exceed 8 km in length. On the other hand, to take into account the inevitable effects of dissymmetry of telephone lines, the lengths not compensated for, to be included in the calculations, must never be less than 500 metres.” This figure is adopted provisionally until it can be definitely laid down from tests under­ taken on this subject by the Mixed International Committee for experiments concerning the protection of telecommunication lines and underground channels. 206 VII.—MINUTES OF THE CLOSING SESSION.

(June ioth, 1929.)

The meeting was opened at 2. p.m. undei the presidency of Dr. Breisig.

The Minutes were read of the Fourth Meeting on Transmission held on June 7th at 10 o’clock.

On a motion by Mr. Hopfner, the following question was added to the list of new questions to be studied by the Third Commission of Assessors : “ What should be the permissible limit for the hysteresis coefficient of loading coils to be used in long-distance telephone cables ? ” Note.—By the term “ hysteresis coefficient ” is meant the additional effective resistance produced by hysteresis for one ampere of alternating current at 800 p.p.s. The minutes were read of the Fourth Meeting on Traffic, Operation and Tariffs held on June 7th; these minutes were passed without amendment. The Plenary Session decided that the date fixed for putting into force the new recommendations regarding traffic, bperation and tariffs should be January ist, 1930, except in regard to recommendation No. 18a (calls with “ avis d’appel ” and calls with “ preavis ”) and recommendation No. 40c (maximum duration of calls). The date when these two special recommendations should be put into force should be October ist, 1929, and the Heads of Delegations were requested by the Plenary Session to ask their Administrations to take the necessary measures to put these two recommendations into force as from October ist, 1929, in the event of their Administration approving the recommendations. The minutes were read of the meeting regarding Protection of Lines held on June 7th; these minutes were passed, and it was decided that they should be brought to the notice of the Secretary-General of the International Union of Tramways, Local Railways and Public Motor Transport. The minutes were read of the meeting of the Organisation Commission and the meeting of the Heads of Delegations which was held on June 8th.

Dr. Breisig: Gentlemen, the new recommendations in regard to questions of organisation, which the meeting of the Heads of Delegations has proposed that the Plenary Session should issue, particularly those in regard to representation on the C.C.I. of private telephone companies, are very important, and I would ask members whether they have any remark to make on this subject. 207 Mr. Christiansen: Will you allow me to make some remarks regarding the position in Denmark, where long-distance telephony is exploited by the State, whilst urban telephony is in the hands of several private companies. These companies have not yet adopted the C.C.I. rules. The easiest way in which to interest these companies in the work of the C.C.I. is, in my opinion, to obtain their collaboration. In view of the large number of such companies in different countries which are members of the C.C.I., I appreciate the difficulties of such a collaboration, and I am in agreement with the recommendations made by the Organisation Commission. I would, nevertheless, ask, are there no means by which engineers of private companies who are interested in the work of the C.C.I., could take part in their meetings ?

Mr. Valensi: The question put forward by Mr. Christiansen with reference to the situation in Denmark is important for the following reasons : In Denmark there are several private companies, already exploiting important exchanges {e.g. Copenhagen), who propose to construct and exploit long-distance cables; these lines will all lie on Danish territory, but they will be linked with international circuits connecting Denmark with other countries, and these international circuits are exploited by the Danish State Telephone Administration. It is, nevertheless, desirable that all necessary measures should be taken to insure that transmission may be satisfactory, in particular, for long-distance international communica­ tions, in conjunction with the laying, maintenance and operation of the inter-urban inland lines in Denmark, as also in the arrangement of exchanges and urban systems in Denmark. It is therefore desirable that the attention of these companies should be drawn to the C.C.I. recommendations, which give interesting information on these subjects. Mr. Christiansen is considering the easiest manner in which these Danish companies could follow the C.C.I. recommendations, either in regard to the maintenance of their cables, or in regard to the organisation of their inter-urban systems from the point of view of the transmission efficiency of lines and subscribers’ stations, junction lines between exchanges, etc. Now, these questions of transmission are studied by Commissions of Assessors of the C.C.I. (in particular the 3rd and 4th C.R.); nothing limits the number of experts at the meetings of these Commissions. It is always possible for an operating company to nominate someone under the title of expert. Actually, however, the experts are attached to the delegates of the Administrations who form part of the Commissions of Assessors. If the Danish State Telephone does not, for example, take part in the 3rd Commission it is not possible, without special authorisation, which does not exist for the moment, for a representative of an operatng telephone company in Denmark to be present, as an expert, at a meeting of this 3rd Commission of Assessors.

Mr. Milon : I think I should mention that the new ruling regarding adherence to the C.C.I. of private operating companies applies particularly to countries where there is no State Administrations. In the case of Denmark, however, where there is a State Administra­ tion, it is evident that the Administration should reserve the right to form its delegation attending the Plenary Sessions of the C.C.I. as it may choose, and, if the case arises, the Administration should include in its delegation representatives of private telephone companies Following upon an exchange of views in which Dr. Breisig, Mr. Sadzot and Mr. Milon were the chief speakers, the Plenary Session passed, without amendment, the draft recom­ mendation prepared by the Organisation Commission under the title “ Membership of the International Consultative Committee of Private Telephone Companies operating in countries where there is no State Administration,” but decided that the other draft recommendation prepared by the Organisation Commission, and entitled “ Representation on the International Consultative Committee of Private Telephone Companies,” should be amended, and that the following text should be adopted :— 208 Representation on the International Consultative Committee of Private Telephone Companies operating in Countries where there is a State Telephone Administration, The International Consultative Committee— Considering :— The first paragraph of Article 91 of the Regulations for International Service (Revision of Paris, 1925) Unanimously advises :— 1. That private telephone companies operating within the territory of an Administration represented on the International Consultative Committee should be considered as forming an integral part of the telephone system of that Administration, which shall have the right of deciding whether it is desirable to include representatives of these private telephone companies in the Delegation sent by the interested country to the Plenary Sessions of the International Consultative Committee; 2. That one country may only be represented at the Meetings of the' International Consultative Committee by a single delegation, representing both the State and the private telephone companies operating within the territory of that State, all the members of this delegation being appointed by the State Administration of the country in question.

The Plenary Session approved the appointment, suggested by the Organisation Commission, of Colonel Sir Thomas Purves, Professor Di Pirro and Dr. Breisig as auditors of the C.C.I. accounts for the year 1929-1930.

The Plenary Session, on a motion put forward by the Organisation Commission, also, passed the report on the budget, drawn up by the Secretary-General and submitted to the Heads of Delegations at the Opening Session on June 3rd, 1929.

After an exchange of views on new questions which the Organisation Commission proposed to study, the Plenary Session decided :— 1. That the two questions below {a and b) should form the subject of an enquiry by che Secretary-General from Administrations or companies adhering to the C.C.I:, the results of this enquiry to be summarised in the management report which the Secretary-General will submit to the Plenary Session in 1930 :— (а) Is it desirable, for the admission of any country to the C.C.I., to demand from this country a minimum amount of international telephone traffic (terminal or transit), and, if in the affirmative, how should this minimum be characterised and determined (number of circuits, amount of traffic, etc.) ? (б) Conditions under which Colonies and Protectorates can eventually participate in the C.C.I. 2. That the study of the following question should be entrusted to the Sixth Commission of Assessors (as well as the study of the other new questions regarding traffic and operation) : “ What would be suitable measures to be taken in regard to international telephone traffic in order that all information which may be of use for the regular development of an international telephone system, and which will keep traffic requirements up to the desired service quality, may be sent regularly to Administrations and operating companies who are members of the C.C.I.? Is it desirable to instruct a Sub-Committee of the C.C.I. (which might, for example, form a permanent Sub-Committee of the Sixth Commission of Assessors) to study regularly estimates of international telephone traffic in accordance with data on this subject given by the Administrations and operating companies who are members of the C.C.I. ?” 209 0 On the motion brought forward by Mr. Martin, of the American Telephone and Telegraph Company, seconded by Mr. Hopfner, the Plenary Session decided to add to the new trans­ mission questions, the study of which had been entrusted to the Third Commission of Assessors, the following supplementary question “ Technical conditions which underground or open wire lines connecting toll and urban exchanges must satisfy in order to obtain good telephone transmission in international service/' Note.—This question should be studied in collaboration with the Third and Fourth Commissions of Assessors. The Plenary Session then proceeded to appoint Commissions of Assessors, to whom should be entrusted the various new questions to be studied. After an exchange of views, in which Dr. Breisig, Col. Sir Thomas Purves, Messrs. Milon and Sadzot took a prominent part, the Plenary Session decided to follow the procedure of previous years, and to indicate, not only the Administrations or Operating Companies which should nominate the various Assessors, but also to include the names of the Assessors whose assistance the C.C.I. desires, subject to the approval of their respective Administrations. Eight Commissions of Assessros were thus established.

FIRST COMMISSION OF ASSESSORS.

Questions relating to the Protection of Telephone Lines against the Disturbing Influence of Power Installations. 1.—(a) How may the disturbing influence of harmonics from continuous current traction installations be characterised ? (b) Examination of the permissible limits of the. amplitude of these harmonics. (c) Measures to be adopted in the case of parallelism between international telephone lines and continuous current traction lines.- 2.— {a) Definition of noise voltage induced on telephone circuits. (See Appendix A, p. 223.) (b) Method of measuring induced noise voltage. Relation between the results of measurements with different testing instruments. (See Appendix B, p. 223.) Possibility of establishing a standard testing instrument for measuring this noise voltage. (c) Permissible limits for noise voltage on aerial circuits and on cable circuits. (See Appendix C, p. 226.) Note.—This question should be studied jointly by the First, Third and Fourth Commissions of Assessors of the C.C.I. (on the basis of the work done by the Sixth Committee of the Mixed Commission). 3. The effect of earthing the neutral point of power installations on the importance of noise induced in adjacent'telephone lines. 4. Special maintenance and supervision conditions which must be fulfilled on three-phase lines with an insulated neutral point, for which it is agreed not to consider the danger caused by a double accidental earthing. Note.—The International Union of Railways will be invited by the Secretary of the C.C.I. to submit proposals on this subject. These proposals will be submitted to the Administrations adhering to the C.C.I.

