US2328951A - Two-way signal transmission system - Google Patents

Description

Sept; 943. N. w. BRYANT 2,328,951

TWO-WAY SIGNAL TRANSMISSION SYSTEM Filed July 17, 1942 2 Sheets-Sheet 1 FIG. I

WL 2 EL COMP 4)0 .39 1/ f /3 l/L/ 714 $2 /0 F161 2 E I AMP I AvflvA'Av V 5: 20 l w 5 AMP AMP a A I L AMP /N VENTOR NWBRm/VT aZCfM A T TORNEV p 1943- N. w. BRYANT 2,328,951

TWO-WAY SIGNAL TRANSMISSION SYSTEM Filed July 17, 1942 2 Sheets-Sheet 2 INVE/V TOR N "(BRYANT Brim-25W 4 ATTORNEV The inventiofi rglqt gg tc tvgg way signal transmiissionsystems and particularly to (iilcuigs ig l;

; 2km purpbs' OI: enablin propel li zymzase k mqmmm an intexmeaiatetzansa p smlttirgg Q15. WW

l-am ssa q m mmsd) I ioq will be un'cier'st'ObdT-rbmth fbl'lqwing tamed description wher gggfig conjunction with hgetd in shunt with tho lipgsoc-tio be't we se ries' resistors? ye backard-ac by. echoes; Howevemsime ythei ex ndfi get! through mthoutrattenuaati'omonlyo atstimqsl when; theyare;maskedqwmheibneakingsignailsi i A mthe signal volume levebof thbrea-lqng parjzyi the: volume oi the! fdnmers signahiat the; outp of his own compressomwifl be lowenthani nonnalo The signal of the breaking partysam-thevinput ofi mnm trgmsmrmw Zfixmhalving a non-41mm; im-isms:

be: a; cophermox dmr ectiml mama; b "as E21 ,4

xresistonlfi': and: ausim-iiannm-Jimaa: J2; Shh-Mada: mama 11mm msis qni 2%.; msxm ml oonnaehedmzsemies wibmnashwsiqm 05 mg; and

linegr; ne'sistomot meal: alum: shunting; tho; 3%;

1 hiswexpandenwill alsobe lower: than nor-man and hhoamiotsinsest thenproper amountof-n gaimim his expander; I'hereiore; while he isxalblg to bneak through, the volumesofi his signals-reachathe 'othemparty will belowe r: than normaliby arr-amount approximately equa h p9; the -d-ifieseno i-mtwlkihg volumesx This; however, is n more his words wi fl getthrough at l normal they occu n du r ing the pauss of flhe other-talker;

Any variation received v'olume isi rio'ii dis-tui'b mg to the latter talkei=- because," ofl the: masking:-

for a talking patty to tmderstainda 4i bz oahing p'agtty whil-e the former istalking h I: has been pomedwuu that .the' increose m not excised (NE+-RL)'. Whenmisisg alowqglue;

the improvement; mayhofi. b sufl ib t; to 1 1151165 the use ofi such devices by themselvs -pzyaotigai1f-as echo suppressors pen Se. To incyease this echo loss, on auxflianyeeho suppressor may be added as in the modifications of: uhsimmmon mus identification characters; The patticulah 59m? i neiiudes in"the-outgoing path EA! hi on L ay into the path by a n for this]compfess x irioluges gongw l0 having its inputicohnectogl 'acfossit eluding ."hhehparallelv comiensem Ski 84351; wfi n m meamm -lizapoom thmprrmaicy-windin on tmoute brid es: haying; its inpmxmmxeotedgi tosthei out-,

out; or .Lampfiflen- 3:4;- anat; its: output-u cemente thazoughhhebseries; diizectibmmristoz:

