US1866592A - Voice operated repeater circuit - Google Patents

Description

July 12, 1932. B G BJORNSON 13566592 VOICE OPERATED REPEATER CIRCUIT Filed June "I, 1950 2 Sheets-Sheet 1 I r- R) 1 Illt I FIG //v l/ENTO/P B. G. BJc'iRA/so/v ATTORNEY Patented July 12, 1932 UNITED STAT S :eroa v e. BJoBNsoN, or nnw Yong, 1p

PATEN T OFFICE essrenoa To Barr. rnnernonn .pnppnnr roams; mcoaroamanyoa new roan, 1v. an, A coax-cannon" cr ne-w Yoniz" v0. 9 or-naarn errarea .QJ B I Application filed June 7, 1930. Serial ll'o, 4 59,652.

The present invention relates .to voice operated transmission circuits, particularly to two-way transmission circuits containingoppositely directed repeaters which are condix5 ltloned for .operation one at a time.

An object of the invention is to improve the operation of voice operated systems, particularly as regards speed of operation, sensitivity and freedom from false operation.

Voice operated circuits areknown in .the art employing an eastwardand a westward repeater which are rendered operative one at a time by speech waves. arriving at the repeater point for transmission through the repeater. To condition the respectiveare- .peaters for operation, some of the voice energy is rectified to produce a'voltage which .is used to change the normal bias on one or both of the respective .repeatersso that one -,g .repeater remains blocked Whiletheother is rendered in condition :to repeat.

In order to prevent clipping, that is, loss of any of the speech either at' the beginning or at the end of a word, it is necessary that gsvthe repeaterbeplaced in operating condition sufliciently soon to transmit the initial portion ofthe speech and also that the repeater have a sufficient hangover time to accommodate the end portion of a word'or syllable.

application of the speech to the repeater so as to permit longer time in-which to condition the repeater, it is obvious thatthe voice conswitching and release operations and secure I minimum of clipping. .7 I

While reference-is made'throughout to 'voiceoperated circuits and totwo-way transmission, it will be understoodthat the invention'in its broader aspects 'isapplicab-le to other types a of transmission than speech transmissions and is 1 also applicable, to .one-

way as well asltwosway. transmission. .a

"The inventionwill be better understood from the following detailed description with positive operation of the repeaters with a concerned in improving comprises the voice Where delay circuits are not used to delay and-amplifier iYZ. The .amplifier'rectifier is reference to the accompanying drawings 7 Sho ng n F g: 1 n chem ti dia ram two-way repeater circuit in accordance with the inventiQIl and in'Figs. ,2 and ,3, curves illustrative of theoperation of the circuit of 1g. 1. r

he g n ral l you o th cirQut 9i E g- 1 is in accordance with prior, art practice and will not require detailed description. 'l he portionof the system which the invention is op a c u sh w in h cent a PQItiQI of the figure.

The westand east linesL and L re speo tive y ar a P v d W h hybrid co l d b a cing network N omm n n the art. The west to east repeater circuit is connected between the bridged conductors 10 of line L and the circuit 11 connected to the series winding of thezhybrid coil of line L For convenience of descriptiomthis. ,vvest to east repeater path will be referred to ajs thetransmitting branch. The east to West transmission path I is con: nected between circuit 12 bridged across the hybridcoil of line L and circuit 13 leading to l n .Lw- F r c venien e o desc ipt iqn this eas o W pa w l b fe ine-. dton-$ the receiving branch.

'Thetransmitting branch contains thevacnum tube-relay circuit 1 4 together with such amplifier stages as may be desired, indicated generally at 15. Similarly, the receiving branch comprises the vacuum tu l relay 11;.6

generally indicated at 18.;andthe receiving 1 disabler or protector circuit is indicatedgenerally at-l H 1 ia th p i r a speec Ware arr ving at. '10 the ransmi ing br nch, pass in ape-13 into, the amplifier detector circuit.- 181 where y are, ra at d n st ady d re c r- .rent voltage WhiQh is used to make. the n'ormally inoperative vacuum, tube re lay ,l lopera iv and t disa e, th norm l y, p ratiy c v ng el y circ itrl Th isl don y V 1 e u g-t no m nega v 1 biasro r ay 14: and pply g negativ bias o. hegrid or. r lay l vThu th amp fie spee h. Waves in the,outputofamplifier'l5, in caseof 3111- no balance of the network and hybrid coil of line L will not find their way from circuit 12 through relay circuit 16 to amplifier 17 and set up singing around the repeater loop, because relay 16 is effectively blocked.