2 1 0 5- Principles of protection and protective devices to be placed on telephone installations to protect the staff and the installations from any possible risks due to the influence of power lines or atmospheric discharges. Note.—Administrations will be invited to send to the Secretary of the C.C.I. their replies to the following questionnaire :—

Questionnaire on Question 5. 1. What are the general circuit schematics, showing the method of protecting toll lines and subscribers’ lines? 2. Fuses. (a) Are different fuses used on aerial lines and on cables ? If so, why ? Is it necessary to insert fuses on toll cable telephone lines when terminated by an insulated transformer ?" (b) What is the fusing current of the fuses ? (c) What is the maximum voltage at which the fuse operates without arcing ? • The voltage referred to is that between the terminals of the fuse. . (d) What is the thermal capacity of the fuse in joules ? Note.—The fuses employed in aerial telephone lines are exposed to atmospheric discharges, which release a considerable amount of energy, and may cause a too frequent operation of the fuses. It may be necessary to rate the fuses higher than is actually desirable for the protection of telephone apparatus. The thermal capacity, expressed in joules, is a measure of the discharge energy which may flow through the fuse without causing it to operate. It is desirable to ascertain the number of consecutive discharges, each with an energy of 8 joules, which a fuse will stand without blowing, such discharges to take place at the rate of 10 in 10 seconds. 3. Lightning protectors. (a) Are lightning protectors used on international telephone cable circuits when terminated by an insulated transformer ? If so, why ? (b) What is the operating voltage of the lightning protectors ? (c) What is their safe current-carrying capacity? 4. Heat coils. (a) What are the operating characteristics of the heat coils (current, time) ? (b) Up to what voltage do they operate without arcing? The voltage referred to is th at between the terminals of the coil. 5. How can the “ Guiding Principles” (p. 12, para. 3; English translation, p. 14) concerning the calculation of noise due to the higher harmonics of direct current installations and alternating current traction installations, be completed? Note.—In the study of this question the experiments of the Eighth Committee of the Mixed Commission will be taken into consideration. 6. How can the arrangement of the wires of a two-wire single-phase line and of a three-phase line be considered in the calculation of the noise voltage on a neighbouring telephone line ? 7. Computation of the coefficient of exposure to danger and the induced noise voltage, under the influence of the electric field at crossings of high tension and telephone lines ? (In the study of this question consideration will be given to the experiments of the Tenth Committee of the Mixed Commission.) 9- Is it possible to develop a single formula to express the noise voltage induced in an open-wire or cable telephone circuit by an adjacent power line? This question should be studied jointly by the First and Third Commissions of Assessors of the C.C.I. io. Comparative study, by exchange of apparatus between the Administrations interested, of various protective apparatus against acoustic shocks. Note.—The basis of this study should be the experiments approved by the Ninth Committee of the Mixed Commission. Note.—In addition, a new edition of the ‘‘Guiding Principles” on the protection of telephone (or telecommunication) lines against the disturbing influence of power lines will be prepared during the year 1929-30. This new edition will be prepared by an Editing Committee of the First Commission, consisting of : Messrs. Brylinski,. Leboulleux, Dr. Jager, Dr. Klewe, Messrs. Collet, Valensi and Oilier. The new publication of the “ Guiding Principles ” will be published in 1930 by the Secretariat of the C.C.I.

Members of the First Commission of Assessors. Administrations appointed to nominate Assessors : Germany (Dr. Jager), Chief Assessor; Austria (Mr. Pfeuffer); France (Messrs. Rochas and'Collet); Great Britain (Mr. Bartholomew); Italy (Mr. ); Sweden (Mr. Swedenborg).

SECOND COMMISSION OF ASSESSORS. Questions concerning the Protection of Telephone Cables against Corrosion due to Electrolysis or to Chemical Action. 1. Revision of the proposed Recommendations concerning the measures to be taken for the protection of cables against electrolytic corrosion, revised at Como in 1927. (Rose Book, pp. 126 to 147; English translation p. 9.) 2. Revision of the proposed Recommendations concerning the measures to be taken for the protection of cables against corrosion due to chemical action, revised at Como in 1927. (Rose Book, pp. 148 to 150; English translation, p. 29.)

Members of the Second Commission of Assessors. Administrations appointed to nominate Assessors : Germany (Dr. Breisig) Chief Assessor; France (Mr. Collet); Great Britain (Mr. Bartholomew); Italy (Mr. ); Belgium (Mr. Parfondry). Experts from the International Union of Tramways, from the principal Electrical Engineering Societies and the principal Gas and Water Distributors’ Technical Societies, also observers from the International Union of Railways and from the Producers and Distributors of Electric Energy, will paiticipate in the work of the Second Commission of Assessors.

THIRD COMMISSION OF ASSESSORS. Questions relating to Transmission and Maintenance. 1. Revision and publication of the Recommendations for the placing in service and maintaining of international circuits...... 212 2. Continued study of means to be adopted to compensate for the variation with time of the transmission equivalent in very long international telephone circuits (for example, those containing more than 12 repeaters). It is necessary to investigate particularly if there are causes of variation other than those of fluctuation of temperature and battery voltages in repeater stations. 3. Possible means of application of System No. II of loading in the telephone networks of different countries. 4. Uniform limits to be prescribed for the cut-off frequency, frequency band to be transmitted, and the attenuation between two successive repeater stations, on international circuits. 5. Revision of the C.C.I. Recommendations relating to the permissible limits of variation of the effective attenuation with frequency in long international circuits (Green Book, pp. 65 to 66; English translation 1928, p. 45). To what extent may one depart from these limits in certain cases, particularly on circuits used for carrier telephony ? 6.— (a) Is it necessary to modify the value of 7.5 nepers indicated as the limit for crosstalk between two carrier channels, or between one carrier channel and a low frequency channel in the same circuit ? (b) What value should be prescribed for crosstalk between any two carrier channels in the same transposition system ? 7.— (a) Is it necessary to reduce the provisional value fixed for the difference of capacity, with reference to earth, of the loading coils used for the two pairs of the same quad of a cable ? This value was provisionally fixed at 100 ^,/xF. Is it necessary to reduce it to a lower-value, say 50 /x/xF ? (b) Is it also necessary to reduce from 0 • 25 per cent, to o • 15 per cent. , the limit provision­ ally fixed for the difference of the inductance of loading coils intended for two pairs in the same quad, when tested under phantom circuit conditions ? (c) Is it, likewise, necessary to reduce from 0*20 ohm to o-15 ohm the limit provisionally fixed for the difference in resistance of two pairs in the same quad, when tested under phantom circuit conditions ? 8. Experimental results obtained with quad-pair cable (cable a paires cablees en etoile— Doppelstern Kabel). Note.—On this subject the German Administration will communicate to the C.C.I. the results of tests made, after laying, on the Munich-Augsburg cable, and the Dutch Admin­ istration the results of corresponding tests made on factory lengths of the Meppel-Leuuwarden cable, and also final tests, after laying of the cable. 9. What frequency should be adopted for routine testing in long-distance telephone circuits ? This frequency is, at present, fixed at 800 p.p.s. Should it be raised to 1 000 p.p.s. ? 10. What electrical testing methods can replace voice and ear tests for crosstalk ? 11. Installation specifications for repeater stations, with particular reference to : (a) Terminating sets, (b) Testing and measuring apparatus. 12. Should the transmission level be specified at the point where a ringer must be placed, in accordance with the recommendations relative to the sensitivity of the ringer (see Green Book, Appendix B, c.4, No. 4; English translation 1928, p. 208, “ Guiding Principles as a help toward the establishment of Essential Clauses of a Specification for .Ringers ”). Should it be the nominal level at the point considered, or should the extreme levels be considered as practicable, and be allowed a tolerance of ^ 0.5 neper (or 4.5 decibels) for the range of sensitivity demanded ? 13. Questions concerning special devices for collective international communications (Conference calls) : (a) The case where the grouped subscribers belong to only two telephone networks. (b) The case where the grouped subscribers belong to more than two networks. In each of these cases, the special devices will be designed to permit each participant to speak and listen simultaneously or, alternatively, only to listen or to speak. (See Appendix D, p. 227.) Note.—This study should be undertaken jointly by the Third and Fourth Commissions of Assessors. 14. Essential clauses for a specification' for the supply of repeaters joining two cables which differ from one another in transmission qualities. 15. Permissible limits of unbalance of a cable telephone circuit with respect to earth. Note.—This question should be studied by the Third Commission of Assessors of the C.C.I. in collaboration-with the International Mixed Commission for experiments relating to the protection of telecommunication lines and underground channels—7th Committee; Unbalance of Telephone Lines, Chairman : Mr. Rochas. (See Appendix E, p. 229.) 16.— (a) Is it desirable to recommend reconstruction of aerial line networks in various countries, in order to obtain international circuits capable of transmitting a very broad band of frequencies ? (b) Choice of a system of uniform transpositions in short sections for such lines in various countries. 17. Is it possible to utilise for telegraph purposes a circuit in a telephone cable, by employing the frequency range lying between the maximum frequency transmitted for telephony and the cut-off frequency ? 18. Conditions under which the super-phantom (“ ghost ”) circuit, or the phantom circuit, may be utilised for international telegraphy (employing, for example, two quads in a quadded Dieselhorst-Martin cable, or two pairs in a star-quad cable). 19. Is it possible to lower the limit provisionally fixed by the C.C.I. for the transmission loss of the operator’s instrument when in the silent listening position (transmitter out of circuit) ? The maximum permissible value, at present, is o . 09 neper or 0.77 decibel within the frequency range from 300 to 2 500 p.p.s. Can this limit be reduced^to 0.05 neper or 0.43 decibel by increasing the impedance of the operator’s set as much as possible, whilst maintaining sufficiently good listening properties for the operator ? 20. What should be the permissible limit for the hysteresis coefficient of loading coils to be used in long-distance cable circuits ? Note.—By the hysteresis coefficient, is meant the additional resistance, introduced by hysteresis, for 1 ampere of alternating current at 800 p.p.s. 21. Technical conditions which should be fulfilled by cable or aerial circuits between toll and local exchanges, in order to ensure satisfactory transmission in international service. Note.—This question should be studied jointly by the Third and Fourth Commissions of Assessors,

2 1 4 22. How can the total power of telegraph currents, corresponding to frequencies used simultaneously on the same telephone circuit when working as a voice frequency telegraph circuit, be measured ? Note.1—This question should be studied jointly by the C.C.I. (Telephone) and the C.C.I. (Telegraph). A provisional limit of 5 mW has been fixed for the maximum value of the mean power integrated during 1/20 second.