20, 2| of the compressox nominal; eimuih In across? the sama diagonaizof theweofigfier bridgsllofimhe Qomnresson variofllosserzvhh A: hsngroxem comthe cazess-jcontnol eircuit iz; v .mAn; auxiharm echo; suppressor, compr sesthe;

elexihiaxxmagnetioz relays-q 318;: having, its Ec me,1 'a,t1ng winding-connected imgserieshwithone; side oh: the. cfosshcontroli cirwit: 5; between the rootifism 3i:

manneriwhiohwmilhbe dsemxbed below 'other diagonalof the bridge If! in vario-lossei The volwne. iahge expanderi VEW incmdes inand aw preceding" varioL-lossep VLQ consisting" of ailoss; tpadw 33; comprisingthe, tandem couneeted:

t-rxansfiormezs 4m amt-4 t: with cmsssd mner. ings, mathewrwnsmission pgnhjm m irant at the; varifli-hlossezz andthe assopiatem resistom l3,

s ime-System01? Big; 2 opyexates as follows: n I :Ifif'iihfi; idle condition; Ofi the: circuit; thatyig: WiEh'HOI SDBBGhXWaYQS beingwqransmibted Outiovexi the; path and: no; speechmves being received ommtho receivingpath Wmthoinner' windings closed: oontzmts: 0.1 the; rlay 38: T of; the auxiliary;

.stantialiyl moulrossiinltheuinpmgv ofi'the path: EA-.; With-no coxitxol 1 cument: ap lied-Ito the: copper:

oxid regtifiersfimthe rectifier bridge; l1 from the associated; commesson' controhoiicuit: k: and the" orossmontrolt circumzi, thmefieotiveyshunt impedi'rice; ofqthekbmidgefi tFl'zis thafi the vario Iosseiu' prom comparat wgly sma l lf loss j in th iaa --EA so-thpt' theeffe'qtive gam s-ms he mso, with no cosine; gu ken ma pueonio ik'gav mwmmu; the impedarioes of the series press'or thelbsfiiwalfis ofiwhibh pad in themathhA -vis controlled bwtho operation ofanelayi 18m, tho

eshocsnppnessor; so thatathe' pad flamsentsesuh coil"- Hwto the .line 'WL overwhich they will be at the other station (not shown) also provides a'rnaximum gain of 25 decibels'and a maximum loss of 25 decibelsy'respectively, so thatthe overall n'et'gain in thefour-wire circuit is zero.

. uissum'e 'that the west subscriber'is speaking.

flisf' 'speech current "received over the line WL will be impressedby hybrid coil Hw on the input of tnepath -EA andwillpassthrough the loss pad 39 -and the vario' -losser 'VLr with little atte'nua-r tiorrfto the input of the amplifier Ill and will be amplified thereby" andtransmitted over the path 'EA' to the east stationJ- Aipor-tion of the amplifie'd waves" intheoutput o'f amplifier l diverted into the compressor con'trol circuit I will be amplified' by amplifier l8, rectified by the rectifier i9 and applied across the timing-network 20',2|

to theire'ctifierbridge. ll ofyario losser- VL1, to 1 controltheim-pedances of {the rectifiers therein insuch' manner asto' increase the loss value of the vario-"losser-Vm in proportion to the increase in applied rectifier current. .I'hewolume range of westfsi amplifiedtwaves thereafter transmitted out' over thepath EA will'therefore be compressed ina'-givenratio (2' to 1 inthe working range).

The action-of the volume 'range expander in the"path EA at the 'east station' (not shown) will be desc'ribed by reference to the identical expander VEw'linthe output otthe path WA at the west-statioh illu'strated; for the case where speech:

currents from ian eastsubscriber are being received over'th'e path'WA.

