US1553625A - Duplex radio system - Google Patents

Description

2Sert l15. ,1925. 1,553,625

J. MILLS l DUPLEX RADIO sYs'ru Filed Dec; 24.- 1920 2 sheets-shet 1 fm2 A;

Ha "6I sept. 15, 192:5. 1,553,625

J. MILLS DUPLEX RADIO SYSTEM Filed Der. 24, i920 2 sneersneet 2 Patented Sept. 15, 1925.

7 UNIT-Eni: STATES-1;,PATENT OFFICE. f

JOHN MILLS, or WYOMING, .NEW JERSEY, AssIGNoR kTo WESTERN ELECTRIC COMPANY, INCORPORATED, or NEW YORK, N. Y., A CORPORATION or NEW YORK. Y

DUPLEX vRADIO SYSTEM.

Application -lel-December 24, 11920.. Serial No. 432,969.

T all whom it may concern:

Be it known that I, JOHN MILLS, .a citizen of the United States, kresiding at Wyoming, in the county of-Essex,-State of New 6 Jersey, have invented certain newanduseful Improvements 4in -Duplex Radio Systems, of which,-thefollowing is a full, clear,

concise,aiid exact description.

This invention relatesto a duplex rad-io.

10 transmission system.

An object of the invention 1s to provide a means-for duplex carrierqwave transmission employing :the vsame carrier frequency for both i directions. l

Another Vobject ofthe invention is toprovide a method lof and means yfor preventing side tone interference at ,a receiving station due to simultaneous reception of the de? sired Signal wave'and the wave from the related or local transmitting cir-cuit. f

Further Objects will occur as the description of the invention proceeds, wherein, for example, it `will be shown `that the discriinination sought isp-independent of the direction of the communicating statioinand also that they correspondence f between the balanced and balancingrwavesissecured in a simple manner fbyderiving them from a the transmitted and received signals. centralsta'tion may be, in a practical case,

the exchange of the local telephone system so that Vany subscriber to the telephone system can be connected to theradio system, al-

though the arrangements, in general, are equally applicableA to telegraphy. ,Y f i `The conjugate relation of the transmitting and receiving-circuits.to the common.

line etfectually prevents theoutgoing energy from the common line entering the receiving circuits. Thecondition Ofuse` of the same high1 frequency for the two. directions of transmission reqnirestlhat the receiving circuits be tuned to thefrequency ofthe waves sent*y out from the relatedr or local transmitting unit, and accordingly thesecir- 'he method of the invention has applica-- cuits may receive afportion of the energy sent out from the transmitting unit andl give an undesirable side'tone in the receiver.

-Further, by reasonof the closed higlifrequency VpathV constitutedby the transmitf ting circuits, transmitting antenna,-receiving antenna, receiving circuits and the circuit connecting the receiving andtransniitting circuits, any imbalance in this connect- The invention provides means to avoid suoli effects by preventing the energy of the waves Aincident on the receiving antenna-fromy the related'ror local transmitting antenna from owing in the receiving circuits.

tionk of preventing interference between transmitted 'and receivedr signals f which would otherwise occur in the event of simultaneous operation ofthe System in both n directions.

The invention contemplatesl balancing out the portion of the transmitted wave that is incidenten therelated or localyrece'iving antenna by rmeans of van'qauxiliary wave simultaneouslyA transmitted therewith. Auxiliary antennae, which rmay be small In size as compared with the main antennae,

yare yused to transmit and receive the auxiliary wave and means are provided at the lreceiving station to equalize and oppose thev two waves. The normally received wave frointhe distant station is unaffected.` The condition of complete balance requires that the Opposed waves must be identical in all respects.' This requirement isk satisfied, in

one arrangement of the invention, by usingy -a common f modulating ywavefor the inainy and auxiliary waves vat the transmitting The ini vention accomplishes the additional func-4 ing circuit causes a tendency to-'sing with -atstation, no necessary relation existing between the frequencies ofthe respective carrier waves, yand effecting, a balance between the Adetected modulating components. an alternative* arrangement effective for components. The requirement to be satislied invthis alternative arrangement is acmodulating characteristics of the opposed waves mustjbe identical. The desired rc I.telegraph transmission, vthe balance is effected between high frequency modulated.

spects the two arrangements are similar.