Members of the Third Commission of Assessors. Administrations appointed to nominate Assessors : Germany (Mr. Hopfner) Chief Assessor; Cuba (Mr. Eriks on); Denmark (Mr. Gottlieb); United States of America (Mr. Shreeve); France (Mr. Lange); Great Britain (Messrs. H art and Robinson); Italy (Mr. ); Mexico (Mr. M. Vos); Holland (Messrs. de Brauw* and de Vogt); Sweden (Mr. Holmgren); Switzerland (Dr. Forrer); U.S.S.R. (Mi. Jouriew). Note.—A permanent Sub-committee has been established under the Third Commission of Assessors to take charge of all questions concerning the application of the recommendations of the C.C.I. for placing in service and maintaining international circuits. This Sub­ committee, of which Mr. Hopfner is Chairman, includes the Administrations of Germany (Messrs. Richter and W inzheimer); France (Mr. Vandewiele); Great Britain (Mr. Chamney), and Holland (Mr. Visser). Administrations who have any difficulty in carrying out the recommendations need only apply direct.to the Chairman of this Sub-committee, who will advise the Administration concerned on the subject of placing in service and maintaining the circuits involved.

FOURTH COMMISSION OF ASSESSORS (PERMANENT). Various Questions concerning the Master Reference System for Telephone Transmission, Reference Systems and Working Standards. 1. Relation between syllable articulation and word articulation of a continuous conversation (intelligibility), chiefly in the case of very long telephone circuits. 2. Description and results of the different methods of testing subscribers’ apparatus and lines under operating conditions, in order to ascertain that subscribers’ sets and lines satisfy the conditions required for international service. 3. Conditions to be fulfilled by volume indicators or peak value indicators in telephono­ metric measurements in order to determine the volume of sound emitted by the speaking operator. Note.—The volume indicator actually in use in the “ SFERT ” laboratory gives rapidly changing readings and is difficult to read. This question is similar to that already studied by the Third and Fifth Commissions of Assessors. It is desirable that the Third, Fourth and Fifth Commissions of Assessors collaborate in the study of all that which concerns volume indicators. 4. Method to be followed in order to fix :— (a) The value of the reference equivalent of a complete connection between subscribers in international communication. (b) The value of the reference equivalent of a connection between the subscriber and the terminals of the international circuit, taking into account the battery supply loss in the subscriber’s set. (See Green Book, p. 64; English translation, 1928, p. 45.)

* Since deceased. 2 I5 Note.—This question could be subdivided under the following three headings :— (a) Maximum permissible limit for the reference equivalent of a subscriber’s set under transmitting conditions (as measured with a working standard). (b) Maximum permissible limit for the reference equivalent of a subscriber’s set under receiving conditions (as measured with a working standard). (c) Maximum permissible limit for the battery supply loss due to the resistance of the subscriber’s line and instrument. 5. Study of a method for international measurements of articulation. 6. Comparison of any type of working standard with the European Master Reference System for Telephone Transmission (“ SFERT ”). 7. Recommendations for the use of Working Standards of any type. 8. Choice of a system of spelling. Note.—In the course of 1929-30 the “ SFERT ” laboratory will proceed to calibrate the European Master Reference System, in accordance with the principles laid down by the Plenary Session in Berlin, 1929, and in co-operation with the American Telephone and Telegraph Company.

Members of the Fourth Commission of Assessors.

■ Administrations appointed to nominate Assessors: Great Britain (Mr. Cohen) Chief Assessor; Germany (Dr. Breisig); United States of America (Mr. Martin); France (Mr. Chavasse). Note.—A Sub-committee under the Fourth Commission of Assessors is charged with preparing a system of spelling and lists of syllables {logatomes) for making articulation measurements according to an international method; this Sub-committee is presided over by Mr. Cohen (Great Britain), and its members are:—for Germany : Mr. Grutzmacher; for the United States of America : Mr. Martin; for Great Britain : Mr. Stevenson; for France : Mr. Chavasse.

FIFTH COMMISSION OF ASSESSORS.

Questions concerning the Co-ordination of Telephony and Radio-telephony. 1. Which is the most convenient method of measuring noise under the special conditions obtaining in a radio-telephone circuit ? What should be the maximum permissible limit of noise measured by this method ? 2. What instrument could most conveniently be used by the technical operator to measure the volume of sound at the junction between the radio and the metallic circuit? Note.—In the study of this question the Fifth Commission of Assessors will collaborate with the First, Third and Fourth Commissions of Assessors, and with the Committee of the International Mixed Commission dealing with similar questions.

Members of the Fourth Commission of Assessors. Administrations appointed to nominate Assessors: Great Britain (Dr. Hansford*), Chief Assessor; Germany (Mr. Hopfner); Denmark (Mr. Christiansen); Spain (Mr. Nieto); United States of America (Mr. Shreeve); France (Mr. le Corbeiller).

* Since deceased; place taken by Mr. Aldridge. 2l6 SIXTH COMMISSION OF ASSESSORS.

Questions of Traffic and Operation. 1. Preparation of service instructions for the use of toll exchange operators to enable them to apply the recommendations of the C.C.I. for the setting-up and charging of international conversations of different categories, making use of phrases agreed upon.

Note.—For the examination of this question the Secretariat of the C.C.I. will confine itself to asking the Administrations of the following countries, Germany, Belgium, Denmark, France, Great Britain, Sweden and Switzerland, to formulate their proposals. The task of preparing the text of the instructions will be given to an editing sub-committee to be formed from the Sixth Commission of Assessors.

2. Completing the typical form of telephone service agreement in pages 417 to 424 of the Green Book (English translation, 1928, pp. 322-326) by the provisions relating to facilities offered to the public (occasional fixed-hour conversations,- requests for information, new provisions for “ preavis ” and “ avis d’appel ” calls, etc.), and also by the new rules relating to charges.

3. Is it possible to arrive at a formula for determining the number of circuits necessary for carrying traffic presented at different times of the day, in order that the waiting-time may always be below a given limit ? This question is important in order to decide, according to the form of the traffic curve between two given areas, in the course of successive years, when it is advisable to equip new circuits available, or to install a new cable.

4. Preparation of a model form to record the results of observation of traffic on the principal international telephone circuits; preparation of a model formula which the exchange- chiefs should employ for communicating to one another each month the results of the traffic observations on the principal international telephone circuits.

5. Should recommendation No. 2, relating to the maximum delays for international calls-, be modified ?

6. In certain countries subscribers have the facility, in case of absence, of having their lines connected to a special service (absent subscribers’ service) position. What provisions are desirable to be applied when an international call (without preavis) is received at this service ?

Note.—In the French internal service the following procedure is adopted :—The call is connected to the absent subscribers’ service position, where the operator answers by saying “ This is the absent subscribers’ service. I can take note of what you desire to say to ...... Littre 09-99.” If the caller declines this service, the call is abandoned and is not charged for. If, however, the caller accepts the service, the call is charged according to its duration.

7. What should be the correct means of forecasting international telephone traffic, in order to furnish regularly to Administrations and Operating Companies adhering to the C.C.I. all information which might be of use to them in the regular development of the international network, so that the needs of traffic and quality of service desired may always be m et? Is it desirable to charge a sub-committee of the C.C.I. (which might be, for example, a permanent sub-committee of the Sixth Commission of Assessors) to make,. regularly, forecast studies of international telephone traffic from information communicated on this subject by Administrations and Operating Companies adhering to the C.C.I. ? 2I7 Members of the Sixth Commission of Assessors.

Administrations appointed to nominate Assessors : Belgium (Mr. Fossion) Chief Assessor; Germany (Mr. Wiehl); Denmark (Mr. Gredsted); United States of America (Mr. J. E. Bratney); France (Mr. Barillau); Great Britain (Mr. Trayfoot); Holland (Mr. Claasen); Sweden (Mr. Lignell); Switzerland (Mr. Moeckli); U.S.S.R. (Mr. Lakhmann).

SEVENTH COMMISSION OF ASSESSORS.

Tariff Questions.

1. Should conversations between frontier places be charged by single minutes after the first unit-call time, in conformity with a wish expressed by the International Chamber of Commerce ?

2. Should the charge for urgent calls be lowered from triple to double that of ordinary calls ?

3. Is there a case for applying a higher charge when placing at the disposal of users, for transmission of pictures or for relaying radio-broadcast transmissions, a four-wire circuit which could be used to form two distinct communication channels working in opposite directions ?

4. Is it not desirable, in order to induce callers to utilise international circuits outside the hours when traffic is heaviest :— (a) To reduce the charge for occasional fixed-hour calls, asked for during the busy period but outside the time of heaviest traffic (this time to be determined, if the suggestion be adopted, by agreement between the terminal offices) from a triple charge (increased by T of the unit rate) to the ordinary charge (increased by T of the unit rate) ? (b) To reduce the supplementary charge, in the case of a fixed-hour call, during the period of light traffic, from -J- of the unit charge to of the charge for a 3-minute ordinary call made during the period of light traffic? (c) To forgo the supplementary charge in the case of an occasional fixed-hour conversation required for a duration of at least one hour during the light traffic period ? (See Recommendation No. 12, Green Book, page 375; English translation 1928, p. 292.) *

5. Is it not desirable to reduce the charge applied in cases of refusal, by either the calling or called party, to accept a connection ? For the present, the cost of a 3-minute call, of the category demanded, is chargeable (International Regulations, Paris Revision, section L, para. 7 (1)).

