\J-mfzl, 193s.‘ } ' ' 'R. A. HEISING 2,028,212 RADIO TRANSMITTING SYSTEM

' ‘ ; , ‘ ' lFileq’vec. 22, 1935 .5 Sheets-Sheet 2 BASE 7 FIG. 3 ' . 1 2’ v ‘ racaueucv ,9‘ 1 > 20

' HARMONIC :3 GENERATOR _

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|| ' ' _ ' 30 | l 22 25 26 27 29 l 1 J ) I) |--- HARMONIC — SELECTOR — PHASE - ' :‘GENERA'WR ._ CIRCUITS __ SHll-‘TER M°°ULAT°R

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B’ um, ATTORNEY ‘

Patented Jan. 21, 1936 2,028,212

UNITED ‘ STATES PATENT OFFICE

‘ 2,028,212 ‘ RADIO TRANSMITTING SYSTEM Raymond A. Heising, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York ‘ ‘ Application December 22, 1933, Serial No. 703,514 9 Claims. (Cl. 250-9) This invention relates to radio broadcasting sions from the transmitting circuits of Figs. 1 system employing very short waves and, in par and 3. , ticular, to e?icient transmitting and receiving Referringto Fig. 1 a base frequency source I ‘ circuits for such systems. a , produces oscillations of, for example, 10,000 cycles A feature of the invention is a system in which and supplies them to a harmonic generator 2 5 a plurality of related frequency carrier waves are associated with which are a plurality of harmonic relatively so phased as to permit the use of a selector circuits 3, 4, etc. each designed toselect common ?nal ampli?er of much lower e?‘ective an individual harmonic of the base frequency output than the aggregate of the peak outputs wave falling within the ordinary broadcast range. The harmonic generator 2 ‘and the selector cir-I 10 H) of the individual carrier waves. _ Another feature of the invention is areceiving cuits 3, 4, etc. maybe of well-known types. The system for distributing multiplex short wave base frequency source, although not necessarily broadcast transmitters to broadcast receivers at so limited, is illustrated as connected to a prime apartment houses by the use of unmodulated lo source of ultrahigh frequency waves 5 through cally‘generatedshort wave oscillations which are a frequency divider or sub-harmonic generator 15 caused to interact with the received short waves 6 of the multi-vibrator type.‘ Such ultrahigh fre to produce modulated beat frequency waves with quency sources and frequency dividers are well in the usual broadcast range thus enabling very known in the art. The high frequency source 5 short wave broadcast programs to be effectively which is preferably a vacuum tube oscillator con handled by the local broadcast frequency dis trolled by a piezo electric crystal has an output 20 tributing network of the apartment house. circuit connected, to a harmonic generator and In accordance with the invention, a plurality selector 1 which serves to, derive and impress of carrier waves lying within the present-day ultrahigh frequency waves upon the input cir broadcasting frequency range are each modulated cuit of a power ampli?er 8. These ultrahigh fre by a broadcast program or transmission individual quency waves may, for example, be of the order 25 thereto. These carrier waves which are prefer of 30 megacycles or higher. ably produced as harmonics of the same base fre Each harmonic selector circuit 3, 4 is associated quency oscillations so as to control their frequency with an individual broadcast channel and since. I spacing are given suitable relative phase dis these channels are alike except for the carrier placements before being modulated. After modu frequencies and the fact that they do not trans- 30 lation they are caused to modulate a common mit the same program a description of one will ultrahigh frequency carrier wave, their phase dis suffice for each. Selector circuit 3 selects an ap placements serving to prevent coincidence of their propriate wave withinthe ordinary broadcast band ‘ peak outputs whereby the ?nal ampli?er may as, for example, one‘megacycle and impresses it have a much lower power rating than, would upon a phase shifting network 9 of well-known 85 otherwise be possible. ‘ type which is variable to permit adjusting the a. The invention may be readily understood from amount of phase shift as may be desired. After ' the following description taken in connection with undergoing phase shift the oscillations are im the appended drawings in which pressedupon an ampli?er l0 and the ampli?ed ,Fig. 1 illustrates schematically the circuit of a oscillations are supplied to an intermediate, fre- 40 multiplex radio broadcast transmitter; quency ampli?er‘ l I. A program orspeech input Fig. 2 indicates'the initial phase relationships ‘ circuit I2 is associated with ampli?ers l3 and H, of the intermediate frequency carrier waves; the output