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TE liPU O ’.lIQUES ii DBfiHDE C1STAI3CE. ' t

INTERNATIONAL ADVISORY COMPVIITTEE

ON

LONG DISTANCE TELEPHONY IN EUROPE.

C o n f e r e n c e

(HELD IN PARIS June 22nd—29th, 1925).

MINUTES OF PROCEEDINGS.

ENGLISH VERSION.

VINCENT CROOKS, DAY & SON, LTD., Llj ccm rrtf consulpatif international des communications

T&J&H0NK8JES A GRANDE DISTANCE.

INCERNAXIONAL ADVISORY COMMITTEE

OH

LONG DISTANCE TELEPHONY IN EUROPE.

- CONFERENCE HELD IN PARIS JUNE 22nd*~29th, 1925.

MINUTES OF PROCEEDINGS.

ENGLISH VERSION.

(The O fficial Text i3 in French) I.

CEHEHAL INDEX.

Page: Introduction ...... 1

List of Delegates (Appendix I) ...... 4

SECTION I - TRANSMISSION;

Specification of International Telephone Cables, Apparatus and Methods of Measurement for Maintenance of Inter­ national Circuits ...... 6

Part I ...... B

(I) Choice of Transmission Unit ...... ' 8

(II) Questions relating to the working of International Circuits ...... 9

(ill) Measurement of the efficiency of Subscribers’ Apparatus, etc...... 14

Part II. System’s Specification ...... 16

•Part III. Methods of Measurement and Apparatus for Maintenance of International Circuits ...... 18

Apparatus for Routine Tests ...... 20

Extract from Minutes of Conference of Permanent Commis­ sion of C.C.I. held in Paris Motember/December 1924 (Appendix Z) ...... 31

Report submitted to Permanent Commission by Rapporteurs o f Germany and Great B r ita in on TU ...... 32

Appendix 5. Signalling with Currents, having an interrupted frequency of 1000 cycles per second ...... 40

Appendix 4. Essential clauses for a typical specification generally applying to factory lengths of international telephone cables of the quadded type ...... 42

Appendix 5. Essential clauses for a typical specification of general application to loading coils for international telephone cables ...... *..... 50

Appendix 6 . Essential clauses for a typical specification for repeater sections of loaded international telephone ca b les ...... 53

Appendix 7. Essential clauses for a typical specification for the supply of 2-wire telephone repeaters ...... 63

Appendix 8 . Essential clauses for a typical specification for the supply of 4^wire telephone repeaters ...... 65

Appendix 9. A method for the measurement of the trans­ mission efficiency of telephone apparatus at a subscriber’s office - by A.J. Aldridge, A.C.G.I. and A. Hudson. 8 -Sc. 67 II.

Page >

Ann&idtx 10, Method of testing subscfibers* instruments from the central office ...... 72

SECTION 2 - INTERFERENCE HUM POWER CIRCOITS:

III. Protection of telephone lines from Interference . by hi^i power installations- ...... 7 4 ^

Guiding principles to be observed in the adoption of measures designed for the protection of telephone lines from interference caused by high power Installations .... 75

I. Measures relating to telephone lines and / Installations ...... 76

II. Measures relating to high tension installations and to traction installations ...... 77

III. Measures to be taken in cases where heavy current or high tension lines run parallel to overhead telephone lines ...... 60

Section A - Buies to be adopted In examining fresh schemes of power lines which w ill run parallel with telephone lines ...... 81

■Section B - fiules relating to existing parallel isms .. 86

IV» Measures to be taken in case of proximities between power lines and telephone cables ...... 88

Appendix 11 (with supplement). Determination of the symmetry to earth of Trunk Telephone lin e s ...... 90

Supplement 10 Appendix' 11. Motes on testing"the symmetxy of telephone lines with respect to earth ...... 94

Appendix 1% (with Supplements 1 and 2). Examination of the conditions under which proximity may be permitted between high tension power lines - poly-phase or single­ phase alternating currents, symmetrical and not connected m etallically to earth at any point - and telephone lines 100

Sunniemeut 1 to Appendix IX. Determination of the Characteristic Coefficient of Exposure to Banger ...... 105

Supplement 2 to Appendix 12. Development of the formulae used for determining electric induction, etc...... 106

A d d ition al S h eets (Supplement 2 o f Appendix" 1 2 ) ...... 121

Appendix IS. Examination of the conditions under which Proximity may be allowable between Telephone Lines and 3-phase or Single-phase High Tension Alternating current Linas which have an Earthed Neutral Point ...... 125

Anneiidix 14. Examination of the conditions under which Proximity (Parallelism; between Alternating Current Sintfle-uhase Hallways and 3—phase Hallways with Bail- HetUrn, on the one hand, and Telephone Lines, on the other hand, may be perm itted ...... *...... 129 P age:

. Appendix 15. Measurement of Interference Voltages induced in Telephdne Circuits 135

Appendix 16. Deterrsinati on of the Degree of Unbalance of Telephone Circuits with reference to Disturbing Lines ...... • ...... 139

SECTION 5 - TARIFFS AND TRAFFIC:

IV. Establishment of Variable Tariffs according to the time of day. Facilities to be- offered to the Public ...... 143

Telegraphic Preparation of Telephone Cells ..... 145

Statistics of Telephone Traffic ...... 146

Exploitation of International Circuits ...... 148

Calculat ion of Int ©mational Charges • • ...... 148

Minimum Traffic to be assured to -Transit Countrios 149

Periodic Meetings between Supervisors of Inter­ national Telephone' Exchanges ...... 152

/' International Code cf Telephone Regulations .... 152

Tables 1-A and 1 -8 ...... 154

Tablo 2 ...... 155

Tables 3 and 4 • 156

• Table 5 ...... *...... 157 International Advisory Communications on Long Distance Telephony in Europe.

Conference held in Paris 22-29 June. 1925.

INTRODUCTION.

- The second conference o f the above ^Committee was h eld in P a ris

from the 22nd to 29th June, 1925.

A 11 at of the Delegates attending is attached hereto. (Appendix I).

At the opening meeting, on the 22nd June, 1925, Id. Milon

we 1 corned the Delegates and said that he was particularly proud, as Chief

of the French Delegation, to be able to emphasise the perfect cordiality which had characterised previous conferences of the Coranittee.

He desired particularly to extend a welcome to the represen­

tatives of the additional nations which had Joined the Committee, viz:-

Lithuania and Esthonia, while regretting the absence of Rumania, which

absence he hoped would merely be temporary.

On the motion of the head of the British Delegation, M. Milon was re-elected president for the forthcoming year.

M. M ilon,.for the benefit of the nations who were not repre­

sented on the "Permanent Commission" of the C.C.I , described the worlr which had been done by that Ccoanlssion, which had assembled in Paris from 24th November to 1st December, 1924. The reports furnished by the Permanent Ccaraaissiou on .the subjects indicated below .would form the principal basis of the deliberations of the Conference:-

(1) D ra ftin g o f a s in g le and coherent programme of work to be done in the construction of international lines in the immediate and distant future.

(2) Construction of a diagrammatic map of lines (overhead or underground), to be laid during the year 1925/26 in Europe.

(3) Drafting of a typical specification for Interactional

European Telephone Cables, together with their accessories (Loading - 2 -

Coils and Repeaters).

(4) Choice of methods and measuring apparatus necessary for the

supervision and maintenance of telephone lines and plant.

(5) Investigation of various methods of measuring the efficiency

of subscribers* apparatus and of the transmission equivalent of the

various pieces of apparatus employed in telephonic communication.

( 6 ) Choice of a Unit of Transmission#

(7) Heasures to.be taken for protecting international telephone

lines from the disturbing effects of high-current or high-tension

power installations.

(8 ) Determination of the lim its which may be permitted' for induced

voltages and noises on international circuits.

(9) Study of expeditious methods of working international tele­ phone circuits, and, particularly, of the advisability of preparing

international telephone calls telegraphically.

( 10) Establishment of rational and uniform bases of calculation of charges for international telephone calls.

(11) The question of minimum traffic to be assured to transit * n. c o u n tr ie s.

In addition to the above, the Permanent Commission con­ sidered it desirable to study the following supplementary questions*-

(a) Choice of the uniform value to be adopted for real or apparent impedance (measured through itransfoncers, suitably adapted) of international circuits.

(b) The determination of the maximum values for which a guarantee may bo exacted for cross-talk, measured between any two circuits on sections of cable included between two successive telephone repeaters, placed at a greater distance than 100 Kilometres from each other.

(c) Standardisation of the graduation of the apparatus employed for adjusting amplification on telephone repeaters. (d) Choice of a single frequency for harmonic signalling currents.

(e) Choice of a single frequency for measuring currents.

(f) Publication of a nomenclature of international circuits at

present existing in Europe.

(g) Publication of statistics of international telephone traffic.

(h) Drafting of a map showing existing or proposed international

telephone cables.

(i) ' Publication of a vocabulary of expressions and symbols of technical telephony in several languages.

These various documents had either been printed already or are in course of printing. Copies w ill be sent very shortly to the various telephone administrations belonging to bi e Committee, and copies w ill be on sale for the public.

The Committee was then sub-divided into three Sub-Commissions

1st Sub-Connnission - to deal with;-

Measures to,be taken for protecting telephone lines fran the disturbing effects of high current or high tension power installations.

2nd Sub-Commission - to d ea l w ith :-

Transmission (Specifications for the supply of linos and their accessories).

3rd Sub-Commissloh - to deal with:-

Traffic, Exploitation and General Administration. -4> Appendix I.

LIST OF, DELEGATES.

GERMANY. Dr. Craemer, M inisterial Counsellor, Head of Department, Ministry of Posts* Professor Dr. Breisig', M inisterial Counsellor. Mr. Brauns, M inisterial Counsellor. Mr. Stegmann, M inisterial Counsellor. Mr. Dohmen, C ounsellor Higher Grade, o f P o s ts . Mr. HOpfner, Counsellor Higher Grade, of Posts. Mr. Wiehl, Counsellor of Posts*

AUSTRIA. Mr. E. Schwanzara, Engineer, M inisterial Counsellor. Dr. Hugo G e lsa l, M in iste r ia l C ou n sellor.

BELGIUM. Mr. J. Dethioux, Principal Engineer of Telephones, Director of Administration. Mr. Bocquet, Principal Engineer of Telephones, Inspector Administration. Mr. Fossion, Head of Department. • DENMARK. Mr. S.P. Had sen, Telegraph and Telephone Engineer.

SPAIN* Mr. A. #Nieto, Head of Department of Interneti onal Service, Chief of Telephone Section.

ESTHONIA. Mr. G. Jallajas, Electrical Engineer, Diiw*,.or-General of Posts and Telegraphs.

FINLAND.

FRANCS. Mr* Milon, Principal Engineer, Director of Telephone Exploitation, Ministry of Posts and Telegraphs. Mr. Paney, Inspector General, Director of Higher .School and of the Investigation and Technical Research Service for Posts and Telegraphs. Mr. Drouet, Principal Engineer, Director of Tele­ phone Service, Paris. Mr. Rochas, Principal Engineer, Director of Technical Services in the Suburban Area of Paris. Mr. Gellee, Departmental Head, Directorate of Telephonic Exploitation. Mr. Lange, Telegraph Engineer.

GREAT BRITAIN. Colonel Purves, The Engineer-in-Chief of the British Post Office. Mr. F.E.S. Grant, Head of Department, Secretariat of the Post Office. Mr. A.3. Hart, Post Office Engineer, Mr. C. Robinson, Post Office Engineer. Mr. H.G. Tray foot, Post Office Inspector of Traffic. Mr. S.C. Bartholomew, Post Office Engineer. Mr. B.J. Stevenson, Post O ffice E ngineer.

HOHQIRY. Under Secretaiy /Ot State, F. Kol, Head of Department of Telegraphs and Telephones. Chief Engineer Ivan Tomits, Head of Eleotrioal Section of Experimental Station.

ITALY* Mr. Cesare Albanese, Head of Section, Higher Institute of Posts, Telegraphs and Telephones.

/ . LETTLAND* Mr. A. Auzin, Electrical Engineer, Director-General of Posts and Telegraphs. - 5 -

l it h u An i a . Mr.. Gaetan Dobevitch, Engineering Counsellor.

LUXffkiBURG. Hr. Leon Klein, Inspector of Telegraphs.

XCWJBU Mr* T. Bngsefc, General Secretary to Telegraph Administration. Mr* A b lld .

HOLUKD. Mr, S .J .J .H . Van Embden, In sp ector General o f Telephones. Mr. Jnr.. VJtf.'Se 3rauw, Chief Engineer of Telegraphs.. Mr. E.F. Petrit 3ch, Telegraph Engineer. Mr. R. -Santing, Divisional Chief, Central Administra­ tion of Posts and Telegraphs.

POLAND. Mr. Jachimski, Engineer of Telegraph Construction, General Administration of Posts and Telegraphs, Warsaw. Mr. Zuchmantowitoz, Principal Engineer of Telegraph and..Telephone Construction, Warsaw Administration.

RQUHAHIA.

SSmS-GKOATPS - Mr. Georgevitch, Director of Telegraphs and Telephones. SLOVENES. Mr. Popovitch, Head of Telephone Service, Minister o f P o sts and T elegraph s.

SWEDEN. Mr. PanTJohan Wiihelra Hallgren, Head of Lines Section, General Administration of Telegraphs, Sweden. Mr. Anders Lignell, Director of Telephones, Stockholm. Mr. Arvid Viktor Abraham Holmgren, Eoad of Department, General Administration of Telegraphs. Mr. Sven Backelin, Controller of Telephones, Stockholm.

SWITZERLAND. Mr. A. Muri, Head cif Technical Section, General Administration of Telegraphs, Switzerland. Mr. J. Forrer, Head of Electro-Technical Experimental Section and of Control of Material. Mr. Moeckli, Head of Telephone Department.

OLEGHO-SLOV AKIA• Mr. B. Chooholin, M inisterial Counsellor, Engineer. Mr. Francois Schneider, Counsellor of Construction, E ngineer.

$ —6—

. LIST 01? EXPERTS OP INDUSTRY ENGAGED IN CONSTRUCTION AND MANUFACTURE OF TELEPHONE MATERIAL.

Director Ltischer, Messrs. Siemena and KalskB. Director Dr. 3churer, Messrs. Pelten & Guilleaume. Dr. Jordan, Allgemeine EloktrizitStsgesellschaft. P^lnoipal Engineers,. Messrs. Kjxpfmtlller and Pohlmann, Messrs. Siemens and Halaka.

'BELGIUM. Mr. Ronlet, Engineer, Ateliers de Constructions Electriques de Charleroi Ltd.

FRANCS. Mr. Viard, Principal Engineer, "Lignes T^ldgraphiques et T^i^phoniques” Ccy. Mr. Leduc, E ngineer, Head o f Transm ission S e r v ic e , "Li&nea Tdl^graphiques st T^l^phoniques" Coy. kr. Cahen, Principal Telegraph Engineer, Director of Investigations for Telegraph and Telephone L ia iso n s. Mr. Cordier, Engineer, "Lignes SMl^phoniques Terrestres et Sous-Marines (T^l^termar)" Cqy.

GILSAT BRIT AIK. Mr. P. Gill ) Mr. P.E. Erikson ) International Western Electric Co. Mr. S.II. Cattersonj

k r . H.T. Warren . _ , nlA/k. . nrt Ur. H.C. Haffiim Clark) 0eaeral 31a0trl0 C°‘

Captain P. Dunsheath - Henley* s Telegraph Works, London.

HUNGARY. Mr. Joseph II0II 03, Consulting Engineer, Incandescent Lamp and Electricity Co. L td . of Messrs. Felten and Guilleaume and Messrs. Siemens-dchuckort {Hungarian Eleotric Co.) Mr. 3^1a Kalasz, Engineer, Director of the Incandescent Lamp and E lectricity Co. Ltd.

ITftLY. Mr. Louis Emanueli, Engineer, "Italiana Retl Telefon- iche Interurbane" Coy.

CZECHO-3I0VAKIA. Dr; Konstantinovrsky, Cable Y/orka Co. Ltd., Brat i slava-Pre sbourg. Mr. Hugo Sonnenfeld, Engineer, Authorised Representative of Cable Works, C9 . Ltd., Bratislava-Presbourg.

LE IE GATES OF -INTERNATIONAL CONFERENCE OP LARGE SYSTEMS OF HIGH TENSION ELEOTRIOAL ENERGY.

Mr. Brylinski, General Delegate of Professional Syndicate of Producers and Distributors of Electrical Energy. Mr. Otto Meyer, Electricity Director, Strassburg. Mr* Tribot Laspiere, General Secretaiy of International Conference of High Tension Electrical Systems. -7 -

IfflgQjffES OF IKPERIIATIONAL US I ON OF RAILWAYS.

Mr. Pe Villeneuve, Assistant Principal Engineer of Material and Traction S err ice, Midi Railway Co. (Prance). ^M r.Gillee, Principal Engineer of Electrical Permanent Vfey Service, Midi Railway Co. (France). Mr. Theodore Muller, Engineer, Assistant to Principal Permanent Way Engineer of Swiss Federal Railways, (Switzerland). i^r, Ronrra&ldo Itegnoni, Engineer to Italian State Railways, ( I t a ly ) . Mr. Alfredo lAicarelli, Engineer to Italian State Railways, (Italy). - 8 -

' SECTION 1 TRANSMISSION.

specification o international telethons c a b ie s. APPARATUS AND METHODS OF l&ASURKKENiT FOR MAINTEN­ ANCE OF INTERNATIOSTAL CIRCUITS,

After having examined communications, received from various

Administrations, til© C.C.I. considered it desirable to draw up rules

and specifications relating to International cables and to the methods

and measuring Apparatus to be used for maintaining international cir­

cuits. The C.C.I. has endeavoured to draft rules end specifications

in such a manner as to ensure a sufficient degree of uniformity of method, while the various Administrations should be as free as possible to adopt their own particular methods.

Part I .

The first part of these minutes contain recommendations and advice which complete, render more precise, or modify, according to circumstances, the recommendations made by the C.C.I. in the course of; its conference on 29th April - 14th May 1924. These may be grouped under the following three-titles

(I) • Choice of a transmission unit.

(II) Various questions relating to the working of international circuits.

(ill) Measurement of the efficiency of subscribers’ apparatus, and transmission equivalent of subscribers’ - circuits.*

(I) The choice of a unit of transmission (A coiy of an English version of the report of the Permanent Commission of the C.G.I. is appended - {Appendix 2).

The C.C.I.,

HAVING REGARD TO THE FACTS, ■

that it is desirable to have a single transmission unit not only in Europe, but also throughout the world, and that such a result could onlyvbe obtained after having heard, in particular, an expression of views on the part of the American Experts themselves, with respect to their attitude upon this question,

g a v e e x p r e s s i o n t o t h e o p i n i o n - 9 -

(i) that no definite decision should he taken In respect of

a Unit of transmission before the next meeting of a

s p e c ia l Sub-Garcrais si bn, to which American E xperts w i l l

be invited.

(ii) that in the meantime, it is desirable to conform to the

general opinion expressed at the Conference of Technical

Experts held in Paris in 1910 and to express in Specifi­

cations transmission data in natural units ("h'*).

(Ili Various questions relating to the working of international circuits.

(a) Method of expressing Frequency.

The C.C.I.,

HAVING REGARD TO THE PACTS,

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, and that the first method has the advantage of giving a physical representation more precise than the second,

EXPRESSED THE OPINION

that, all things considered, it is preferable to express fre­ quency in periods per second, in accordance with common practice.

(b) Frequency of Ringing Currents.

A cojy of the conclusions arrived at by the Permanent. Commis­ sion at their session November-December, 1924, is appended. (Appendix 3).

The C.C.I.,

HAVING REGARD TO THE PACTS,

that,, for convenience of international relations, it is desirable to adopt a single frequency for ringing, that this frequency should be sufficiently high .for ringing currents to be transmitted by repeaters under normal conditions, that experiments made in various countries with currents of 500 periods frequency per second have given satisfactory results,-that the disturbing effect of cross-talk'due to -10-

currents of frequency of 500 periods per second is generally less than

the cross-talk due to currents of a higher frequency, that in view of

facilitating the adjustment of apparatus used for receiving calls, it

is desirable that in the present state of telephone engineering

development to modulate or interrupt at low frequency, the currents

of musical frequency,

EXPRESSED THE OPINION

that for currents, used for international communications,

and, for the time being, a ringing current of a frequeney of 500

periods per second, modulated or interrupted, should be chosen in

accordance with a frequency between 15 and 25 periods per second.

(c) Choice of a single Frequency for Measurement Currents.

.After having read the reports of the British and German

Delegations, and having taken advice from the-delegates of the various

Administrations, the Sub-Commission proposed to give expression to the

following opinion

The C. C•X•*

HAVING REGARD TO THE FACTS,

that It is desirable to have, for ordinary measurement, a

current of definite frequency - and a frequency which is always the

same - that this frequency should be as near as possible to that of . the average frequency of spoken sounds, that it has been provisionally admitted, up to the present, that this frequency should be 800 periods per second and that the experience hitherto acquired with currents of different frequency appears to be still inadequate to enable one to consider a change in the present practice,

GAVE EXPRESSION TO THE OPINION

that, provisionally, currents of a frequency of 800 periods per second should s till be employed for ordinary measurement, that the various Administrations should be invited’to continue investiga­ tions, which they have already undertaken on this question, arid to -1 1 -

state, later, their opinion,

(d) Repeaters.

Characteristics of Amplification.

The C.C.I. expressed the opinion that repeaters should ensure

a faithful reproduction of the human voice. I.e. transmit telephone

currents of such a type that the total resulting attenuation of tele­

phonic communication between tejroinsl exchanges should not differ by

more than

b = 1 for any two frequencies between the intervals of

frequency indicated below:

Two-wire telephone circuits - 300 to 2000 periods per second.

Four-w ire telep h on e c ir c u it s (medium heavy loaded) 300 - 2,200 periods per second.

Four-wire telephone circuits (extra light loaded) 300 - 2,500 periods per second.

In order to obtain this result, amplifiers which magnify, in

the same proportion, all the frequencies within these intervals {and,

i f necessary, associated with independent correcting devices) may be

employed, or amplifiers constructed in such a manner as to affect the necessary correction may be used.

Device for Adjusting Amplification.

The C.C.I.,.

HAVING REGARD TO THE FACTS,

that it would be desirable that a uniform method of adjusting amplification should be employed for regulating the gain of all tele­ phone repeaters.

th a t, in a n y case, the general opinion on the question is not sufficiently definite to enable a single solution to be arrived at, at the present time,

EXPRESSED THE OPINION

that the most important manufacturers of telephone material in various countries should get into touch with one another, with a -1 2 -

view to arriving at an agreement on this question, and should communicate

their proposals to the C.G.I.,

that, moreover, although this standardisation may chiefly con­

cern the manufacture of apparatus, this is an entirely independent question

from that of the methods of exploitation and maintenance which may he

ultimately decided upon.

Maintenance of International Circuits: Control Station.

' The C.C.X.,

HAVING REGARD TO THE PACTS,

that, in so far as the maintenance of.international circuits

Is concerned, it w ill he necessary to work out a complete system of

tests which, w ill pemit of the rapid localisation of faults, and for

the adjustment of questions of detail relating to each group of circuits,

^that, independently of this, general rules.may also he recom­

mended to serve as a basis for such ^rsteros of tests,

EXPRESSED THE OPINION

that one of the terminal stations of each group of circuits,

termed the ''Control Station" (Station Direct rice) for that group of

circuits, in accordance with agreements arrived at between the Adminis­

trations Interested, shall be entrusted with maintenance control. This

station w ill be responsible for the following matters

(1) D ra ftin g o f a programme o f t e s t s in con jun ction w ith a l l

the other stations interested.

(2) Preserving reports of these tests, and ensuring that they w ill be carried out in accordance with the procedure laid down.

(3) Supervision of the localisation of faults.

The Administration in whose territory lies the section of line in which the fault is found w ill be responsible for removing the fault. The Control Station will be informed of the cause of the fault, and of the time at which it has been removed. The Control - 1 3 -

Station will keep a record of all faults.

(4) The giving of instructions with respect to the position on

the scale of the apparatus used for adjusting' amplification. This

adjustment* w ill not be changed without the authority of the Control

S ta tio n . j

(5) The Control Station will be responsible for maintaining the

normal transmission efficiency of each of the circuits, as well as

the organization of a system of tests, of such a nature that the

periods during which the circuit cay be out of use in consequence of

the tests may be9 reduced to a minimum.

(f) Uniform value to be given to the Impedance of International Circuits.

The C .O .I.,

HAYING REGARD TO THE FACTS,

that* for various'general reasons, it is desirable to main­

tain a uniform value of impedance for all international circuits measured from a Repeater Station, or from one of the terminal exchanges, by the suitable adaptation of Intermediate transformers,

that this impedance should be chosen in such a manner ss to avoid, as far as possible, reflection losses at the ends of the long distance circuit 3 , i.e ., th£t its value should be as near as possible to that of the- local circuits to which these long distance circuits are generally connected,

that it has been found from tests carried out in various countries that the values of the impedance of local circuits varies appreciably/with the frequency of the measuring current, with the length of the circuits and with the nature of the subscriber's apparatus,

that, in spite of the lack of precise infounation, it is, however, possible to give, provisionally, to this typical impedance an average value sufficiently approximate for practical- needs, and -1 4 -

that, in many cases, 'satisfactory results have already been obtained,

that t h is ch oice (which, however'* i s su bject to r e v isio n )

w ill itself constitute an experimental basis for the^iuture,

EXPRESSED THE OPINION

that the value to be given to the apparent impedance of

international circuity (measured across the tenoinnl transformers,

and measured or calculated at a frequency of 800 periods per second;

shall be provisionally fixed at 800 ohfss + 12^, i.e. it shall remain

within the lim its of 700 and 900 ohms.

(g) Cross-Talk.