East's s'pe'ech Waves with the icompression in volume range produced by the compressor in thepath WA atgthe east station (not shown); corresponding to the compressor in the path EA at thiwest station,'-on arriving at the weststation, will' be divided between'the main transmission path and the common input to the expander cohtrolicircuit 3 and the cross-control circuit 5. The portion of eastsspech waves transmitted intothe expander control circuit 4 willbe amplifled by the amplifier 30- and rectified bythe rectifier 3| therein an'd will be applied through the timingnetwdrkl32g33 to the vario losser. VLe by the I connectionsto the ini'd taps of the shunt resistor 29 and'ofthe primary winding of output transformer .24' therein; The applied rectified currents willfiow through the series rectifiers 25 and" 2] in the vario-losser VLz in the direction iniswhichTthey-are-pointed so that their series resistance-is decreased by anamount (25 decibels)i.*equal to the loss'introduced in eastsspeech- Waves by the,..compressor at the east station:-

Thus the main :portion of-leasts speech waves passing throughthe vario loss'erfVLz andamplified bytheamplifier 22 in the output of'the path 7 WA areeffectively expanded in the .same degree as 1 they: are. compressed atthe east terminal. These waves are thenpassed through the hybrid transmitted tothe west subscriber.

:Anotherfportion of eas'tfs speech waves in the input of the vario-losser Vlein path :WA are divertedinto'the cross-control circuit "and are amplified by the amplifier 34 and rectified by the rectifier-:35 therein. As the latter, rectifier isconnectedin parallel .withtherectifier l9and the timing network 20,, 2! of the compressor control circuit tacross the same diagonal of the rectifier bridge H -in;vario-1osserVL1,' therectified ourin thepathEA being equal to the effective gain inserted bythe volume expanderVEw in response to. easts incoming signals in the path WA, and operateszto produce a corresponding suppression of the echoes of .ea'sts signals reflected into the input-of path EA.: As pointed out previously in connection with Fig. 1 the maximum value of this echo loss is limited to. (NL+RL), i. e., half the companding range, or about 25 decibels for'th particular compandor used.

- Hang-over condenser 31, which is connected across the rectifier 35 of the cross-control circuit 5,"provides a means for holding the loss inserted in jthe'path EA by the cross-control circuit, long enough togattenuate echoe returning from, the

circuit connected to the four-Wire circuit.

The condenser 31 is'charged whenever the cross-- controlo-perates to insertloss in the compressor: VCw, and prolongs theaction after the signal at. the input-to the cross-control circuit 5 has passed.;, In .order to prevent this hang-over .condenser.

from :afiectingthe; attack and recovery times of the-regular compressor control circuit '4, it is isolated 'frorm-theirectifier E9 of the latter control circuit by the directional vvaristor 38, which may'consist or a number ofc'opper-"o-xide rectifier discs'; The length of the-hang-over is determined-by the time constant of the network comprising condenser 31,*theiso1ating varistor '36;

the .rectifiers 35. :19 of the? two controls, the resistance-condenser network connecting these two controls to thecompressor rectifier bridge ll, andthe-;rectifier-bridge H itself. q

;'I he result of connecting the cross-control cir'- cuit 5-and the compressor control circuit. 4 to- 1 gether is to. give the control circuit ,With the larger output control of the compressor VCw, except when the two outputs are approximately equal, at which point both control circuits take partial control. Thisactionmakes break-in easy since 'atalker trying to breakcan take control of the compressor at his endof the circuit, if hetalks as-loudly as the other party, making the action; of that compressor the same as if the other party were not talking. Thus the volume at theoutput of the compressor and therefore at; the input to'expander v(in the breaking path) is normal. This means that the expander will fully compensate for the loss in the compressor and; the received volume will be normal. Even if the breaking party doe not speak-loudly enough 1 to-take control of thecompressor at his end of output of. rectifier 35 inthe cross-control circuit 5 whenever that cross-control circuit is operated the line he will still be heard at the receiving.

end. but ata lower volume.

he additional echo-loss required to make the system of Fig. 2 practical as an echosuppressor is provided by the auxiliary suppressor. comprisingtherelay 38 andthe loss pad 39 and associated linear resistoriz. The relay 38 is operatively energized by the rectified current in the by incoming speech; currents. Theoperation of relay 38 to open its contacts opens the normal short-circuitia round the resistor 42 connecting that resistor effectively in series with the inner cross-connected windings oft-he'transformers 40-v and..,4l in losspad 39 so as-to increase theloss rentsofthe cross-controlcircuit 5 operate insimilar manner. as the rectified currents of the compressor control circuit I, described above, to effectively increase the loss value of the variolosserillminthelpathEe, 1 0 thus i serted the input ofthe path EA'by the value of that The amount of loss inserted by the auxiliary I suppressor cannot'be made large without seriously affecting the break-inc The volume of the breaking party is reduced by the loss inserted. In addition, the breaking signal, when iteperates A -nect'ed "coils in "loss pad 19 to connect them in series-aiding condition in which the padprovides minimum-loss inthe path EA; I