circuit ‘of the latter of which is induc Fig. 3 illustrates schematicallyra modi?cation tively. connected to the platecircuit of ampli?er 45 of the circuit of ‘Fig. 1 in which in lieu of succes I l in accordance with the well-known plate mod- 45 sive modulation, a separate unmodulated carrier ulator ampli?er circuit of U. S. Patent to Helsing, wave is transmitted; . i No. 1,823,322 issued September 15, 1931, whereby Fig. 4 is a diagram indicating two different ar the one megacycle oscillations are modulated by rangements of the modulating frequencies of the the ampli?ed program currents from circuit II. unmodulated and modulated carrier waves of Fig. In similar fashion the intermediate frequency 50 .50 carrier wave supplied to intermediate ampli?er 3, and V y - _ a, Figs. 5 and 6illustrate apartment; house receiv I5 is modulated by the program‘ or other currents ing and distribution systems adapted to receive of its respectively associated speech or program at‘ will either ordinary broadcast transmissions input circuit. ' 55 or the ultrahigh frequency broadcast transmis The modulated intermediate frequency waves 55 2 2,028,212 produced in the output circuit of ampli?er ii waves these two conditions of periodic phase co are transmitted through a band pass ?lter l6 incidence and proportionality of phase to fre and impressed, in series with the plate supply quency are inseparable it follows that periodic emf. derived from source H, on the plate circuit phase coincidence may be avoided by ‘imparting of power ampli?er 8. In like manner each of the to the harmonically related waves arbitrary ini other modulated intermediate frequency waves is tial phases related in some random manner de impressed through its respective band pass ?lter parting widely from that of proportionality to It on the series plate circuit of power ampli?er frequency. - 8. The band pass ?lters l6 serve to con?ne the Stated somewhat differently the relationship modulated wave bands .which they respectively 10 between phasev of vectors and their frequencies 10 transmit to their appropriate ranges eliminating is such that if this left-hand diagram represents any harmonics or other components which might vwhat occurs at one instant, the middle diagram fall in the range of and interfere with any of the representswhat will occur at some later instant other intermediate frequency bands. They also and there will be found at all times an orderly exclude bands from other channels from the arrangement of phase of vectors with respect to plate circuits of their respective intermediate their frequency. To prevent the situation por frequency power ampli?ers, thus preventing un trayed by the left-hand diagram from ever occur desired intermodulation which might result in ring, we must set up. as an initial condition a cross-talk or interference between two different disorderly relation of phase angle with respect program channels. Accordingly, oscillations of to frequency which is what is shown in the third 20 the extremely high frequency produced by the diagram of Fig. 2. Once a disorderly arrange harmonic generator ‘I are simultaneously modu ment ‘is set up, the phase agreement of all the lated in the modulating ampli?er 8 by all of the vectors as illustrated in the left-hand diagram modulated intermediate frequency carrier waves. will never occur. From another viewpoint, a 25 These modulated high frequency oscillations are random phase arrangement of the various vectors transmitted in the usual manner to an antenna is what is desired. or a transmission line. ' ' Referring again to Fig. 2, the third diagram In Fig. 2, certain phase relationshipsof the un shows one arbitrary phasing of the components modulated carrier waves are illustrated. Assum in accordance with the present invention. As 30 ing that the various intermediate carrier fre-v sume that the-vectors a, b, c, d, and e as gener quency waves originated as harmonics of the ated were in phase coincidence at their maxima same fundamental frequency wave, it will be ap as indicated in the ?rst diagram. Suppose that parent that at a particular instant the maximum the 10th harmonic vector a be utilized in its po of the fundamental wave will coincide with the sition of a" as generated. The 11th harmonic 35 maxima of each of the harmonics. At that in b may be advanced 135° to b". The ‘12th har 35 stant, therefore, the phase relations of the vari- monic 0 may be-advanced45“ to c". The 13th ous harmonics selected as intermediate fre and 14th harmonics may both be advanced 270° quency carrier waves may be represented by the or what is the same thing retarded 90°. It will , vectors of the