6. Conditions in which free publicity calls might be admitted in the international service. Is it desirable to grant such calls during hours of light traffic with the reservation that no inconvenience to the service in general shall result; the duration of free publicity conversations being limited to 3 minutes ?

7. Can it be agreed that, in order to cover the canvassing expenses of terminal Administrations or Companies, the portion of the charges allocated to them for outgoing calls be greater than that for incoming calls ?

2 1 8 8. Requests for information : Is it desirable to charge as follows for requests for information ? A request for information is charged for {a) When it is for genuine information, and the subscriber does not ask immediately after a call. (b) When the caller refuses a connection after having received the information. (c) When the caller annuls his enquiry after his exchange has transmitted this to another exchange. (d) When a conversation cannot take place because the called subscriber does not reply. A request for information is not charged for :— (a) When the exchange which received the request, or another internal exchange, for example the international-line terminal exchange, is able to give the information. (b) When the request is in connection with a demand for a call, and the communication takes place immediately after. (c) When the conversation cannot take place because of breakdown in the apparatus or lines. Note.—Requests for information are dealt with and charged for differently in the countries where they are admitted. In some countries, the regulations on the subject are interpreted so that each request for information (a subscriber’s number, address, etc.) must be charged for. Other countries, on the contrary, are of the opinion that the information should be furnished gratuitously when the enquiry results in a call. 9. Who should be considered the “ caller ” in the case of radio-telephone transmission and, consequently, which Administration should be responsible for the collection of the charge ? Members of the Seventh Commission of Assessors. Administrations appointed to nominate Assessors : Belgium (Mr. Fossion) Chief Assessor; Germany (Mr. W iehl); Denmark (Mr. Gredsted); United States of America (Mr. J. F. B ratney); France (Mr. Barillau); Great Britain (Mr. Townsend); Holland (Mr. Claasen); Sweden (Mr. Lignell); Switzerland (Mr. Moeckli); U.S.S.R. (Mr. Lakhmann).

EIGHTH COMMISSION OF ASSESSORS. Questions having both a Technical and Operational Character. 1. What are the best measures to adopt in the construction of operators’ telephone sets, so that in the “ Speech ” position (transmitter in circuit), the quality of the conversation between the operators themselves, and between operator and subscriber, shall be as good as possible, without the quality of the speech transmission between two subscribers being too greatly affected in cases where the operator “ cuts in ” ? 2. What are the technical measures to be adopted (in repeater stations, toll exchanges, local exchanges, and subscribers’ installations), and what are the operating rules to be applied, in order to establish a connection between an international telephone circuit and a subscriber, in the special circumstances given below ?— (a) Where an international telephone line is rented to two subscribers. (Green Book, page 377; English translation, 1928, p. 294.) (b) Where an international telephone line is used for “ collective ” transmission (conferences). (Green Book, page 379; English translation, 1928, p. 295.) (c) When an international telephone line is used for picture transmission.

2 1 9 Note.—In cases (b) and (c) above, it is desirable that a four-wire circuit, extended by means of four conductors to the subscribers’ stations concerned, should be used. 3. Essential clauses of a specification for the supply of desks equipped for the super­ vision of telephone traffic over the principal international circuits, the control of the operation of the circuit, the working of the operators, and the relations between subscribers and the Administration. 4. Study of arrangements for giving toll calls priority over local calls, and, in paiticular, for the holding of the subscriber by the toll office at the moment of the preliminary call, without, however, preventing the subscriber from using the local network until the toll call can be passed to him. 5. Is it desirable for toll offices to adopt the practice of warning the subscriber originating an international call that the duration of conversation is approaching, 3 minutes, then 6 minutes, etc., by an audible signal being put on the line 10 seconds before the end of each 3-minute interval? Note.—In the study of this question, the Secretary of the C.C.I. will issue a preliminary enquiry to Administrations asking them if they already have such automatic systems in operation; if so, they will be asked to advise the Secretary of the C.C.I. concerning the general arrangements, results of tests, and, if possible, some indication of the price of such equipment. Members of the Eighth Commission of Assessors. Administrations appointed to nominate Assessors : France (Mr. Drouet) Chief Assessor; Germany (Messrs. Hopfner and W iehl); Belgium (Mr. Haem ers); Cuba (Mr. Catterson); United States of America (Mr. J. F. B ratney); Great Britain (Messrs. H art and Trayfoot).

Dr. Breisig : The place and date of the next Plenary Session must now be fixed. Mr. Valensi : Gentlemen, various unofficial suggestions have been made on this point. Several Delegates have remarked that this year there were few discussions at the Plenary Session, particularly at those meetings devoted to questions of transmission, where the meeting has limited itself to the ratification of the suggestions put forward by the Commissions of Assessors without making any amendment. Certain Delegates have also expressed an opinion that the programme of the next Plenary Session could perhaps be reduced to the examination of new questions of organisation, traffic, operation and determination of tariffs. So far as technical questions are concerned, it has been stated that it might, perhaps, be sufficient to inform the Administrations who are members of the C.C.I., of the results of the work done by the Commissions of Assessors, to whom, in addition, there should be accorded the right to propose new questions for study, if they consider it advisable. On the other hand, a large number of other Delegates consider that it is necessary that the proposals made by the Commissions of Assessors should be examined every year in Plenary Session, in order that the Delegates of each Administration might, during the Plenary Session, ask the Assessors themselves for any supplementary verbal explanations on points which are not clear to them or which do not give entire satisfaction to their Administration. Moreover, in the course of 1929-1930, there are not only important questions regarding transmission to be studied, but also the observations of the International Union of Tramways (in regard to the proposed general recommendations elaborated by the C.C.I., at Como in 1927, for the protection of cables against corrosion due to electrolytic or chemical actions) which must be taken into consideration. Therefore, the Delegates should first state their views regarding the question of the programme for the next Plenary Session. 220 Dr. Breisig: Is it necessary, as has been done hitherto, to include in the programme of the Plenary Session all the new questions entrusted to the Commissions of Assessors, including the technical questions ? The Meeting approved this opinion, and decided that the next Plenary Session of the C.C.I- should be held from June 16th to 23rd, 1930. Dr. Breisig : Has anybody any proposal to make in regard to the place where the Meeting should be held ? Mr. Sadzot: In the name of the Minister of Posts, Telegraphs and Telephones of Belgium, I have the honour of inviting the C.C.I. to meet in Brussels in 1930. (Applause.) Dr. Breisig: This unanimous applause shows clearly that the Meeting is pleased to.* accept the invitation of the Belgian Telephone Administration, which Mr. Sadzot has so kindly transmitted to us. After an exchange of views the Meeting decided (1) That if the Recommendation, regarding the constitution of a Revision Committee for the Regulations for International Service (Telephone Section) issued in conjunction with the International Bureau of the Telegraph Union, were approved, the, C.C.I. representatives, forming this Revision Committee, would be the members of the Sixth and Seventh Commission of Assessors, and (2) That if the Recommendation regarding the constitution of a Mixed Commission appointed respectively by the C.C.I. (Telephone) and the C.C.I. (Radio-electric) is sanctioned at the next meeting of the C.C.I. (Radio-electric), in September, 1929, at the Hague, the representatives of the C.C.I. (Telephone), forming this Mixed Commission shall be members of the Fifth Commission of Assessors. Dr. Breisig: Gentlemen, the Sixth Plenary Session of the C.C.I. is drawing to its close. If I were to put the question as to whether the hope (which I expressed at the Opening Session), that this Plenary Session should follow the example of its predecessors pleasantly and honourably, had materialised, I think we could confidently reply in the affirmative. As usual, much good work has been done. In the C.C.I.’s international garden there are many plants, and to each one we give the same care and, within the limits of our knowledge, the best methods of cultivation. There are some which mature quickly; as in nature, these form the majority. There are others (among which are some which we consider as being most important for the future) which seem to develop slowly. They merit all our attention. It is also necessary that the C.C.I. should deal with new questions, which up till now have presented themselves in a rather vague form. Each one of us, on hearing these words, will think of certain examples in his particular province. I am happy in being able to congratulate all my colleagues, among whom I include the guests and the representatives of the organisations with which the C.C.I. collaborates, on their very good work. In particular, I would thank the Vice-Presidents who have so excellently assisted me in the accomplishment of my task, and the Chief Assessors who, outside the Plenary Session, have presided over a great many meetings' of the Commissions of Assessors. It is with the greatest recognition that we warmly thank our indefatigable Secretary-General, who, according to his very modest metaphor, considers himself purely in the light of the string which ties the big bouquet of flowers gathered in our work, and finally the Office Secretaries, who have succeeded in keeping up to date the immense number of papers which we have received. (Applause1.) Mr. Milon: My dear colleagues, although your applause gives adequate proof of the manner in which you have appreciated the kind speech of our greatly esteemed President, I am sure that I am your interpreter, when I voice the thoughts which have already entered your minds,, in tendering Dr. Breisig the thanks which he deserves. -221 His eminent qualities are too well known by all of you since he has presided over the meetings of the C.C.I. to render it necessary for me to recall them. Thanks to his indefatigable zeal, thanks to his authority, thanks also to the conciliatory qualities which he has shown towards all the Delegates of the great nations (in particular of the principal transit countries), our work has been pursued, as hitherto, in an atmosphere of perfect harmony, and once again results have been achieved, the efficiency of which we are pleased to recognise. We must thank the German Minister of Posts and the German Telephone Administration for the way, both lavish and cordial, in which we have been received here. We were all equally amazed at the spectacle of intense activity which we obtained on the visit made to the Reichspostzentralamt this morning. Within the C.C.I. we always rather play the part of profiteers. We confirm results, we consider them as almost natural, but it is well that, from time to time, we should be made aware of the price of the efforts at which these results have been achieved. These efforts, this work, we have been able to see within the Reichspostministerium, within the Laboratories of the big German companies of Siemens & Halske and the Allgemeine Elektrizitats Gesellschaft, who have been good enough to receive us. Col. Sir Thomas Purves has already had the occasion to thank the Allgemeine Elektrizitats Gesellschaft in his customary humorous fashion. Circumstances have not enabled us to thank the Siemens & Halske Co. in person for the wonderful reception accorded to us, but we would ask you, dear Dr. Breisig, to be good enough to transmit to them our hearty thanks. Finally, we must accord our warmest thanks to the German Reception Committee, who have given so much care to the pleasures and comfort of our stay in Berlin, that we gained the impression that we were in our own countries, I might almost say amongst our own families. ¥ Dr. Breisig: I had thought that my task was completed, but Mr. Milon’s very kind words oblige me to reply again. So far as I am concerned, I only did what I could, and I am very happy that you should be pleased with my efforts. As for our Administration, it is certainly very pleased that your stay in Berlin should have pleased you. The Minister, after the dinner that he gave you, expressed the very great satisfaction which that agreeable evening had given to him and to his colleagues. The industrial companies, Messrs. Siemens & Halske and the Allgemeine' Elektrizitats Gesellschaft, have really made great efforts to give you a good reception, and it has given them pleasure to see you so satisfied by the visits to the factories, as also by the excursions and receptions which they arranged for you. Permit me to wish you, in the name of the German' Delegation, a pleasant journey to your respective countries, and that you may meet again in Brussels in good health. Mr. Valensi: Permit me, Gentlemen, to add one word to thank our dear President for the very kind words which he addressed to the Secretariat and which I must convey to the Secretaries, since it is they who have done the greater part of the work. For my part, I only preserve the very pleasing memory of a week spent with you in an atmosphere in which the feeling has grown more and more cordial. The Meeting rose at 4.30 p.m.