The O .C .I.,

HAVING REGARD TO THE FACTS,

that precise rules have been specified in Appendix No. 3 for

the maximum guaranteed values of oross-talk between any two circuits

in a repeater section of cable,

that, moreover, the values indicated are only higher lim its and apply to cables carrying generally, not .only international cir- * cuits, but also international trunk circuits,

that international communications can only be carried out under good conditions upon circuits which are as free as possible from disturbing induction due to neighbouring .oircuits,

EXPRESSED THE GFlxNlON

that in cables used simultaneously for local traffic and in te r n a tio n a l t r a f f i c , th e "Quads" fo r which the* measurement o f cross-talk shall have given lower values, shall be allocated to international communications.

(Ill; Measurement of the efficiency of Subscribers,! Apparatus, and of the Transmission Equivalents of Subscribers1 C ir c u its .

The C.C.J. considers that it would he desirable to have an invariable reference apparatus for telephone transmission which would serve-as an absolute standard for testing subscribers’ apparatus. -1 5 -

After'having examined vjarious proposals ,v;ith respect to* ‘

such reference apparatus., the C.C.I. .thinks that a. definite apparatus

for this purpose cannot be proposed at the presept time: it recom­

mends that Administrations be invited to continue the testing of

their .apparatus In accordance with the methods which they are

employing the present time, until a definite system has been

established. •

The C.C-I. was of opinion also that it w ill only be

p o s sib le to recommend a d e f in it e method fc r t e s t in g th e com plete

Installation of a subscriber from the local Exchange to the private

Excnange after*a mora complete study of the question h*s been made.

For the purpose of reference, a few methods are enumerated,

details of which w ill be found in the complete Minutes when published.

0 ) Tests of Subscribers* AnnaxatuB before these have •been brought Into use.

The C.C.I. then‘desoribed, as a method which has given 1 satisfactory results for several years, the system employed in Great

Britain details of which will-be found in Technical Instructions

No. VIII, P t.l, Section? VI to VIII. The most important test from the international point of view is $he comparison of the apparatus under test with a standard apparatus, the test being a speaking test,

(2 ) Tost of Subscribers* Apparatus and Lines after Installation*

Experimental, but premising methods of making this test are given f-

in the "Post Office Electrical Engineers* Journal Vol. 17, pt.2, July, 1924, p. 125 (Appendix-9) .*

(b) in a memo, dated 24th September prepared by the International Western Electric Company (Appendix .10).

The C.C.I. was of option that it is desirable that such • subscribers* set used in connection with international circuits should be tested once per annua. The precise method tp bo followed

,for this test w ill be decided by tbje Administratians concerned. PART I I .

(a) Tha C.C.I. finds that it has;not been possible to toaft a

typical specification of a general character for complete 3ystarns ■

longdistance cables with repeatera. It points out, moreover*-

that tha conditions to which long international circuits

are subjected ware formulated in tha report of tha first Conference

Of tha C.C.I., held in Paris in i924;

that tho efficiency of a long distance cable (containing

several repeatersj depends to a large extent on questions of. details

of construction and of the general arrangemont of the; system.

(b) The C .C .I. proposes to recommend to an A dm inistration which

would prefer to leave the proposal ‘for a complete cable, including

several repeaters, in the hands of the Contractor, instead of having

a service of specialised engineers and of assuming the responsibility which would result from the acceptance of the various portions of the

system, separately, to discuss matters in detail with the Contractor, in order to obtain necessary information with regard to the lay-out, general arrangements etc., and to demand a ll tha guarantees desired in order that the conditions specified in the partial specifications, appended, shall ,be duly fulfilled. At tha outsat, this Administra­ tion should give the Contractor information in respect to the circuits \7hich w ill be necessary and with respect to the probable t r a f f ic .

(c) . Certain Administrations show, in their proposals respecting specifications for underground cables, details with*respect to methods of construction, laying, etc. .The3s are not included in the typical specifications dealt with in Appendices 4 to 8 because the C.C.I. is of opinion that it is preferable to give a free hand to the various Administrations in respect to the choice of their methods relating to everything that concerns construction and laying of th 3 cables, subject to the condition that the circuits -r e ­

established will 3ati3fy the conditions imposed by tha appropriate specifications#

It must be reoognised in this respect that if the electrical conditions are specified, it is not generally necessary to prescribe also details of ^construction# The C.C.I* considers, moreover, that in many cases better eablea w ill be obtained by leaving to the

Contractors the task of arranging details of construction.

(d) It is spsoified in Appendix 4 that when the processes of 4 manufacture do not admit of realising, with sufficient approximation, equality of the capacitias of the various loading sections included between two successive telephone repeaters, this equality might be obtained as perfectly as possible by suitably distributing factory lengths amongst these loading sections.

(e) Precise rules have been specified in Appendix 5 in respect to the spacing of loading coils in cables. If, in consequence of local circumstances, a regular spacing of these loading coils cannot be observed, the special arrangements adopted in this oase should be such that the result shall not be detrimental.

(f) Soma Administrations prefer, in carrying out tests of di­ electric strength of the cables in tha factory to apply the .testing voltage foi two ( 2 ) minutes instead of two ( 2 ) seconds specified in

Appendix 4. The C.C.I. does not see any objection to this method of procedure. -1 8 -

' PART 111.

Methods of Measurement and Measuring Apparatus for the Maintenance of International Circuits.

In order to erasure satisfactory co-operation between Adminis­

trations interested in the maintenance of one and the same circuit, tha

C.C.I. gives, under this heading, a list of the tests which should be

made on international cirouits and a description of the appropriate

apparatus and operating methods. Localisation of faults and the

estoration of lines are not dealt with in this report. The apparatus

described for maintenance purposes i 3 sufficient to determine the position of faults, but it w ill, in addition, be necessary to draw up detailed instructions, with a view to ensuring that the tests shall be

satisfactorily carried out in practice.

List of Perlodioal Tests.

I. At Terminal Stations* Tests to be made on the circuits.

(1)• Insulation resistance Monthly

(2) Conductor resistance "

(3) . Overall transmission test "

(4) Overall signalling te 3t D a ily

(5) Overall speech test ,f

II. At Repeater Stations: Tests to be made on the cirouits,

(1) Insulation resistance Monthly

( 2) Conduotor resistance w

(3) Line impedance measurement Yearly

(4 ) Singing point test Monthly

(5) End-to-Snd transmission test between repeater stations and between ter- •* Yearly minal stations and adjacent stations

( 6 ) Transmission level test Yearly - 19 -

iy . At Beoeater Stations: Test3 upon repeaters.

(1) Check of battery voltage and currant D a ily

( 2 ) Bapaatox- gain test at single frequency ifaekly

(3) Bapeater gain toat over range of frequencies llal f-yearly

(4) Valve rejection t 93t As required

(5) Tost of signalling apparatus Monthly

( 6 ) Singing point to 3t of repeaters Q uarterly

(7) Calibration of repeaters Half-yearly

IV* Miscellaneous Tests (made as required):

(1) Crosstalk tests

( 2 ) Koise measurements -2 0 -

apparatus for making routine tests.

I (1) and II (1) Insulation Resistance.

The C*C.I. does not desire to specify the- type .of apparatus

to be used for this test. Whatever instrument is used, it should

fu lfil the following conditions:-

(1) I t 3hould be dead-beat so as to. permit of rapid readings.

( 2 )** It should indicate the insulation resistance correct to

i - xo%. '

(3) It should require a voltage of not more than 600 volt 3.

(4) It should give a steady reading with a capacity load,

even if a current is produced by manual operation

(m egger).

(5 ) ’ Means should be provided to prevent a sudden discharge

of the line after test so as not to damage the load­

in g c o i l s .

I (g) and i t (2) Conductor Resistance.

The- C.C.I. does not desire to specify the type of apparatus

to be used in this case. It should be accurate to i Q.l per cent and

lend itself td quick manipulation

I .(5V Overall Transmission Test.

This test is made with the-object of;ensuring that the

transmission efficiency of the circuit under test is up to, its nominal

value. A routine test of‘.this- type should be mads monthly. It'is

also employed when speech on a circuit

result o.f the measurement indicates that the circuit is below its

nominal efficiency, 3 transmission level tost (No. II .(6) ) w i l l

generally be made in order to localise the trouble.

The principle of the measurement is to apply a known alter­ nating. voltage or currant to- the sending and of the circuit and to measure th9 corresponding voltage or current at the receiving end of .

the -Circuit. - .The apparatus necessary consists essentially,of a generator capable of-producing alternating current, of audible -2 1 -

fraquencios, and a means of ooagparlng tha 3ent and received voltages.

Tha apparatus should comply with tha following requirements: -

C enarator.

Tha generator., which is preferably of the valve oscillator

type, shall be capable of giving an output of not le 3s than 0*2 w a tts.

The wave-forra shall be.practically sinusoidal. For purposes of test II

(3) and III (3) the power output at all frequencies throughout the audible range shall be approximately constant. For the purposes of tests I (3),

II (5), III (2) and III (7) the frequency should be constant at 800 p.p.s.

The frequency shouldxnot vary appreciably with the output power within the range, required or with the variations of battery volt ages occurring in practice.

Measuring Apparatus.

(1) Th9 impedance of the apparatus at the sending end and at the receiving end shall be adapted to that of tha circuit under test.

(2) The result of the tests shall be expressed in absolute units

(b) and the apparatus employed shall be calibrated so that tha measurement can bo read directly in these units.

(3) Tha artificial cables and other apparatus, indicating the transmission equivalent of the line under test, should r 3ad to b .*• 0.05.

The measuring instrument shall indicate, with sufficient accuracy, a difference of b * 0*05.

(4) The instruments for indicating the received voltage should give a visual reading.

(5) Within the range of frequency 700 p.p.s. to 1100 p.p.s. the apparatus should be capable of reading transmission equivalents with an accuracy of b * £ 0.05 (see also test II ( 6 ) on this subjact.

Within the ranges of frequency 300 to 700 p*p*s* and 1100 to 2400 p.p.s. the apparatus should be capable of reading transmission equivalents with an accuracy of b » £ 0 . 2.

( 6) The apparatus should be capable of measuring transmission equivalents over a range b » C to b * 5 ’(see ais<5 test Ho. II (5) in this connection).

(7) For international circuits, which contain not more than

Z telephone repeaters and which are not intended to be connected to

other circuits, which contain repeaters, measuring apparatus may be

used, employing listening devices for comparative measurements, the

accuracy of which may be in the order of b = 0 , 1.

II (5) End to end Transmission Test between successive Reneater Stations and between Terminal Stations and Adjacent Stations.

The object of this test is to check the transmission efficiency

of the circuit between adjacent repeater stations and between the terminal

stations and adjacent repeater stations.

A routine te 3t Bhould be made on each circuit yearly in order

to check any change-in the transmission efficiency of the circuit due,

for.example, to changes in the inductance of loading coil 3. The t e s t may

also.be made.in cases of faint speech,' which may be due to faults on the

c ir c u it .

The test is made in tha same way and with the 3ame apparatus

as in the case of test No. I (3).

XII (a) Repeater Gain Test at Single Frequency.

The object of this test is to check'the performance of the

telephone repeaters with, the gain-regulating adjustment in its working

position. If the gain indicated is below tha specified value, the

valve, rejection test (No. Ill (4) ) should be applied.

The test is ordinarily applied weekly and also .in localising

faults .which may be due to failure of a repeater.

The apparatus used for this .test is similar in prinsiple

to that.in the.two previous.tests. Nos,I (3) and II (5), with the exception that the circuit under test consists of two- sections.of artificial, cable with the repeater connected between them. The characteristic impedance of the artificial cable should be equal to the impedance of the telephone repeater and equal to that of the balancing networks, connected to the repeater. Since both ends of -2 3 -

the circuit are available, a direct comparison between the sent and

receiv ed v o lta g e s can bo made.

Ill (3) Repeater Galp test over a Range, of Frequencies.

The object sf. this tost-is-to determine the frequency-

amplification characteristic of the repeater.

The test is made- by measuring -the improvement given’by the

repeater wi th the normal adjustment of the amplification-regulating

device at frequencies throughout-and slightly beyond the efficient

range of the repeater. Measurements should be made at frequencies,

d iffe r in g by not more than 20Q periods per second.

The method of making each measurement is the same as in the

case of test No. Ill (2).

The input should be kept- constant at all frequencies.

T e st III (7) Repeater Calibration Test.

The object of this test is to ascertain the improvement given

by the repeater at a definite, frequency, in each position-of the

amplification-regulating device.

In addition to ensuring that the repeater i 3 in an efficient

state,'the results obtained ih this test are used in interpreting the

. singing point" tests.-

The method of'making, each measurement is the sarre as in the

case-of.tost No. Ill (2), the input-being kept'constant a 3 regards

amplitude .and frequency for a ll measurements.

No. I I - ( 6 ) Transmission Level Test.

Tha object of this test is to ensure that all repeaters in

circuit are functioning correctly, and that tha attenuation duo to the

circuit or to apparatus connected’ in circuit i 3 normal. ’ The test

al30 ensures that the transmission levels throughout the circuit fall within the specified maximum-and minimum lim its.

The results of the routine te 3ts are recorded and form a

record showing what transmission levels should be obtained when the

circuit is in normal working order. -2 4 -

In addition to the routine measurements, test No* II ( 6 )

• is also used to localise- tha* position of the fauit w h en the overall

transmission measurement (No* I (3) } has indicated,• that tha trans­

mission efficiency of a circuit is below normal*

The apparatus should conform to tha requirements given

above'and in addition the impedance of the instrument bridged across

the line should not be less than 5000 ohms, at 800 periods per second*

I (4) Overall Signalling Test.

This test should he made daily by the operators to ascertain

whether calling signals in both directions are received correctly.

The test is made by operating the cord-circuit ringing key

in the normal way.

I (5) Overall Speech Test.

This test should bs made daily by the operators immediately

following the ringing, test. The operators should ascertain by

exchanging a few words over tha circuit whether it is in good condition

for commercial work, especially as regards volume of speech and freedom

from noise.

IX (3) Line Impedance Measurements.

This test consists in measuring the impedance of the line at

frequencies throughout the efficient range of the repeaters. The

object of the test Is to ascertain whether any change has taken place

in the impedance of the circuit which would affect the accuracy of the

duplex balance or produce reflections.

The impedances may be measured by means of any of the

recognised alternating currant methods.

* The distant end of the circuit 3hould be closed by an

impedance approximately equal to the characteristic impedance of the circuit. The measurements should be made both with and without the

line transformers actually'in use on the circuit. Measurements, should be made at intervals of approximately-40 periods per second.

The voltage across tha sending end of the circuit should be -2 5 -

approximately 2 v o lt s .

The results of the tests should he expressed as tha resistance

and reactance (+ or -) components of the impedance at each frequency.

Each component should he expressed in ohms.

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 tesi may be carried, out either with the repeater normally

working in the circuit, or by means of a specially adapted repeater

u n it. Tha la .tte r method- i s the more accurate and should be adopted

whenever the importance of the equipment warrants its use.

To make the test a request should be first made to the stations

in both the East and West directions to close the circuit to be tested by

an impedance approximately that of tha circuit. At terminal stations

this should, be done by means of a rheostat of the required value, unless

a special impedance is provided. 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 tha Vest repeater

balance jack. This converts the differential transformer in the

direction Vest to an intervalve transformer, and the unit gives the

improvement of a two-way 2-valve repeater. The two potentomoters

should be raised together until "Singing" is heard when listening on

the monitoring circuit, and -than reduced alternately step by step until

singing ceases. The test should be than repeated with the positions

of the short circuiting and open circuit plugs interchanged#

The singing point should be then taken as the sum of the

gains represented by the positions of tha potentiometers, in whichever

of the two tests gives the lower value. An allowance of 0.7 absolute

u n it3 (b) should be added, due to the increased efficiency of the West

transformer, acting as an intervalve instead of a; differential one. - 26 -

The gains, represented by the sum of the potentiometer

readings, should be taken from the records of test III (7), giving

•the c a lib r a tio n o f the r e p e a te r s. .

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, hereinafter described, may be Used to deter- • * mine the maximum gain, which a repeater my give without "singing".

The cirouit 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 (1000 ohms) and the oth er by a v a ria b le r e s is ta n c e R. The gain o f the two rep eater elem ents are raised to their maximum value. The value of the resistance R is then decreased until "singing" occurs. The limiting value of the relation

R/lOOO, obtain ed in t h is manner, i s a d e f in it e fu n ctio n o f the maximum permissible gain. For this reason it is possible to calibrate the variable resistance S directly in terras of gain (b).

A record should be made of tha results of these tests when the circuit is first formed and the variation from these figures on subsequent tests should not exceed b * 0 . 2.

In the event of this figure being exceeded an impedance test, should be made of the circuit and the balancing network.

Ill (1) Cheok of Battery Voltages and Currents.

The object of these tests is to ensure that*the' battery voltages are maintained within such lim its that the repeater gains do not vary beyond the allowable lim its.

Ill (4) Valve Rejection Test.

Tha object of thi3 test is to ascertain whether a fault in a telephone repeater, indicated by the measurement of repeater gain,

Is due to a' change in the characteristics of the valve.

A suitable voltage is applied to the incoming terminal^ -2 7 -

of the repeater -th e voltaga being determined in each oase in accord­

ance *?ith the type .of repeater and: valve employed* The battery

potentials on the plates and filament are then given their max imam

permissible values and verification is made as to whether tha degree

of. gain corresponding to the desired value (also specified in advance

for each type of apparatus) and as to whether any apparent variation

of the continuous current of the plate Circuit ocCurs, i*e*f whether

any such variation is detected* When these conditions are not ful- / filled the valvo should be rejected*

6. Determination of tha Singing Point of Telephone Pepeaters.

This test is to ensure that the balance of the repeater unit

is maintained.

The test is made in a similar manner to test II (4), except

that balanced non-reactive resistances are substituted for the circuit

and for the balancing network* respectively. The repeater should not

"sing” when the gain adjusting device on each half of tha repeater is

set at.full gain.

17. Misoellaneous Tests (made as requirad).

(1) Definition and Measurements of Crosstalk.

Tha cross-talk between two cirouits is defined by comparing

the impedance net-work and the connections which join the incoming

terminals of the disturbing circuit to the outgoing terminals of the disturbed circuit with an heterogeneous transmission line having the

same output of energy and characteristic terminal impedances Z1 Z'Z, equal respectively to the real impedance of the disturbing circuit* regarded from the side' of its incoming terminals and to that of the disturbing circuit* regarded from the side of its outgoing terminals.

The intensity of cross-talk corresponding to a given frequency is measured by the co-effioiant of attenuation b or the corresponding exponent* a~^* o f t h is e q u iv a le n t.lin e *

In the particular case where the two terminals impedances

Z^ and Zg* are equal to one another as well as the impedance R* to -2 8 -

whloh the disturbed (Circuit is looped, the fractional number 0“*^ i s

equal to the ratio of the intensity coming from the disturbed circuit

to the intensity given to the disturbing circuit.

The measurement of tha cross-talk is than reduced to a

direct measure o f this ratio,

'When theae conditions have not been satisfied, the true

value of the cross-talk is deduced from the direct measure -J-* or of

that of the ratio of i to the applied voltage U, by one or other of

the formulaes-.

__b i K + Z2 1JL- „ 1.B.+ Z2 f zj ® 1*2 J Zl Z2 u 2 / Z2

When the measurement, - properly so called, is being carried,

out, the end3 of the disturbing and disturbed circuits, other than

those used for supplying current and for listening, w ill be closed with the corresponding characteristic impedance. Current w ill be

supplied by the same generator to the disturbing circuit, and a potentiometer, artificial line or any other apparatus which enables

U3 to attenuate the alternating energy within known proportions.

(The latter may be joined up in series or in parallel with the line or substituted for tha latter.)

The same telephone r e c e iv e r w i l l be s u c c e s s iv e ly shunted across the end of the disturbed circuit and that of the apparatus in question, which w ill be adjusted to give equality of sound, and con­ sequently of current, in the two listening positions. The value of the ratio ^ in the .series arrangement, or of the ratio ^ in the parallel arrangement, w ill be obtained from tha adjustment of the attenuating apparatus and in a ll cases wi 11 perm it e“*^ to be c a lc u la te d .

It may be convenient, finally, to adapt the impedances Zq, Zj>t and R to one another by means of suitable transformers, so long as the latter have a sufficiently high output and are sufficiently well balanced 30 as not to modify the results of the measurement.

"Whan voice tests'are made, the same operating methods -and -2 9 -

correcting formulae as those indicated above may be allowed; the value

of the cros3-talk w ill be deduced from tha readings shown by the

apparatus in tha same manner as if equality,of sound had been obtained

by unaffected (pure) sound. The elements which enter into the measure­

ment and which are adapted to this purpose w ill then be adjusted to

values corresponding to a pulsation of 5000.

The C .C .I .,

HAYING REGARD 20 THE FACT

that it is desirable to render oross-talk tests, to be carried

out by maan3 of the voice, mutually comparable, but that in tha present

state of telephone engineering tha result of measurements is not yet

sufficiently independent of tha method of making the test which may be

used in each case,

CAME TO THE CONCLUSION

that tha various Administrations should be invited to continue

the study of the methods of measurement and of tha conditions to be

imposed on apparatus, with a view to permitting of a precise interpreta­

tion of tests made by the voice.

(2) Noise Measurement on Telephone Cirouits.

The object of this test i 3 to obtain a measurement in some

definite unit3 of the amount of disturbance on a telephone circuit.

Tha C.C.I. considers it desirable to postpone the choice of the

method of making these measurements until further experimental work

has yielded more definite results.

Three methods have been considered:

(a) Comparison o f tha sound produced^ by the d istu rbance w ith a

standard source of sound attenuated by a known amount.

(b) Measurement of the voltage produced by that portion of the disturbances falling within tha audible frequency range.•

(c) Measurement of tha roduction in intelligibility due to the disturbance.

Methods (a) and (b) are described in detail in tha section -2 0 -

of tha report entitled "Limits of voltages induced in telephone circuits".

Method (c) gives a true indication of the effect of the disturbance, but the test is very laborious to make and the results depend, to a certain axtent, on personal factors.

Among the questions mentioned above are scsne which the C.C.I. proposes that the various Administrations should study. The following are the more important: ,

(1) Standardisation of the graduation of apparatus for

adjusting repeater gain.

{£) Possible modification of provisional decision regarding

the question of using a single frequency for measuring

cu rren ts.

(2 ) Greater precision with respect of the method of measuring

cross-talk by means of the voice. -5 1 -

Appendix 2.

EXTRACT FROM MINUTES OF CONFERENCE OP

PERKiKENT COMMISSION OF C .C .I.. HELD

IK PARIS. NOV/DSC. 1924.

Choice of a Transmission Unit.

Tha Permanent Commission, after reading the reports by

Professor hr. Braisig and Colonel Purves on tha choice of a trans­

mission unit (Reports attached hereto - see page ) and after an

exchange of vlew 3 on this subject, proceeded to take a vote on the

following question*. -

"What transmission unit is it desirable to adopt?"

The principal delegates of the Administrations from tha

countries mentioned below, declared themselves in favour of the natural,

absolute unit (b):

Germany. Sweden. Austria. x Switzerland. Franca. Czecho-Slovakia. Italy. Yugo-Slavia.

Great Britain declared itself in favour of adopting, ex­

clusively, the transmission unit, T U. i Belgium voted for the use of both the natural, absolute unit

(b) and the transmission unit.

The Permanent Comission, considering tliat it is desirable to

adopt only one transmission unit, proposes to invite the various

Administrations and particularly those who are not represented on the

Permanent Coramission to continue tha study of tho question of the

transmission unit with a view to submitting a definite proposal for tha ratification of the International Consultative Committee. »r<2-

REPORT SUBMITTED TO PERMANENT COMISSION OF C .C .I. BY "RAPPORTEURS" OF GERMANY AND BRITAIN ON TH3 CHOICE OP THE ■ TRANSMISSION UNIT.

in the report of tha Conference of April, 1924, it was decided

that transmission efficiency should be expressed alternatively in

absolute units, voltage or currant ratio (b) or in miles of standard

c a b le .

At the data of this session, however, the Bell System of

Amorica had just adopted a unit based 011 Power ratios which is pro­

visionally called a "Transmission Unit" (T U). It was considered

advisable to take this unit into consideration, since it is stated to

offer certain technical advantages and would result in uniformity of

practice in Europe and America.

It has also been proposed that a unit one tenth the magnitude

of the absolute unit should be adopted. This unit would be termed a

"Deci".

A number of communications ware received from European

Administrations referring to tha relative advantages of the absolute

u n it S3 compared with the "Deci". A large majority of the Administra-

tions were in favour of the absolute unit itself. . The rapporteurs

are in agreement with this opinion and it is therefore thought that

the proposed adoption, of the "Dacl" should be abandoned.

If this course is adopted the choice lias between the

absolute unit (b) and the Transmission Unit (T U). The rapporteurs

have been unable to reach a comnon agreement on this point. It has

been considered advisable therefore to set out the arguments for the

adoption ^of each system in appendices to this report (see page } and to leave it-to the decision of each Administration which system

shall be adopted by them. A table of conversion factors is annexed.

Before giving the arguments referred to, it is desired to make sorfte remarks as to the conditions which would obtain if a uniform practice is not adopted. The chief difficulties would occur In Overall transmission measurements, transmission level measurements,

’gain adjustments and co-ordination of records and general literature.

Y/ith regard to overall transmission and transmission level

measurements, it is suggested that an instrument which reads directly

in absolute units, current or voltage ratio (b) can be made to indicate

Transmission Units (T U) or*vice versa, by the employment of a correcting

transformer used in conjunction vrith the voltage indicating instrument.

Alternatively, double scales could be used on the potentiometers or

artificial cables, but this would lead to difficulties when two dials

are used#

With regard to the gain adjustments, it is considered that

no serious*inconvenience w ill be caused if the reconwendations, made

in paragraph 10 of this report, are adopted.

No method is apparent of co-ordinating records and literature

but the two methods have a simple linear relation, which makes mental

comparisons oasy; that is, a transmission length, expressed in T U,

is roughly nine times the same length expressed in b. (Actually

6,6 8 6 b - measurement in (T U) ).