diagram at the left of Fig. 2. The be apparent that this arbitrary phasing so de 40 power which the aligned vectors represent at that parts from frequency proportionality that the instant is proportional to‘ the square of their condition essential to maximum amplitude coin- ' vector sum or twenty-?ve times the power which cidence is avoided. Moreover, it will be appar would be represented by each vector alone. The ent that the sum of the vectors a", b", c", d", power capacity of the ampli?ers which this con and e" is very much less than they sum of their in dition would make necessary is very high. It is dividual magnitudes and, in fact, much less than OS accordingly highly desirable that the condition the sum of two aligned vectors such as d" and represented by the left-hand diagram of Fig. 2 e". Assuming a base frequency of 10,000 cycles never occur and that the possibility of any condi the phase relationship of vectors cf’, 1)", c", d", tion aproximating it be precluded, if possible. and e" indicated in the third diagram will re 50 Consider the conditions at a later time assum-' cur’ periodically ten thousand times each second, ing that the vectors 01, b, c, d, and e represent but will not impose an inordinate load upon the respectively the 10th, 11th, ‘12th, 13th, and 14th common ampli?er. harmonics of the base frequency. The expres The relative phasing ' between carrier waves sion 11th harmonic is used here as connoting the when these carrier waves are produced in a har harmonic whose frequency is eleven times that of monic series is important in carrier current sys 55 the base frequency. When a has shifted from its tems if the unmodulated carrier wave is trans starting position through any given number of mitted together with the sideband or sidebands. cycles to the position a’ as indicated in the second . This same type of disorderly or random phas diagram of Fig. 2, b will have shifted to a posi ing is desirable if-several carrier wave channels 60 tion b’ in which the angle of vector b’ is such are provided over a wire. line as would be the that the total angle through which the vector has case if the several channels in Fig. I delivered swept will be related to that traversed by vector their power through ?lters I6, it etc., to a car— a by the ratio of 11 to 10. Similarly, vectors 0, d, rier transmission line rather than to ampli?er 0. and e will have dvanced to positions 0', d’, and The technique of imparting desired phase shifts 65 e’ determined in the same fashion. The total to single frequency waves and the circuits em 85 angle of advance of each vector will be directly ployed for that purpose are so‘ well known in proportional to its frequency. It will, therefore, the art as to requireno description. be appreciated that in a system of waves of fre In the circuit of Fig. 3, the base frequency quencies harmonically related to the same base oscillator l8, preferably a piezo electriccontrolled 70 frequency wave the condition for periodic phase electron discharge device, is associated with the 70 coincidence of all of the wave maxima is that at harmonic generator 19 and power amplifier 20 any instant their individual relative phase angles from which ultrahigh frequency oscillations are are such with respect to an arbitrary initial point supplied to antenna or transmission line 2! to that each is proportional to the frequency of its be radiated in unmodulated form. The same base 75 respective wave. Since, for harmonically related frequency oscillator 18 supplies base frequency 75 2,022,212 . 3 oscillations over a number of lines 22, 23, 24, etc. dinary broadcast range by the well-known prin to remote broadcasting stations each comprising ciple of interaction employed in superheterodyne a harmonic producer 25, a selector 23, a phase circuits and to amplify them by means of am shifter 21, a speech input circuit 28, a modula pli?er 34 before impressing them upon the apart tor 29, and antenna‘ 30. In this circuit each ment house distributing network comprising the transmitting channel or station modulates ultra shielded distributing leads 35. In one apart. high frequency waves by speech frequency cur ment 5| 2. variable selecting device 33 is shown rents rather than by modulated intermediate associated with the broadcast receiver 31 which frequency waves as in the system of Fig. 1. Un may be of ordinary type. In another apartment 52 a similar variable selector 33 and broadcast 10 10 modulated ultrahigh frequency waves radiated from antenna 2| and the different frequency receiver 39 are provided but an intermediate‘ modulated waves radiated by the antenna: 30 of switch 40 is included