Similarly, received waves in the circuit 12 are transmittedthrough the normally operative relay circuit 16 and amplifier 17 and are impressed on the west line L A portion of thewaves in the output of'amplifier17 is rectified at 19 and applied to the amplifier detector circuit 18 to disable this circuit so that it is not operated by energy that may be present in circuit 10 dueeither to noise or lack of balance of the hybrid coil of line Lwp v i The improvements provided by the present invention will-now be described. As stated above, these are concerned-with the design of the amplifier detector circuit18 and the disabler circuit 19.

The amplifier detector circuit 18 comprises an initial push-pull stage 20 followed by an amplifier stage 21 and a rectifier stage 22. There is also a bias reversing stage 23 cooperating' with'the'rectifier 22 as above described to reduce the normal bias of relay 14.

Initial push-pull stage 20 has a normal negative bias impressed from source 2% slightly in excess of a value sufiicient to reduce the space current substantially to zero. It was seen in the foregoing description of the operation of the circuit as a whole that received speech waves operate through the disabler 19 to impress an additional negative bias on push-pull stage 20. This bias is applied across resistance 25. If the push-pull stage 20 had normal space current flowing through the tubes, theapplication of the bias to resistance 25 from the disabler would first have to reduce the space current to zero, after which a further increase in the negative bias would effect'the blocking of the push-pull circuit 20 against false-operation. Such sudden reduction of the space current to zero wouldbe likely to cause the transmission of an impulse through the rest of the amplifier detector circuit 18 such as might interfere with the operation of the vacuum tube relays 14 and 16. The use of push-pull tubes in stage 20 would tend to minimize that efiect 'es'peciallyif perfect balance could be obtained. However, by making the negative "bias from source 24: such as to reduce the space that the application of additional bias to recurrent in stage 20 to zero, it will be clear sistance 25 as described makes no change whatever in the output of stage 20andtherefore precludes the possibility of a disturbing impulse from this cause in circuit 18.

mplifier stage 21 (which may be one of several amplifier stages, depending upon the amount of gain required in any case) contains a high resistance 26 in the gridvcircu-it, theefi'ectof which isto cause stage 21 to rent curve 1 reams That is,-it does not respond to input levels below a certain minimumbut transmits cur rent nly when the minimum level is ex ceeded.

The effect of the foregoing provisions in the amplifier'detector circuit is readily seen by reference to the graphs of Fig. 2. The zero line at the left indicates the condition with no input from circuit 10. As the input level increases from zero there is a marginal range of no operation represented'by the distance between the zero line and the vertical line B. This marginal region is determined by the amount of. normal negative bias in stage 20. With further .increase of input level stage 20 begins to transmit current in accordance with the characteristic I On account of resistance 26 in stage 21 this stage reaches saturation very quickly after the initial input voltage is applied. This is indicated by the grid current curve I The rectifier current is shown by the curve I which shows a slight marginal operation with respect to I This is secured by the use of negative bias voltage 27. By the use of suificient amplification between stage20 and rectifier 22 the current curve I of the rectifier ismadevery steep and tube 22 is caused to reach saturation when the input level has-exceeded by a few decibels, the minimum operate level. As. indicated by the labeled points on curve I the complete operation point isreached atan'inputlevelof less than 1 db. and preferably 0.5 db. above the initial operate point. ,By initial operate point is meant the pointat whichthe circuit 18 is biased, that is, the level of input at which the amplifier detector begins to transmit current. r

If there were no marginal, operation in the stage 20 orin the rectifier stage 22, it will .haps double the rectifier current, and so forth.