The invention provides for the balancing out of the interfering wave at the receiving station without special regard to the relative directions of the distant and related transmission stations. Further, the transmission 'telephone system.l

of the auxiliary wave byradiation results in the advantage, as compared with wire transmission, thaty a balance can be more simply and easily effected, inasmuch as the effectsof differentialattenuation and of phase shift are substantially avoided. i Y

For a'further disclosure of the invention,

reference is made to the detailed description which follows, together with the appended vdrawing,`in which Fig. lv shows in schematicform,a circuit arrangement embodying the invention at one of a pair of similarcom-` muiiicating stations. Fig.2 shows a more specific type of the system disclosed in Fig. l, and Fig; 3 shows Vthe system of Fig. 2 with the circuits `ofthe several elements of the system disclosed in detail.

In the drawing, the reference letters applied to the several parts are chosen with reference to the conventional terms descriptive of their function. For example, amplifiers, detectors, modulators and filters have been designated, respectively, Vby AM, D,M andF. v A Referring to Fig. 1, 1 indicates, generally, a balanced or hybrid coil arrangement of a well known .type interconnecting the respective outgoing andincomiiig lines2 and 3 with the line L which may lead toa central control station or to an exchange of a local By the arrangement shown, a local subscriber, for example, may transmit speech currents over linesL and 2 to the modulators M1 and M2, and may simultaneously receive from` receiving antenna Al. l

M1 and M2 are modulators of any type, on the input circuits of which currents of carrier frequencies are impressed by'generators G, and G2, respectively, of convenienttype 1 and size. To insure that the modulated carrier waves transmitted by antennae` A, and

A2 areidentical as to their modulation coinponente, thecarrier waves impressed on the linput circuits `of the two modulators are modulated by currents from thesarne telephone 'line L. To insure the complete separation of output energy transmitted from the modulators, the carrier frequencies p hybrid coil.

are chosen widely different. The transmitting station transmits the two waves with markedly different amounts of rradiated power, since ,antenna A1 is designed to work with the corresponding receiving Vcircuit at thedistaiit station, while antenna- A2 with its associated circuits and apparatus needs Vonly to have sufficient energy capacity to transmit efficientlyto the auxiliary antenna A2 of the local receiving station.

The waves radiated from aiitcnnAl' and A2, hereinafter to be called, respectively, the

main and auxiliary` transmitting antennae,.- (the waves being similarly designated and e distinguished) are received respectively-shy main ,and .auxiliaryl receiving antennae A",

'andlAwantenna Alalso receiving the norinally received wave from adistantqsource.

it is the purpose ofthe invention to combine the main and auxiliary waves received from the localtransmitting station in suchl manner that they neutralize and 'produce no effect in the hybrid coil, whereas 4the normally received wave from the distant station, which is received by only *oneA of the receiving circuits, is transmitted afterkdetection through the hybrid coil in the usualv manner; 1 n r A ready-solution of the problem is found by producing in t-he two 'waves radiated from the local transmitting antennae, modulations having identical frequencies, wave forms and phases. Since-the carrier frequencies are not identical and, in fact, have no predetermined'orfixedrelation toeach other, aV