2 2 2 APPENDIX A.

Referring to question 2 (a) entrusted to the First Commission of Assessors by the Plenary Session of Berlirp, 1929.

DEFINITION OF NOISE AT THE END OF AN INTERNATIONAL CIRCUIT.

Proposed by the Plenary Session of the C.C.I. (Berlin, June 3-10, 1929). The International Consultative Committee- Considering that it is necessary to. define induced noise precisely, And considering that it is now possible to state' the principle from which the definition can be laid down, Unanimously advises :— 1. That it is desirable to define induced noise by an equality of audible impression between the real noise and an artificial noise produced and recorded, under conditions to be defined, by an apparatus of which all the components have been well calibrated; 2. That this equality should be expressed in millivolts by a voltage called “ noise voltage," read directly from the instrument.

APPENDIX B.

Referring to question 2 (b) entrusted to the First Commission of Assessors by the Plenary Session in Berlin, 1929.

VARIOUS METHODS OF MEASURING NOISE VOLTAGES.

I.— Apparatus for measurement of disturbing voltages, by Siemens and Halske (see diagrams on page 224). The intensity of induced noise which is observed in a telephone circuit is compared with the intensity of noise produced by a vibrator (o> = 5 000). With the aid of an indicator, the load resistance of the vibrator is first adjusted, so that the reading of the potentiometer r represents exactly the millivolts between its output terminals. This adjustment having been made, the potentiometer is set so that the same sound intensity is obtained from a telephone receiver connected across the output terminals, as when the same receiver is connected directly to the disturbed circuit. In this way, the value of the alternating voltage of co = 5 000, which is equivalent to the disturbing voltage, is obtained. The use of a vibrator having a constant frequency ensures that the adjustment can be reproduced with certainty at any time. Tests made with various observers have shown that there was no difficulty whatever, after a short training and even for noises of deep tone, in determining the value of the equivalent alternating voltage of to = 5 000; the results of tests obtained by different observers, working under the same conditions, are in satisfactory agreement. The disturbing E.M.F. induced in the circuit is applied to the characteristic impedance Z of the circuit, so th at the disturbing voltage measured at the ends of the circuit is consequently diminished. Therefore, to obtain test results comparable between themselves, a resistance must be inserted between the receiver and the potentiometer terminals to attenuate the vibrator voltage under the same conditions. Tests with this apparatus are easy to make and have a relatively high degree of security. It is desirable that the impedance of the telephone receiver be adapted to the characteristic impedance of the line. 223 II.— Noise-measuring Set of the Western Electric Co. The Western Electric Co. uses, for the measurement of induced noise on a circuit, a source of artificial sound incorporating a vibrator giving a complex tone, dry batteries and an interruptor. The regulating screw of the vibrating reed is carefully sealed to ensure uniform operation. A potentiometer is connected to the output terminals of the vibrator, which regulates the volume of noise produced in a telephone receiver.

-O

Siemens and Halske Apparatus for measuring noise voltage.

The measurement of the noise induced on a telephone circuit is made by connecting the telephone receiver alternately to the source of artificial noise and to the circuit under test; the potentiometer is adjusted so that the noises obtained in the receiver in both cases are equivalent from the point of view of affecting the intelligibility of a telephone conversation.* In order to be able to compare the results of tests on telephone circuits of different impedances, a variable-ratio transformer is employed to reduce the impedance of the circuit tested always to 600 ohms; the telephone receiver, the impedance of which is about 200 ohms, is permanently connected in series with a resistance of 400 ohms, which adapts the receiver impedance to the circuit impedance. The potentiometer is graduated in conventional “ noise units.”

* An operator, with a little experience of these tests, soon becomes able to estimate satisfactorily the disturbing effect which a given noise can introduce in a telephone conversation.

2 2 4 This apparatus enables a measurement to be made of either the noise induced in a telephone circuit, or the noise induced between the two wires of a telephone circuit and earth; in the latter case, the transformation ratio of the variable transformer is made unity, and the primary winding, in series with a resistance of 100 ooo ohms, is connected across the two wires of the circuit under test, in parallel, and earth.

III.—Method of Noise Measurement proposed by the British Administration. The test in question is necessary to determine if the noise in a telephone circuit exceeds the maximum value specified. It is important, therefore, that these test results be independent of the personal factor. This condition excludes all methods which rely on comparison, by ear, of two dissimilar sounds. It is proposed, therefore, to specify a definite value for the maximum permissible voltage due to noise on a circuit, the value specified being based on laboratory measurements on voltage values of noises of various kinds necessary to reduce the articulation by 5 per cent. The curves below give the relation between noise voltage and percentage articulation for sinusoidal currents of different frequencies, and for telegraph currents. The sinusoidal currents may be considered to represent, disturbances due to power lines and, when specifying the permissible noise voltage, the frequency producing the maximum effect should be con- ' sidered. This is about 1 150 p.p.s., and the voltage which, at this frequency, reduces the articulation by 5 per cent, is approximately 0*9 mV.

It will be seen that telegraph currents have more effect than sinusoidal currents on the articulation, and it will, therefore, be necessary to adopt smaller values for noise voltage arising from telegraphs, say, about 0-3 mV. A valve voltmeter, integrating over a definite period and associated with filters to eliminate currents of other than audio frequencies, is employed for measuring the voltages. ' Consequently, the noise permissible at the end of the circuit may be specified thus : “ The noise at the end of a circuit shall not exceed a value such that the corresponding voltage, measured on a valve voltmeter integrating over a period of...... seconds, is not greater than 1 mV within the frequency range from 200 to 3 000 p.p.s.” " In the case , of disturbances arising from telegraphs, the maximum permissible noise voltage shall not exceed 0-3 mV.” ; ■

225 p APPENDIX- C.

Ref erring to question 2 (c) entrusted to the First Commission of Assessors by the Plenary Session of Berlin, 1929.

PERMISSIBLE LIMIT FOR INDUCED NOISE.

1. Proposal by the Third Commission of Assessors of the C.C.I. {meeting at Cologne, March, 1929) for the definition and permissible limit of induced noise.

The noise at the ends of an international circuit should be defined by the reduction in syllable articulation caused by the noise. The maximum permissible reduction in syllable articulation should be fixed, provisionally, at 5 per cent. The direct measurement of the reduction in.syllable articulation, due to noise, being very long and difficult, it is desirable to employ direct methods for the measurement of the noise voltage at the end of the circuit. Research should be made into a more precise method for the measurement of induced noise. Meanwhile, it is desirable that the various Administrations should study the application of the three methods described in Appendix B above (pp. 223-225), i.e., the two methods described in Appendix 5 of the “ Guiding Principles concerning measures to be taken to protect telephone lines against the disturbing influences of heavy-current or high-tension power lines,” and the method proposed by the British Delegation. According to measurements made up to the present, the noise voltage at the end of a circuit (having a transmission level of — 1 neper or — 8*7 decibels) which produces a 5 per cent, reduction in syllable articulation, is equivalent to a voltage of about 5 mV at a frequency of 800 pip.s. This value assumes that the noise is continuous, and that the noise frequencies are contained within the frequency band from 300 to about 2 000 p.p.s. The permissible noise voltage at any point of an intermediate section of line subjected to induction by a high-tension line, is defined by the differences of the levels at the point considered and at the end of the circuit. For cable circuits, this difference is about 1 neper and, therefore, the noise voltage at the two ends of a repeater section, including the inter­ mediate section affected, should not exceed 2 mV. Where it is not possible to satisfy these values, as, for example, on a cable exposed to heavy induction in a tunnel, it is necessary to increase the speech transmission .level in that part of the telephone circuit exposed to induction. For open-wire circuits, on which the lowest transmission level is, in general, — 1 neper in a repeater section, the noise voltage at any point of an intermediate section, influenced by a high-tension line, should not exceed 5 mV.

2. Suggestions of the International Standard Electric Corporation concerning the permissible limit for noise voltage on telephone circuits.

In the studies of this question the Third Commission of Assessors of the C.C.I. has suggested that the permissible noise be limited to a value for which the syllable articulation is reduced by 5 per cent. It is also recommended, however, that the noise value which would produce this reduction in articulation at the extremity of a circuit having a level of 1 neper be 5 mV for all frequencies between 300 and 2 000 p.p.s. In the “ Review of Work of the Sub-Committee on Wave Shape Standard of the Standards Committee ” published in the Transactions of the American Institute of Electrical Engineers,

2 2 6 . the figures given by Mr. H. S. Osborne, and on which is based the curve of the American apparatus called “ Telephone Interference Factor Meter ” give prominence to the following results. The figures given in the table below and taken from the above Review correspond to a relative decrease of the syllable articulation due to noises of sinusoidal form, and of different frequencies. They do not represent, in absolute value, the reduction in syllable articulation, as Mr. Osborne has multiplied them all by a constant factor before recording them and has not indicated the value of this constant factor. Relative Reduction in Frequency. Syllable Articulation.