It appears, from the above, that, although it is highly

desirable that uniformity of practice 3hould obtain in this respect, it

would be possible to obtain co-operation if the two systems were in use,

1, Arguments by Dr, T, Breisig, in favour of the adoption of the

absolute unit for the expression of transmission lengths.

In connection with the question of the Transmission U nit,

I wish to clear the situation by stating that on our side there is no

opposition at all to an extension of the ideas hitherto prevailing of

an attenuation of current and voltage to power problems. Although we think that in the majority of cases ths problems oan be dealt with by considering currents and voltages simultaneously, we acknowledge that the development of technical telephony has brought forward some

facts, in regard to which the power point of view would be simpler;

But I would point to the fact that I always proposed that

transmission systems be treated as quadripolar. In this case always

two linear equations are given, binding voltage and current at the

sending end to those of the receiving end. Treated in that way

every problem includes power in principle, even if, in many cases,

there may have been no object in referring to it expressly. In all

respects we are convinced that a transmission unit, adapted to present

and future use, must include the possibility of being applied also to

attenuations .of power. But we need not deal further with this

because it is recognised on both sides that all existing systems,

and especially the more modem systems without distortion, are

adapted just as well to comparions of power as of currents and

v o lta g es*

All systems which have been proposed are logarithmic in

character* The standard cable systems have been recognised as not

adapted to modern practice because they are not independent of

frequency. The intermediate system of the 800-cyole mile is

distortionless but, applied to problems regarding different fre­

quencies, it leads to expressions difficult to understand.

There remain the 30-called "b" and the so-called

"Transmission Unit" systems.

It may be useful to remember that the physical meaning of p

is, that it represents the loss in percentage of current or voltage

from the beginning to the end of a section of unit length, provided

this length is taken sufficiently small, and that the circuit beyond

the point in question be of such length that the propagation of the waves is not altered by reflected waves. In this case 2(3 is the loss in percentage of power in the same unit length. Just as in the ca ses o f compound in te r e s t, i f we p ass from a sm all u n it o f -3 5 -

length to any length, the simple relation indicated is changed into

the relation that or a~^ is the relation of currents or

voltages and e”2^ or is the relation of power between the

Input' and the output.

The selection of the irrational number 2.7182818 as the

basis of natural logarithms is justified by the well know formula*

d a* Qr d loge X m 1 dy . * dx X

while for every other base fractional coefficients result, which

depend on their arbitrarily^ ohosen base.

That an exponential relation exists in many cases, in which

for a given increase of the independent variable quantity is added or

lost, is a well known fact in physics and engineering.

What we call "attenuation factor’* in telephone circuits is

called "decrement" in galvanometry and in w ireless telegraphy.

Nobody has hitherto objected to the application of natural logarithms

to these cases. The latter differ from the case of telephonic

transmission in that here the independent variable quantity is the

length taken along the line, while in the former case it is the time

measured while the process is going on. It follows that, in principle,

both cases apply the same definition.

To adopt any other base than t and any other logarithms than

Napierian logarithms in telephone transmission problems would

therefore.; mean an exceptional treatment of the latter^ a 3 compared

with tha treatment of closely allied problems in other departments

of applied physics.

We th in k th at more than a c e r ta in amount o f convenience ;

for,people hot engaged in theoretical-and experimental, research

.ought.to be demonstrated in order to justify such an exceptional

departure from general methods.

- There is the following difference between the absolute t • system and the T'U, which however is-only a formal one : -3 6 -

t

01 or b is the expression for the attenuation of current or voltage

and 2 pi or 2b is the corresponding expression for power, while in the

T U - system, one T U means the attenuation of power in a given length

and l/2 T U is to be reckoned for current and voltage* Moreover,

power differs from current and voltage in another respect by a factor

2, that is, in frequency. Would it not be logical in a system,

based expressly on power, to define its frequency ahoording to the

power and give currents and voltages one half of that frequency ?

Such a system might easily be carried out in so far as the designing

engineer is concerned; he would always put 1 /2 f when f is the power

frequency.

2. Arguments by Colonel Purvas in favour of the adoption of the

T U for the expression of transmission lengths.

Before going into the particular reasons for advocating

the adoption of the T U, it should be stated that absolute units

would still be used for purposes of calculation when this is most

convenient. For instance, in the calculation of the propagation,

constant from measurements of the open and closed impedances, it

would probably be most convenient to carry out the calculation in

absolute units.

The following arguments are therefore directed not towards

the suppression of tha absolute unit but towards the adoption of the

T U for the expression in everyday practice of transmission lengths

of telephone'circuits and in many other cases where it is considered

advantageous to do so .

Th3 reasons for the adoption of the TV in America are given

in an article written by R.V.I. Hartley in "Electrical Communication"•

for July, 1924.

Tha reasons for tha adoption of a unit based on a power ratio say bo summarised as follows s- -3 r-

(I) In a telephonic transmission line tha fundamental require-'

mant is tha efficient transmission of power. Tha efficiency of a

circuit -can therefore be more logically expressed in terms of a

power ratio unit than by means of a unit based on current or voltage

r a t io .

(II) In the case of a line, which changes in impedance from

point to point, the energy distribution can be expressed simply in

terms of T U without any additional particulars as to impedance.

(III) The effects of the insertion of transformers or other

apparatus in circuit can be expressed simply in terms of a power

ratio unit,

(IV) Efficiency of lines and instruments can be compared directly,

independently of their impedances.

(V) Losses at the junction of dissimilar lines and of line and

apparatus can be expressed directly in power units. The "Kogative

loss", which occurs in certain cases when the loss is expressed in

current ratio units, does not occur when power units are used.

(VI) In the case of combined radio and wire telephony a trans-

J . mission level diagram of the whole system can be expressed in power

units but not in currant units.

(VII) The overall efficiency of a telephone system, including

the transfer of tha originating sound energy into mechanical or

electrical energy, and also the reverse process, at the receiving

end of the circuit, may be conveniently expressed in terms of a

power unit but not in terms of a currant unit,

Tha objection to a unit based on a power ratio ha3 been urged that the frequency of power is double that of current and that

to be consistent the usual frequencies should be doubled. This objection Is not considered to be a practical one, since the

frequency of an electrical supply is always associated with current or voltage and not with the qualities of the transmission line to -3 8 -

which it is connected. It would not be consistent to say that the

frequency of an electric supply is doubled when it i 3 put on load as

compared with its frequency on open circuit. Kb difficulty in this

respect is experienced by power engineers, who woik on a power unit

b a s is .

The magnitude of the unit is such that whole numbers of T U

represent approximately simple power ratios, which can be easily

computed. Thus:

IT U represents a power ratio of approximately 1.25 to 1

2 T U represents a power ratio of approximately 1.6 to 1

If tha ratio for any one value of T U is remembered tha whole

scale can be reconstructed very easily.

It affords an easy method of visualising the power ratio.

Whenever the T U figure is a round number the power ratio is

also a round number, e.g. 40 T U * 10+i*; 50 T U ** 10+^; 70 T U =» 10+^

It affords a simple method of quickly grasping power ratios

of large magnitude. For example, the statement that tha transmission

loss is 20 T U*s immediately suggests that tha power ratio is 102 «

100, whereas the statement that tha loss is 2 in absolute (b) units

does not convey, without the assistance of a book of tables, that tha

power ration is 54.6.

Apart altogether from the inherent advantage, claimed for the

use of T U, it is strongly urged that it is most desirable to seize the

opportunity to secure tha adoption of a world-wide unit, which w ill permit the use of a coazaon language in technical literature and in the working regulations of transmission engineers of a ll Administrations; as well as common designs and calibration of testing and measuring apparatus. This object is now within immediate grasp. This object is surely worth some small sacrifice. The Bell System of America did not adopt tha T U until after considerable support in Europe hal been indicated. TABLE OF CONVERSATION FAUP0B5.

T U p i Unit

ITU 1 . 0.1151

1 p i U nit 9.686 1 . -4 0 -

Appendlx 5.

SIGNALLING with currents, having an INTERRUPTER

FREQUENCY OP 1000 CYCIES EER SECOND.

In any voice frequency signalling astern there are certain

major considerations, which must be borne in mind, in making a choice

of the-frequency which it is best to employ. The choice of a 1000

cycles per second interrupted system, father than a system using a

500 cycles per second continuous or interrupted tone, is based on the

following considerations:-

(a) The receiving system w ill be bridged across the telephone

circuits during conversation and, since the efficiency of subscribers*

apparatus is highest at 1000 cycles, the power required to operate the voice frequency ringer could be more easily spared at this frequency rather than at 500 cycles per second.

Future development. tends in the direction of the use of a relay for reception rather than a vacuum tube (valve) device, which is at present being used. A relay receiving device w ill probably take more energy from the line for stable operation than a acuum tube (valve), and the argument, given in the previous paragraph, w ill have even more weight in the future than it has at present.

(b) Interference from power lines is liable to cause false operation^of the receiving device, and American experience has shown that the interference from power lines is greater at 500 cycles per second than it is at 1000 cycles per second This in all probability, is due to the fact that the ninth harmonic of 50 or 60 cycle power systems is prominent and is near 500 cycles per second. -4 1 -

(o) Early tests were made with various frequencies for

signalling and it was found that interference from telegraph circuits

and from switchhook operation was greater at the lower frequencies.

(d) Routine transmission tests on circuits are made at 1000

cycles per second and thus ensure without any further tests that

the circuits are in an efficient condition for ringing at this

frequency.

The adoption of 1000 cycles per second as a signalling

frequency w ill allow a common source of alternating current to be used for both ringing and tasting.

(e) An uninterrupted frequency was suggested during develop­ ment of voice frequency signalling and early trials showed that the use of an uninterrupted frequency was unsuitable for commercial op era tio n .

This was due to tha false operation of the receiving cir­ cuits by voice currents and tha introduction of 20 cycle inter­ ruptions has removed this difficulty and resulted in a system, which is imrauhe from false operation due to the voice currents, power and switchhook interference.

(f) The Bell System of America has adopted as its standard ringing system a 1000 cycles per second tone interrupted at 20 cycles per second. This system is at present in service on 8500 circuit miles, which include submarine cable, land toll lines and carrier systems, and no complaints of crosstalk have been received during the commercial operation of the system. The freedom from crosstalk has been obtained by making signalling currents sufficiently small; at the same time, however, tha receiving circuit is sufficiently sensitive to allow a wide margin of operation.

It is planned to instal a further 40,000 circuit mil83 using this system, during the coming year in America, and similar systems are being installed in Sweden and on the Paris-Strasbourg cable in

F rance• -4 2 -

APPENRIX 4 .

ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION.

GENERALLY APPLYING TO FACTORY LENGTHS OF INTER­

NATIONAL TELEPHONE CABLES OF. THE QUADDSD TYPE.

G eneral.

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 w ill be suitable for:

(1) Phantom working.

(2) Loading of pair and phantom circuits.

(3) Efficient long distance working in conjunction with repeaters.

These requirements do not apply:

(1) To cables in which the conductors are smaller than eight-tenths (0 . 8 ) of a millimetre (approximately 16 lb. per mile).*

(2) To groups of one gauge of conductors of less than ten (1 0 ) quads.

(3) When tha total number of circuits of each gauge specified is such that the lay-up of the cable is necessarily unsyrametrical, 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.

Popper 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 equal to that specified by the International Electro-technical Commission

(Berlin, 1913), that is, one fifty-eighth (i^f) of an ohm for the resistance of a wire of standard annealed copper one (1 ) metre in -4 3 -

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 coeffi­

cient specified by the same Commission w ill be admitted, that is, at

a temperature of twenty (2 0 ) degrees centigrade, the "constant mass"

temperature coefficient of resistance of standard anneals! copper

is 0.00393 per degree centigrade.

The diameter of the wira3 used shall not vary by more than

one and a half ( 1*5 ) PQ** cent above or below tha nominal diameter.

Factory Joints.

Whan it is necessary to join conductors in the factory,

the joint shall be made by a method which meets the following

requirements*

Tha 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 cen t

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 f^om 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 (approximately 2 .5 m ile s) le n g th o f paper o f the same dim ensions and the same q u a lity . -4 4 -

Sheathing and Armouring M aterial.

The requirements for these materials shall be specified

separately for eaoh 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 size of the

conductor considered.

The average resistance of a ll the wires in a group of one

gauge shall not exceed the nominal value, as defined above, by more

than one ( 1) per cent.

For the maximum and for tha average value an additional

allowance^ for the increase in length, due to tha stranding, shall be

made in accordance with the table below:

Overall diameter of outer layer containing Allowance for the the gauge considered increase in length in millimetres. due to stranding.

Below 30 1. 0^ 3 0 - 4 0 .1. 6J& - 40 - 50 2.5r/o. 50—60 3.7?4 60-70 5 .0 ^ 70 - 60 7.0J4

In any length of cable'tha difference between the direct

current resistances of-the two conductors of a pair shall not exceed

one ( 1) per cent of the loop resistance of that pair.

Insulation Resistance.

In a length of cable each conductor, when measured for

insulation against all other conductors and the sheath connected to

earth, with a potential of not less than ten thousand ( 10, 000) megohms p er k ilo m etre o f Cable (approxim ately 6,200 megohms per m ile ), -4 5 -

the potential difference employed being at least 100 v o lt s and not

more than 3ix 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 60° F).

Dielectric Strength.

When specially called for, the cables shall bo designed so

-that the insulation on every length of cable shall be capable cf

withstanding for two ( 2 ) seconds without rupture a fifty (50)cycle

alternating current potential of the R.M.S. value specified in each

particular case, but not exceeding two thousand ( 2 , 0 0 0) volts, when

applied between all conductors of the cable connected together and

tha cable 3haath earthed.

Tha 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

3ama R.1I.S. value.

Mutual Capacity (Alternating Current).

The mutual capacity of a pair is the capaci ty measured

between the two conductors of the pair when all tha other conductors

in the cable are connected to the lead sheath,

Tha mutual capacity of a phantom circuit is the capacity

measured between the two pairs of a quad with each of tha pairs

short-circuited, and all other conductors in tha cable connected to

tha 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. (5000 radians per second) at not les 3 than fifteen (15)

degrees centigrade (approximately 60° F .) w ill be taken as final.

In each length of cable the average mutual capacity of

all the pairs of each gauge, shall be as specified by the Adminis- * tration concerned, a tolerance of plus or minus five (i 5) per cent —4 6 —

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 (£ 5) par cent from the value, which shall

be determined by multiplying the average pair-capacity of that group

hy the factor 1.62.

The mutual capacity of every pair and every phantom cir­

cuit shall be measured on not less than tan ( 10) per cent of the

t o t a l number o f fa cto ry le n g th s.

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$

Maximum 1 3 .1 /2 $

By "capacity deviation" is meant the difference of the

capacity of any circuit v f 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 bgtween.succe.s_s.ive repeaters.

For each group of physical circuits of the cable the average capacities of the various loading sections between repeater stations should not differ by more than i 2$ 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 lim its indicated, it is recommended that the factory lengths be distributed in eaoh loading section in such a manner that the capacities of the various loading sections shall fu lfil the con­ dition mentioned above. -4 7 -

Leakanoe Constant.

The average laakance of tha pair and phantom circuits shall he determined on a small percentage of factory lengths with an alternating current of 800 p.p.s. (5,000 radians per second).

The average leakance constant for each type of circuit for any length tested shall not exceed twenty-five (25). This constant

3hall be taken as being equal to the ratio of the average leakance and the average mutual capacity measured with alternating current.

Tliia alue may also be expressed as the ratio: G/w 0 =

Leakance/^usceptance, which must not exceed 0.005.

Csi>9J3l_ty_,Unbalance.

in a cable two hundred and thirty (230) metres (approxiraatsly

750 ft.) in length, tha 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:

Limits for Capacity Unbalance in micro-microfarads per 230 metre lengths. Average Maximum

Side to side 40 150

Phantom to side 150 750

Phantom to Phantom between adjacent quads in a layer or between quads in 80 300 the centre and in the first la y er

Side to Earth 150 720

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 m.ra.f.

In every length of cable other than two hundred and thirty -4 8 -

(230) matros the capacity unbalances, measured with alternating

current for each gauge, shall not exceed the values determined by multiplying the figures, given in tha above table, for two hundred and thirty (230) metres, by the square root of tha ratio between the

length ixi question and two hundred and thirty (230) metres.

This correction shall not apply to lengths of cable less

than one hundred (100) metres (approximately 110 yards). For such lengths the lim its for a one hundred (100)' metre length shall apply, computed in accordance with the preceding rule.

ITote: For lengths of cable one tenth (0.1) of a mile (approximately 161 metres), the lim its for tha capacity unbalances would in accordance with the conversion rule, given in the preceding paragraph, assume approximately the following values:

Approximate lim its for capacity unbalances in micro-microfarads per 0 .1 mile length. Average Maximum

Side to Side 33 125

Phantom to Side 125 625

Phantom to Phantom 67 250

Side to Earth 125 600

The lim its here specified aro based on the follovring definitions for tha capacity unbalances.

The capacity unbalance between a phantom circuit and either of its side circuits is the capacity unbalance which would be produced or corrected, S3 the case may be, by the insertion of a capacity between one wire in the aids circuit in question and the sheath'of th 6 ca b le.

• Some Administrations define this capacity unbalance as the unbalance which would .be produced or corrected, as tha case may be, by thq insertion of a capacity between one wire of a pair and a wire of the other pair. In this ca3e the- limits of tha —49-

unbalanca in micro-farads are thos3 given.above, but divided by two (2 ).

The capacity unbalance between the side circuits of a quad is th8 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 two phantom-circuits is defined as 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 tha pairs of the other quad.

The capacity unbalance to earth of a side circuit is .ths difference between tha diraot capacities of the two wires of the pair to the conductors of all other quads in tha cable connected together and to the sheath, which shall be earthed.- . -50-

APP3KDIX 5 .

KS3T-TKTTTAT, CLAUSES FOR A (TYPICAL S3?£CiriCATI0IT

0? ftEITSRAL application to loading COILS FOB

INTESMTIONAL TgLEPIPEE CABLES.

Tha loading coils shall ha suitable for loading both side

and phantom circuits, Tha coil3 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 3hall 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 tha compressed

iron dust type or other approved material having equally satisfactory

characteristics,

Jfou3 la g .

The coils shall be encased in suitable protective cases

which shall be hermetically sealed. The cases 3hall be waterproof

and able to withstand being buried in damp ground without deterioration,

Uean3 shall be provided for easily connecting the loading

units to tha main cable.

Magnetic Stability.

Tha magnetic stability of the core mftteridi shall be such

that the inductance of a coil shall not vary by more than i two and

one half {2-1/#) per cent after direct current-of any value between

zero (0) and two (2) amps, has bean alloy/ed to pass through one lino winding. * Thi3 test shall be made five f5) minutes after the application of the direct current. This is a destructive test and

should bo applied only to sample coils.

Inductance.

The inductance measured with a current of one (1) m,a. at

800 periods par second (5,000 radians, to be exact) s h a ll be equal to the values stated for side and phantom circuits, with a tolerance -5 1 -

of i (2) per cant.

Effectiva Resistance.

. - The affective resistance of tha side or phantom circuit

measured v/ith a current of ona (1) m.a. at 800 periods per second

(5,000 radians, to be exact) shall not exceed ona hundred and fifty

(150) ohms per hanry of the specified inductance.

Crpastalk.

Tha crosstalk in potted loading coils shall be measured

with an alternating currant of not less than five (5) milliamparas

at 800 p.p.s. (5,000 radians, to be exact), or'with speech, under

conditions in which the side circuits are terminated with non-reaotive

resistance of twelve hundred (1200) ohms and the phantom circuits with

a non-reactive resistance of eight hundred (800) ohms. The incoming

terminals of the circuit under test and tha outgoing terminals of the*

apparatus U3ed for comparison w ill be joined in parallel and to the

source of current. In the correcting formula corresponding to this

arrangement 1200 ohms or 800 ohms w ill be taken as the values of 2^ or-

22, as the case may be.

In cases of dispute speech tests shall be taken as final.

Tha maxima v a lu es o f a tten u a tio n , corresponding to the

crosstalk values expressed in absolute unit3 (b) shall not be less •

than tha figures quoted below: b Between.side circuit and side circuit in the coil unit .•.•••••••••••••• 9.

Between side circuit and phantom circuit in the coil unit ••••••••••*•••••• 8.

Between phantom circuit and phantom * c i r c u i t ...... 9.

Insulation Resistance.

Tha insulation resistance of any line winding of a loading coil unit against all other line windings (both in the 3ana u n it and in all other loading-coil units) and tha case, 3hall not be less than ten thousand (10,000) megohms. This test shall be made with 52-

a potential not lass than one hundred (100) not more than five hundred (500) vplts at a temperature of not les3 than fifteen (15) degrees centigrade (approximately 60° F .)

Dielectric Stren£th.

The insulating material he tween any two line windings shall withstand, without rupture, a difference of potential, with a H.M.S. value not exceeding five hundred (500) volts* This t33t shall be made with an alternating currant of a frequency not less than fifty j (50) cycles 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 affective value not exceeding two thousand (2,000) volts, applied during-two (2) minutes.

The maximum value of the testing, voltage 3hal'l not differ by more than ten (10) per cent from that of a true sine wave of tha • same H.M.S. v a lu e.

I APFBKD1X 6.

ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION

FOR REPEATER SECTIONS OF LOADED niTRRNATIONAL

TELEPHONE' CASL,^.

G eneral.

This specification covers tha chief electrical requirements

of installed repeater sqction lengths of loaded cable, whore the factory

lengths of cable and tha loading coils are in accordance with their

corresponding specifications.

The clauses of this specification are drawn up so as to ensure

that the cables shall be suitable for phantom working in the cables and

for efficient long-distance performance in conjunction with 2-wire or

4-wire repeaters.

The clauses below apply to circuits whioh may be used for

either 2-wlre working or 4-wire working, except when otherwise

indicated in the test.

; Resistance Unbalance.

. In any cable section between telephone repeaters, not

exceeding 100 km.f the difference between the.direct current resis­

tance of the two conductors of any pair shall not exceed six (6)

ohms for conductors of 1 mm., maximum diameter, nor 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 tha

terminals of tha cable, and not including tha internal office wiring,

shall not be less than five thousand (5,000) megohms per kilometre

of oable, this insulation resistance being measured with a difference

o f p o te n tia l o f a t le a s t 100 v o lts and n ot more than 600 v o lt s , the

readings to be taken after one minute's electrification. -5 4 -

Impedance Balance.

The balance ’between the impedance 2C^ of any aide or phantom

circuit and the corresponding network impedance ZQ^, 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 tha impedance Z0^ and Zeq,

tha difference between the real consonants and the difference of the .

imaginary components* w ill be expressed in percentages, d^ and d^,

of the impedance ZQ(j of the balancing network, and if de and dj are

taken as tha Cartesian oo-orlinates of a point, this point should be 18 situated v/ithin a circle having a radius of for all the circuits

and for any frequency between 300 and 2,200 periods par second.

Furtter, for 90 p3r cent of the circuits and for all the frequencies

indicated above, the corresponding point should fall within a circle having a radius

System of Loading and Cut-off Point#

By way of example, two systems are described below under the titles: System No. 1 and System No.2. Both systems are equally satisfactory from an International point of view.

In the application of either system to any repoatered section of cable, the \vhole of the specified requirements for that particular system must bo adopted. There is no objection to tha two systems being used in adjacent repeatered lengths of cable respectively, provided that, in any circuit, the cable between two adjacent telephone repeaters is of one system.

The requirements of System No. 1 are given in paragraphs

(I), (IX), (III), (IV) and (V).

The requirements of system No. 2 are given in paragraphs

(VI), (VII), (VIII), (IX) and (X). -5 5 -

SYSTEM NO. 1.

(i ) Loading Coil Spacing.

In any cable section between successive telephone repeaters

the average loading coil spacing shall be eighteen hundred and thirty

(1830) metres within limits of plus or minus two ( - Z ) per cen t.

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 tha 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 3even (177) millihenrys

.for side circuits and sixty three (63)millihenrys for phantom circuits

(alternatively, one hundred and seven (107) millihanrys may be used

for the phantom circuit inductance). The limit of seven hundred

kilometres may be extended to one thousand (1,000) km. for 4-wire

circuits, provided that no disturbing echo currants are produced.

For circuits which are planned to exceed seven hundred*

(700) kilometres in length, with the exception stated'in tha

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 Point.

The cut-off point for the various systems of loading for

both side and phantom circuits shall be calculated by the formula:

o>0 ■ 2 / J L C where ui0 ■ cut-off point, expressed in radians per second.

L » inductance per coil,in hanrys.

C « mutual capacity of the cable circuit between loading coils, in farads. - 5 6 -

* Tha cut-off point has approximately the nominal values given

in tha following table

— ■ 1 Side rhantom P eriods P eriods Radd an 3 p er Radians per Second' Second

C ir c u its le s s than 700 ion. in lefajerth-

With 177 mh* side 63 mh. phantom , 18,000 2,900 23,600 3,600

With 177 mh. side 107 mh. 18,000 2,900 18,000 2,900

Cirouits over 700 km. in len g th .

With 44 nh. side 25 mh. phantom 36,000 5,800 37,400 6,000

(iv) Impedance.

The characteristic impadanca of side and phantom circuits,

loaded in accordance with the foregoing systems of loading and

calculated by tha formulas z0 ~SV5

{whare Z0 » the characteristic impedance, I and C being the constants

referred to in paragraph on "Cut-off Point") has the values given in*

tha following tablet

Ohms"' Impedance Side Phantom Circuits less than 700 km* in le n g th .

With 177 mh* 3ide 63 mh* phantom 1590 740

With 177 mh. side 107 mh. phantom 1590 970

Circuits over 700 km. in len g th y

W ith 44 mh* s id e 25 mh. phantom 790 470 - 5 7 -

(v) Attenuation Constant.

Tha average attanuation constant for all circuits-of ona

type, in any section between successive repeaters, loaded in accordance

with the foregoing systems of loading, shall not exceed the values

quoted in the following tables.

Tha 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 giva3 the values of the attenuation

constants for circuits loaded with 177 mh. side circuit coils and

63 mh. phantom circuit coils on 1830 m. nominal spacing.