'balance must necessarily be effected between the modulating, oraudio, frequencycomponente; To-this end the received waves are detectedV by .detecting tubes or devices D1 y and D2, intheioutput circuits of `whichvwill accordingly appear aywave of audio frequency together with `lhigher frequency waves, `which latter are effectually sup-` pressed by low pass filtersFL, which permit the audio frequency wavesr topass. The

amplitude of the voice frequency wave derived from the auxiliary antenna is, by means of amplifier AMl, caused to be the same as that transmitted to the other antenna, and these two voice frequency waves are finally superposedin an opposing sense in the device AM2 which may function additionally as an amplifier, as is indicated in the drawing. The received wave from the distant station is detected by the device D, in the usual manner and isk transmitted through vfilter FL and device AM2 to the Although i there have been shown low pass filters betweenthe detecting` tubes andthek amplifier AM2, these filters are not essential to thev functioning `of the systeinof the invention, and have been added kmerely tofelimin'ate disturbance in the telephone receivers, .inasmuch as the higher frequencies resulting from detection, may, in

particular cases, depending uponthe relalused throughout the system, the-invention is not dependent 1n any Way on the use of par-v ticular types ofmodulating, vdetecting and amplifying devices, and should not be con sidered as so limited l Referrrngnow to the modification illustrated by Fig. 2, which 1s especially adapted for telegraphic= transmission, the systemk shown 'iis seen to have many features in coininon Awith the more general system( illustrated inFig'. 1, these featuresbei-ng'similarly designated, and not requiring 'special explanation. "The systemof Fig..2 differs from that of Fig. v1 principallyinth'eluse of a common sourceof main and auxiliary carrier Waves toinsu'rethat the frequencies of these Waves have a fixed and-constant relation -to `each other,`and also rthat one shall bea multiple of the other, the two Waves accordingly being readily convertible by the use of l-:nownimeans into Waves of the same frequency.l Y' c The arrangement for deriving the main and auxiliary carrier Waves consists .of an overloaded repeating tube fed by generator G. By virtue of abnormal loading, a tube used in this manner can ber caused to function as a harmonicgenerator. A harmonic generator of this type is described in some detail inl BritishPatent 142,571. cuits for this, as well Aasthe other elements of the system are shown in Fig. 3, and only brief mention of them Will be made'here.

The output energy from thegenerator HG is divided and deliveredto rthe, modulators lrfl and M2 intwo portions. Filters Fl and F2 are used in order topinsure that ,current having'lonly kthe desired frequencies shall tion" `in the circuits of which they form a part. For exan'iple, the frequency of the currents delivered tomodulator `-M2 is preferably madeV to correspond to the fundamental frequency of the output current from generator LHGr, ivhilefthe current delivered to ymodulator YM1 has a frequency vcorresponding to the first even harmonic of this fiuidamental. Since the fundamental frequency of the output current of'HG is the same as the frequency/of` generator G, an alternative arrangement Would be that in which the input energy to modulator M2 isA taken directlyfrom the output of generator f1 The` filters `Fl and F2 may be of the welll-mourn Campbell type fully described in 'Patent No. 1,227,114, patented May 22, 1917. The circuits o'f one form of this filter are shown in Fig. 3. The carrier. Waves ob-v tained in :the ymanner .described above are modulated in the same manner as in the sys- The cirtemof Fig. 1,-and the modulatedcarrier- Waves Vare radiated from antennae Aland A2. lngthis system, as Well asin the other,gtheY antennae, both transmitting and receiving, are tuned tothe particularcarrier frequency used. A `i `The modulated carrier Waves transmitted by the main and auxiliary transmitting` antennae A, and A2 are received, respectively,- on main and auxiliary receiving antennae fr', and AgQ rlllie wave received byantenna A', may, in accordance yWith conventional practice, be considered as made upy of three components; an unmodulateld carrier fre-l quency con'ipon'ent having' frequency l), andv the upper and lcWer sidebands having frequcncics respectively equal'to P-l-S, and P- S, S being used to representr the frequency of the telegraph or other modulating Wavey and P to` represent the carrier fre-r quency. The corresponding frequencies of the Wave received by antenna AQ, are 1/2 P, f

1/2 lll-S, andi/2 P-S. Since thisiniodification einbodiestlie idea of a high frequency balance as distinguished from loW or audiok frequency balance, the vtwo high frequency' Waves must be identical at the balancing means and this requires that both the modulation frequencies and thecarrier frequencies shouldbe equal in the tivo Waves. The

` former have been made equalby the use of a common modulating source oaf-frequencies. The latterare made equalby thev use in a particular Way of the detector D3. inthe auxiliary receiving circuit.