3° ° 0-2 800 1*0 1 1 0 0 2*6 1 300 0-2 These figures show that for the frequencies between 300 and 1 500 p.p.s. the syllable articulation can vary in a ratio greater than 10 : 1. Therefore, if the value fixed at 5 milli­ volts is correct for one frequency, the margin of safety can be too great or too small for other frequencies. It is possible to calculate the effect on the articulation of the introduction of different sinusoidal sounds of various frequencies in a telephone circuit, by using the new method of calculating articulation from the constants of the circuits (see study entitled “ The Calculation of the Articulation of a Telephone Circuit from the Circuit Constants). This calculation is now being studied. If the method using the apparatus of the Western Electric Co. were employed for the measurement of disturbing noises (see above, page 224) a value of 200 noise units measured at the extremity of a circuit (at a level of 1 neper) would correspond to a modification of 45 to 50 per cent, in the syllable articulation for an average commercial connection.

APPENDIX D.

Referring to question 13 entrusted to the Third Commission of Assessors by the Plenary Session at Berlin, 1929.

ARRANGEMENTS FOR COLLECTIVE COMMUNICATIONS (CONFERENCE CALLS).

1. Description and Schematic of an arrangement for Collective International Communications, used in Germany (see Question 14).

Successful experiments have been made in the territory of the German Administration, using the arrangement shown in the diagram on p. 228. The characteristic of this arrange­ ment is that subscribers living in a certain locality assemble in a hall where one or more transmitters and one or more loud speakers are installed. The conference halls of the various localities (two or more) are interconnected by four-wire circuits, in such a manner that the speech currents from the transmitters follow a path electrically separated from that taken by the currents feeding the loud speakers. The figure shows, as simply as possible, this arrangement adopted for the four conductors of the four-wire circuits and their connections to the conference halls when the terminal apparatus is disconnected. At the president’s seat, the network of conversation circuits is connected to the network of listening circuits through an artificial line having an attenuation of approximately 2 nepers, in order to allow of exchange of communications between the interconnected conference halis. 227 Acoustic coupling by reaction between transmitters and loud speakers must be avoided; the arrangement of the conference halls must be such that the' transmitter is sufficiently damped when the loud speakers are in full service, and vice versa.

2. Description and Schematic of the Arrangement for Conference Calls used by the British Administration. For a long time a system allowing of connecting together a certain number of exchanges in different towns by means of circuits equipped with two-wire and four-wire repeaters has been used in Great Britain. The connections of this system are shown in the schematic on p. 229, which shows the conditions in a repeater station where two two-wire circuits and two four-wire circuits are connected together.

Each circuit is equipped with a special differential transformer, T1? T2 . . . ., whose terminals on the line side are all connected in parallel. A balancing network B1; B 2. . . ., is connected in the usual manner to each differential transformer, and is constructed with an impedance approximately equal to that of the other circuits connected to the “ line ” terminals. The repeaters are joined to the differential transformers as shown in the figure. The system functions as follows :— The incoming speech currents pass through the winding of the transformer associated with the circuit on which the currents are received. Corresponding speech currents are induced in the differential windings and are transmitted to all the other circuits across the trans­ formers T. The speech currents, however, are not transmitted to the output of the circuits over which they were received, on account of the balancing method employed. In this manner, stability of the circuit is maintained. This system allows of the connection of a certain number of circuits to a repeater station:

2 2 8 APPENDIX E.

Relating to question 15 referred to the Third Commission of Assessors by the Plenary Session in Berlin, 1929. ' SUGGESTION BY THE INTERNATIONAL STANDARD ELECTRIC CORPORATION CONCERNING THE USE OF “ NOISE RATIO ” AS A MEASURE OF THE BALANCE OF A CABLE FROM THE POINT OF VIEW OF NOISE INDUCTION. 1. General.—When a telephone cable is paralleled by a high-tension power system or electrified railway, electro-motive forces are induced in all the conductors of the cable. If

O NETWORK INPUT TERM/NAL .

® NETWORK OUTPUT TERMINAL. Omnibus Repeater for Two-wire and Four-wire Circuits, used by the British Post Office. 229 p there are any series or shunt unbalances in a given circuit, a voltage will be produced at the ends of the metallic circuit and will therefore produce voice currents in any terminal apparatus connected to the circuit. The unbalances which produce noise are not the same as those producing crosstalk, for reasons dealt with in the following section. Some simple measurement is therefore required by means of which it will be possible to determine whether the balance of a cable is satisfactory from the noise point of view. The object of this contribution is to describe a quantity, called the “ noise ratio,” which can be used for this purpose. The noise ratio of a cable may be defined as the ratio of the voltage induced to earth at the end of the circuit and the voltage produced in the metallic circuit. We are here con­ cerned, of course, only with the voltages at low frequencies. The voltage to earth at the end of the circuit may be looked upon as a measure of the severity of the induction conditions, while the voltage in the metallic circuit is a measure of the effect of the induction on the circuit. The ratio of the two may, therefore, be taken as a measure of the susceptibility of the circuit to interference. In order to simulate actual conditions, the metallic voltage is measured with the circuit terminated by its characteristic impedance, and the earth voltage is measured with the end of the circuit insulated from earth. 2. Unbalances Producing Noise.—When a telephone cable is subject to induction, all conductors have the same E.M.F. induced in them. The conductors in the outer layer, however, have a direct capacity to the cable sheath. The induced E.M.F. in the outer conductors will therefore cause currents to flow to earth and these currents, flowing through the series impedance of the conductors, will produce a voltage drop along the conductors. The actual voltage to earth of an outer conductor will therefore be less than the induced E.M.F. by an amount depending on the voltage drop in the conductor. Conductors in the next inner layer will have no direct capacity to earth but only to the conductors of the outer layer. The voltage tending to cause current to flow from the inner layer to the outer layer is thus only the difference in the voltages of these two layers. The currents flowing in the inner layer are, therefore, less than those in the outer layer and the voltage drop in the conductors of the inner layer is correspondingly less. For the second inner layer, if there is one, the same state of affairs will exist; the currents and voltage drop being still smaller. We therefore have the largest currents in the outer layer, and the currents in the inner layers get progressively smaller as the centre of the cable is approached. The voltage between the. outer layer and the sheath will be large, and the voltage between two layers will get progressively less as the centre of the cable is approached. The effect of the series unbalances in producing noise depends on the current flowing in the conductors; for this reason, a given series unbalance in the outer layers will produce more noise than the same unbalance in an inner layer. The effect of the shunt unbalances in producing noise depends on the voltage across them. For this reason, a given shunt unbalance in the outer layer will produce more noise than the same unbalance in an inner layer. The result is that the noise in the different layers becomes increasingly smaller from the outer layer to the innermost layer. As a consequence, for given unbalances, the noise ratio of the innermost layer is high, and becomes progressively lower as the layers get nearer the sheath. Since all conductors in a given layer have approximately the same capacity to earth or to the next layer, their potential to earth will also be approximately the same. All conductors in a layer will therefore have the same potential but different layers will have different potentials. Consequently, the shunt unbalances between a given circuit and other conductors in the same layer will produce no noise in the circuit. The only shunt unbalances causing noise will thus be unbalances between the circuit and the next outer layer and, to a less degree, unbalances between the circuit and the next inner layer. The method of measuring noise ratio must therefore be arranged in such a way that the result is only affected by those unbalances which produce noise by actual induction. 230 3. Conditions for Measuring .Noise Ratio.—In order to measure the noise ratio of a circuit in a telephone cable, it is necessary to put voltage on the circuit in some way. There are several different conditions under which the voltage may be applied and, since some of these do not fulfil the condition given at the end of the previous section, a brief description of the different conditions is given here.

• (a) Actual Induction. The noise ratio of a circuit can be measured, of course, when voltages are induced in it by actual induction.. Since, however, the currents in the power system causing the induction may be varying from moment to moment, it is difficult to make any reliable measurement under these conditions. A further disadvantage is that the noise ratio measured at the end of a circuit, using the actual induced voltages, will vary accoiding to the point along the cable at which the induction is taking place. The nature of the parallel will also affect the result, i.e., whether- the parallel is a long uniform one, or whether the induction is all taking place over quite a short section of cable. All these facts make it very difficult to use noise ratio, as measured with actual induction. as a criterion of the balance of the cable. Some method of measuring noise ratio with artificially applied tone is therefore to be preferred.

(b) Tone a'pplied only to circuit under test. One suggestion that has been made is that tone should be applied through a retard coil connected at the end of a circuit to be tested; the voltage being applied between the mid point of this retard coil and earth. This would mean that only the circuit being tested would have voltage applied to it. This would be correct in the case of a single isolated circuit, but in the case of a cable containing a number of circuits, it would not be satisfactory. The reason for this is that, if tone is applied only to ope circuit or one quad in a cable, there would be a difference of voltage between that quad and adjacent quads in the same layer. This means that the unbalances between the given quad and other quads in the same layer would contiibute to the noise; whereas in actual practice, as already pointed out, they do not. This method of applying the tone is therefore not to be recommended.