When west stops talking or pauses so o'f the compressor control circuit 44', the condenser ll discharges through the varistor 48 and theresistor 49,-resistor5i] and V113, the discharge time of this circuit being approximately the sameas the i'ecovery 'time of the=compressor= VCWi. f'Under this condition; condenser 82 also "dischargesreducing the positive bias on the control grid of the tube 12 so that the (DIFF) re- -1ay-.'M:in =its output releases. t-- i master d s gnal jollo z o ed by received signal If whilena transmitted signal is present and the circuit of Fig. 3 is ingthe transmitting con- 1 dition;-asignalfrom theeast subscriber is received over; the incoming path WA, the portion ofgthis signal entering the expander'controlcir- Jcuit 53 and the cross-control circuit 62 will producegvoltages-across the condenser 51 at the v,outputof the expander-rectifier 55 and across the; condenser 65 at the output of the cross-controlrectifier 53,, The voltage across condenser 51 ;.will cause biasing. direct current .to flow throughthe directional varistor 58 and theresistor 59 to,the expander vario-losser VL4-in V such direction as to, reduce the impedance of its series varistors andthus to reduce the losszin the path WA toeasts incoming signals, thereby ,ef-

fectively expanding, the volumerange of the latter. f. s i The voltageproduced across thecrossecontrol circuit condenser 85,,if. sufficient, causes current that-thetransmitted signal is removed from the input If whileithe received signal from east is still present wests transmitted signals terminate, the voltage drop (TCV). produced'betweenpoints H .and Grim the cross-control circuit 62 decreases tozero. and the circuit functions as it would if no transmitted signal had been present.

Ifthe signals received-from east terminate while the signals transmitted by west are still 5 flow from Etc F-throughthe resistor .66 and v the directional varistor 61, charging "condenser lfipa nd then-fromli toG through: directional .v aristor 68 and resistor 69,-.to the rectifier bridge 5| of the compressorpvario losserV113;- '(When the voltage produee d across the compressor losser bridgetl *bythe compressor control circuit ljinrresponseto wests transmitted signals i is. greater: than (the voltage "produc'ed' across con- .densr 65in the-cross- -controlcircuit BZ by the -signals'receivedfrom east, nosteady-state cur- .:.rent will flow from E to G- in the cross-control .circuitiIGZ.) .-.-'Ihevoltage-produced between E and .F .bias'es. the control 'grid of the tube H positively. andg whensufficient, increases the ;.plate current of that tube. to a point where the -relaylchain'comprisin g relays 13' and 18 operates. The operation of these relays does not cause the blockingof the transmitting'circuit EA'by the present the voltage drop (RCV) produced between F and G in the cross-control circuit 62 will gradually decay andthe (DIFF) relay 14 will'reoperate. The (SUP) relay l3. and the relay 18 after its hang-over period will also release. Which occurs first will depend on the relative amplitudes of the transmitted and received signals. In either case, the suppression provided by the variable loss pad i9 is removed from the transmittingcircuit EA.

Received signal only; The signals received overtheincoming path WA from the east subscriber will pass through the fixed loss pad 84, variorlosser VLi, amplifier 52 andhybrid coil Hw to the line LW over which n they will be transmitted to the west subscriber.