According to theory'ivhich is Well understood in the art, the detecting operation iesults `in afcomplezi Wave consisting of separable components having frequencies,equalto the sum kand difference frequencies of the currents impressed on the input of the detector, as Well as other components having frequenciesk which yare y.double the impressed frequencies. Since currents of frequenciesA 1/ 2 P, 1/2 P-l-S and'g 1D-S are impressed on the input of detector Di, the output current Will include the coniponent currents' of` frequencies P, P-l-S and P-S, P-l-2S and ijf-2S, all having a frequency'comparable ywith frequency l?. The band filter F B is designed` to pass currents of frequencies P, P-,l-S and P- S and ysuppress currents of frequencies P-2S and P-l-2S. Accordingly, the Wave transmitted to amplifier AM, has the form of thewave transmitted from the antenna A, and received by antenna AQ. This Wave is amplified by device AMland superposed in device AM2 in lan opposing` sense with the Wave receivedby Al, as has been described with reference to Fig. 1. It should be noted that the system of-Fig. 2j is especially adapted for a mode'of operationinwvhich there is a constant modulating frequency asf, for example, in telegraphy, in which ease the .band filter FB is capa-ble ponentis of a double frequency and doublesv with each passage of the high frequency ci'rcuit,lthe local transmitting and receiving circuits will not sing.

In Fig. V3 there has been shown a detailed circuit arrangement in which the system illustrated schematically in Fig. 2 may be embodied. The `circuit details corresponding to the several elements are conventionally shown and do not require further explanation. It should be understood, however, that these circuit arrangements are illustrative only, and that any one of the various arrangements commonly usedk is equally adaptable to the system and other amplifying, detecting, generating means, etc., may be used. In this figure, elements are designated similarly to corresponding elements in Fig. 2 and are similarly arranged, the only exceptions being amplifier AM, and high pass filter FH, which are shown in inverse relation.

It is to be. noted that the two systems shown have in common the idea of transmitting from the main andauxiliary antennael of the local transmitting station radically different amounts of power at radically different frequencies, `the main carrier wave energy being intended for distant reception, and the auxiliary 'carrier wave energy for nearby or local reception, and of balancingv out at the nearby point such ofthe main carrier frequency energy as may be there,V

f received. Although systems to accomplish the purpose sought have been disclosed in detail, it should be understood 'that the invention is broadly as expressed above, and accordingly should not be construed as limited in any way to the specific arrangement shown, but only by the appended claims.

VVhatis claimed is:

l. The method Yof preventing side tone interference in a duplex radio signaling system which comprises radiating an auxiliary wave of different frequency from the rmain radiated wav@ and balancing out by said auxiliary wave at the local receiving station,

such of the main radiated wave as may be there received.

' A2. The method of preventing side tone interference in a duplex signaling system which comprises radiating to 'the receiving station a wave of the same modulating characteristic as the normally transmitted wave, but having a different carrier frequency, resonantly receiving said wave at the receiving station, converting it to a' wave identical with the normally transmitted waive, and

terference in` a duplex radio signaling sys` temarranged for non-directive transmission and reception, which comprises separately radiating an auxiliary wave, separately receiving said wave, and balancing out thereby at the receiving station such portion of the interfering energy as may befreceived at said station by combining said auxiliary received wave therewith in an opposing sense. v 1l. The method of preventingside tone interference at the receiving lstation of a rei lated pair of-non-directive transmitting and receiving stations in a duplexradio communicating system whichy consists in non-directively receiving an auxiliary wave at said receivingstation and balancing out the interfering' wave by combiningr therewith said auxiliary wave.