(c) Tone applied to all conductors. Since, under conditions of actual induction, all conductors have the same E.M.F. induced in them, one method of applying the test tone to a cable is to apply it to all conductors at once. The tone can be applied at one end of a length of cable, a repeater section for instance, while the noise ratio is measured at the other end. This is called “ far end noise ratio.” Alternatively, tone can be applied at the same end as that where the measurement of noise ratio is made. This is called “ near end noise ratio.” In this case, tone must be applied to the circuit under test through the mid point of a retard coil connected across the circuit. The disadvantage of measuring near end noise ratio is that, since all conductors at that end are of necessity all held to be at the same voltage above earth, quite large capacity unbalances from one layer to another may exist at the near end without producing much noise in the metallic circuit. This effect is particularly noticeable in the case of circuits in inner layers. The use of far end noise ratio overcomes this difficulty, since by the time the far end of the cable is reached, the different layers have had time to assume different voltages to earth. Far end noise ratio, however, has a disadvantage in that it varies with the length of the cable much more than near end noise ratio. This is shown by the curves of Fig. I (p. 232), which indicate the variation of noise ratio with the length of cable. These curves show that the near end noise ratio is approximately constant after the cable length exceeds about to kilometres, whereas the far end noise ratio falls steadily as the length of the cable is increased. This large variation of far end noise ratio is a great disadvantage when it is desired to specify limits for noise ratio, because it is necessary to give different limits according to the length of the cable to be tested. To avoid this trouble, and to combine the good points of both near, end and far end noise ratio, it is proposed to measure noise ratio in the following way.

(d) Tone only on one layer. We require some method of measuring noise ratio so that the unbalances of a quad to other quads of the same layer will not affect the result, while unbalances of a quad to other layers will do so. To obtain this condition, it is proposed that noise ratio be measured on circuits in a given layer with test tone only on that layer. Under this condition, near end noise ratio can be used, because, owing to the fact that only the layer being tested has voltage applied to it, the unbalances to other layers have their full effect. The advantage of near end noise ratio of being approximately constant for different lengths of cable, is therefore obtained by this method.

LENGTH or CABLE - KILOMETRES. F ig : i . Variation of Noise Ratio with length of cable.

There is only one drawback to this method, and that is, that the noise ratio measured in this way on a quad in an.inner layer will be less than the value obtained under actual inductions. This is because under actual conditions an inner layer is only acted upon by the difference in voltage between it and the outer layei, whereas in this measurement the same test voltage is used as for the outer layer. This really means that in actual practice higher unbalances, or a lower noise ratio, can be tolerated for circuits in an inner layer, than for circuits in an outer layer. This drawback to measuring noise ratio in this way can therefore be overcome by using different limits of' noise ratio for circuits in inner and outer layers. 232 In this discussion a layer includes, of course, all layers or quads in a cable which are cross-spliced or inter-connected. 4. Formula for Noise Ratio.—It is instructive to consider the theoretical formula for noise ratio, since it shows how the various cable constants affect the results. The formula for near end ratio when measured as described in (d) above is as follows :—- 1 R

where

2 (cosh 2 /3£N — cos 2 c^N)

}

xo R 2 + o>2 L 2 K » = 4 za.z„ • C — R.M.S. capacity unbalance per loading section. R = R.M.S. resistance unbalance per loading section. L = R.M.S. inductance unbalance per loading section. Zm = Characteristic impedance of metallic circuit. Ze = Characteristic impedance of earth return circuit, i.e., of outer layer-sheath circuit, or inner layer-outer layer circuit. Rx = Impedance of receiver (so that the metallic circuit can be terminated by its characteristic impedance; it is assumed that a transformer of a suitable ratio is inserted between the circuit and RT). j3m = Attenuation constant of metallic circuit per loading section. j8, and ae = Attenuation constant and wave length constant, respectively, of earth circuit.

6 = ta n ~ 1-£y N . = Number of loading sections. Pm It will be seen that there are two terms in this expression, K e depending on the capacity unbalance, and R m depending on the series unbalance. These are each multiplied by a rather complicated function. For ordinary cables, and with unbalances such as normally occur in practice, the K e term is larger than the K m term, so that the latter may be neglected in general. By evaluating the other constants of the cable, therefore, and from the measured value of R, it is possible to determine directly the value of R e or the corresponding value of capacity unbalance. In the case of actual induction, the K e term also predominates, except in the case of a long uniform parallel. Here, in certain cases, it is possible for the K m term to approach the K e term in magnitude so that the series unbalance plays a certain part in the producing noise. Under these conditions, it should be realised that any value of noise ratio measured with artificial tone applied at one point does not give a true criterion of the unbalances producing noise, since the measured value is only affected by the capacity unbalance.

2 3 3 The actual cases where the K m term, becomes as large as the K e term are so few, however, that the method of measuring noise ratio with artificial tone would appear to have a very useful application in general. 5- Variation of Noise Ratio with Frequency.—Noise ratio varies with frequency in much the same way as crosstalk. This is shown by Fig. 2 below. Any single frequency measure­ ment of noise ratio on a given circuit is, therefore, of little value and measurements should either be made with complex tone or a frequency run should be made.

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

FREQUENCY - PERIODS PER SECOND. Fig. 2. Variation of Noise Ratio with Frequency.

6. Conclusions.—The discussion given in this contribution shows that “ noise ratio,” if measured under proper conditions, can be made to serve as a useful criterion of the balance of a telephone circuit from the point of view of noise. These conditions are that tone should be applied only to the layer being tested, and that the noise ratio should be measured at the near end. Under these conditions, the value of noise ratio obtained is reasonably constant with the length of the cable. It is also affected only by those unbalances which produce noise in practice. It would appear, therefore, that the noise ratio, as measured in this way, fulfils all the necessary requirements. No mention has been made of the actual apparatus to be used for measuring noise ratio since any of the well-known methods can be used.

2 3 4 VIII—INDEX.

A ccidental earth : Page N o. Double accidental earth on a three-phase line with neutral point insulated ...... 204 Acoustic shocks, Protective devices against...... 205 Acousto-electric index of a transmitting system, Definition of ...... 21 Arrangements between Administrations for international telephone service, Typical Form of Agreement ...... ' ...... •. .. 197 Articulation and Intelligibility: . • Intelligibility of words ...... ,. . • • ■ . . 22 Intelligibility of phrases ...... 22 Intelligibility : ...... • • • • • ... • • 22 General method to be employed for testing syllable articulation ...... 60 Comparative articulation tests in various languages ...... * .. . . 62 Attenuation constant ...... 22 Attenuation due to echo (“ singing point ”) definition and measurement ...... 81 Attenuation, effective ...... • •. • . 22 Attenuation, image ...... 21

D ibliography ...... •. • • . . 170 -•-^Bourse calls ...... • • • • • • • • .19° Bourse-exchanges ...... • • • • - • 74

ables : C • Cables inserted in open-wire lines, Rules for the construction and loading of ...... 79 Calls with avis d’appel...... •• •• •• -• 186 Bourse-calls ...... ■ . • • •. • • 19° Proposed Regulations for calls originating from or destined to Bourses .. .. ., .. 191 Calls, Maximum duration of ...... • • • • • • • • 196 Calls, Recording the chargeable duration of...... 196 Calls demanded by aeroplane pilots in cases of forced landing ...... 185 Calls w ith preavis ...... • • • • • • • • • ■ • • • • • 188 Carrier current telephony ...... • • • • 69 Circuit assignment charts ...... * .. . . • • • • • • 105-6 Circuit chart ...... • • • • • • • • • • • • • 102—3 Closing Session, Minutes of the ...... •...... • • • • • • 207 Co-existence of telephone and telegraph circuits in the same cable ...... 119 Simultaneous telegraphy and telephony (over the same conductors) or infra-acoustic telegraphy 119 Co-existent telegraphy and telephony (over separate conductors) .. . . ■ ...... 120 Voice-frequency telegraphy ...... ' ...... 120 Conversion table of transmission units (nepers and decibels) ...... 20 Correctors, special, for relaying broadcast transmission ...... 126 Crosstalk : Definition of Crosstalk ...... ■ ,. .. •. .. 21 Measurement of Crosstalk ...... •• .. .. •• .. no

D amping, definition of ...... • • ...... 22 Decibels : ...... •. • • .. ' ...... •. 20 Delegates : * List of Delegates from Telephone Administrations and Operating Companies ...... 1 List of Delegates from Electro-technical Associations ...... • • 4 Directories, Telephone ...... ‘ ...... • • • 184 235 Page No. P lectro-acoustic index of a receiving system, Definition of ...... 21 •‘-'Emergency lines : ...... 182 Method, of use of ...... 183 European Master Reference System for Telephone Transmission (" SFERT ”) ...... 23 Adjustment of the “ SFERT ” ...... •...... _ . . 28 Expenses involved by the C.C.I. Distribution of the expenses incurred in the operation of the C.C.I...... 13 Distribution of expenses for the maintenance of the European Master Reference System for Telephone Transmission ...... 13 Expressions used in questions of telephone transmission, Definition of some ...... 2.0

Oactory lengths of international cables ...... ’...... 129 Fixed time calls by subscription during the heavy traffic period ...... 184 Forced landing, Calls demanded by aeroplane pilots in cases of ...... 185 Frequency : Method of expressing frequency...... 19 Cut-off frequency ...... 135, 138, 141

Gain, Definition of

Harmonics due to direct current traction installations

Impedance ...... 127,128,129 * Impedance Unbalance, measurement of ...... 84, 88 Induced noise on open-wire lines and in cable circuits ...... 201 Induced noise, Permissible limits of ...... 201 Instructions : Suggested Instructions for putting into service and maintaining international telephone circuits 96 Instructions to Broadcasting Organisations and to Telephone Administrations for putting into operation a connection to be used for broadcast transmission, and for the re-establishment of this connection in its normal service ...... 112 Intelligibility ...... 22 International Bureau of the Telegraph Union : Collaboration between the International Consultative Committee for Long-Distance Telephone Communications and the ...... 16

I evel, Definition of 21 ‘-'Level diagrams 101, 107-108 L ines : Open-wire lines ; Setting up of ...... ■ . . 77 Loading of .. .. v ...... 77 Cables inserted in ...... 79 Mixed lines : Rules for the construction and loading of cables inserted in open-wire lines. . 79 Loading of circuits : Loading coils 143 System No. Ia 135 System No. Ib .. 138 System No. II 141 Loading coils, Inductance of 135, 138, 141, 144 Loading coil spacing . . 135, 138, 141 Local exchanges : General conditions which should be satisfied by the new Bourse-exchanges regarding the use of international circuits ...... 74 Loss, Definition of ...... 22 2 3 6 Page No. A ll ain ten an ce : j v * Question of maintenance of lines and installations .18 Advice of the C.C.I. concerning questions of maintenance 80 Membership of the C.C.I. of Private Telephone Organisations which operate in countries where no State Telephone Administration exists ...... 14 Minutes of conversation : Checking the number of minutes of conversation between terminal exchanges on international lines ...... 197 Mutual induction : . Determination of the coefficient of mutual induction...... 205