A portion of these signals will be diverted from the path WA after passing through the fixed loss pad 84, into the common input of the expander control circuit 53 and of the cross-control circuit 62, and will be amplified by the common 1 amplifier 54 therein. The portion of the amplisea waves passing through the transformer 56 .willbe rectified by the expander-rectifier 55 and will produce a voltage across condenser5'l. This will cause biasing current to fiowthrough directional varistor 58 and resistor 59 to the variolosser VI in suclrdirection as to reduce the impedance of the series varistors therein and thus effectively expand the volume range of easts signals passing through that vario-losser.

- through the transformer (to the cross-control .suppre'ss'or co'il pad 19 because the (DIFF) relay -i4'in -the outputof tube 12 is still operated holdingithat padin the low loss condition. When the-voltage dropproduced 'between F and Gby uthe-cross-controlcurrentis'equal to the voltagedmpbtween. H. and Gr dueto the-compressor r 1 controlcurrent the plate current of; the tube 12 decreases toa point'where the (DI-FE) relay "M releases at which' time the short-circuiting connection across the inner windings ofthe suppressor coils of pad- 19 are opened to connect these windings in series-opposing relation; providingka' blocking loss in the transmitting circuit "EA. "The"blocking-ofthe circuit EA in this man-- her is considerably-slower than when there is no-transmitted signal and theiDIFF) relay [4 'is not'joper'atedi "Until the latter relay releases, tra'nsmitted speech can pass out over the path to-th east statiomand will mask any initial rectifier 63 and will be rectified thereby to produce avoltageacross the condenser 65. This w llcause current to fiow from E to F'charging condenser I0, and then from F to G and to the rectifierbridge 5| in the compressor vario-losser VLa causing the latter to insert a loss in the path JEAN Thevoltage produced between E and -E.1n .the control circuit biases the control grid ,7 of the tube ll positively, increasing. the plate current of that tube, .current is sufilcient, the suppressor relay chain If, the increase in plate 13, 18, will be-operated to open the circuit of .the suppressor coil loss device 19- to blockv thetransmitting path EA. When the signal received ,from east is a few decibels or more above the marginal value required, to operate tube H, the

- echo suppressoris operated in less than 3 milliseconds. This fast operation is necessary in any receiving .type of suppressor in. order to suppress echoes properly.

1 ;';The voltage drop'produced between and I u The 1 ;other..portion:ofthe amplified waves will pass 'ee 5. I

Will ey ieiete jerbs'e smart-i t mused-to t e w a1 OverfinterVubY the hemmed e: -3,"tIferecitmersfhiithndg"Gamay he f'ed that interval vanstor we, we aascrfiwa ymmn mew-mm 'theism ana s"ec 'e *o the: im/(attain mum aware m smuae etion ebress the *suisprssei in said receiving preventing the loss from affecting the input w 75 channel to reduce the loss value of said seconq mm wev-er, mmmameam Kine s siemwantm@emm; m "the isystem Mervin-mixer asingle 'transiomer 150mm yariorlosser in proportion, to thezamplitude, level of said incominig signals: said cross-LcontroI'cirvcuit comprises: a thirdfrectifier control circuit having its input connected to. said receiVinnhannel and its output-connected'lto the vario-losser I of said compressing meansiin the same manner as'the first rectifier control circuit thereior cone trolled-from said transmitting channel,v said auxv -iliary means "include ,a variablezloss ,padoi nor- 7 mallow loss value connected in said transmitting channel, and relay means responsive'to the .rec-

..-tified waves insaid cross-contrclrircuit; to increase thelloss valuecf said rvariablewloss pad to said fixed amount; said crosscontrol;c ircuit includinga oneway transmissiondevice connected between said relay means and-said first rectifier control circuit ofsaid compressing means; to, prevent false operation of said; relay means in re.- sponseto outgoing signals in said transmitting channel. r