Mean mutual capacity of cable: side circuit 0.0385 m.f. per km., phantom circuit 0.0625 m.f. per km.

Maximum Average Attenuation per km. at 800 periods per second. Side Circuit Diameter of Phantom Circuit Conductors. P (3 0 .9 mm. 0.0217 0.0228

1.3 m . 0.0121 0.0125

Maximum Average Attenuation per km. at 1900 periods per second.

Side Circuit Phantom Circuit

P P 0 .9 mm. 0.0250 0.0245

1 .3 mm. 0.0164 0.0147 58-

Ths 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 1830 ra. spacing.

Mean mutual capacity of cable* side circuit 0*0385 m.f* per km., phantom circuit 0.0625 m.f. per km.

Maximum Average Attenuation per km. at 800 periods per second. Side Circuit Phantom Circuit Diameter of Conductors. P P 0 .9 ma. 0.0214 0.0177

1.3 mm. 0.0119 0.0099

Maximum Average Attenuation per km. at 1900 periods per second.

Side Circuit Phantom Ciresult

P P 0 .9 mm. 0.0251 0 .0202

l1 .3 ram. 0.0159 0.0127

The following table gives the values of the attenuation for circuits loaded with 44 rah. 3ide circuit coils and 25 mh. phantom circuit coil3 on 1830 m. spacing.

Mean mutual capacity of cable; side circuit 0.0385 mf. per km. f phantom circuit 0.0625 m.f. per km

Maximum Average Attenuation per km. ■ at 800 periods per second. .

Side Circuit Phantom Circuit Diameter of Conductor. . P P 0 .9 ram. 0.0390 0.0328

Maximum Average Attenuation par don. at 1900 periods per second.

• Side Circuit Phantom Circuit

P P 0 .9 ram. 0.0410 0.0339 -5 9 -

SYSTEM NO. 2.

(vi) Loading Coil Spacing.

For cables with wires of 0*9 mm. diameter (having a mean

mutual capacity of 0*0335 mcrofarad par kilomatra for tha side circuits

and 0,054 microfarad per kilometre for tha phantom circuit) and with wires 1,4 mm, diamater (having a mutual capacity of 0,0355 microfarad par kilometre for tha side circuit and 0,057 for tha phanjtom circuit)

tha nominal loading coil spacing sliall ba two thousand (2000) ‘metres

- 2$’. . .

In any cable section between two suocas3iva telephone repeaters

the actual length of any loading section (measured along tha cable) shall not vary«■ from the nominal spacing by more than plus or minus ten

(1 10) raatra3.

(vii) Loading Coil Inductance.

For circuits which are planned not to exceed seven hundred

(700) kilometres in length, the units of loading shall hava nominal inductance values for wires of 0.9 run. diamater, 190 mh. for sida circuits and 70 mh. for phantom circuits; for the wires of 1,4 mm, diamatar 190 rah. for side circuits and 70 mh. for phantom circuits.

The lim it of seven hundred (700) kilomatres may ba extended to one thousand (1,000) kilometres in case of 4-wire circuits, provided always that this does not give rise to disturbing echo currents.

For circuits which axcaad 700 kilometres in length, excepting as provided in the preceding paragraph, the units of loading shall hava nominal inductance values of fifty (50) mh. for the side circuits and twenty (20) mh. for the phantom circuits.

(viii) Out-off Point.

The cut-off points, calculated by tha previously mentioned formula, w ill hava tha approximate values given in the following ta b le: - 6 0 -

r ~ Side Pliant om

Radians P eriods Radians P eriods

Circuits les3 than 700 km. in len gth .

Wires of 0.9 mra. diameter (200 mh. sid e 70 mh. phantom) 17,300 2,750 23,000 3,670

Y/iras 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. aide 20 mh. phantom) 33,500 5,340 43,000 6,840

(ix) Impedance.

Calculated by the previously mentioned formula, the

characteristic impedance shall have the values, given in the following

ta b le:

•Ohms Impedance

Side Phantom

Circuits less than 700 km. in len g th .

Wires of 0.9 rcm. diameter (200 mh. sid e 70 mh. phantom) 1730 805

Wires of 1.4 diameter (190 mh. 3ide 70 mh. phantom) 1630 775

Cirouits over 700 km. in len g th ,.

Wires of 0.9 mm. diameter (50 mh. side 20 rah. phantom) 855 440

(x) Attenuation.

The table below gives the values of the attenuation for circuit Of:- (l) 0.9 mm. diameter (loaded with 200 rah. side circuit coils and 70 mh. phantom circuit coils, with 2000 metre spacing, and mean mutual capacities of cable:- side circuit 0.0335 microfarad - 6 1 -

par Kilometre, phantom circuit 0.054 microfarad per kilometre);

(2) for circuits of 1.4 ram. diameter (loaded with 190 mh. side circuit

coils and 70 rah. phantom circuit coils with 2000 metre spacing, with

a mean mutual capacity of cable:- side circuit 0.035 microfarad per

kilometre, phantom circuit 0.0585 microfarad per kilometre).

Maximum Average Attenuation per km. at 800 periods par second.

Side Circuit Phantom C ir c u it Diameter of Conductors. 8 0 0 .9 mm. 0.0197 C.0210

1 .4 mm. 0.0097 0.0101

Maximum Average A ttenuation par km. at 1900 perio ds per second.

Side Circuit Phantom C ircu it

8 P 0 .9 mm. 0.0236 0.0234

1 .4 mm. 0.0133 0.0131

The following table gives the values of tha attenuation

for circuits of 0.9 ram. diameter, loaded with 50 mh. coils on the

side circuits and 20 mh. coils on the phantom circuits, the normal

spacing being 2000 metres and the msan mutual capacity 0.0335 m.f.

per km. side circuit,and 0,054 m.f. per km. phantom circuit.

Maximum Average Attenuation per km. at 800 periods per second.

Side Circuit Phantom C ircu it Diameter of Conductors. P P 0 .9 mm. 0.0307 0.0350

Maximum-Average A ttenuation per km. at 1900 periods par second.

Side Circuit Phantom Circuit

. P P 0.0308 0.0353 -6 2 -

Qross-talk.

Tha following tab la 3 stata tha maximum cross-talk allowable

between any circuits as specified above and measured on any repeater

section of cable between two successive repeaters. The values are thsse

which would be measured from the terminals of the cable and inolude only

cross-talk contributed by the cable and loading coils. They do not

include cross-talk introduced by arrestors, repeating coils, repeater

station cabling and other equipment located in the.repeater or terminal

buildings..

The cross-talk values shall be determined by means of a

talking test or by tone approximating, in energy distribution, to speech

(in cases of dispute, speech tests shall b3 taken as final).

The measuring circuits employed shall ba such that both the

disturbing and disturbed circuits are closed at both ends through

impedances which conform to tha impedance of the disturbing, and disturbed

circuits, respectively.

Tha lim iting value of attenuation correspending to the cross­

talk expressed in absolute units (b) shall be at least equal to the

values quoted be low: -

Near End Cross-talk. 2-wire circuits. M Side to Side o f same quad ) Phantom to Side o f same quad ) Phantom to Phantom ) 7.5 Phantom to Pair-of different quad3 ) Pair to Pair of different quads )

Near-End Cross-talk. 4-wire circuits between opposite going 4-wlre groups.

Pair to Pair ) Phantom to Phantom ) 9 Phantom to Pair )

Far End Cross-talk. 4-wira circuits.

Side to Side o f same quad ) Phantom to Side o f same quad ) Phantom to Phantom ) 7.5 Phantom to Pair of different quads ) Pair to Pair of different quads ) -6 3 -

APPENDIX 7 .

ESSENTIAL CLAUSES FOR A TYPICAL SPECIFICATION

FOR THE SUPPLY OF TWO-WIPE TELEPHONE BEFEATERS.

G eneral.

This Specification covers the most important electrical

requirements concerning the essential qualities of repeater unit 3 as

supplied by ths Factory. It does not cover the requirements for

installed repeaters.

SZBSa

It shall be a two valve vacuum tube repeater, associated with

balancing networks. It shall give two-way amplified transmission with­

out introducing appreciable distortion for all frequencies within the

efficient speech-range of the cable circuits and for the maximum inputs

occurring in practice.

B alance.

The telephone repeater shall not "sing", i.e ., it shall

generate oscillations which do not cause ’’singing" at maximum gain, when the circuit and network terminals on either side 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 aro open and short circuited, respectively, or vice versa.

Gain.

Means shall be provided for regulating the gain of the tele­ phone repeater, preferably by steps not exceeding b ** 0.2.

Within the efficient speech range of the cable the repeater gain shall be approximately uniform for all gain settings.

The repeater circuit and apparatus shall be so designed, thet the variations of power voltage and current occurring under normal maintenance conditions shall not cause an average variation from the working gain greater than b « 0.05. -6 4 -

Imnedance.

The impedance of the repeater, looking Into the line terminals,

shall he approximately equal to that of the circuit in connection with

which it is intended to operate. Suitable terminal transformers shall

bo provided, if necessary, to adjust the line impedance to that of the

repeater vvhere the latter is required to operate on circuits of imped­

ance other than that for which it is designed.

ftfonitoring.

Means shall be provided so that it is possible to monitor on s the circuits 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 the monitoring device shall not exceed b » 0.03.

C ro ssta lk .

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

b » 8, on the understanding that when these measurements are being

carried out the repeaters w ill be'joined to impedances having a value

equal to that of the uniform impedance fixed for international circuits. -6 5 -

AgPSMDIX 8 .

ESSEKTIAI CLAUSES FOR A TYPICAL SPECIFIQ-flTIOX

FOR THE SUPPLY OF FOUR-WIRS TEIRPKOKE KKPEIPER3.

■General.

This Specification covers the most important electrical

requirements concerning the essential questions pertaining to telephone

repeater units as supplied by.the factory. It does not cover the

requirements for installed repeaters.

T ype.

It shall be a vacuum tube repeater and shall give one-way

amplified transmission without appreciable distortion for all frequen­

cies within the efficient speech range of the cable circuits with which

it is associated, for the maximum inputs occurring in practice.

Gain.

Means shall be provided for regulating the gain of the

repeaters, preferably by steps not exceeding b * 0.1. in the case of

very long.circuits it may be necessary to provide for an adjustment by

steps not exceeding b * 0.03.

Within the efficient speech range of the-circuit, the repeater gain shell increase with frequency so as to compensate for the distor­ tion of the circuit, contained between successive repeaters.

The general 3hape of tha gain frequency characteristic curve

shall be maintained for all gain settings of the repeater. Suitable terminal transformers shall be provided at the ends of the circuits, if. necessary♦ to adjust the line impedance to that of the repeater, where the latter is required to operate on lines of impedance other than that for which it is designed.

Monitoring.. . Mean3 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 t a lk on th e c ir c u it vfoen n ecessary.

Whpn monitoring on a through connection the losses caused by monitoring shall not exceed b = 0.03.

C ro ssta lk .

With repeater units mounted either side tysid e or one over the other and operated by batteries, as in practice, the crosstalk between units, measured between the out-going terminals, shall not - : less than b * 8, on the understanding that, when these measurements are being carried, out, the repeaters w ill be joined to impedances having a value equal to that of the uniform impedance fixed for inter­ national circuits. - 6 7 -

APPENDIX 9.

A ME2JH0D FOR THE JgEASPHEMENT OF THE

TRANSMISSION EFFICIENCY OF TELEPHONE

APPARATUS AT A SUBSCRIBERS OFFICE *

By A.J. Aldridge, A.C.G.I. and a . Hudson, B.Sc.

j

At the present time transmission measurements of one sort

or another, both by means of speech testing, and by purely alternat­

ing current measurements, are becoming increasingly more preciBe and

accurate. Two parts of the circuit, however, have not so far

received the attention they should- • Both are very important, viz.,

the subscriber himself and, the transmitter on his premises. The

efficiency of the transmitter is tested before being taken into stock

but, after that, unless complaints are received, no further tests are

made. ' It is a commonplace that many subscribers speak far frcm

properly into the mouthpiece of their instrument, often speaking in a ) leisurely fashion from a distance of six inches or more. The possible

deterioration of the transmitter and faulty speaking on the part of the

subscriber may have a serious effect upon the general efficiency of the

service, but no means have so far been available to test it,

A new. and it is believed, original method of carrying out

such measurements has been evolved in the Research Section of the P.O.

Engineering Department, and v/ill no doubt, be; of general interest.

Briefly, the operation consists in measuring, at the exfchai^e, and

quite unknown to the subscriber, the average maximum voltage impressed / upon the line, by the subscriber, durin any conversation in which he

is concerned.

K An article published in the VPost Office Electrical Engineers* x Journal" Vol. 17, July 1924. -68-

This voltage is compared with that obtained by an average

s p e a k e r -using a stand.axd.ised instrument.. The readings can be taken

on any suitable needle galvanometer. That actually used was a Weston > model No. 1 voltmeter. The' circuit arrangements are shown in the

accompanying diagram (Fig'. 1) .

A tap is taken from the outgoing junction terminals to.an input transformer T^. This has two windings, one. being provided

■ with several taps in order that the sensitivity of the arrangement may be varied., From this transformer the output voltage is ampli­ fied in valve-.NO. 1 end passss to a special cumulative grid rectify­ ing valve No. 2*. It is from the variations in the anode current of this valve that, the measurements are made. In ordlnaiy circumstances there w ill be the usual plate current flowing through the microamrceter; this is polarised out as shown, enabling a sensitive instrument to be used*to show the variation in plate current, caused by the changes.in grid potential of the valve 7g. The "Voltage from the second winding of the input trunsfoimer is amplified in valve No. 2 and passes thence to the anode rectifying valve No. 4, and is used to operate a high resistance 3 type relay. The amplifier on this circuit is arranged to cause-the B relay to operate with the faintest speech to be expected *in practice. The operation of the B relay closes the leak circuit, on valve No. 2 and causes rectification.

Therefore, during the whole tine that speech is passing, . rectification is occurring and a deflection recorded on the galvano- / meter. Should any sudden increaseiin, volume of speech occur, there w ill be a momentary increase in deflection, limited, however, by the fact that a fairly large condenser, v iz., 1 mfd.,must be charged before the effect is recorded. Immediately this extra speech volume ceases the, endenser discharges through the leak until its -69-

P.D. again corresponds with the average. Any gaps in the conversation

have no effect, since the grid leak is only in operation during speech;

at other times the grid is polarised by the charge on the highly

insulated condenser and the galvanometer deflection remains stationary.

It is found that any ordinary telephone conversation gives

practically a steady reading (the sending allowance can be read to

within about 1 S.M.). The deflection soon reaches its value; in fact,

it lias been found possible to record the sending allowances of each of

two parties on a local connection, provided the conversation is not

too disjointed, or the two speakers differ too much in.volume to allow

the deflection to .adjust itself with each speaker.

The accompanying curves show the changes in deflection

caused by differencies in the sending efficiencies. These curves

were obtained on an experimental set and give a total range of

nearly 40 S.M. Obviously the range is only a matter of the sensi­

tivity of the "galvanometer, but a practical limit is set by zero errors

in the galvanometer. If too sensitive an instrument be used, d iffi­

culties are experienced due to small changes in battexy voltage, .or

in resistances, upsetting the balance. The horizontal lines mark the deflections obtained with average speakers using standard instru­ ments. From these, and the deflections actually obtained in practice, it is possible to, obtain at once the amount, by which the transmiSsion differs from what it should be*. D.E.j dull emitter,

0.06 amp., valves are quite satisfactoiy and the whole apparatus, excluding cells, can be mounted in a small, portable case.

The method has distinct possibilities for the rapid routine testing .of transmitters and its use in this, and other directions, is being examined. -70-

CIRCUIT DIAGRAM

TRANSMISSION TESTING SET

( fig.I ) Mll.ES OF* STANDARD CA0L_EL RNMISO TSIG ET. T SE TESTING ISSION TRANSM CALIBRATION CU R V ES ES V R CU CALIBRATION - 1 7 - FIG. 2. 7 2 -

APPENDIX 10.

METHOD OF TESTING SUBSCRIBERS1 INSTRUMENTS

FROM‘THE CENTRAL OFFICE.

The Western Electric Company is now developing a method of

testing subscribers* instruments from the Central Office. All the

testing equipment is located at the Central Office, except a reference

instrument;, which is taken to the subscriber's premises and there

replaces his instrument during part of the test.

The method consists fundamentally in the correlation between

the direct current resistance of the carbon transmitter ard Its alter­

nating current output. There is no simplex transmission Involved and

a ll the measuring as mentioned above is done at the Central Office.

Briefly, the method of testing depends upon the measurement at the. Central Office of the direct current resistance of the subscribers* transmitters. A band of frequencies is sent from the Central Office

07©r the subscriber’s loop through a transformer in series with a coTjaenser to a -standard receiver at the subscriber station.

in the. transni fetor test, sound from this standard receiver is used to agitate the transmitter. The standard receiver is coupled to the transmitter under test by. means of .a coupling unit so constructed that it w ill screw ipto a transmitter in place of the mouth-piece.. By means Of a spring device the receiver is held in place at the other end of the coupler. The resistance of the transmitter is-measured directly on a mater at the Central Office. This meter may be calibrated in ohms regardless of the length of loop. Knowing the. correlation between transmitter efficiency and the direct current resistance of the trans­ m itter, when agitated by a given sound from t h e standard receiver, the ->73-

efficiency of the transmitter can be found*

For testing the efficiency of the subscriber's receiver, it

is planned to agitate the transmitter first with a standard receiver

and then with the subscriber's receiver under test. The transmitter

is agitated to a certain number of ohms by the standard receiver with a certain loop voltage applied at the Central Office. The standard receiver is then replaced by the subscriber’s receiver and the loop voltage varied until the transmitter again indicates the same resistance. The ratio of loop voltages should give a measure of the efficiency of the subscriber's receiver because a low efficiency receiver would require larger current to produce the same agitation. SECTION 2 - IHEEREEHEBCB ERCEf POViER QJ3CUI!r3>

III. -Protection of (Telephone Lines from Interference by High Power Installations.

The report on.this subject prepared by the Permanent

Commissi on, entitled "Guiding Principles to be observed in the

Adoption of Ifeasures designed for the Protection of Telephone Lines from Interference caused by Hi^i Fearer Installations in the Vicinity*' w a s discussed in detail and considerably modified.

NOTE: III CGmCCION WITH THE GUIDING PRINCIPLES {"DIRECTIVES")

"WHICH ARE CONTAINED IN TIE PAGES 75 ET SEQ. IT SHOULD BE NOTED.

THAT THESE "DIRECTIVES" have not been adopted in th eir entirety

BY THE BRITISH POST OFFICE. -7 5 -

GUT&ING PRINCIPLES TC BS OBSERVED IN THE ADOPTION OF MEASURES DESIGNED FOR THE PROTECTION OF TELEPHONE LINES FROM INTER­ FERENCE• CAUSED BY HIGH POWER INSTALLATIONS.

In nearly all countries with wall developed telephone systems

it has been found that the working of telephone circuits suffers from

tha disturbing influence of neighbouring power lines. On account of

future developments, which doubtless w ill take place in power, distribu­

tion lines and eieotrio traction progressive diminution in the quality

of telephonic transmission and an increase in tha danger to the personnel

and telephone plant is to.be feared, if measures ara not taken immediately

to'provent interference to the telephone service by power installations.

These measures relate to:-

(1) Telephone Lines. (I)

(2) Power Line and Installations. (II)

(3) The Proximity (Parallelism) of Power Linas to Over-ha ad Telephone Lines (III).

(4) Th3 Proximity (Parallelism) of Power Lines to Underground Telephone Circuits. (IV)

Although it is relatively simple, and beyond discussion to lay down in

detail, even at tha present time, the principle governing the major part of the technical regulations to be adopted, it is not generally possible

to fix exactly the limits, within which these regulations may be carried out. Any further contribution to tha study.of the phenomena of electro­ magnetic and electrostatic induction, as wall as any progress mad9 in the construction of telephonic and industrial material and any modification

in the normal conditions of exploiting telephone lines and high power lines, would, however, Involve a revision of the figures proposed.

Nevertheless, it.appears to be useful, even at tla present time - in order to fix ideas on the subject.- to give; certain numerical data of a.precise character with regard to the lim its within which the technical regulations recomnanded should ba applied, with a v-iew to preserving a

Footnota. These measures have been studied particularly for protecting telephone lines, other measures may be insisted upon for the protection talagraph linos. certain degree of efficiency* It is in this spirit that the numerical

conditions laid down in ths text of the "Directives" have been.determined.

On tha other hand the "Directives" should be regarded only

as the expression of the o p in io n common to the technical experts who are

taking part in the work o f tha C.O.J. Any questions of an administrative

O'r economic nature relating to the problem of the proximity of power lines

are not within the competence of tha Committee and have bean left aside.

In particular, the Coiuuittea has abstained from entering into

details of the rules of. procedure which Telephone Administrations and

the services engaged in the production or distribution of electricity

should.follow in their mutual relations. The Committee thinks, however,

that it is able to make a very general recomtnendatipn.

In onier to obtain the most advantage from the measures to be

taken for tha protection of telephone lines ‘and in order to facilitate

their practical application, it is. desirable that the telephone or telegraph

services concerned should evince the utmost goodwill by way of collaboration.

Systematic and regular exchange of all useful information relating to the

construction of existing or proposed lines and to-changes in the conditions of the working of installations which are concerned at the present time, or in the future, in proximities is much to be desired.

I . MEASURES RELATING TO TELEPHONE. LINES AND -INSTALLAT T HNre.

The sensitivity of telephone lines to the electromagnetic and e-leotros tatic inductive effects of power line3 depends on how they are constructed and maintained as well S3 upon the telephone equipment. It

is essential that the apparatus, the circuits and tha installations, generally, shall be as symmetrically arranged as possible in order to secure adeouate protection against these influences.

The telephone circu its’Should therefore fu lfil the following co'nditlons:-

(a) All telephone apparatus, which i3 connected directly to earth, or ha3 an unsymmetrical relation with respect to earth, must not bs connected to the line except through, the medium of transformers, so - 7 7 -

aa to preserve symmetry. It is not permissible to earth the neutral

point of the outer, winding of a transformer in a loaded line without

inserting a resistance in the earth connection.

(b) The two wires of a circuit shall ba of the 3ame metal and of

the Same cross-section. Differences in the resistances of protective

devices, inserted in the two wires of a circuit, are not permitted.

Permanent or other connections in circuits or installations

shall be so made and maintained a3 not to introduce any resistance

(poor contacts particularly), which would be detrimental to the telephonic

c u r r e n ts..

It is equally important that the leakance of circuit should

be as small as possible and not differ appreciably in each branch of . the

c ir c u it .

These rules also apply without modifications to groups of

conductors, which may form phantom cirouits.

(o) It is desirable to endeavour to balance as perfectly as

possible the electrical constants of aerial lines with respect to earth;

this balance can be obtained by means of. transpositions, which may be of

th9 rotating type or of the type in which the wires are crossed.

Appendix I describes methods which govern the balancing conditions of

o ircu it3 .

Provisionally, cirouits w ill be considered sufficiently well balanced, If, when tested by a comparative method, using an artificial line with attenuation, the latter is not less than b * 4; or if measured by the potentiometer method, using either a high or a low resistance, the unbalance i s not greater than 4#.

More exacting conditions w ill be laid dov/n regarding the balance of cable conductors.

I I . MEASURES RELATING TO HIGH TENSION INSTALLATIONS AND TO TRACTION INSTALLATIONS

Disturbances to the normal telephone service, due to power installations, are generally caused by the presence in the current or -7 8 -

/ voltage curve of harmonics higher than the fundamental frequency of

tha current developed by the generators or motors*

So far from being useful fqr the transmission of power,

these harmonics actually .cause energy losses* For this reason, alone,

these harmonics should be reduced as far as the present state of

technical practice permits.

The importance of tha disturbing affects of these higher*

harmonics manifests itself particularly in power installations using '

earth returns or where only part of the return current passes through

earth, or in those cases where the neutral point of the system is

earthed.

It is therefore necessary to arrange the systems for the

generation and distribution of energy in a manner to satisfy the

following requirements.

(a) All fixed rotary machines, which form part of alternating

current installations (three-phase, single phase with metallic return,

alternating current for railways) shall furnish voltages having a wave

form which i 3 practically a sine curve - either between phases or

between phases and neutral point - whether they operate under no-load

or under any load whatever.

By-"practically a sine curve" is meant that the "coefficient

of deformation", as hereinafter speoified, is less than 5^.

The equivalent 3ine curve of a given wave form i 3 onewhich

has the 3ame effective value. Superposed on the given wave fora, it

marks the differences of the ordinates. The maximum of these difference

with reference to the maximum sine-wave ordinate is the "co-efficient of

deformation". In the case of continuous current machines other than

converters, the maximum deviation of tha voltage curve in respect to

the average voltage should not exceed 3^».

(b) In tha case of motors and auxiliary motors of electric

\ locomotives efforts w ill be made, by means, of all technical devices -7 9 -

possible, to eliminate tha higher harmonics resulting from the

commutation and from the slots.

(c) When single or three-phase currant is being transformed into

continuous current by means of converters or mercury-vapour rectifiers,

it is necessary to take special precautionary measures in order to

reduce, a3 far as possible, the amplitude of the ripples superposed on

the continuous current.

(d) Tha iron in transformers shall not be allowed to become too

highly saturated. The currant on no-load must not exceed by more

than 10^ the current on full-load, at normal voltage at least for

transformers of great capacity.

(e) In the case of .traction installations where the rails are

used as conductors, particular importance w ill ba attached to the

•ensuring of satisfactory conductiy^ty of the line of rails.

In installations other than those used for traction purposes

employing pressure abovo 250 volts with respect to earth, the earth,

should not ba used even partially as a conductor;

(f) In a polyphase system endeavours-should ba made"to distribute

tha load as equally as possible between the various phases.

(g) In three-phase installations the neutral point may be earthed, subject to tha condition that the circulation via earth of currants of the 3rd harmonic (or tha harmonics which are multiples of 3) shall be reduced as much as possible, by the use, if necessary, of special d e v ic e s.