] \J epers Noise voltage : Various methods of measuring noise voltage 223 Length of telephone circuits to be used in the calculation of noise voltage 206 Nomenclature of international circuits, Establishment of the 177 Normal calling intensity to be used in phonometric tests 5i

Qpening Session, Minutes of the ...... O p e ra tio n : Methods of operation 185 Questions of operation 185 Organisation : Organisation and working of the C.C.I. . . IX Questions of general organisation 11 Advice of the C.C.I. concerning questions of general organisation 11

■parallelism: Steps to be taken in the case of parallelism between international telephone lines and direct current traction lines ...... ; . 201 Phase compensation 142 Picture transmission : Conditions relating to picture transmission over telephone circuits 72 Picture transmission between correspondents over general service circuits; conditions relating to acceptance and tariffs ...... 195 Private Telephone Organisations : Representation on the C.C.I. of private telephone organisations operating in countries where a State Telephone Administration exists ...... 14 Protection of lines : Calculation of noise voltage on telephone lines, taking into account the disposition of the conductors of a two-wire single-phase line and of a three-phase line 202 Comparative study of various protective devices against acoustic shocks by exchange of apparatus between interested administrations ...... 205 Danger caused by a double accidental earth of a three-phase line with neutral point insulated 204 Determination of the coefficient of mutual induction 205 Disturbing effect of harmonics from direct current traction installations : 200 Disturbing current equivalent 200 Disturbing .voltage equivalent ...... • 200 Telephone interference factor of the wave form of the current. . 200 Telephone interference factor of the wave form of the voltage. . 200 Guiding Principles for the protection of lines 200 Modifications to be made to the Guiding Principles for the protection of lines 200 ■ Permissible limits for induced noise on open-wire circuits and on cable circuits 201

uestions of interest to the C.C.I. and other international organisations, Methods to be followed Q in the study of .. i 5 237 Page No. D adio-broadcast transmission : ' Alterations made in cable circuits in order that they may be suitable for broadcast transmission 70 Conditions which open-wire lines must fulfil in order to be used for ...... 70 Electrical conditions to be considered as a criterion for the good condition of lines for relaying 71 Essential clauses of a typical specification for the supply of repeaters and special correctors for the relay of ...... 126 Maintenance of circuits used for the relaying of . . • ...... ■ .. i 'i i Division of responsibility between Telephone Administrations and Radio Broadcast services in Instructions to Broadcasting Organisations and to Telephone Administrations. (See also Instructions) ...... 112 Maintenance tests ...... m Technical responsibility in connection with the renting of international telephone circuits to Broadcasting Authorities...... •• m Maximum and minimum transmission levels to be adopted for ...... 69 Radio-telephony, Co-ordination of radio-telephony and telephone systems ...... 120 Rates and Tariffs: Rates applicable between primary zones of two contiguous countries ...... 194 Rates applicable to press calls ...... • . . 194 Rates applicable to.calls originating from, or to be completed at, a.public call box . . . . 194 Reference equivalent, Definition of ...... 21 Reference systems : Calibration of reference systems...... 28 Comparison of reference systems with the “ SFERT ” ...... 28 Conditions which should be fulfilled by reference systems ...... 23 Object of reference systems ...... 23 Setting up of reference systems ...... 23 Relative equivalent, Definition of ...... 21 Repeater Gain : Automatic gain regulation of cord circuit repeaters. (Note of the I.S.E.C.) ...... 150 Automatic gain regulation ...... 151 Gain control of cord circuit repeaters ...... 150 Gain reduction key ...... 153 Repeaters : Cord circuit repeaters : Cord circuit repeaters used at Amsterdam, and operating always at the same gain.. .. 145 System of cord circuit repeaters used in Great Britain; gain control; connection of four- wire circuits ...... •. . • 146 Four-wire repeaters ...... 128 High frequency repeaters...... •• . • 125 Repeaters for relaying broadcast transmission...... • .. 126 Two-wire repeaters ...... 127 Repeater sections, Essential clauses for a typical specification for ...... 134 Repeater stations, Compensation of the effects due to temperature variations ...... 76 Repeating Coils (Toroidal coils) ...... " ...... • . . 48 Representatives invited to the. Plenary Session in Berlin ...... 1 Representatives of telephone organisations not belonging to the C.C.I...... 4 Representatives of the International Bureau of the Telegraphic Union .. . . : . . . . . 4 Representatives of the International Consultative Technical Committee on Radio Communications 4 Representatives of the International Consultative Committee for Telegraph Communications . . 4 Revision of International Regulations (Telephone Section), Committee on ...... 16 Routine tests : Programme of routine tests." (See also under Tests) ...... • • • 109

Qchematic plan of international cables, Establishment of ...... • • • • • 177 ^-'Service, Typical form of agreement ...... • • • • 197 Singing point (attenuation due to echo), Definition and measurement of ...... 81 Singing point test set ...... • •. • • 88 Standardisation of long distance telephone systems, Possibility of . . .. • • • • • . 67 Subscribers’ instruments : Tests on subscribers’ instruments and lines in operation. (See also under Transmission efficiency) 73

2 3 8 Page N o. Subscribers' numbers, Enunciation of ...... 192 Subscription call, Establishment of a subscription call with or from telephone stations other than those indicated in the subscribers’ agreement ...... ' ...... 185

'T'echnical organisation : Technical collaboration between the C.C.I.. and technical organisations dealing with questions likely to have a bearing on international telephony *,...... 15 Telephone Directories : Establishment and purchase of ...... ' ...... 184 Temperature variations, Compensation in repeater stations for the effects due to ...... 76 T ests : Programme of routine tests ...... 109 Routine tests to be made in order to ensure satisfactory operations of the circuits : Daily tests; weekly tests ; monthly tests ; quarterly tests; half-yearly tests ; yearly tests; sundry tests; localisation of faults ...... 98 Tests on subscribers’ instruments and lines in operation ...... 73 Toll exchanges : Conditions to be satisfied by cord circuit repeater positions from the point of view of facilities for regulation of the repeater, as well as for supervision, and charging of calls ...... 75 Conditions to be satisfied by international positions, as regards the type of operator’s set and the transmission losses due to the operator listening on the line ...... 75 Traffic : Questions of Traffic, Operation and Tariffs ...... 177 Supervision of international telephone traffic, form of report to be used by exchanges .. .. 198 Traffic statistics : ...... 198 Supervision ...... 198 Transient phenomena .. ,...... 67 'Transmission : Transmission efficiency : Information concerning methods utilised in the U.S.A. for testing subscribers’ instruments and lines in operation ...... 169 B.P.O. method of measuring the efficiency of a subscriber’s station from the central office by means of alternating current...... 156 B.P.O. method of measuring the transmission efficiency of a subscriber’s installation from- the central office ...... ;...... 154 Method adopted by the French Telephone Administration for testing subscribers’ installations in operation...... 162 . Method of measuring by speech test, the sending and receiving efficiency of a subscriber’s installation 'in situ (alternative to the preceding method) ...... 157 Method of the German Administration for testing complete subscribers’ installations from the local telephone exchange ...... 168 * Transmission equivalent: Practical limits of transmission equivalents ...... 66 Transmission level, Definition of ...... 21 Transmission measurements, Description of apparatus for making ...... 113 Transmission questions : ...... 1 8 List of Appendices on ...... 145 Transmission standards ...... 19 Transmission systems : Brief description of the “ SETEM working standard system ...... 51 Comparison of the “ SETAC ” with the “ SFERT ” ...... 33 Comparison of the “ SETEM ” with the " SFERT ”.. .. ' ...... 54 General rules concerning the composition of transmission systems ...... 69 Instructions for the use of a “ SETAC ” ...... , . . 36 Instructions for setting up and using a “ SETEM ...... 57 Periodic calibration of standard instruments by the “ SFERT ” Laboratory ...... 59 Working standards employing carbon transmitters (“ SETAC ”) : description of . . .. 32 Working standard systems using electro-magnetic transmitters (" SETEM ”) ...... 51 Transmission units ...... ’. 19

2 3 9 Page No. Typical specifications : Essential clauses of a specification for the supply of repeating coils (toroidal coils) .. .. 48 Essential clauses for. a typical specification generally applying to factory lengths of international cables of the quadded type ...... '. .. .. 129 Essential clauses of a typical specification for the supply of four-wire telephone repeaters .. 128 Essential clauses for a typical specification of general application to loading coils for inter­ national telephone cables ...... 143 Instructions for drawing up a typical^ specification for the supply of a multiple telephone installation using high frequency carrier currents for international service ...... 123 Instructions for drawing up a typical specification for the supply of a high frequency repeater station ...... 125 Essential clauses for a typical specification for repeater sections of loaded internatonal cable . . 134 Essential clauses of a typical specification for the supply of repeaters and special correctors for the relay of radio-broadcast transmissions ...... '...... 126 Essential clauses of a typical specification for the supply of two-wire telephone repeaters . . 127 System No. Ia : Loading coil spacing; loading coil inductances; cut-off frequency; impedance; attenuation constant ...... 135 System No. Ib : Loading coil spacing; loading coil inductances; cut-off frequency; impedance; attenuation; cross-talk ...... 138 System No. II : Loading coil spacing; loading coil inductances; cut-off frequency; impedance; attenuation; phase.compensation; cross-talk ...... 141

I T nits of transmission : ^ Conversion table of nepers and decibels ...... 20

V I faiting times, Equalising waiting times in both directions ...... 193 ** Working standards : ...... 28 Comparison of working standards by comparison with the “ SFERT ” ...... 28 Experiments to determine the normal calling intensity to be used in phonometric tests . . 51 Working standards employing carbon transmitters (“ SETAC ”) ...... 32 Working standards using electro-magnetic transmitters (“ SETEM ”) ...... 51

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