However, by the use of. a suitable marginal operation I together with sufficient amplification, the rectifier current might be multiplied by, say, 10 for only a small .percentage increase in' input level. The bias in. stages 20 and 22 plus the use of sufficient amplification make for a very steeply rising rectifier cur- It is important from the form hangoveri and uniform. release. operation, that the rectifier currentcurve I reach a maximum shortly. after the full-operate level. This action is secured-by use of the grid resistance 26'making stage 21 saturate quickly.

standpoint of 'unigradually reducing level as the end of a word 7 or sentence is approached, would gradually reduce the amplifier detector voltage with likelihood that the final portion of the speech would be lost by clipping. In accordance with the invention, however, the rectifier current is kept up at its full saturation level for input levels only slightly greater than the initial operate level. Gradually weakening input speech therefore tends to maintain the same bias voltage on the system as do stronger sounds. This action makes the release operation practically uniform for sounds of weak as well as strong ending.

In Fig. 3 curves are given showing the variations in gain with time and also with input level of the vacuum tube relay circuits 14 and 16. These curves are self-explanatory. It. will be observed that the system possesses the following desirable operating characteristics: V

1. The receiver is blocked before the transmitter gets into full operation.

. 2. The receiver gain plus the transmitter gain is less than normal gain at all times during the switching or transition period.

3. The change from normal receiving to transmitting is completed for a small change in input lever (AL=O.5 db-.).

4. The operate time is very fast, of the order of 0.001 second, for suddenly applied tones, greater than about 2 db. above initial operate point.

5. The release time issuflicient to give slight hangover to prevent terminal clipping.

The disabler circuit 19 of Fig. 1 comprises an initial amplifier stage 30 and a push-pull rectifier stage 31. The negative bias source 32 and the grid resistance 33 give the circuit 19 suitable marginal and saturation characteristics of the general nature indicated above in connection with the amplifier detector circuit 18. The use of a double wave rectifier 31 avoids delayed or wrongly timed operation due to phase shift. The use of a very small condenser 34 across the resistance 25 of stage 20 gives a fast build-up time for the disabling voltage. All of these factors cooperate to give fast operation and uniform operate and release conditions. By adjust-' ing the characteristic of the full wave disabler rectifier 31 in relation to the characteristic of the push-pull tubes of stage 20 practically a straight line relation can be obtained between the disabler input level and the limit of suppression of the transmitting vacuum tube relay circuit 14. This is desirable since the limiting action of relay circuit 14 must increase to give greater protection against false operation as the waves in circuit 10 increase. The fast action secured by this circuit is necessary to prevent a momentary impulse being sent through the transmitting control circuit where no receiving delay is used, as in the case of the circuit of Fig. 1.

What is claimed is:

r 1. In a voice operated circuit, a circuit for producing a direct current voltage from speech energy, comprising a-rectifier preceded by an amplifier, and means to make the operation of said rectifier and amplifier marginal, said amplifier reaching substantial saturation at the input level corresponding to initial operation of said rectifier.

2. In a voice operated circuit, a vacuum tube rectifier normally biased against operation, a three-element space discharge amplifier feeding into said rectifier, means to im press speech waves on said amplifier, said amplifier having a high input resistance causing the amplifier to reach substantial sat uration at the input level at which the rectifier begins to operate. V

3. In a voice operated circuit, a push-pull space discharge circuit normally biased against transmission, means to impress. speech waves on the input of said push-pull circuit, a three-element space discharge device coupled to the output of said push-pull circuit and having a large resistance in its grid circuit, a rectifier connected to the output of said three-element device, normally biased against operation, the bias on said push-pull.

stage and that on the rectifier and the grid resistance of said three-element device all being proportionedto prevent production of rectifier current in response to input waves below a certain minimum level and to produce saturation current in the rectifier in response to input waves exceeding. said minimum level by a small fraction.

4. In a two-way voice operated system, an amplifier rectifier circuit for controlling transmission in both directions in response to impressed speech, said circuit comprising a push-pull space discharge tube stage normally biased to the zero space current level, V

and means operating in response to waves from the opposite direction for increasing said bias, said push-pull stage working into amplifier rectifier stages with steeply rising characteristics reaching saturation at input levels slightly in excess of initial operate level. I

In witness whereof, I hereunto subscribe my name this 29th day of May, 1930.

BJORN G. BJORNSON.

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