(h) In three-phase or single phase lines, in which the neutral point is not directly earthed, the installation should be provided with devicss which, v/hen a conductor is earthed, would be capable of preventing, as far as possible, the arc which produces the transitary.waves and which may causa simultaneous earthing of a second conductor (Such devices are:- discharge coils, earthed inductances, automatic interrupters of earthing contacts, etc.). - 8 0 -

{.!') Linas carrying three-phase or single-phase currant shall ba

transposed either by rotating or crossing tha wires throughout thair

whole length; these transpositions shall ba made in such a manner as

to equalise the potentials between each of the conductors and earth.

The length of one transposition section (one complete revolution) shall \ not as a rule exceed 36 ton. when the conductors are arranged in

triangular formation,* nor exceed 18 kilometres for other arrangements

of the conductors.

For double*lines carrying single phase current, continuously

in parallel, carried on tha same poles, and such that tlie polarities of

the one with respect to the other are inverted, transpositions are not

n ecessa ry .

(j) The preceding regulations apply only to

(a) new lines to be constructed;

(b) existing lines which are to be extensively altered.

They do not apply to existing lines, unless tha latter are to

be extensively altered.

I I I . MEASURES TO BE TAKES' IN CASE3 WHERE HEAVY CURRENT OR HIGH TENSION LIKES RUN PARALLEL TO OVERHEAD TELEPHONE LIMES.

When power lines carrying heavy current or high tension are

in the immediate vicinity of telephone circuits, they influence the

latter electromagnetically and electrostatically.

These influences cause such a flow of energy in the telephone

circuits as may be sufficient to endanger the personnel and the telephone

equipment or they may simply disturb the service by causing extraneous noises in the receivers, which interfere with conversation or impair a u d itio n .

In order to ensure that long-distance international telephone communication shall be as reliable as possible it seems desirable that:

* A triangular .formation is an arrangement such that the height of the triangle is greater than half the longest side. - 8 1 -

(1) Telephone Administrations shall ensure in future that the

schemes for the construction of new high power lines shall certify

certain conditions in respect of separating distances which shall

obviate the causes of danger and interference with working. When

tha Administrations themselves construct now lines in the neighbour­

hood of existing power lines they w ill have to satisfy the same

conditions.

(2) For long-distance international telephony only circuits

which are not exposed to danger and interference which may be caused

by proximity to existing power lines shall be allocated.

It is possible to protect the telephone lines against danger

and interference caused by tha presence of power lines. This can be

done by allowing sufficient distance between the power wires and the

telephone conductors and by reducing the length of parallelism as

much a3 p o s s ib le .

The rules outlined below do not apply to cases of power

lines, either overhead or underground, of which the voltage (potential

between the conductors and earth) does not exceed 1,000 volts under normal service conditions nor to casas of underground power linos, r the conductors of which are symmetrical but not earthed at the neutral point. It is recognised that the proximity of such lines is not likely to cause disturbances in the working of the neighbouring telephone circuits nor to cause accidents dangerous to the personnel and the telephone plant.

Nevertheless symmetrical; power lines carried in underground cables which are earthed at the neutral point, and of which the voltage is 1,000 volts or more, are subject to Rule 1(c) of Section A.

Section A. Rules to be adopted in examining fresh schemes of power lines which will run parallel with telephone lines. ^

With a view to ensuring that the proximity of power lines or of alternating-current electric traction shall not be a source of -8 2 -

danger or interference to tha wording of neighbouring telephone

circuits, it w ill be sufficient to ensure that, even in the most

unfavourable circumstances, danger or interference i3 eliminated.

In the following paragraphs only these unfavourable circumstances

are dealt with.

(1) There is danger, particularly :

i* (a) When the conductors of the telephone lines, are* during

an extremely short time (such as the time occupied in closing of the

switch in the power line) raised to a potential - with respect to

earth - hi^ier than 300 volt3 (instantaneous value) and when, besides,

the energy induced in the telephone circuit during the time when this

excess voltage occurs is greater than 0.02 joule, which would corres­

pond to the dissipation of an energy greater than C.01 joule, in' the

telephone receivers joined to the end of the circuit.

It is necessary to foresee this possibility of danger and to

ensure by calculation that the danger i3 avoided only in the case of

single-phase or 3-phase currant lines which are not m etallically joined

to earth at some point, and in the case of single-phase or 3-phase

electric traction lines, which use the rail as a return conductor.

The effective voltage taken for this calculation should ba

double the amplitude of the normal voltage.

When, under the noimal working conditions of an alternating

current traction line, conductors of the adjacent telephone circuit are subjected, by magnetic induction, to an electromotive force

(longitudinal voltage) the value of which exceeds 60 volts (effective).

In certain exceptional circumstances (for example, when the contour of tha ground - tha presence of a number of obstacles) does not allow the observance of this rule, it appears possible to admit that in the calculations for the planning of lines 100 volts (effeotive) may be taken as the value of the maximum permissible voltage, on the understanding that tha telephone line shall be constructed in an excepttonally robust manner and shall be subject to special supervision -8 3 -

and maintenance. Each section of circuit w ill be separated

m etallically from the other sections by means of transformers.

Nevertheless, this sectionalisation will not take place if excessive

attenuation of the telephone transmission on the circuit would result.

In examining the question it is necessary to consider what

may occur in each of the sections included between a locomotive and

the supply stations which feed the contact line on both sides of the

locomotive.

In the comparatively simple case of a sectionalised contact

line, in which each element is fed by a single sub-station at a single

point, the worst case which need be considered is that of the maximum

current absorbed by two powerful locomotives at the end of the section

of the contact line.

Where the contact-line is not sub-divided and is fed from

several sub-stations working in parallel, sufficient experimental data

are not yet available to calculate with certainty the effects of

induction produced.

(c) When, during the short time required for the actuation of a

circuit breaker of a power line, normally earthed at the neutral point,

or of a single-phase or 3-phase, electric traction line, suddenly'and

accidentally earthed, the conductors *of the telephone line are subjected

to an induced electromotive force (longitudinal voltage) greater than

300 volts (effective).

In estimating the voltage induced by magnetic induction,

allowance should be made for the value of the intensity of the short

circuit current, consistent with the characteristics of the power installation.

The preceding rule need not be applied to traction lines working with continuous current. It may be accepted that, by reason of their short duration, the accidental earthings of a traction line can be regarded as not causing any danger to adjacent telephone lines.

(2) Interference to telephone working occurs when a power - 8 4 -

line, by electrostatic influence, develops between the conductors

of tha telephone circuit a voltage equivalent (as regards the intensity

of noise in the telephone receivers) to an alternating voltage greater

than 5 m illi. volts at a frequency Q00 periods (5000 radians) per second.

In determining the disturbing voltage by calculation, the

hypothesis may be accepted that the higher harmonics of the power

installation produce the same disturbance as a periodic current of

5000 radians per second, of which the voltage would be equal to l/50

of the voltage of the fundamental current. However, if it is found

that the amplitude of the voltage of tha resultant of the harmonics is

less than 1/50 of the voltage of tha fundamental current, the calcula­

tion can be made by starting from the knov/n value of that amplitude.

The length to be dealt with in the calculation w ill be the

effective length of the parallelism? however, if the telephone line

includes rotations or transpositions only a .length which is not more

than ljs- times that for which the inductive effects on the most exposed

part of the telephone circuit, are not compensated by these trans­

positions. In any case, this length should not exceed 8 km.

(3) The disturbing voltage caused by magnetic induction,

iue to the higher harmonics of a power installation, working

symmetrically, may be considered a3 negligible as compared with that

caused by the effect of electrostatic induction.

As regards the effect of magnetic induction, duo to the

higher harmonics of power installations in which the earth is used,

wholly or partially, as a conductor, there are not yet sufficient

experimental data available to provide a reliable method of calcula­

tio n . The 3ama applies to the disturbing effect of the higher

harmonic currents which are produced by continuous currant railroads . \ with rail returns, for, at the moment, the frequency and intensity

of these currents are not sufficiently known, nor the path they take

in the earth. 8 5 -

(4) In the numerical determination -of the effects of influence

of 3-phase or single-phase lines worked symmetrically, the hypothesis

w ill be adopted that one phase of these lines may, daring certain periods,

have leakage to earth. As this is not possible in the case of lines

directly earthed at the neutral point or through a low resistance, a

c a lc u la tio n need not be made in th at c a se .

(5) In Appendices 12,15 and id w ill ba found directions as to

the method of making certain, by calculation, that the conditions

enumerated above are complied with.

(6) In Appendices12,13 end 14, no account has been taken -

so far as danger is concerned - of the inductive effects of a short-

circuit current through the earth, or of high tension single or three-

phase alternating current installations, affected by the accidental

earthing of two conductors. Hor - so far as interference in working

is concerned - has account been taken of the inductive effects of

currents of higher harmonics which, in case of a leakage to earth

affecting one phase, pass to earth through the capacity of the conductors,

nor of the inductive effects of higher harmonic currents in the case

of B.C. railroads.

In establishing the formulae, account has not been taken of

the noise already existing in telephone circuits, due to existing power

installations, even those in a perfect state of maintenance. It is

very advisable, therefore, not to adhere too strictly to the results

of calculations for the choice of distances, but to adopt the greatest

possible distances consistent with technidel and economical interests.

This is all the more advisable when it is necessary to retain a certain

latitude as provision for other parallelisms, which may occur later in the immediate proximity.

The use in electric traction installations of lines with so-called ’’balanced voltage” or of ’’suction transformers” affords telephone circuits an excellent protection against dangers and dis­ turbances. For suction transformers the use of a special return line '-8 6 -

is preferable to connecting the transformers to the rails. These

transformers have the effect of reducing the inductive effects of the

current traversing the traction line to a certain fraction. To deter­

mine the permissible distance of the parallelisms, only this fraction

need be taken as a basis of calculation.

It is, however, recommended, in the case of long sections, to

keep a distance of at least 100 metres between the telephone circuits

and the traction line, even if the calculation should indicate shorter

distances, because, in the absence of defective working of some of the

suction transformers, or in case of defects in the line which balances

the voltage, the protective effect of these devices may be greatly

reduced or even cancelled for certain periods of time.

In the case of a very long parallelism, a separating distance

of at least 200 metres should be observed.

Section B. Rules relating to existing parallelisms.

(1) For long distance international communications no use

should be made of telephone circuits in which (despite their sufficient

symmetry with regard to disturbing lines) there w ill normally be induced,

by neighbouring power installations, a disturbing voltage equivalent

(as regards the intensity of noise caused in the telephone receivers),

to an alternating voltage of more than 5 m illi-volts at 500 radians per

second.

The part of this disturbing voltage which arises from each

of the sections of the lines included in the different countries will not be greater than the ratio of the total length of each of the

sections to the total length of the circuit. To measure the disturb­ ing voltage and the degree of unbalance of the circuits with reference to the disturbing lines, one of the methods shown in Appendices 8 and

9 may be utilised.

(2) The telephone circuits which, in accordance with paragraph 1, are likely to be allocated to long distance international -8 7 -

traffic, should he watched with regard to the intensity of noise mani-.

fasted. With this object it will be necessary to determine and to

note for each circuit the disturbing voltage and the degree of unbalance

existing under ordinary conditions. The same course w ill be followed

for each one of the different sections of the circuit between the

frontier of the same country. If one of these sections considerably

exceeds 150 kilometres the sectionalisat ion will be made in lengths of

about 150 kilometres (maximum lim it).

(3) In cases where noise becomes particularly noticeable,

it w ill be necessary, first of all, to determine, by tests on successive

sections, on which section the increase of noise is manifested; in this

determination it should not be overlooked that the unbalance of the line

rasy come from a section different to that where the source of the dis­

turbance arises. The cause of the trouble w ill be fcund by measuring

the disturbing voltage and the unbalance of the circuit with reference

to' the disturbing line.

An increase of the numerical value of the unbalance of the

circuit indicates that' the condition of the circuit has deteriorated.

On the contrary, if the degree of unbalance of the circuit has not

changed, an increase of the disturbing voltage is an indication of a

change in the normal working condition of the power line.

(4) In many cases an excessive disturbing voltage can be

reduced to a tolerable value for the length of line included in the territory of a particular country, if it is possible to improve the balance either of the telephone circuit or of the.power line or even of b oth .

(5) With regard to existing, proximities, which do not conform to the conditions laid down in Section A, it is desirable to foresee the possibility of a danger arising from the effects of electrostatic induction and induced longitudinal voltages. . If it is not possible to eliminate this danger by the application of 8 8 -

special measures in the power installation, the danger of acoustic

shocks can he reduced to a certain extent by the use of transformers,

protectors of the coherer or vacuum-tube type, etc.

IV. MEASURES TO BE TAKEN IK CASE OF PROXIMITIES BETWEEN POWER LINES AND TELEPHONE GABLES.

When the telephone line is cabled, the effects of electro­

static induction may he regarded as negligible.

Consideration of the danger caused by longitudinal induction

determines the minimum distance to be allowed between the power line

and the cable. In-these circumstances, this distance is suph that,

as a general rule, it should not be possible for a voltage sufficiently

high to disturb telephonic transmission to he developed on the circuits

by magnetic induction.

If, in isolated cases, it should not; be possible to obtain

tho minimum d ista n ce req u ired , i t would be d e s ir a b le to form ulate some

specially rigorous requirements with regard to the balance of the telephone circuits as well as the breakdown strength of the conductors of the cable with respect to the lead sheath and that of the installa­ tions which are connected thereto.

By. reason of the small degree of cross-talk admissible for international telephone lines in cables, the permissible disturbing voltage on the circuits should not exceed the value equivalent (as regards the intensity of noise set up in the telephone receivers) to an alternating potential, at 5000-radians per second, of 2 m illi-volts.

By ensuring as perfect symmetry as possible of the circuits in the cable, interference to working, due to magnetic induction, can be sufficiently eliminated or neutralised.

Even if it be true that proteption against disturbances does not require a fixed minimum distance of separation, it is nevertheless advisable not to instal on the railway tracks themselves, or in their immediate neighbourhood, underground telephone cables intended for long distance international communication. -8 9 -

When a cable armoured with iron bands is employed, and the

sheath (including armouring)1 is suitably earthed, the currents induced

in the sheath of the cable provides some degree of protection, reducing

by about .40^ the magnetic induction of the power lines v/hen a short

circuit occurs as well s s under normal working conditions. In this

case, in order to determine the figures expressing the danger, only

60fo of the value of the short-circuit current or of the traction

current corresponding, to the most unfavourable load need enter into

the calculation. •

If the underground communication lines terminate in repeat­

ing coils and are not provided with lightning protectors between

lines and earth, the maximum admissible of the values expressing the . danger of induction, when short circuiting occurs, is considered to be

6C^o of the value of tha breakdown voltage between the cable conductors and the lead sheath, that of one winding of the repeating coils and another winding or between the.windings and their m etallic sheath.

When work is boing done on cables which are exposed to considerable inductive effects due to short circuits and which, con­ sequently, under nonnal.working conditions of the traction system, are liable to heavy increases in these effects, special measures of precaution should be taken. -9 0 -

Appendix 11 (with supplement )

JBgERMINAT'lON 0? THE SYMMETRY TO EARTH

OF TRUNK TELEPHONE LINES.

s ^

1. Method of Comparison by Means of an A rtificial Line with Attenuation (See Fig, 1).

The primary of .a transformer is connected between the conductors

of the circuit to be tested. The secondary of the transformer remains

open. The middle point of the primary is connected to one of the outgoing

terminals of an artificial line having a fixed attenuation b s 2. The

( other outgoing terminal of this line is connected to earth. The incoming

terminals of this artificial line are shunted by a buzzer. The object

of this line with fixed attenuation is to maintain the effective voltage

co n sta n t.

Between the terminals of the primary of the transformer there

is a difference of potential corresponding to the extent of the unbal­

ance of the circuit under test. A telephone receiver, the impedance of

which should be equal to the characteristic impedance of the circuit, is

connected alternately to the line and to the terminals of a special cir­

cuit comprising, in addition to the buzzer and the fixed artificial line,

an artificial line having variable,attenuation. The test consists in

adjusting the value of this variable attenuation in such a manner that in j either position the same sound intensity is observable in the telephone .

r e c e iv e r .

The unbalance of a line with regard to earth may he represented

* by the value: -

/ , - K*. - Rb - = Ra - % A e " l/2(Ra-* R

(vide Supplement: Equation 1). It is possible, by this method, to measure the value of b in the equation

A e = 2 e_b (vide Supplement: Equation 6a). , -9 1 -

The minimum valu e ad m issib le fo r b i s taken as 4 .0 .

This method has been found to be simple, .reliable and easy

to carry out.

II• Method of Measurement by Means of a Potentiometer of Low Resistance (See Fig. 2 ) .

The mid-point of the primary of the transformer is connected

via a resistance of 1000 ohms to one of the terminals of a buzzer; the

other terminal of the buzzer being connected to earth.. A telephone

receiver, of which the impedance ought to be equal to the characteristic

impedance of the line, is connected alternately either between the two

branches a b of the circuit or between the terminal c and the movable

contact of a low resistance potentiometer c d (c d *= 10 ohms). In

the latter case, an impedence equal to the characteristic impedance, Z,

of the circuit should be inserted between the receiver and the potentio­

meter-. The test consists in adjusting the movable pontact of the

potentiometer to such a point that in either position the telephone

r e c e iv e r g iv e s th e same in te n s ity of sound.

Let therefore, be the ratio of the pote tiometer. We

then have the r e la tio n = -J2L. (vide Supplements Equation 8).

A value p * 4$ (vide Supplement: Equation 9) here corresponds <

to the minimum value of b (« 4.0) permissible by Method 1.

Method Z is just as practicable'and simple as Method 1.

I ll. Method of Measurement by Means of a Potentiometer of High Resistance (See Fig. 3).

In this method also, as is in Method 1 and 2, the buzzer

voltage is joined between earth and the centre point of the primary

of the transformer winding which closes the line, by inserting a re­

sistance W (e.g., 1000 ohms) between the buzzer and the transformer.

A telephone receiver, of which the impedance should be ©quarto the

, characteristic impedance, Z, of the circuit,,is connected alternately

either between the branches $ b of the circuit, or shunted to the

fixed portion (600 ohms) of'a high resistance potentiometer. A . - 9 2 -

movable contact permits the variation of the total effective resist­

ance of the potentiometer, which should be at" least 6000 ohms. This

movable contact is connected to’earth. Here, again, the test con­

sists in finding equality of sound Intensity for both positions of

the telephone, by suitably selecting the earth point on the potentio­

meter. Let p^, therefore, be the ratio of the potentiometer. We

then obtain the relation (vide Supplement: Equation 10). r 0 ioo This procedure, which is as simple and'reliable as the

preceding, offers the advantage that with the seme circuit arrange­

ment measuring apparatus can be usedi which may also be employed for

the determination of the degree of unbalance of a telephone circuit with respect to lines causing interference (see Appendix 6). It is

only necessary for the actual measurement to connect to the terminals

of the circuit the primary winding of a toroidal coil and a buzzer. - 9 3 -

a

DIAGRAM 1. MEASUREMENT OP THE 6YMMETRY OF" A TELEPHONE! LINE BY MEANS OF A COMPARATIVE ATTENUATING RESISTANCE

a.

DIAGRAM 2. MEASUREMENT OF THE SYMMETRY OF A TELEPHONE LINE BY MEANS OFA LOW RESISTANCE POTENTIOMETER

a.

DIAGRAM 3. MEASUREMENT OF THE SYMMETRY OF A TELEPHONE LINE BY MEANS OFA HIGH RESISTANCE POTENTIOMETER. -94

Supplement to Appendix 11.

NOTES ON TESTING AND SYMMETRY 0? TELEPHONE

LINES WITH RESPECT TO EARTH*

a) Definition. If Ra anl R^ are the impedance of wires a and b with

respect to earth, the degree of dis-symmetry or unbalance of tha

circuit with respect to earth is defined by tb 3 formula: Ra ~ Rb u9 = 1 /2 (Ra + Itb ) (1)

If uQ is small, it is evidently equal to Rg - Rk)/Ra or

"(Ra - R-b)/R^j. In this 3tudy u0 is considered to be small, so that,

where Ra and Rb are not greatly different in magnitude, both may be

* replaoed by their mean value R* b) Principle of Measuring Method. uQ is determined according to tha

principle indicated diagrammatically thus:

An inductance (the primary winding of a toroidal coil) is

bridged across tha two line wires and the constant voltage, E, of

an earthed alternating current generator (buzzer) is applied to the

centre point of this inductance* The constancy of the circuit

under different loads is secured by the use of a derivation through

a small part only of a potentiometer or by means of a suffic\ently -9 5 -

high series resistance. If Ha and Rb differ in value, it follows

that the potentials Ea and 2b at the two terminals of the winding

of the transformer w ill differ from one another. The difference

of these two potentials produces a current i =• (Ea - Eb)/?

tha measuring apparatus (the telephone receiver impedance ** ).

Tha receiver is then joined across tha outgoing terminals of an

artificial line, having varying attenuation, with a working

I voltage E, or it can also be joined in parallel with the arm of

a potentiometer to the ends of which tha same voltage 2 is applied.

The attenuation of the artificial line or ratio of the potentiometer

is regulated so that tha intensity of the sound in the receiver

(i.e., the current flowing through the latter) is the same as

before. The attenuation value, b, obtained after balance,

satisfies tha equation: Ea - 2-^ ~ E x e ; if a potentiometer

is used and if the adjustment is obtained for the ratio pjb we

have: (Ea — E^) =» x S (see explanations below). From these

relations tha value uQimay be calculated. c) Theory. In order to determine the relation between u3 and the

attenuation, b, defined as above, or between ue and the ratio p?o

of the potentiometer, it is necessary to compute the value3 Ea and

E'0. If 1 represents the coefficient of self-induction of each of

the branches a c and b c, and likewise the coefficient of mutual

induction, then, when we neglect the fall of potential in these

windings, caused by the ohmic resistance of the two branches, we

have: ,

Ea =* 3 - j u> L (il - i£ ) =* Ra (il - i)

33b - E -J u> L (i2 - ixj » Rb (i2 + i)

Sa-Efc-^i

.If, in solving these equations it is assumed that uj L i 3 ■* much greater than (l « 10, ur = 5000, ^ 500) and that therefore

l/uiL can ba neglected in comparison with 1/?, we have, as the

* approximately equal to -9 6 -

solution of tha39 equations: 2 Ra (

2 ? (Ra - Rb) Ea - Bb* 2 4 r3 Rt hT^> (Ra + Rbl (3)

If there is "but slight dis-synanetry, (Ra, Rb ~ R)

So that Ea =^E# Eb »~E

Ea * Eb - E Ra ^ Rb x 9 = 2 x ua . ^ (4) R

Consequently, uQ ■ R x - - T ffi3.

E is in all casas tha potential at tha mid-point of the winding of tha transformer.

If, instead of an inductance coil, wa usa two ordinary re­ s is ta n c e s as p ro p o rtio n a l arms the v o lta g e s , Ea and Eb* would ba much smaller than E, while in this case E lias ‘between Ea and Eb* When tha dis-symmetry is small (small values of Uq J, Ea, Eb and E are practically equal. It is, therefore, of relatively small importance, in comparative -measurement, whether the attenuator or the potentiometer is connected directly to E or - when a line is Joined up (as in the method employing a high resistance potentiometer) - to Ea or E^; provided always that in such cases the distribution of the voltage is not greatly modified. This condition evidently holds good only whan a high resistance potentiometer is used as a substitute for the attenuator. '

The value of (Ea - Eb)/s is determined for each case.

As alread y deduced,

u0 - ( ? + 2,R)/

u Q » 2 (Ea ■*" Eb ) / E (6) -9 7 -

&} Measurement of Symmetry by Maan3 of Comparative Attenuation.

For measurement "by means of comparative attenuation the

following relation holds good:

jEe'k =* E

-A/vVW /VWWt VWVAr

13 BUZZER y RECEIVER i <0 y

AWW -AAAAAr -AAA/W-

Indaod the potential across the receiver (adjustment to

equality of sound being pre-supposad) should hava the same value

as that obtained when either the receiver is joined to the

attenuator or to tho terminal of the winding of the transformer.

The value of" b corresponding to this adjustment should be

reduced .by about 0 ,7, because

u9 ~ 2 (Ea - Efcj/s -.2 I a-- - a (0.7 - *), g-l* - 0.7) (6a) e) Measurement of Unbalance by Means of a Low Resistance Potentiometer.

On the same assumption (*> = 2 R ® Z) a low resistance poten­

tiometer, that is to say, one in which only a low resistance is shunted

across tha receiver, w ill only give one half the value of ue, since

equation (5) is equally applicable to potentiometers. If, when con­

nection is made between th9 potentiometer and telephone receiver, the

resistance Z is joined up in series with the receiver, we shall have

a potential

E ■ x i f e ‘ x ?/(*> 4 ^

when the ratio of the jjo tantieme tor is py> at the telephone receiver.

This expression is equal to Ea - Eb, if the same intensity

of sound is obtained when adjustments are made so as to obtain the -■ -9 8 -

same in t e n s it y o f sound.

In that case, if the value of (Ea - Eb)/s is inserted in

equation (5), v/a get:

= u Q x ( ? + Z)/[?& 2 3) ■ uQf jqj

if 2 * 2 B,

In t h is cslsq a maximum p e r m is s ib le v a lu e p « 4^ corresponds

to the permissible minimum value b * 4 - as measured by moans of tha

comparative attenuation method - since: -

u * - 0 .7 ) a .JL_ or p io o a“3 *3 « 4 (9) f) Measurement of Unbalance by Means of a High Resistance Potentiometer.

The same result may be obtained by means of a high resistance

potentiometer which is connected for measuring to the point a,, in'tha

first diagram. The circuit of this potentiometer is arranged in such p a manner that, v/hen it indicates the ratio xoo, the resistance R^

(see diagram below: not to be confounded with R) ha3 the value

R “ — 1) x 600. If 9 is extremely great, the potential across p tha receiver would be-E x 10Q. In reality the fixed 600-ohm resistance

shunt is shunted by a resistance 9 + Z - 600 (see diagram below.)