in the circuit to permit the a receiver 39 to be switched'from the distribution _the various stations are preferably separated by system 35 to an ordinary broadcast frequency not more than the usual broadcasting carrier antenna H, at will. This system economizes 15 frequency. Moreover, oscillations from antenna 2| are of relatively very high ‘power. Conse with respect to the special detecting and am quently, at any receiving station, the ?rst de plifying equipment required for the extremely modulator will receive a large amplitude unmodu high frequency program waves and, also, avoids lated frequency wave from antenna 2| and a the di?iculty of distributing ultrahigh frequency waves over the apartment house distributing sys 20 20 plurality of differently modulated carrier waves of much smaller amplitude and for the waves tem. The same system may be used for receiv received‘ from each broadcasting station will yield ing from the transmitters of Fig. 3 by discon an ordinary broadcast frequency modulated wave necting the local oscillator 33 or by disconnecting as a result of the interactions which occur be ampli?er 20 and antenna 2! at the transmitter. tween the ,unmodulated and modulated received Fig. 6 illustrates an alternative ‘system in which waves. If, for example, the‘ unmodulated wave the ultrahigh frequency waves extend over a received from antenna 2! is 30 megacycles and greater range than ordinary broadcast-programs. the modulated carrier wave received from the To meet this situation, the range of the high fre- ' ?rst antenna 30 is of 31 megacycles,‘ the ?rst quency programs is arbitrarily divided into two lesser ranges, each of which is handled by an in 30 30 demodulator will produce a correspondingly mod lated difference frequency wave of one megacycle. dividual ultrahigh frequency converting ‘unit. Inasmuch as the various intermediate fre One unit comprises an antenna 42, detector l3, quency waves resulting from the detection of oscillator 44, an ampli?er 45. The other unit comprises an antenna 46, detector 41, oscillator the principal carrier wave of Fig. 1 are so phased 35 as to avoid coincidence of their maxima there 48, and ampli?er 49. Except for the frequencies will be less tendency for the intermediate fre— involved each of these units resembles the units quency ampli?er of the receiver to become-over 3|, 32, 33, 34 of Fig. 5. Each unit supplies broad loaded and to cause intermodulation with result cast program waves converted to the ordinary ant cross-talk. The same fact is true with re broadcast range to the distribution system 50 spect to the ultrashort wave ampli?ers used in which corresponds in every respect to the distri 40 40 receiving systems cooperating with the ultra bution system 35 of Fig. 5. What is claimed is: > short wave transmitting antennae 30 of Fig. 3 1. A multiplex system for transmitting signals if two or more of the radio transmitting chan nels are located at the same point. To meet that comprising a plurality of channels, a power am condition phase shifters 21 may be provided, these pli?er common thereto and means for applying 45 phase shifters being constructed and adjusted in to each of said channels signals of a frequency similar fashion to so relate the phases of the individual to the respective channel and in such various carriers that phase coincidence 'of their phase relationship as to cause their aggregate maxima does not occur. magnitude to remain at all times much less than Fig. 4 shows diagrams of two arrangements the sum of their individual peak magnitudes. 50 50 of carrier frequencies which may be used in the 2. A communication system comprising a plu system of Fig. 3. In the ?rst diagram the ab rality of channels, a source of carrier waves for scissa of the ?rst vertical line at MC indicates each channel of a carrier frequency individual to the channel with which the respective source is the frequency of the main unmodulated carrier 65 wave transmitted from the antenna 2| and the associated, means for modulating said waves, a 55 abscissae of W, X, Y, Z, etc. those of the modu common ampli?er connected to all of said chan lated carrier waves A’, B’ from the-other sta nels to simultaneously amplify all of said modu tions with their associated program side bands. lated carrier waves, and means for maintaining The modulated intermediate frequency waves re an arbitrary relationship between the peak mag sulting after the ?rst demodulation are repre nitudes of said carrier waves such that the sum of 60 sented by the lengths A, B, etc. The second dia said peak magnitudes remains at all times con gram illustrates conditions when the main