5. The method of preventing side tone interference in a duplex radio signaling sys- Vtem which comprisesradiating a main wave modulated in accordance with signals, radiating an auxiliary modulated carrier. wave of low power and frequency as compared with the main wave-and modulated in the same manner, receiving said auxiliary wave, detecting the saine, selecting from the detected `wave that component which has the saine frequency and waveform as the said main wave, and combining in an opposing sense said component amplified to the proper degree with such portion of the main transmitted wave as may be received at the related receiving station, whereby said last mentioned wave portion is effectually balanced out. f

' 6. The method of preventing side tone interference at 4the receiving station of a related pair of transmitting and receiving stations in a duplex radio communicating system which consists in generating a main carrier wave, generating an auxiliary wave,

said vauxiliary wavelhaving a frequency which is a subharmonic of the frequency of said main wave, modulating each of said waves in accordance with signals, resonantly receiving said modulated wave, detecting said modulated auxiliary wave, selecting from the rdetected wave that component which has the same frequency and wave form as the said main modulated wave, and

combining in an opposing sense said component, amplified to the proper degree, with such portion of the main modulated transmitted wave as may be received at the related receiving station, whereby said 4last mentioned wave portion isfeifectually balanced out. y

7.y A station of a duplex radio system comprising Vin combination, means for transmitting a modulated radioV carrier wave, means for radiating an auxiliary wave of different frequency, means for receiving modulated carrier waves from a distant station, means for receiving said radiated auxiliary wave, and means using said radiated auxiliary wave for balancing out such portion of the normally transmitted wave from the same station as is incident on said receiving means.

8. In a communicating station of a duplex radio system adapted for modulated carrier wave transmission, the combination with transmitting and receiving circuits for modulated waves, of separate means associated with said circuits for transmitting and receiving an auxiliary wave having equivalent modulation characteristics, and further means associated with said receiving circuit for combining said received auxiliary wave in an opposing sense with such portion of the modulated transmitted wave as may be there received Vto balance out the latter.

9. In a communicating station of a duplex radio system adapted for modulated carrier wave telephony, the combination with normal transmitting and receiving circuits for modulated carrier waves, of means associated with said circuits for transmitting and receiving an auxiliary wavey having equivalent modulation characteristics, and

a frequency which is a subharmonic of t-he normal carrier frequency means associated with said receiving circuit for converting said auxiliary wave to a wave identical in frequency and form with the normally transmitted wave, and means for combining said converted auxiliary wave in an opposing sense with suchy portion of the normally transmittedwave as may be received at said receiving circuit. y

10; A communicating station of a duplex radio system provided with means for preventing side tone interference comprising a main transmitting antenna, an auxiliary transmitting antenna, means for the radiat` ing from said antennae equivalent mo-dula- `tions on two different carrier frequency waves, the wave having the lower frequency being radiated from said auxlllary antenna,

a receiving antenna, an auxiliary receiving antenna, means in circuit with one of said last mentioned antennae -to change the carrier frequency of the wave thereby received to a frequency equivalent to that received by the other receiving antenna, and means for equalizing and opposing the received waves, wherebyv the effect of the wave received from said main transmitting antenna is effectually balanced out.

11. A communicating station of a duplex t radio system comprising a related pair of transmitting and receiving stations, the former of which comprises in combination, a main antenna, an `auxiliary antenna arranged to' transmit low power waves and tuned to a lower frequency than said main antenna, modulating means in circuit with.

, tivelyto the main and auxiliary transmitting carrier frequencies, a vacuum tube device and an amplifying device both in circuit with said auxiliary receiving antenna and adapted to equalize the frequency and amplitude of the modulated carrier wave received by said auxiliary receiving antenna with the corresponding wave in the main receiving antenna circuit, and means for combining said waves in an opposed sense, whereby such portion of the main transmitted wave as may f bereceived on the main receiving antenna is efectually balanced out.

12. The combination as specified in claim l1, having a detecting means in circuit with f said combining means whereby the normally received waves may be received and detected. In witness whereof, I hereunto subscribe my name this 21st day of December, A. D.

i JOHN MILLS

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