RECEIVER (?) Z” 600 -VWWv—i

A/WWWWSA---- ^VVVWWsA/VVVWNA 600

Igl BUZZER __ LfJ Y /# /m

The potential across the terminals of this resistance is

,therefore E loo x (?+ 2 - 600)/(?+ 2), being supposed to have

a high value as is the case in ordinary practice), and tha potential

across the terminals of tha receiver itself is E x jfaj x ? / ( ? + 2 ). The adjustment consists in choosing p so that this potential equals J2a - E^.

We then have:

u9 - <9+ 2 R)/9* (Ea - E„) / E - (9+ 2 R)/(9+ z) x ^ - U2-

Z again being * 2 R, -1 0 0 -

Appendix 12,

With Supplements 1 and 2 .

Examination of the Conditions, under which Proximity may he permitted between High Tension Power Lines' — Poly-phase or Single-phase Alternating Currents, symmetrical and not connected m etallically to earth at any point - and Telephone Lines.

A. OBJECT OF THIS APPENDIX - DEFINITIONS.

1) The term ’’high tension lines” includes all overhead lines of

the same high-ten3ion system which are directly connected to one another,

i.e ., without any intervening transformers, to which the current is

supplied by a common generating station or transformer plant or by

several generating plants or transformer plants, working in parallel.

2) To determine the degree of proximity (parallelism) which is

allowable, each high .tension system should be considered independently.

It is not to be presumed that several independent high tension systems'

in the neighbourhood of the same telephone line, may cause danger or

interference simultaneously. It may be assumed, indeed that a fault

(e.g., an earth leak), in the high tension system such as is taken as a ba3is for determining interference, w ill not manifest itself simultaneously in several high tension systems nor w ill it be main­ tained for very long. .

3) The voltage of supply is the nominal value of the voltage U3ed in tha high tension line.

.£) A "parallelism” occurs where a telephone line runs equidistant with a high tension line.

5) An oblique proximity occurs where a telephone line and a high tension line are separated from each other by a distance which varies uniformly between the two terminal points of the line. This oase is analogous to a parallelism comprising a separating distance equal to the geometric mean between the lines at the extreme points (maximum and -1 0 1 -

minimum distances of the two lines).

6) The length of parallelism is taken as tha projection of the

telephone line- on the high tension line within tha same zone of

separation, in which' the distances between tha .lines are not widely

d iffe r e n t.

7) Tha point where the high tension line passes from one side of

fcha telephone line to the other is called a "crossing". The "crossing”

is assumed to finish on each side of the telephone line at the points,

where the distance from the telephone line is equal to 10 metres. The

adjacent sections are regarded as "proximities".

5 PAKGER.

1) To estimate the danger, to Which tha telephone lines are

.exposed by parallelisms or proximities of power lines, a zone of

influence is to be considered as extending to both sides of the tele­ phone line, and bounded by the latter,and a line parallel to it at a distance?

The distance aq, calculated by this formula is expressed in metres when the supply voltage is expressed in volts.

2) Proximities are not dangerous so long as the high tension line is outside the zone.

3) If, on the other hand, the high tension line is situated within this zone, it is necessary, when taking into account the proximities Of this line already existing within this zone, to

.arrange the proximities in such a manner that the electrical energy which acts in the telephone circuit and which is caused- by the sum total of all the proximities, does not exceed l/50 Joule.

4) a) To determine whether this value of the induced energy is exceeded or not, the characteristic coefficient of the exposure to danger is employed: -1 0 2 -

in which E b x c V " Ton x 2 2 p x q x r 400 ^ x b^ x c 4

In these equations:

£ s* length of the proximity in kilometres.

Z a number o f w ires in the system to which telephone circuit belongs.

E * working voltage of the high tension system (expressed in volts).

a » distance, in metres, between the two lines.

b » average height, in metres, of the high-tension line above earth.

e » average height above ground of the telephone circuit, in metres.

The factors p, q, r, express.the effect of the voltage drop

(screening effect), due to neighbouring earthed bodies. The following values w ill be inserted.

In the case of an earth wire running the whole length-of the system (lightning protector) p ■ 0.75.

in the ease of a continuous row of trees in close proximity to the high tension line q 0.75.

In the case of a continuous row of trees in close proximity to the telephone line r « 0.7.

In the two last cases the distance between the rows of the tr e e s and the lin e s are a'ssumed not g reater than 3 m etres. In the absence of earthed bodies of this kind, the corresponding factors p, q, r, should be expressed by unity.

When the high tension lines are carried on poles more than

120 metres apart, b may be taken as 12; in other cases generally b » 8. The height of the telephone circuits, o, is usually taken as being equal to 6. -1 0 3 -

b) The characteristic coefficient of exposure to danger, f,

should be determined separately for each of the sections, within which

the distances between the lines remain fairly constant. If the

coefficient p, q,, r or z vaiy in any one zone, the length of proximity

should be suitably sub-divided and the characteristic coefficient of

exposure to danger should be determined separately for each part of the

line. Crossings do not enter into consideration.

c) The telephone circuit should be regarded as exposed to

danger when the sum of the various characteristic coefficients of

exposure to danger exceeds 50.

d) When the high tension line has a voltage applied to it by

means of an interrupter of low power or by means of other plant capable

of eliminating transit oiy waves, the sum of the coefficients of exposure

to danger should not exceed 100.

e) To calculate the characteristic coefficients of exposure ■

to danger in the case of single-phase or 5—phase high tension lines

the example given in “Supplement 1 may be used.

C. IKTERFEREHCB.

1) It is recognised that, even if disturbances are partially

compensated by twisting or. transposing the telephone line wires, an unfavourable proximity may nevertheless coincide with a section of the

telephone line, in which the system of transposition employed does not

completely compensate the effects of induction without the influence

of the adjacent sections of the telephone line annulling or diminish­

ing the interference effect. On the other hand, it cannot be admitted that the telephone line w ill be affected in the sama manner in two or more sections .of this type without the disturbance being diminished or entirely annulled by the. influanc8 exorcised by tin other sections.

2) Only proximities which lie within a zon8 bounded by the telephone line and line parallel with it at a distance a * 4y^5 a/ eZ" -1 0 4 -

need be considered. Crossings dp not enter into consideration.

3) In the case of proximities which do not satisfy the conditionss-

a > 1 /4 V Y 2 ( f o r 3-phase high tension lines}

or

a* > l /5 V %£ (for single-phase high tension lines)

a disturbing voltage of more than 5 m illivolts nay be feared.

The distances a and are expressed in metres when E is expressed in volts and & in kilometres.

Tor 'C the effective length of the parallelism w ill be taken; in the case of a telephone line, provided with transpositions, the le n g th forwill be taken as, at most, equal to one and a half times that of the section in which complete compensation of the effects of induction has not bean assured. In any case this length should not exceed 8 km.

D. FINAL OBSERVATION.

The conditional equations for determining the degree of danger(B) and of disturbance (C) to which telephone lines are exposed hava been derived from well known calculations which are used for determining the disturbing influence of tha electric field of high tension line 3. Account has been taken of standard constructional practice and certain quantities have been neglected as being of small importance. In the case of special methods of construction or, if in particular cases, the hypotheses formulated and the approximations obtained do not seem to be warranted, the conditional equations developed in Appendix 2, which lead to the conditional equations given in the introduction to thi3 Appendix, may ba referred to, in order to determine the degree of danger or interference. - 105 -

S u p p l e m e n t X ^ 0 A p p e n d i x 1 ^ .

DETERMINATION OF THE CHARACTERISTIC COEFFICIENT OF EXPOSURE TO DANGER

LINE _ VOLTS BETWEEN-______AND ------

TELEPHONE LINE EXPOSED ------,------

LIMIT OF THE ZONE CL* m

v = f = N“ LOCATION OF LENGTH CL *b. C P

1 e 3 4 5 G 7 6 9 l b 11 12 13 14 15

,

TOT/LL,

£ f a 3 0 FOR r V 100,000 VOLTS. /

- 1 0 6 -

Supplement 2 to Appendix IS .- .

Development of the Formulae used for determining Electric Induction (the Capacitative Influence) exerted on Telephone Circuits by symmetrical Three- phase and Single-phase High Tension Line3 w ithout Earth Return.

I. Development of the General Formulae.

II. Development of the approximate Formulae for direct calculation, derived from the geometric constants of the line.

III. Development of the conditional Equations, B 1 & 4 (Dangerous Cases) Appendix .2. *

IV. Development of conditional Equations C 3 (Interference) Appendix 2.

I.

' Development of the General Formulae.

The basis of the general formulae is a system comprising the

tnree high tension lines 1, 2, 3 and the two telephone conductors 4 and

5 (F ig . 1 )» and earth.

. V1# V2* v3 ara th9 voltages of the high tension lines

o f frequency w. , V4 and V5 are the voltages, to be determined, of the s telephone conductors mutually connected by apparatus of resistance R,

in which the current I4 5 » (V4 - ¥5 )/% is flowing. It is further

assumed that the telephone circuits are completely insulated with

respect to earth. If now we oall the partial oapacity per

F ig . 1. - 1 0 7 -

kilometre of the conductors jx and v, one with respect to the other, and

the partial capacity between the conductor fx and earth; and if L

represents the length of the circuits, we get the following equations/

by applying'Kirchhoff’s Law to circuits 4 and 5, respectively:-

j w€ku (Vj - v4 ) + j u i € k 24 (Vg - v4) 4 i mlzM (73 - 74)

+ j ui-£k45 (7g - V4 ) 4 1/H (7g - 74 ) - 3 w'-fcCK) V4 - 0

(1 ) J ui€k15 (Vi - 7g) + j u>/k25 (V2 - Vg) 4 j ui£ k 35 (V3 - Vg)

4 j w / % (74 - Vg) + l/R.(74 - 7g) - J » / x 50 7g - 0

In order to simplify the calculations we transform the capacities

to coefficients of induction and the capacities C^ , according to Maxwell's

theory; .. these have the following relations to X^r:

C/AV " " f 7 ).

Cyxyti- X^Ul + XyU.2 + • • • • K^xjjL— 1 + Xyu.0 + XyUyu+ 1 + • • • • Kfxn ( 2 )

thus, for example: C14 - - K14, « Ku 4 4 Kg4 4 K40+ K45

Equations (1) now become:

- J. w£ (\\ C14 4 72 C24 4 73 034 4 74 044 4 ,7 5 C4 5 ) 4 l/R (Vg - V4) - 0

- 3 111 i - ( C16 4 V2 C25 4 7 g CJ5 4 74 C45 4 Vg Cgg) 4 l/H (7 4 - Vg) ■ 0

. <4 ^>

and these, wh9n solved for V4 and V5 , g iv e:

? .

7 g - - J nj/( 014714C24724G2473 ) (Jm&4S-l/R ) 4 3«^0x571402572403573) ( > & 444l/R)

{ } w £ o i 5 - l/ R ) 3 - U ( u / c 4 4 4 l/R ) (3u)/c55 4 l/R ) -1 0 8 -

The currant, which flows through R is evidently I45 * (V4 - V5 )/R; b y a simple transformation we obtain tha expressions

I 4 5 =, w>l(Qx4Yl* C24V2‘fC54v3) (C4 5 +C5 5 ) - (gi5Vx-^25v2+C35Y3) (G45 4 G44 ) ( 5 )

«J (c44+2 G45+G55^ + R fC452“°44C55^

In all cases which arise in the telephone service, with the possible exception of telephone communications carried on the same poles as the high tension line, R is small compared with the capacity reactances, and V4 i s practically equal to V5. To simplify matters R is therefore assumed to he zero. It follows that Y4 * Yg and I 45 is at its maximum value. Tha following formulae hold good in this case:

- Vi (C14 + 0151R) + Yp (C’24 + °25 °44 + 2 G45 + °55 ( 6 )

- j « l { t c 14Vl ‘^2 4 V2‘f034Vg') " ^c15Yl'fC25Y2+C3575 ^ G4-5't'C44 ^ *45 044+2 C45 + c55

In order to compute Cyuv W9 assume that, for the electrostatic problem in hand, the action of the earth, as regards its surface, can be replaced by the image of the conduotor with respect to the earth’s surface; also, that, on the other hand, all the lengths of the circuits are large compared to separations, in order that logarithmic potentials may be applied.

If now we call a/xv (Fig. 2) the

distance between tha conductorjjl

■ and the oonductor v% a/iyu. the radius

of the conductoryu., D^ the d is ­

tance between the conductor v and

.the image of the conductoryu, Dynyu.

I twice the height of conductor jll

above the ground (that is to say,

tha distance which separates it

from its own image); if, finally, F ig . 2. we put: -1 0 9 -

»)

d uV = x ^ V' (7) * /UiY

and

dl l d l2 dl3 ...... d in

u d23 ...... n (8 ) 0 d2l d 22 2

d dn l dn2 dn3 ...... nn we have with sub-

e tc . or determinants ^ 1 2

a d ^ + d 12 A 12 * d13 ^ 1 3

we obtain:

l/u.\ 'juy ~ 15* x ■ / A x 10 p/kb* (9)

The development of (9) can be found, for example, in "Theorat-

ische Telegraphic" by Breisig, 2nd Edition^ 201, and on page 130 of

Braun*3 "Telegraphan-u. Femsprachtechnik", Berlin, 1919* -This

development, it may oe briefly remarked, is based on tha fact that, in

tha linear equations which express the potentials of tha various con­

ductors as functions of thsir own charges, tha d values, which repre-

sent the differences of tha two logarithmic potentials, are tha charge

factors. If these equations are solved according to the charges, the

^/uly valU9S are the coefficients of tha potentials and are related to

the dvalues by the determinant A of the system.

By substituting (9) in (6) we get:

V ■ V a V1 ^ 1 4 + A i15 s )) + v2 V2 ( A s 4 ^+ ^ 25) + v 3 ( ^ 3 4 + ^ 35) A 44 + 2 A 45 + A55 (10) I w jm-l (A^-h A45) (vx A^g+V^ A35+V3 A35M A 55+ ^45) (7qA14^V2A^Vg Ag4 ) t O 18 x 106 A (A ,. + 2A«+A«) ■44 ~ ‘-% S *^55'

These equations form the basis of the following calculations.

x) I n denotes: a natural or naperian log. -1 1 0 -

Note that in the aquation for Y4 tho frequency no longer appears. Tha

equation therefore is valid for any form whatever of the voltage curve,

thus, for example, for surges (ondes transitoires).

II.

Development of Approximate Formulae.

A. Single-phase Current Lines.

In the case of a single-phasa current line with a working

voltage E, tha equations (10) may be reduced to:

( 11) * ^ ^ A 44+A 45) ( 7 1 A 15-fv2 A 25) - (A 55+A45) (VpA X4~f v2 ) I 18 x 10^ A ( A 44 + 2 A 45 + A 55)

because conductor 3 is absent.

In the '’Recommendations"' ("Directives") in order to estimate

the degree to which a telephone line is exposed to danger and interference,

i t i 3 presumed that tha high tension installation with one phase earthed is

affected by the earthing of one phase. In this case tha effects which

the high tension line would produce in tha absence of faults are negligible

in comparison with those produced by this earthing. In order to simplify

tha calculations 59 may therefore assume that A q4 * A ^ and A 15 * A 25;

that is to 3ay, we assume that tha high tension line ha3 transpositions

sufficiently near each other. If conductor 2 for example, is earthed arid we now have:

V2 a 0 and Vq » E ( 12 )

Therefore:

* -^E (A q4 + A i 5) /( A 44 + 2A 45 + A 55)

(13)

j u i 'C E [/& 1 5 (^ 4 5 +A44) —A | + & 4 S ) J I ■45 IQs ( A 4 4 + 2 A 45 -1 1 1 -

Ina3rauch, however, as A 4 4 * A 5 5 sufficiently approximately,

the equations (13) take tha following simplified forms:-

v4 * v5 - - g (A I4 +A15 )/(A 44 + A45 )

(13a) * 4 5 * W ^ ^ (A 1 5 ~A 1 4 )/(/S x 10 *3b)

For the 3ake of farther simplification we may introduce the

d values in place of the A values. If, in evaluating the determinants,

we consider that the values of d, in installations of ordinary types of

construction, are of the follov^ing magnitudes: dqq, d22, <144, d55 )

approximately 9; d45 approximately 4; dq2 approximately 2.5; ) (14) ) dq4 , dq^, d ^ , dgtj approxim ately 0 .6 or less, and if we neglect the )

minor terms, v/e have, as developed in the "additional sheet" (where it

i s assumed th at dqq =*■ d22, d44 * 1 55).

A =* (d q q 2 - d 122 ) ( d 442 - d452); ^44 + A ^ 5 « (dq q2 - d q 22 ) ( d 44 - d4 5 );

A 15+ A q 4 * -(^ll-^iaHiqs+^uJ^^^sJsAqg-Aq^ -(d 11~d1 2 ){dq5-4 14)(d 44+d4 5 )

and hence

y , , £(dn - d12) (d15 + d 14) (d44 - d4 5 ) _ E 2 dl s + di4 (15) 2 X ( d jj2 - d122} (d^ - d45) ^ dn + d 12

r » Jm^Etdis - d14) (d12 - dn ) (d^-t- d45) .Im^EfdiA- diR)_ jl g . 18 x lO ^i^-di/H d^-d^2) x 2 3£xl0 6 (di;L+d1 2 ) (d4 4 -d45 )

Th9 denominators of (15) and (16) depend only on tha geometric dimensions of tha high tension and telephone lines and, since these dimensions do not vary appreciably between one installation and the other and are confined to their Napierian logarithm, these denominators may be replaced by the numerical values obtained# When aqq * 4 mm.; Dqq * 2x10 m.; dqq w ill, for example, be =* ^n 99999. * 8*5, and when the distance between A - 4 , , 0 2Q&QQ the twin phase conductors is 1.5 m.; dqg * n qsoo * when, furthermore, a44 * 2 mm., D44 * 2x 6 m.; and when the distance between -1 1 2 -

the two telephone circuits is 30 era., d44 * ^ ** 8*7,

d.45 “ =* 3.7. It follows that dqq + dq2 «* 11*1 and vUO £44 *- d4g « 5*0. Only dq4 and dq5 s till appear in th® numerators;

they can be simplified by development in logarithmic series. By

giving a, b, o the signification indicated in B4, Appendix 2 of the

"Recommendations" (“Directives'^ we got:

1 + 2 b c 1 /£n a2 + (b + c )2 l / a* + b2 + c ‘ dq4 n £ l l * I— —5--;------r r ** — 4,e a *_ (b - c - b o S14 2 2 )2 2 1 2 (17) 2 b o a2 + b "+ c 2

if we neglect the higher terms in tha development in series. The

value (17) of dq4, as also that of dqs is thus rather too small; if

it be substituted in (15) and if dqq + dq2f are given the value 10 by

way of compensation.

b o V4 - V5 = I x a 2 + b2 + c 2 (18)

We obtain from (16) (by inserting £44 - £45 « 5 in the denominator

dl l + d 12 * 11«1 )

45 0 .5 u) (d i4 "• dqg) 10 ^ A (18a)

(Tha operator j has been eliminated).

dq5 - dq4 can be calculated most simply by differentiating with respect to a and c, the expression (17) for dq4._ If x and y are the components of the width <0 of telephone line loop in the directions a and c (Fig. 3), wa have:

^ > { 2 a 0 x - y (a^ t2- o2)} A 'H b • X C • *

-*----a ----

F ig . 3. -1 1 3 -

Since in four-wira groups tha loops may as 3um8 any position,

wa assume tha most unfavourable ona, for which:

x * 2 a c < * - ( a 2-fb2- c 2 ) x

V (a2 +b2 -c2)^ + 4 a2 c 2 V^(a^+b^-c^)2 + 4 a2 o 2

In this case, tharafora, it follows that:

2 b <£a / T s1* V •b'* —' c^ )2 -f 4 as d14 “ d15 (a2 + b^ + and

(19) tu£ E \>dV (a^ + b2 - 0^)2 + 4 a2 02 ^ lo*"® L45 (a^ + b^ + C2 )S

B. Three-phase Currant Linas.

If E is tha working voltaga, V * e//" 1T is tha absolute valua

of the potential of tha phases, wa hava for a normal installation

(i«e» ona without any faults):

Vx » V /a Cl + iVz); V£ - V/2(1 - j

If line 3 is accidentally earthed wa have:

s V/2 (3 + jV^T); Vg » V/2 (3 - jy^3); V3 « Vi + Vg + V3 « 3V ( 21)

If, in order to simplify as before, wa assume at once - as a first approximation - that A jj * A 2g * ^ 33* ^ 14 * ^ 2 4 “ ^ 3 4

A 15 - A 25 “ A g g ? A 44 ® A 55» equations (lCty whan conductor 3 is earthed, become:

( A u t.A 1 5 )(5 + jV ^ H (A 1 4 4 A i 5 )(5-J,y/5) , -1.5V (A 1 4 + A 15) V4 ~ *5 -V / 2 2 (A44+ A45) A44+A45

( 22)

^A44^ A 4 5 ) { ( A i 5^ A 14 )( 34:jV 3 )-f ( A 15- A i 4 )( 3-j V3)} a jo/vi A 15-A 3.4 )

18 x 106A ? 2 ( ^ 4 4 + A 45) 12 x 106 x A -1 2 4 -

Tha determinants which appear hara ara sim plified in tha

Appendix, the-values given in (14) being taken into account. In

order to complete (14) 433 is therefore expressed by 9; and\

d<>3 by Z .s 1 and d^., d35 by 0.6 r ' We then have:

A - (d-n - dl 2^2 (dl l + 2 d12^ (d44W - d452 ^

44 + 45 * (dl l - d12) 2 (dl l + 2 d ig) (d44 - d4 5 )

(23) 15 14 (dn - d12)2 (d15 + du ) (d45 - d4 4 )

15 14 — (d2]_ “ dl2^ ^15"" ^14^ (dAR45 + , dA*) 44'

(22) and (23) now assume the following values (- j being eliminated, sinoe we seek only the absolute value of I4 5 ):

1 .5 V" (di 4 + d ^ ) -r d L11 2 12 (24) (d^g d^4 ) 45 12 X 10^ (dXl + dTp)12' (dv 4 44A ** dA R)

As in the case of the single-phase problem,it is possible here to give tha denominator a uniform numerical value for the different lin e s . Th9 numerators have already been calculated (sea (17) and (19) ).

If, now, we replace V by the working voltage E a V x^/3, wo hava:

I, V4 * V5 =* E /4 x ( i f 7/e. put d^i + 2 dig * 13.9) a I •f c ‘

1.5 U) £ E b ^ ^ ( a 2 -t b2 - c 2 )2'* 4 a 2 c 2 ~ (25) b45 (a2 + b2 + c2)2

If we put (dn * 2 d12^ * (d44 “ d45^ " 64*3 -1 1 5 -

111.

Development of the Conditional Equations*BI & 4. /

As has been laid down in the directives” (Chapter III,

Section A, Paragraph 1), it is admitted in principle that the most

unfavourable circumstance which should be taken into consideration for

purposes of ensuring that the proximity of a high power line (with

•neutral point insulated) or of an electric traction line, to a tele­

phone line, shall not be a source of danger, occurs when the phases

of a switch are closed, but not all simultaneously> and one of the

conductors remaining at the potential of the earth, at the moment when

the voltage is applied to the line..

In order to avoid danger in that case, therefore:-

Elther the telephone wires must not be subjected to a voltage

higher than the break-down voltage of the vacuum protectors (which are

fitted between the telephone wires and earth) - 300 volts - in order % that no acoustic shock can occur;

Or, if the above circumstance arises, the condenser formed by the telephone circuit and earth must not, during its discharge, bring into play sufficient energy to cause a dangerous acoustic shock.

It is possible to determine a zone, such that outside the latter, the first condition Ivoltage below 300 v.) shall always be fulfilled (Condition Bl). If a line penetrates into -this zone, the second condition shall be regarded as applicable to the determination

Of the degree of danger to which the telephone line is exposed.

A. For Three-phase Currents.

It is assumed that when a switch is closed for the purpose of applying the voltage to a high power line while one phase remains earthed a surge (onde transitive) will occur, the potential of which, hy reflexion, attains double the maximum value of the working voltage, ( i . e . 2 .Q e. xho voltage in the telephone circuit, therefore, by virtue of (25) and in the light of the remark given at the end of Chaptar I, is raised to:

V4 « (O.^/b c)/(a 2 + b2 + c2 ) (ae)

Notes: We have just admitted that aftar tha application of tha

voltage to a power line, tha tension at a particular instant reaches

double tha maximum value of the working voltage (2 x 1*4); but this

hypothesis is valid only if tha section of line put into circuit is

short and at the same tima is situated in the immediate neighbourhood

of the source of electric energy. Iii ordinary casas we deal with

sections of line of greater length. Wa must, therefore, expect a

very appreciable attenuation of th9 voltage wave because of the enormous

increase in resistance due to the "skin effect". It appears therefore

that we are justified to take as a basis for tha calculation of the

voltage induced in a telephone circuit, not the exceptional voltage

2.8 E, but rather - in normal casas - the average value 2.1 E. The

formula giving the voltage of the telephone circuit then becomas:-

0.525 b c £ (A t a.) a2 + b2 + c2

In-order to determine the lim its of the zones according to

B1 of Appendix 2. in the "Directives", it is sufficient to take a£

as being large compared with b^ and c2. We then have

V4 < 3 0 0

E* 0.525 be <300 a2

We thus obtain, assuming c «* 6 m ., b =* 10 m. (mean v a lu es)

a ^ 0.324 y5s or, in round numbers, the first zone is defined by

a-L =* “ 27)

The energy transmitted by induction to a telephone circuit of cap acity “ c" i s -117-

N otes:

(a) In order to guarantee as high a degree of security as possible,

it may be presumed that the energy induced in tha telephone line produces

its full effect at only ona end of the line. This is true in the most

unfavourable cases when the telephone circuit is not longer than the

parallelism; but in all other cases the interference wave is sub­

divided, each half flowing to each end,of the circuit, where it

arrives more or less attenuated according to tha length of the path

traversed. It is, therefore, permissible to suppose that, on tha

average, only the half of the energy induced reaches the telephone

receiver. Actual experience has shown that acoustic shocks, dangerous

to personnel, are produced when an energy 0.01 joule is applied to tha

telephone receivers. The energy engendered in tha telephone line

should not therefore exceed 0 .0 2 jo u le .