' 5. The terminal ofclairn linjwhichlsaid-auxil iary means is operated byth e voltage drop produced ina portionof said cross-,controlcircuit response to said incoming signalsand said other means includesmeans for] producing an oppcsing greater voltage dropin said cross-controlcirinfitting' channel'fo'r a given hang-over time interval after thesignal' input to said cross-control circuit ceases. Q 1 1' 7. The terminal of claim 3 in whichsaidauxiliarynieans comprises a variablefloss. pad normany of low loss value, in said transmittingfchangnel beyond the outputof said compressing" means, and relay means responsive to the voltage drop produced in a'po rtion of said cross-control circuit by applied incoming signals to. increasethe loss value of said'p'adtosaid fixeda'mounfland said other means includes means foreffe'ctively disabling said relay means when the signal'oiitput of said compressing means exceedsjt'he: signal input to said'ex'panding means by a given amount. f f ,1 ,1 V ,8. The terminal of claim 3, in whichsaidco-mpressing means comprises a .vario-lossr of, nor l mal low loss value insaid. transmitting channel, and a rectifier-"control circuit responsive to out? going signals in the output ofsaid vario-losser forincreasing the loss value of said'fvarioelosser in proportion to the amplitude level of "said outgoing signals, said cross-control circuit comprises a second rectifier controlcircuit respdnsivlto the incoming signals insaid receiving channelin front of said expanding means,of suificient, level to operate thelatter, in the absence of'outgoing signals of greater. level 'in 'theoiitpflt '0f ,'sa'id vario-losser, to, increase thei'lossyalue' of said vario-losser by'an amount equal to the increase ingain of said expanding meansinfresponseto said incoming signals, said auxiliary meanscomprisesrelay means which when operatedinserts a loss of said fixed amountlin saidtransmitting channel, an electron discharge device responsive to a voltage drop produced in a portion; orJsaid second rectifier controlcircuit byincoming signals ofZsaid sufiicient level, to cause the opera tlon of said relay means, and' neans iorinainltaining said loss of fixed amount in saidtranse a ance v l au e whe e out i s s..-

nals applied to said first rectifier control circuit areof higher level than the incoming signals applied to said second rectifier control circuit, and a second relay means responsive to opera tion of said second electron discharge device for disabling 'the first relay means and-said hang- 9. The terminal of claim 1 in which said compressing meansincludes a vario-losser insaid transmitting channel, and a backward -acting control circuit controlling its loss value; in acicordancegyvith the amplitude le velof the out;

going signals in the output of said vario losser the output of said cross-control circuit alsocontroll-ingthe loss value of saidvario losser inthe same manner as said backward-acting control circuit, in response to the incoming signals in the in- P f pand a ean n dJQ iY n channel, said backward-acting control circuit and said crosscontrol circuit including individual re.- sistors connected in opposition, respectively traversed by the control currentto said vario-losser due to, said outgoing signals and due to said incoming signals, and of such relative-values that the control circuit with the larger output obtains control of said vario-losser except when the -tjilp I outputs areequal when each obtains partial control, said auxiliary means being operatively responsive to thevoltage drop produced insaid cross-control circuit by :the incoming signals when their level ise qual' toor greater than the levelof the outgoing signals applied to said crosscontrol circuit. Y f I} IOJ I n a two-'Way' signal transmission system including a signalitransmitting path and a signal receiving path at each terminal, means in each Signal transmitting path controlled by outgoing signals forvariably compressing their vol.- ume'range, means in'each signal receiving path controlled by incomingsignals for variably expanding their volume range, a unilateral crosscontrol circuit at each terminal responsive 'to in coming signals in the input of the. expanding means in the signal-receiving path, in the, absence of outgoing signals'cf greater. volumelevel in th output ofjthe compressing means in the transmitting path. at' the. terminal, to control that compressing means to-insert an echo suppres'sionloss of avalue dependent on thefvolume level of the controlling signals, in the signal transmitting path, and a differential echo suppressor at each terminal controlled by the voltages set up in the cross-control circuit by the incoming and outgoing signals, to cause an additional fixed amount of suppressionloss to be inserted in the transmitting path when the volume level of the income 'ing signals applied to thecross-control circuit is equal to or greater than the volume level of the outgoing signals in the output of the compressing -means' in the signal transmitting path at the terminal.

Y 1 I NEWTON W. BRYANT',.E.

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