car siderably in excess of the aggregate of the waves rier is positioned in frequency intermediate the applied to said ampli?er. - modulated carrier waves thus permitting spacing 3. In combination, a source of base frequency between the modulated waves to be larger while waves, a harmonic generator associated with said 65 at the same time enabling the desired interme source to produce a plurality of harmonic fre diate frequencies to be obtained. quency carrier waves therefrom, a plurality of A schematic diagram of a receiver suitable for channels associated with said harmonic generator and each including means for selecting an indi use in conjunction with the transmitting system 70 of Fig. 1 is illustrated in Fig. 5, in which a re vidual harmonic frequency carrier wave, and means for modifying said carrier waves in accord ceiving antenna 3| is connected to a detector ancewith signals and for impressing them upon a 32 with which is associated a local ultrashort common medium, said means including a power wave oscillator 33. This apparatus may ‘be placed ampli?er, at least one of said channels including on the roof of an apartment house to convert the phase shifting means for shifting the phase of 75 75 very short wave program transmissions to the or 4 2,028,212 , its carrier wave with respect to that produced by mon fundamental by signals individual thereto, the harmonic generator. 'means for transmitting the energy of said car 4. A successive modulation system comprising rier waves over a common medium, and means for an ultrashort carrier wave source, means for mod restricting the aggregrate energy of said waves at ulating waves produced by said source by a. plu all times to a magnitude much less than the sum rality of lower frequency carrier waves which are ‘ of their peak magnitudes without at any time re each of. a carrier frequency different from that stricting their individual magnitudes. of any of the other lower frequency carrier waves, 7. A transmitting system comprising means means for insuring that the aggregrate magni for modulating each of a plurality of carrier waves 10 tude of said lower frequency carrier waves re of different harmonic frequencies of a common 10 mains at all times much less than the sum of fundamental by signals individual thereto, means their peak magnitudes, and means for modulat¢ for transmitting the energy of said carrier waves ' ing each of said lower frequency carrier waves .by over a common medium, and means for shifting a signal individual thereto. the phase of the carrier waves with respect to 15 5. In a chain system of broadcasting transmit each other to restrict the aggregate energy of said ters, a control station and a plurality of widely waves to a magnitude much less than the sum of separated radio broadcast transmitters associated their peak magnitudes without at any time re with said control station, said control station _ stricting or diminishing their individual magni comprising a base frequency oscillator, including tudes. . 20 a piezo electric crystal to control the oscillator 8. A communication system comprising means 20 frequency, a harmonic generator associated with for modulating each of a pluralit‘ of carrier said base frequency oscillator to produce an un waves of different harmonic frequencies of a com modulated carrier wave, means for radiating said mon fundamental by signals individual thereto, unmodulated carrier wave, transmitting channels means for transmitting the energy of said carrier 25 individual to said broadcast transmitting stations waves over a common medium, and means for and extending to said control station, means for random phasing of the carrier waves so that the impressing upon each of said transmitting chan maximum value of all the carrier waves will never nels oscillations from said base frequency oscil occur at the same instant. lator, each of said broadcast transmitting stations 9. The method of transmitting a plurality of in 30 comprising a Harmonic generator, a carrier wave dividual carrier waves of different harmonic fre 30 selector, a phase shifting device and a modulator quencies of a common fundamental over a com wherebya harmonic carrier wave may be produced mon medium which comprises the step of arrang from incoming base frequency oscillations and ing the carrier waves in random phase so that the may be selected, properly phased and modulated. sum of their peak magnitudes is greatly dimin 35 6. A communication system comprising means ished without changing their individual magni for modulating each of a plurality of carrier tudes. waves of different harmonic frequencies of a com RAYMOND A. HEISING.