(b) The capacity of_a group of lines - according to measurements

made on a single group of circuits - is given by the enpirical formula:-

— x 1 0 ” 9 P/lfin.

(3 represents the number of wires in the network). Theoretically,

the capacity attains the value;

- i f — x 10“9 F/ffln. (28 a ) Zi + c

As the use of this formula involves a certain mitigation to the clauses relating to parallelisms, it appears to be legitimate to make use of it

in the calculations.

Factors which cause a reduction in the value of the induced voltage (lightning-protector wire, row of trees) should be taken into consideration. This may be dona by multiplying tha expression previously given'for the induced voltage by factors les3 than unity;- p, q, r (defined in Appendix 2.). By virtue of the above remarks

tr -* 2.1 ______h ° »4 = —r ~ * ^ ” ? 2 P ‘I r 4 a + b + c

Let v ba a coefficient defined by;

v * -JL- *----—------k p q r 40° a2 + *2 + a2

We have then:

V4 « 210y

Tha energy manifested in the circuit is, therefore:

I ' 4 V ^ -tv ■ W r 1 4 * a * ^

It should not exceed 0.02 joule. Therefore:

^vg - f < fip°2-a.is! - 50.4 Z + 2 9 x 2102

In round figures f

coefficient of the exposure to danger).

As this coefficient represents an energy, we may, quite

simply, add together the energy values due to proximities where the

separating distances of the two lines are 1different. In this way

we obtain the condition:

50

Note: In certain high tension^installations safety starting

switches are used, with "preparatory" contacts or other devices which permit of the full voltage being applied progressively to the sections

of the power line. In this case no increase in the maximum value of tha voltage takes place; consequently, in the above formulae 2.1 S should be replaced by 1.4 E. Und9r these conditions we obtain, as the limit of the characteristic coefficient of exposure to danger -1 1 9 -

B. For S in gle-p h ase C urrants. a s Tha same considerations ara applicable in this case^for the

three-phase currents. The vdltage V4 for the same separating distances

is about EO/'o less - compare (25j and (18). The difference has no

practical importance in defining the zones.

IV.

Development of tha Conditional Equation C 3.

The "Directives'* lay down - Chapter III, Section A, para. 2 •

that telephone wording is interfered with when the power line, by

electrostatic induction, causes a tension to occur between the con­

ductors of the telephone circuit equivalent - in so far as concerns

the intensity of the noises which it produces in the telephone receivers

to an alternating voltage of 800 p.p.s. frequency (w ** 5000) exceeding

5 m illi-volts.

In tha pre-determination by calculation of the interference

voltage, we accept tha hypothesis that the higher harmonics of the

power installation cause the same interference as a periodic current

(oj * 5000) the tension of which would be equal to l/50 of the

fundamental current.

We suppose moreover ("Directives", Chapter III, Section A,

para. 4 ) that ona phase of the power line may have an 9arth leak for

a certain time.

Finally, wa assume that the telephone receiver at the end

of tha line has a resistance of about 600 ohm3 i.e., of the order of

tha characteristic impedance of the line to which the apparatus is

supposed to hava been adapted.

A. For Three-phase Current.

We simplify, first of all, Equation (25), neglecting b2 x .o ^ , as compared to a2. Thi3 is permissible in most cases.- Wa have then:

j _ 1,5. Ifi * < x Hr A. • 9 (32) a - If this current flows entirely through terminal apparatus,

dt corresponds for Z * 600, to a voltage:

( 9 « / e W X 1CT7 x V )/a 2

If, in accordance with the "Directives", we now assume that

the voltage curve of the high tension line contains a frequency

u> * 5000 with an amplitude E/50, we have as value of the interference

voltage (expressed in volts)f

9 x 5000 x 35/50 & b

According to the "Directives" this interference voltage

should be less than 5 iailli-volts; hence it follows that with b = 10 m.

<6 *» 0 .4 m.

We should have:

(E X £ j/a2 < 500/(9 1 IO 1 0.4) = 13.8 or

3 >

that is, in round figures:

a > i VSZ that is precisely the Condition C

B. For Single-~phg.se Currents.

On the assumption that, by virtue of (19) and (25) I^ 5

hare has only 2 /3 of the value which it has in the three-phase case,

the lim it defined in (34) can be fixed at:

a ^ \/lr x 13.8 * ^ 475 * V®

\ •or, in round figures* -121-

Additlonal Sheets

(to Supplement 2 of Appendix 12)

Simplification of tha fourth determinant for single-pha 3a current:

The figures, in brackets following each of the produces*

represent tha values of these products, when the orders of

magnitude indicated in (14) are given to d. The products struck

out are neglected.

The determinant of the system:

a n d 12 d l4 d15 dl l d 12 d 14 d15

d12 d 22 d24 d25 d 12 dl l d 14 d15 A = becomes =» i f we put ax4 d24 d44 d45 d14 d14 d44 d45

dX5 d25 d45 d55 d15 d15 d45 d44

rrr - d bll 22’ d14 24» d15 “ d25* d44 " d4 5 *

dX2 d l l d15 d 12 d14 d44 U 3 .5 ) + d11 d45 d15 ( 21. 6)

A 14 d14 d14 d45

d15 d 15 d44 ~ dll d14 d44 ^46*6) - dl£ d45 di 5

!dXX “ 4 12^

d 12 dl l d14 dj^^^^tOTS) + d.jLl d14 d45 (^1. 6)

A 15 dI4 d X4 d44 * d12 d44 d15 ^13*5) - dl£ d14 d45 ^

dX5 d15 d45 dl l d44 d15 (4 8 .6 ) —

(d H - a 12)

dXX a X2 aX5 d n 2d44 (729) ----- V t t )

A 44 d 12 axx dX5

dX5 dX5 d44 — ^*1 2 ^ 4 4 (5o .2 ) —^ —(3t2T”

d44 (dxx2 - ) - A 55,

dXX d 12 a X4 ^ld-iu-^iS— + di2^d45 A 45 <*12 axx d X4 dH d45 ^24)

^ 5 d^15 d 45 n oq

* - d45 ^dll 2 " dl 2^

A * d 14 A 14 + d 24 A 24 + d 44 A 44 + d45 A 45

^12* ^ 1 5 ^ 4 5 ^ d 14 a44^ + d4 4 ^ dl l 2 ~ d12^ (6‘13°)

- d452 Cdl l 2 “ dl£ 2 ) iXZlZ)

A * (d-H2 " d122 ^ ^d442 ~ d452 ^

A 44 + A45 * ^dll 2 - d122>

A l 5 + A14 « (d15 -f d14) (d12 - d ^ ) ( d ^ - d4 5 )

A l 5 - A 14 * (di5 - d^4) (dig - d^) (d^ + d4 s )

2, Simplification of the fifth determinant for three-phase current*

Given dn * d22 - d33, d12 - d23 * d13# d ^ - d55, dM - d ^ »

d34* d i 5 * d25 “ d35 wa obtain til9 determinant of the system*

d l l d 12 d13 d 14 dX5 h i dX2 d X2 dX4 dX5

d12 d22 d23 d 24 d 25 d X2 d U d X2 dX4 dX5

tm d13 d23 d33 d34 d35 d12 di2 dXX dX4 d15

*14 d24 d34 d/M44 d45 d14 dX4 dX4 d44 d45

d15 d 25 d35 45 d55 d 15 dX5 d X5 d45 d44

3 d14 A 14 + d44 A 44 + d45 A 45*

0 d 0 d12 h i dX2 dX5 11 - d12 dl2 ~ dll

dX2 hz dxx d X5 d12 d12a dl l d 15 at M » mm d X4 d X4 dX4 d45 d14 d14 d 14 d45

dX5 d X5 d15 d44 d 15 d15 d15 d44 / s dl2 dl l d15 d I2 dX2 dX5 + d14 d 14 d45 dX4 dX4 d45

d 15 d 15 d44 d X5 dX5 d44 N / -1 2 3 -

d12d14d44f13*5^ + dlld45d15^S1* 4-^12d45d15^r

(dll " d12* i "(illd14d44^48*6J ~ d12i45(i15 (8) -dj^44*i44^:5T^ ~ ^2^4-5^15^57

* (dn - d12)2 (dl5d45 - d14d44^ 5" *7 analogy

A 15 k l l ~ d12^ *d14d45 ~ d15d44^

0 0 dll- d12 d12 d15 dll~ d12 d12-d U

d12 dl l d12 d15 d,..12 du dl2 d15 3 44 d d d d. d. d. d„, d, _ A 12 12 11 15 12 12 11 15 d d d d d d. d 15 15 15 44 15. 15 15 44

dl l d12 d15 d12 d12 d15

{dll ~ dl2* d12 dll d15 d12 dll d15 d15 d15 d44 d15 d15 d44

* lf d44<729) ±ii2d1^at07Tr du du d44(202.5) +di^dIS%rr?]

d )S *dl l " 12 lS i 2di s s ^ ' ■'-iv£vF***r

1 2 ^ 4 4 (8 8* 2 ) *^12^44 {5 6*8 ) “**argdS£^f&^ T '

(dl l “ d12^2 d44 ^dll‘f2d12^

1 dl l d12 d12 d14 dl l “d12 d i2- d ii 0 0

at M d12 dl l d14 A 45 d12 dl l d12 d14 *» dl2 d12 dll d14 d12 ' . d12 dl l d14

d15 d15 d15 d45 d15 d15 d15 d45 ;'K'

dl l d12 d14 d12 d12 d14

- ( d u - d d + d. d „ d. f> d12J< 12 11 14 12 11 14 d J d. d d„ r d ,c d,' 15 15 45 15 15 45 -124-

f di2d11d4g(90)

( d u - dl g ) + +!b*W 4*^^14

^ ~^122d45(25) wmilS ^ i^ l5 ^ r^

“ - (dxx d12 )2 d45(dll + ^la)

£ m 3d 14^ 11" *12 )& (d15d45~ '^34^44^ Cg ^ ^d^Cdxx-^xa^2 d44^dl l +2d12^ (*70.000)

- d45 (d11^12)2 *45 -

A -

A 4 4 4 A -,5” (4 u +aiu}J ^rr'Ha ) 2

A 15 + A u-(du -412)2 (djg-Hl^) (d45^ 44)

A l 5 ■“ A l4 :* (d^^-d^4 ) (dAe,+diA)45 44' -125-

Apoendlx \Z.

Examination of the Conditions under which Proximity may be allowable between Telephone Lines and 2-phase or Single-phase High Tension Alternating Current Lines which have an Earthed Neutral Point.

(A) OBJECT OV THIS APPENDIX - DEFINITIONS.

1) The definitions given under A in Appendix 2 hold good if nothing

to the contrary is stated in the following paragraphs:

Z\ By an earthed neutral point is meant a neutral point which,

under normal working conditions, is connected permanently to earth. The

neutral point of the overhead lines is joined to the windings of the

generator or transformer without the interposition of any resistance or

with the interposition of small resistances in such a way that, when an

earth occurs on one of the wires of one line, this line is automatically

disconnected by the action of interrupters.

3} Short-circuit induction is the magnetic effect, produced in

the telephone circuit when a short-circuit occurs in the high tension

l i n e .

4} For the purpose of these definitions the short-circuit current

is taken to mean the effective permanent current traversing the line

and earth v/hen an accidental earth occurs on a high tension conductor, after the surge caused by the short-circuit has been dissipated. This

current should be calculated by taking into consideration the load of the machines in the generating station, voltages and total impedance of all the apparatus and sections of line, included between the genera­ tor and the place where it is supposed that the earth has occurred.

5 } The accidental "earthing11 of the power line is considered to occur at the end of the section of proximity (with the telephone line) which, when we measure along the line, is the farthest from the generating station. tfhen there are several proximities we consider the '*earth" to occur at the farthest end of the section of proximity -1 2 6 -

most remote from the generating station.

6 ) By longitudinal voltage ("tension longitudinals") is understood

the voltage to earth, which is induced in the telephone line by the

alternating electromagnetic field* set up by the short-circuit current.

3XANGEB. (Induction caused by Short C ircuits).

1 ) For new -’proximities", measures will be taken to ensure that

the longitudinal voltage induced in the telephone line by the short-

circuit current of the high tension line, shall not exceed 200 v o lt s ,

effective, due regard being had to existing proximities.

2) The following formula, which indicates the degree of danger,

provides a means of verifying that this value is not exceeded:

4 x 10~8 x I k x Z x w / V a ” g

(This may be described as the "characteristic co-efficient of exposure to danger).

I k indicates the-short-circuit current in amperes.'

£ indicates the length of the proximity in kilometres.,

w is the frequency of the currents in the high tension line, multiplied by 27*

a is the distance between the parallel lines, in metres.

3)“ The above equation is applicable only to low frequencies up

to 60 p.p.s. (approximately).

4) The characteristic co-efficient, g, of exposure to danger

should be calculated separately far each section within which the

distances between the lines are more or less uniform. "Grossings"

are not included in the calculation. It is not possible at the

present- time to give the formula for calculating the co-efficient when the lines exceed 1000 m etres.

5 ) The telephone lino should be regarded as exposed to danger if the sum total of all the characteristic co-efficients of exposure to danger exceeds 300 V. -1 2 7 -

C. IJffEREERENCE.

As a high tension line having an earthed neutral point is

automatically disconnected b*r interrupters as soon as an accidental

earth occurs on one of the conductors, it is not necessary to take

into consideration the disturbing effects on telephone lines such as

may be produced by the more or less lengtby earthing of a symmetrical

non-earthed high tension line. On the other hand, interference with

telephone working need not be feared from hi$i tension lines (with

neutral point earthed) when these are free from faults, so long as the

stipulations laid down in paragraph II g of the "Directives" are

observed, and that in proximities the minimum separating distances

laid down in vLew of the inductive effects of• 3hort-circuits are duly

resp ected .

D- FINAL OBSERVATION.

1) The equation, giving the characteristic co-efficient of

exposure to danger, g, is based on the results of induction measure­

ments, which have been carried out with frequencies of 15 to 50 p.p.s.

on high tension and telephone lines earthed at both ends. The cal­

culations of the co-efficient of mutual inductance M of two earthed

c ir c u it s which have been made on the b a sis of data obtained by ex p eri­ ment have given the following mean value for

M * (4 x 10"*^ x } km.

A s the path taken by the return currents in the earth plays a large part in the determination of,this co-efficient of mutual inductance, geological conditions may cause the value to be different from that given above.

2) In telephone cables, in which the lead sheath and armouring are well bonded together between one section of cable and another and are provided with good "earths", the short-circuit induction produced in the conductors of the cable is effectively compensated by the current -1 2 8 -

induced in the lead sheath and in the armouring. The calculation of

the- characteristic of exposure to danger, g, may in this case be made

on the basis of a short-circuit current, reduced by about 40$ of its

effective value.

3) If the high tension line is in a lead-covered, armoured

cable, of which the sheath and the armouring are well bonded together

between one section of the cable and the other and provided with good

"earths", the characteristic co-efficients of exposure to danger, g,

may be calculated on the basis*of a short-circuit current reduced by

about 50$ of its value, so that in the case of an underground tele­

phone line we need only introduce into the calculation (100-50)

(100-40)= 30/6 of the value of the short-circuit current.

4) If the circuits in the cable are sectionalised by means of

repeating coils and are not fitted with protective devices, connected

to earth, the highest permissible value of the characteristic co­

efficient of exposure to danger is.equal to 60$ of breakdown voltage between the core of the cable and the lead sheath or to that between the windings of the repeating coil themselves or between the windings and the m etallic case, or the breakdown voltage between the windings of the loading coil3 and their metallic case. -129-

Appendix 14.

Examination of the Conditions under which Proximity (Parallelism) between Alternating Current single­ phase Railways and 2-phase Railways with Rail Return, on the one hand, and Telephone Lines, on the other hand, may be p erm itted .

A. OBJECT OF TH13 APPENDIX - DEFINITIONS.

1) The definitions are in accordance with those given under A in

Appendix 2, except when not modified by the following:

2 ) Single-phase and 2-uhase alternating current railways, referred

to'in this Appendix, are railways operated by means of alternating current

with a sectionalised route in which electric and magnetic influences are r not effectively compensated by the establishment of special installations,

e.g. compensating lines, suction (booster) transformers.

3) By supply section ip understood a section of a contact line -

or contact lines, in the case of railways with several permanent way3 -

supplied by one sub-station only and in one direction only.

4) ^ Short-circuit Induction is the magnetic influence, to which

the short-circuit current of the contact line exposes the telephone line.

5) By short-circuit current - such as is considered in this

Appendix - is understood the effective permanent current which passes

over the contact line, when an accidental earth of this contact line

occurs, after the surge, caused by the short-circuit has been dissipated.

In calculating the value of this current it has to ba supposed that the

short-circuit occurs at the end of a supply feeder section. In calcu­ lating the short-circuit current, account must be taken of the output of | the machines of the generating station supplying the sub-stations, the voltages as well as the total impedances of all the apparatus of all the lines from the generating station up to the point where the short-circuit to earth is supposed to have taken place.

. 6 ) The maximum induction during normal working is the magnetic effect, produced on the telephone lines when the supply section is

under the most unfavourable load conditions,

'7) The least favourable load corresponds to the current absorbed

by two powerful locomotives at the end of a supply section. When

there are several tracks the least favourable load is found by multi­

plying the value of this current by 1.5.

B. DANGER■

a) Effects of Electric Induction. \ ’ . 1) The rules to be applied are those laid down in Appendix 2,

Sub-sect3on B, traction lines worked by alternating current being

regarded as single-phase high tension lines and traction lines worked

by 3-phase alternating current as 3-phase high tension lines.

Z) The value, b » 12, w ill be adopted for b, as the average

height of the traction line from the ground, the system of suspension

of the contact line being taken into consideration (separating distance

greater than the normal distance of the power lin es).'

3) Each supply section should be treated separately. Hence the

conditions to which the projected parallelism must conform have to be

.fulfilled by each supply section considered by itself. It is not assumed that the telephone lines now in question w ill be affected by induction throughout several supply sections.

b) Effects of Magnetic Induction.

oC . Induction produced by Short Circuit. .

1) The rules set forth in Appendix 3 , S u b-sect ion 3, on the subject of symmetrical high tension lines with earthed neutral point, apply without reserve. In addition, the rule laid down in B (2) -

(3; of this Appendix should be applied.

2 ) In the calculation of the characteristic oo-efficients of exposure to danger, only SOfi o f the short-circuit current heed be considered; it may indeed be assumed that during the time of the short- circuit, tlie inductive effects due to the current in the contact wire -131-

are reduced by 40$? by the current-In the. rails; this applies even if the

rails are not joined together by means of special electrical bonds,

p. Maximum Induction under Working Conditions.

1) The considerations developed in Appendix 3, Sub-section B,.

dealing with the subject of symmetrical high tension lines with an

earthed neutral point are equally applicable to induction under working

conditions. In addition, the rule laid down in B*2, Par. 3, of this

Appendix should be applied.

2 ) In place of the short-circuit current (indicated-in ©C) the traction current has to be considered under th 9 least favourable con­ ditions of the supply section. When the rails are bonded, electrically, only 60/? of the current value need be taken to determine the character­ istic co-efficients of.exposure to danger. If the rails are not bonded,

35$? of the value of the current should be considered.

3) ^he telephone line is regarded as exposed to danger when the total of the characteristic co-efficients of exposure to danger exceeds

60.

.4 ) In accordance with III.a, Sub-section l.b. of the "Directives". this total value can be taken as high as 100 if special protective measures are observed. . These measures include, among others, sectional!sation of the telephone lines by means of repeating coils, provision for preventing contact with uninsulated parts .of the conductors, very careful construc­ tion and maintenance of the lines and installations, exposed to danger.

0 . I INTERFERENCE.

1) As regards the interference with the working of the telephone system, duo to electric charges, the rules laid down in Appendix 2, Sub­ section C, are applicable without reserve. Railways working on single­ phase alternating current are considered as single-phase high tension a lte r n a tin g current li n e s , and railw ays working on 2-phase alternating current are considered to be equivalent to a 3-phase high tension -132-

alt ernating current system. The rules laid down under B.a, Sub-sections

2 and 3 of this Appendix apply in addition.

2) There is not generally any risk of interference with the tele­

phone service by magnetic inductive effects, arising from the higher

harmonics of the traction current on long sections of parallelism between

the traction line and the telephone line, provided that such separating

distances between the lines throughout the sections of parallelism are

maintained that the telephone line is not exposed to danger. It is

nevertheless advisable to verify wnether the parallelism satisfies the

co n d itio n :

oC>0.1 x X x €

a .formula, of which the validity in the general case should be checked

further by more complete measurement and. experiment. In this formula cL

represents the distance in metres between the lines, J the maximum

possible value of the traction current in the section of parallelism

(expressed in amperes), and ^ the length of the section of parallelism,

although, however, this value does not exceed 1-J- times the length of the longest section of the telephone line, for which the effects.of

induction have not been compensated by transpositions (Appendix 2 -

Section G, Paragraphs 1 and 3).

3) In the case of parallelisms, which do not satisfy the con­ ditions indicated in % the interference voltage w ill undoubtedly exceed 5 m illi-volts.

D. FINAL REMARKS.

l) Trouble due to electric induction cannot arise in telephone cables. The trouble due to magnetic induction can be eliminated or sufficiently reduced by balancing the circuits as perfectly as possible.

Even if it is true that the protection against operating troubles does not necessitate a definite minimum separation, it is advisable, never­ theless, not to instal long distance international telephone circuits -1 3 3 -

along railway permanent ways themselves or in their immediate vicinity.

2 } Y/hen a cable with iron-band armouring is.used, and one section

of cable is well connected, m etallically to the next, and, a good connec­

tion to earth of the cable sheath (including the armouring) is assured,

the currents induced in the cable sheath produce a protective effect

which reduces by about 40$? the magnetic induction due to short-circuit

and the induction under normal operating conditions. In this case it

is necessary only to use, in the calculation, the 6 0 values of~the

short-circuit current (calculated according to B b 06 2 ), or of the

traction current, corresponding to the most unfavourable load (calcu­

lated from B b (3 2), in order to determine the characteristic coeffi­

cient of exposure to danger.

3) If the underground circuits terminate in repeating coils and

are not provided with li^itning arrestors between wires and earth, the

maximum permissible value of the characteristic coefficients of exposure

to danger, in the case of short-circuit * w ill be taken as the breakdown

voltage of the conductors of the cable with respect to the leed sheath;

that between the two windings of the repeating coils or that between the

windings of the repeating coils and their metallic cases.

Any work carried out on cables exposed to such a degree of

short-circuit induction and consequently to a highly increased induction

under normal working conditions, necessitates special measures of pre­

ca u tio n .

4) The use of neutralising conductors and of suction (booster)

transformers in an electrical installation form an excellent protection

against danger and interference. In the case of the suction (booster) transformers a special return wire is to be preferred to the connection

of transformers to the rails. The effect of these transformers is to reduce to a small fraction the induction duo to the current in the contact line. In determining the permissible separating distances in -124-

parallelisms, only this fraction w ill be taken as a basis of calcula­ t io n .

In the case of long sections, however, it is recommended that a separating distance of at least 100 metres should he maintained between the over-head telephone circuits and the traction line. This applies even if calculations show smaller separating distances, because when some of the suction (booster) transformers are absent or are working badly or when faults occur on the neutralizing conductor the protective effect of these devices msy be non-existent for long periods - or largely reduced to a degree which cannot be permitted. -135-

Appendix 15.

Measurement of Interference Voltages induced in Telephone Circuits.

The intensity of noise induced in a telephone circuit can he

determined by the apparatus for the measurement of interference voltages,

designed by Siemens and Halske of Berlin (Garauschspannungmesser), and by that of the Western Electric Company for the measurement of induced noises (Noise Measuring Set).

I . Siemens and Halska apparatus for the measurement of disturbing voltage.

The effective intensity of noise in the line is compared with that of a buzzer (w = 5000). The resistances of the buzzer circuit are adjusted by means of an indicator in such a way that the reading of the poten tiom eter g iv e s d ir e c tly the number o f m illiv o lt s between the output terminals.

This adjustment having been made, the position of the potentio­ meter is determined, for which a receiver, connected to the output ter­ minals, gives a noise producing the same impression of intensity as that given by the same receiver connected directiy to the disturbed circuit.

In this way is obtained the voltage of the tone, of 5000 radians per second, equivalent to the induced voltage.

The employment of a buzzer, of which the frequency is main­ tained constant, ensures that we can always be sure of repeating the same adjustment with exactitude. It has been demonstrated by tests carried out by veiy different observers that, after a short period of training, it is not difficult for the observers to determine, even for noises of low frequency, a value for the equivalent voltage of

5000 radians per second; the results of measurements obtained by d iffe r e n t observers working under the same co n d itio n s have shown satisfactory agreement. -126-

The disturbing electromotive force induced in the circuit meets

the impedance Z of the line in such wise that the disturbing voltage

measured at the end of the line is reduced. To.obtain measurement

results, which are mutually comparable, it is necessary, therefore, to

insert between the receiver and the terminals of the potentiometer, a

resistance which reduces the voltage of the buzzer to the same extent.

Measurements by means of this apparatus ai’e easy to carry

out, and the degree of reliability is relatively high.

It is advantageous that the impedance of the receiver used

for measurement should be adapted to that of the line.

I I . Western E le c t r ic Company’ s Apparatus fo r th e Measurement of Noise (Noise Measuring Set).

For the measurement of noise induced in circuits, the Western

Electric Company use a source of artificial noise, produced by a buzzer

giving a complex wave form; the set includes dry batteries and a switch.

The adjusting screw of ths vibrating reed is carefully sealed so as to

ensure uniform operation. A potentiometer is connected to the outgoing

terminals of the buzzer and serves to control the volume of noise pro­

duced in a telephone receiver.

In measuring the noise induced in a telephone circuit, the

telephone receiver is connected alternately either to the source of * * artificial noise or to the circuit to be tested; the potentiometer is

adjusted in such a way that the noises produced in the telephone

receiver in the two cases are equal, from the point of view of the

reduction in intelligibility, of a telephone conversation. (An

operator, reasonably accustomed to these measurements, can very quickly

estimate, in a satisfactory manner, the disturbing effect which a given

noise may cause to a telephone conversation).

In ord8r to be able to compare results of measurements made

on telephone circuits of different impedances, a variable ratio trans­

former is used .to reduce, in each case, the impedance of the circuit - 127-

under test to a value of 600 ohms; the telephone receiver, which has

an impedance of about 200 ohms, is connected permanently in series with a resistance of 400 ohms, which adapts the impedance of the

receiver to that of the circuit under test. The potentiometer is

calibrated in-conventional "noise units".

This apparatus can be used to measure either the noise induced in a telephone circuit or tha noise produced between the two wires of the telephone circuit and earth; in the latter case the ratio of the variable transformer is equal to unity, and the primary winding of the transformer, in series with a resistance of 100,000 ohms,, is connected between the two wires of the circuit under test

(joined up in parallel) and earth. - 138“

Ct. ARrtANG-MCNT OF APPA^ATUi

RECEIVER 5 . U.2 (£ee appendix 6 ) x E l» | o flc

Z> 600 tooo 1400 l&OO 2400

■XwXwXv'XvvCvnXv^/v\Xv>I 8 I 8 S S S M -

o o ° o 2 § j n 0 o 0 0 O 6 0 0 5 4 0 0 (0 CO 2 N w** w$ t O <59 28 - - W W W " •

U = lO iy.

T

J. PRINCIPLE.

k o RECEIVER

pvw w w vw ■2.- 600 .

x

600 5400 600 6000 vaaaaAaaa^vv^w^vvvvvv------ww^ww^ |0 9 8 . 17,1

DIAGRAM.I. APPARATUS TOR MEASURING THE DIS- SYMMETRY OF DISTURBANCES.

a. MEASUREMENT OF NOISE tSETV/EEN CONDUCTORS.

1900 Receiver ( impedance: - 200 ohms at 000 p e r io d s p e r se c o n d ) 3 2 5

b. MEASUREMENT OF NOISE CAUSED BY DIS- SYMMETRY TO EARTH

„______100000

VARIABLE SHUNT AND SOURCE VJ T OP NOISE A® IN Cl. A oAVM

DIAGRAM.2. NOISE! MEASURING APPARATUS. OP THE WESTERN ELECTRIC O? -1 3 9 -

Appendix 16.

Determination of the Degree of Unbalance of Telephone Circuits with reference to Disturbing Linas.

A telephone circuit may be perfectly symmetrical with regard * ^ to earth and ‘yet may carry considerable noise, arising from induction

from neighbouring lines. It is, therefore, out of balance with res^-

pect»to these lines owing to.marked inequalities either in the

capacities of the wires a and b with respect to the disturbing lines,

or in the coefficients of mutual inductance with respect to these

lines, or in these two effects together. The degree of this disturb­

ing unbalance is, of course, modified and generally increased by un­

balances of the telephone circuit with respect to earth. Hence, an

indication of the degree of unbalance with respect to the disturbing

lines can only serve as a means of comparison when the degree of

balance of the circuit with respect to earth is determined at the

same time (see Appendix I ).

The degree of unbalance of a circuit with respect to the disturbing, lines may be determined by means of an apparatus specially devised for the purpose by Siemens and Halsi® of Berlin (Ger&uschun- symmetriemesser) or by means of the apparatus of the Y/estern H lectric

Company type for measuring noise interference (Noise Measuring- Set).

I. Apparatus of Siemens and Halske'of Berlin for measuring the degree of unbalance of circuits with respect to disturbing lines (Ger&uschun- svmmetriemesser). (3ee Fig. ).

The disturbing voltage induced between the conductors of the telephone circuit represents a certain fraction of the disturbing volt­ age induced between the circuit and earth. This fraction is termed the "noise unbalance” (Ger&uschunsyrrmetrie/. When the disturbing voltage with reference to earth is being measured the distant end of the line is insulated in such a way that, in the case of overhead -14-0-

circuits, the capacity ■unbalance rnay also have effect. At the measuring

station one of the wires of the circuit is connected to one end of a

high resistance potentiometer, the other extremity' of which is earthed.

This earth connection can be moved in such a w£y as to apply to the

telephone receiver (shunted across the fixed arm of the potentiometer)

a definite fraction of the disturbing voltage between wire and earth,

which is applied across the whole resistance of the potentiometer. The* impedance of the receiver, moreover,;is equal to the characteristic

impedance of the circuit. This definite fraction (determined by the

potentiometer setting) is chosen in such a manner that the telephone

^receiver, connected across the potentiometer, gives a noise which

appears to be equal to that given by' the same receiver connected

directly to the ends of the circuit. In both cases the receiver is

connected across the same impedance, that is to say, the impedance of the circuit under test, or to the equivalent impedance 2 ; consequently, the voltage across the terminals of the receiver is always equal to the / effective electromotive force diminished by the same fall of potential produced by 2. ^ The measurement, therefore, gives mutually comparable values in all cases. The ratio of the resistance of the potentiometer shunted by the receiver (600 ohms fixed) to the total variable resist­ ance represents the ratio of the disturbing voltage between the two wires to the disturbing voltage between wires and earth, that is, by definition, the degree of unbalance of the circuit with respect to the disturbing lines. The method is simple, reliable, and technically sound. The same apparatus can be used without change to measure the unbalance of the line with respect to earth (see Appendix 1).

II. Western Electric Company's Apparatus for the Measurement of the "Ratio of Disturbing Noises” (Noise Ratio Measuring Set).

In order to measure the unbalance of a telephone circuit with respect to neighbouring disturbing lines, the Western Electric Company -1 4 1 -

use an apparatus called “Noise Ratio Measuring Set”, which enables

measurement to be.made of the relative value of the noise induced in

a telephone receiver connected between the two wi res of the telephone

circuit in relation to the noise induced between the two wires and

earth ("Noise Ratio”).

A switch enables the primary winding of a variable ratio

transformer (the secondary of which is connected to a telephone

receiver in series with a resistance of 400 ohms) to be connected

either between the two wires of the circuit under test pr between

these twos wires and earth. In the latter case a variable artificial

line is put in seVies with the primaiy of the transformer, and the

attenuation of this line is adjusted in such a way that the noises

observed in the receiver in the two cases are equal from the point of view of the reduction of intelligibility of the telephone conversation.

This method is comparable to the method of Siemens and

Halske described above, except that the potentiometer Is replaced by an artificial line with a variable attenuation.

The variable ratio transforaer, in the initial stage of measurement, permits of the impedance of the circuit under test being reduced to 600 ohms; the resistance of 400 ohms placed in series with the telephone receiver serves to adapt the impedance of the receiver to that of the line•

In the second stage of measurement (when it is connected between the wires of the circuit and earth) the transformation ratio of the variable transformer is equal to unity.

By reason of these precautions, the results of measurements carried out on circuits of different impedances may be mutually com­ pared. - 1 4 2 -

O. ARRANGEMENT OF APPARATUS.

(s e c a p p e n d i x s )

U2

BUZZER

DIAGRAM 1. APPARATUS TOR MEASURING DISTURBING VOLTAGES (S.&H.)

NOISE MEASUREMENT BETWEEN DIFFERENT WIRES

RECEIVER (IMPEDANCE * 200 OHMS AT QOO PERIODS

DIAGRAM 2. NOISE MEASURING ' APPARATUS OF THE WESTERN ELECTRIC C* - h s -

SECTION 3 - TARIFFS AND TRAFFIC.

XV• Establishment of Variable Tariffs according to the Time of Day.

The C.C.I.,

HAVING REGARD TO THE PACT

that the application of variable tariffs has given satisfactory

results and that many Administrations have manifested their interest in

this manner of charging,

EXPRESSED THE OPINION

that a variable tariff, comprising two or three stages, deter­ mined (as well as the hours of the day during which the tariff is applied) in accordance with the traffic conditions of the interested countries, should be brought into force when new international lines are constructed, and applied to the circuits already in service, but, in any case; so far only as the number of available circuits permits of this being done.

FACILITIES TO BE OFFERED TO THE PUBLIC.

The C.G.I.,

HAVING REGARD TO THE FACT

that, the ’’Notice of Call” (avis d’appel) system, now used by the majority of countries in conformity with the decisions of the

Lisbon International Conference, seems to offer to the public less security than the system of "Particular Person” (pre-avis), as used in the United States and the Scandinavian Countries,

EXPRESSED THE OPINION

that, in the International service the "Notice of Call"

(avis d*appel) system should be completed as far as possible by that of the "Particular Person" (pre-avis) system, which permits the calling subscriber to obtain communication v/ith a particular person, who i s s p e c if ic a lly named.

The C.C.I.,

HAVING REGARD TO THE FACT

that, “Particular Person" (pre-avis) calls necessitate -144-

service communi cat ions on the circuits in question which occupy periods

which should not be unproductive, and that it is legitimate for the

caller to pay for the special service permitting him to obtain the

"Particular'Personal" (pre-avis) call.

EXPRESSED THE OPINION

that each "Particular Person" (pre-avis) call shail be

subject to a special charge, the consequent conversation being chArged

for at normal rates, and that this special supplementary charge shall

not exceed l/Srd of the charge for one unit of conversation between

the exchanges affected.

The Q.C.I.,

HAVING REGARD TO THE FACT

that, certain Administrations do not at the present time

allow communications with persons specifically named in their internal

s e r v ic e ,

EXPRESSED THE OPINION

that Administrations which do' not, in their internal service,

permit‘.communications with persons specifically named w ill have the

right to refuse "Particular Person" (pre-avis) calls In the Inter­

national Service.

The C.C.I.,

HAVING REGARD TO THE FACT

that the facility given to subscribers for obtaining com­ munications st .fixed times has given satisfactory, results in the internal service of Great Britain, Belgium, Finland, Czecho-Slovakia,

Denmark, Norway and Sweden, also for the service which is common between the last three countries,

EXPRESSED THE OPINION

that, in the international service, fixed-time calls,-which the Lisbon Conference has admitted only for night time and for sub­ scribers paying special subscript ions, be also allowed during the day, -145-

v/hen the number of lines permit, and subject, in this case, to the

application of not more than the ".urgent" tariff, the calls being liable

to a delay of a few minutes, when necessary, on account of circuits

being engaged.

The C.C.I.,

HAVING REGARD TO THE FACTS

that it is desirable to comply as far as possible, with

requests for information from the public, and that it is reasonable

to impose a charge for the necessaiy service conversations between

exohanges,

EXPRESSED THE OPINION

that certain requests for information relating to the inter­

national service be allowed, subscribers thus being able to ascertain,

without demanding a call, whether a particular person in the area of

another exchange is a telephone subscriber or not, when this information

cannot be obtained from their own exchange, and also to ask the name of

the person corresponding to a certain number in another exchange and to

be informed of the name of the person who has called his own number;

that this request for information be subject to a charge which w ill not exceed one-third of an ordinary call unit between the .exchanges

concerned.

TELEGRAPHIC PREPARATION OF TELEPHONE CALLS AND RAPID METHODS FOR THE OPERATION OF TELEPHONE CIRCUITS.

The C.C.I.,

HAVING REGARD TO THE FACTS

that experience has shown that the preparation of long distance telephone calls mu3t conform to varying methods, depending on the number of circuits served by one telephonist, in order to obtain the best possible efficiency in each case,

EXPRESSED THE OPINION

that, for those routes which consist only of a small number of -1 4 6 -

long distance circuits (net exceeding two or three circuits at a

maximum), the allocation of one circuit to each telephonist (if possible

with telegraphic preparation of calls) shall be recommended:

that, where one telephonist attends to two circuits to the

same destination, this telephonist shall prepare the calls by tele­

graph - and, more particularly, if these two circuits may be allocated

for carrying traffic in the same direction - the increased hourly effi­

ciency of each*circuit that can be obtained by this method of operation

being more than half a paid unit:

th a t, when four c ir c u it s to the same d e stin a tio n are d i s t r i ­

buted between two adjacent telephonists, the telegraphic preparation

be effected by an independent telegraphist placed between the two '*

telephonists, this method being particularly advantageous if the four

circuits may be employed for traffic in the same direction, and may

increase the hourly efficiency of each ’circuit by more than half a

paid u n it :

that telegraphic preparation, which ceases to be of any particular value when a single telephonist attends to more than two circuits, may, however, be employed in the case of three circuits, when the hourly efficiency of each circuit may be slightly‘increased by this method.

STATISTICS OF TELEPHONE TRAFFIC.

The C.C.I.,

HAVING REGARD TO TEE FACTS . ,

that, in order to facilitate the control of traffic and to furnish the elements necessary for improving the service, it would be desirable to draw up statistics in a standard form;

that, in order to permit of the framing of schemes cf instruction, it would be desirable to adopt common rules in respect to probable traffic and to arrange for the supply of statistics on -1 4 7 -

a uniform basis in respect to traffic between one country and the countries with which the country in question is connected or proposes to he connected,

EXPRESSED THE OPINION

(i) that each Administration should compile separately, once per

annum, statistical data respecting each group of important

international circuits and that, provisionally, this informa­

tion should be furnished in the form indicated in tables 1A, t . IB, 2, S and 4, appended hereto;

(ii) that each Administration, once per quarter, should extract

from their statistics of observation of operators* work

details of the time occupied in effecting the various opera­

tions carried out in establishing important international

commanicat ions, bringing into prominence the "Co-efficient

of Use” (co-efficient ^utilisation) of the circuit and that

the Administrations concerned should communicate mutually

the data in question {using* for example, table No. 5

appended hereto);

(iii) In order to estimate the increase of probable traffic, it

m&y be accepted that the law of growth w ill be the same as

during the preceding five normal years. If the "waiting

times", the quality of audition or the charges have been

modified during the period of these five years, or should

be modified during the future period in question, it w ill

be necessary to take account, in the estimation, of the

future probable traffic, and to supply all useful informa­

tion on this subject. If the localities in question are

not yet connected telephonically, an indication of increase

may be found in the report upon the telephone and telegraph

traffic between localities of the same order, an analogous

ratio being presumed for the future telephone traffic in

q u e stio n . -148-

EXPLOITATION OF INTERNATIONAL CIRCUITS.

The C.C.I.,

HAVING REGARD TO THE FACT ,

that, on the one hand, the adjustment of telephone accounts

between States necessitates a control of the duration of the communica­

tions to each of the two ends of tha circuit, and that, on tho other

hand, order-wire working of routes carrying heavy traffic and having

numerous circuits makes it almost impossible to control efficiently the

duration of calls at the receiving end of the circuits,

EXPRESSED THE OPINION

that, in the present state of the number of circuits and of

International regulation, \vorking by .order wires should be eliminated

from the international service.

CALCULATION OF INTERNATIONAL TELEPHONE CHARGES.

The C.C.I.

WAS OF OPINION

(1) that tho tariff for International Telephone Communications

should consist, normally, of:-

(a) terminal charges accruing to the Administrations of origin and destination {Terminal Administrations);

(b) of transit charges accruing to the intermediate Administrations, if such exist (Transit Administrations);

(2 ) that, in fixing terminal charges, each country may be divided

in to zon es, th e charges w ith in th e same zone b ein g th e same fo r th e same

country, and calculated in accordance with the distance between the zone

and the frontier/ this distance being fixed for eacn zone by the.Adminis­

tration concerned, the latter being free to determine the limit of it A

zones in accordance with its own traffic or in accordance 'with financial

or .oVher considerations, different zones being,- if-necessary, defined in # the same country for the traffic exchanged with different countries;

(3 ) ' that in the distance used for purposes of calculating charges the length of any submarine section should be multiplied by a co-efficient -1 4 9 -

to be decided upon by tha Administration concerned, regard being had

to the annual charges (including interest, depreciation and mainten­

ance );

(i) that, in the case of countries of a mountainous nature,

fsyant un relief tr^s accident^), or having a special geographical

situation, in which the actual route followed by the circuits is

unavoidably very devious, it should be admitted that the distance

upon which the charges are calculated may be considerably higher

than the distance measured as a straight line between the frontier

and the point of the zone in question vfoich is at the greatest

distance from the crow-fly distance;

(5) that, when telephonic communications between two Adminis­

trations make use of the territory of one or more intermediate

Administrations, the charges applied by the transit countries should be calculated in. accordance with the average crow-fly distance between the points where the international circuits enter or leave, this crow- fly distance being liable to increase in accordance with paragraph 3 , if submarine cables have to be used and Increased in accordance with paragraph 4, if a mountainous countly has to be traversed or a country possessing a particular geographical configuration;

(6 ) in any case, the charges for international telephone calls,, with respect to the unit of distance, should be calculated in each country on the basis of their cost price, increased by a reasonable percentage;

(7) that any Administration whatever should have the right of - fixing its own terminal or transit charges in accordance with a tariff which is lower than that which would result from the adoption of the general basis of calculation indicated above.

MINIMUM TRAFFIC TO BE ASSURED TO TRANSIT COUNTRIES. ■

The C.C.I.,

HAVING REGARD TO THE FACTS -150-

that, on the one hand, terminal Administrations should have

substantial liberty of requesting transit Administrations to place

circuits at their disposal, and that, on the other hand, transit Adminis­

trations should be able to meet requests for direct circuits without

being restrained by the fear that the traffic carried on these circuits

may not provide sufficient revenue to meet the construction and mainten­

ance costs of the transit circuits,

CAME TO THE CONCLUSION

that it should be admitted that an Administration from which

a circuit is required for transit traffic should have the right of

requesting, In return, the guarantee of a minimum revenue. / The C.C.I.,

HAVING REGARD TO THE FACTS

that the traffic which rosy be carried by a particular circuit

depends to a large extent on the manner in which it is maintained, and

that it appears to be desirable to induce the transit pountry to interest

itself (by means which would be more effective than the fixing of an

annual payment) in the maintenance of an efficient service, producing

satisfactory revenue because of the section of the circuit for which

the transit country is responsible being maintained in a thoroughly

efficient condition,-and that this result may be attained by making the

transit country interested in tho total volume of traffic carried by the

circuit in the form of a proportional participation by the transit country

in the number of calls passed, with a minimum of revenue guaranteed,

EXPRESSED THE OPINION

that this procedure should be preferred to that of an annual payment, without, however, excluding the latter.

The C »G.1.,

HAVING REGARD TO THE FACT

that, experience hitherto acquired does not seem to be sufficient to justify, even provisionally, the fixing of o normal -151-

value of the minimum and that the point of view of transit countries

on this subject w ill depend to a considerable degree upon the con­

struction costs at the present time of the circuits requifed, as well

as upon the possibility of using available wires;

EXPRESSED THE OPINION

that the determination of this minimum by direct negotiations

should be left to the Administration concerned.

The C.O.I.,

HAVING REGARD TO THE PACT

that the revenue obtained by a telephone circuit depends to

a considerable extent .upon the daily maintenance of this circuit;

EXPRESSED THE OPINION

that, if a minimum revenue be guaranteed, it is desirable i also to arrange for .a rebate where the circuit is interrupted in the

transit country (preferably on a pro rata basis with the interruptions)

unless the transit country undertakes to replace the defective circuit

by another in good condition (this rebate should take account of all

interruptions lasting a complete day - "a complete day” being regarded

as the time included between 9 a.m. and 3 p.m.). ,

The 0 .C.I •,

HAVING REGARD TO THE FACT

th at th 8 legal hours of the countries concerned may not be

th e same,

EXPRESSED THE OPINION

that the precise times of the beginning and termination of the periods of interruption v/hich should be considered (9 a.m. to

3 p.m.), as well as of other details relating to rebates in respect of interruptions, should be fixed by direct agreement between the countries concerned;

that the minimum guarantee should be applicable only to . lines allocated by transit Administrations to the exclusive use of -1 5 2 -

terminal countries, the partial use of other lines being remunerated,

in the ordinary way,_ ty means of a transit charge for each call made

effectively on the circuit.

PERIODICAL MEETINGS. FOR PURPOSES OF STUDY. BETWEEN SUPERVISORS OP INTERNATIONAL TELEPHONE EXCHANGES.

The C.C.I.,

HAVING REGARD TO THE FACTS

that the professional instruction of operators and supervisors

is of quite special Importance, in order to ensure a satisfactory output

on circuits used for international purposes;

that experiments made in this respect in Great Britain and

Switzerland, in the form of periodic meetings of supervisors, have had

the most beneficial results,- allowing the personnel concerned to study

the organisation of the service and the composition of the telephone

system at the other end of the circuit, and permitting the staff to

enter into direct mutual relations end to straighten out, verbally,

possible difficulties which may occur In the working of the service,

EXPRESSED THE OPINION ■

that meetings of this nature should take place frequently

between exchange supervisors of various countries whenever these

meetings are justified by circumstances and by the intensity of traffic.

INTERNATIONAL CODE OF TELEPHONE REGULATIONS.

The C.C.I.,

HAVING REGARD TO THE FACTS

that th e O.C.I. has, as one of its functions, the preparation

of the organisation of International Telephony in Europe, and, in the

meantime, of ensuring unity of views in the international European tele­

phone service,

that the present provisions of the International Telegraph Gode of Regulations in respect to the telephone service are inadequate, and that it is desirable to modify these rales and to ccmplate them in large measure, . -1 5 3 -

E£PRESSED THE OPINION

that the Permanent Commission, which is particularly wall

qualified for this purpose, should prepare as soon as possible a draft

,of an International Telephone Code of Regulations.

The closing meeting of the C.C.I. took p la ce on th e 29th June,

1925, under the presidency of M. Milon.

M. Milon regretted that, for reasons of State, M. Choumet,

Minister of Commerce and Industry for Posts and Telegraphs, was not

able to be present, as he had intended, at the closing meeting of the

Conference.

M. Chaumet, at th e C.C.I. banquet, had expressed his benevolent

sympathy with the objects of the C.C.I., and Delegates had no doubt

appreciated thi3.

In thanking the Delegates appointed by the High Tension

Systems for their presence at the Conference, as well as the Inter­

national Union of Railways for their highly appreciated.co-operation,

M. Milon then thanked the various Administrations for the substantial work which they had contributed to tho Conference. He said that he believed that the C.C.I. could congratulate itself upon the results

ob tain ed.

•'Results of our labours have been very important from the "point of view of international relationship, but I may "add that they w ill not be less important from the point "of view of the development of telephony within each of '•the countries concerned.

"So far as the French Delegation is concerned, we are , "happy to have such important documents as have been “provided, worked out by persons of such competence in •'telephony, with whom we w ill be able to maintain "constant relations.’’

M. Milon concluded by expressing the hope that the Conference would meet again, in good health, next year.

If changes were made in the organisation of the Committee, be: hoped that they would not change either the methods of xvorking or the cordial feelings of reciprocal confidence with which members o f the committee .had worked in the past. -1 5 4 -

Statistical Tables of tho Traffic on the Circuit(s) Number(s)......

Outgoing

Alternating

Incoming

.-.Between...... a n d ......

- ..../ ...... /192...

TABLE 1A.

Circuit(s) disengaged owing to lack of Calls.

Disengaged time shown in Minutes for each hour indicated below:-

Dates

T otal Average a:.sengaged tim e .

TABLE IB.

Average engaged Time ner hour for the six days.

Min. ' Min, 60 7 8 9 10 11 12 13 14 15 16 17 18 19 '20 21 22 23 60 -1 5 5 -

gABXE-' 2 , '

WAIT IK G T-Iiaas.

Huznbar of Outgoing Calls Ho. o f

JLXlwX X 0 C * E ffected w ith delay tive

J a te s without w & l X O « d ela y not exceeding Exceed­ c in g 90* T o ta l. * oth ers 10* 20* 30* 40* 50* 60* 90*

T otal per cent

m Subscription Calls and Calls at Fixed Hours, -156-

A

TABLE 5.

Number of Units.

D ates 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 7

T otal Aver­ age.. .

TABLE 4 ,

Number of Ineffective Cutgoing Calls at th e beginning of th e Hour*______

D ates 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 25 7

'

T o ta l

Ay er­ ase ......

Subscription, Call periods and Fixed-hour Calls to be effected during the following hour, should be included, in th e number o f I n e ffe c tiv e C a lls .

In the cases of Tables 2, 3 & 4 ordinary calls w ill be shown in black and urgent calls in red. TABLE 5.

5TAKE OP EXCHANGE DESIGNATION OP THE DESIGNATIONS OP THE (from th e commence* (of the Sectional CIRCUIT OTHER CIRCUITS OP (raent of the obser- (Supervisor DATE AND HOUR THE TAB IE.» (vat ion ( DURATION ( NAHS3 ( OP DELAY (to the termination (of the Operator (of the observation (observed / ______J...... (...... a • b. c d. e . f . 5our o f S eria l No .o f Time elapsed from end of Duration 1 RECAP ITULAX ION CONTROL OBSERVATIONS com­ lumber sub­ nrecedinp: conversation until o f con­ Times given by . Total Dura­ D ifferen ce Number of Indicate briefly mon co­ o f s c r i­ Ring­ Reply End o f Begin­ End of L ines v ersa tio n the difference o f tio n between u n its in ­ the causes of lost rn ent o f calls ber ing from service n ing conver- d i s - (d iffe r ­ between colum ns: tim es in d i­ cols. 10-16 d icated • time subtracting shown cated o b ser- sffec- c a l l ­ Ex­ conver­ o f con­ sat i on conn- ence be­ nlii m i nu s bv nti c o l . 6 from col.7 . v e r sa ­ between ected tween 9-8 in by th e Ex. lack of pre­ vat i on ted.. ed change sa tio n 5-4 6-5 7 -6 obser— the su b s. cols. c s lc u - paration; caller (end o f tion columns vation t ic- con ver- between 8 & 7 ) . 10-14 lcgraph Irpt fails to answer sation). su bs. or is waited for; delay in obtain­ ing particular person requested, &c. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 s 20

\