US2455914A - Voice operated antisinging repeater - Google Patents

Description

Patented Dec. 14, 1948 j vol rbrtnmn i Francis J. Biltz, Eaton'town, N. J.

A plication July is, 1944', ser ain sissoi .7

aims. (CL179-170y x '(Grantcd "under the act of. Marchx 3,?11883, as amended April 30, 1928; 370 0. G. 7 57) The'inven'tion described herein may-be manufacturedandused by orfor the Government for governmental-purposes, without the payment to me of any royalty thereon.

invention relates to signal-controlled repeaters for two-way communication over a single lineor channel. 1 *In prior repeaters of this type,'a limitation exists in the maximum permissible amplifier gain in order that self-oscillation, "or singing, be avoided. In one widely used system known as the' type 522 'repeater-(two-e1ement, two-way), a balanced-bridge circuit is used to prevent singing. The gain of such .repeater must, how- 'e'ver be--- kept 'low to avoid self-oscillation due to'slight line unbalance." In systems using hybrid transformers, the unbalance must be so small that no transit tones will follow the loudest spokenwordl l [An importantlimitation ofthe balanced type of repeater that halfthe energy is lost inthe balancing network of the bridge, which loss, I f or reasonsab ovem'entioned, cannot be compensated for byprovidinghigh gain in the repeater.

Moreoven since it" is difiicult to balance the taken dn connection with the accompanyingdrawings, in which:

Figure 1 is a block diagram of the invention;

Figure 2 is a schematic circuit diagram of the invention- For a general description of the invention, reference is made to the block diagram in Fig. 1, "wherein there is shown interposed in a single transmission line a :pair of amplifying channels I A and B for handling signals coming through directions W and E, respectively. Both channels are identical in structure, and respectively comprise input amplifier stages Ai and B2, output amplifier stages A and'Bo, and control stages Ac and 30. Because of their connection to a common transmission line, it will be seenthat the input stage of one channelmust necessarily be coupled to the output stage of the other channel. Under 'ordinary circumstances, feedback will take place and give rise to self-oscillation.

To avoid this condition, input stages A1 and B2 are, in the absence of signals, made normally operative; and output stages A0 and B0 are normally biased toicutofi by potentials from control stages A0 and Be respectively. Each of said control stages'will, in response to a signal fromtthe input stage of its channel, first bias the input stage of the other channel to cutofi, and then unblock the output stage inits own channel so as. to provide amplification and transmission of signals from the inputstage in said 7 channel;

For example, assume that a signal arrives from direction. W. Imput stage A2 will amplify said signal and impose it upon control stage Ac and upon the normally blocked output stage A0. Control stage Ac will, in response to said signal,

first generate a potential which is impressed,

throughdine I00, as a blocking bias upon input stage B2 in channel 13. A short interval later, control stage Aowill remove theblocking bias from amplifier A0 so that signalsirom the W direction can be amplified sand transmitted .over

the line. The "blocking of the input stage Bi will prevent transmission of signals from the E direction; and will also prevent signals in the 'output stage A0 frombeing fed back to the input stage Az, *so' that self-oscillation, and hence,

1 singing in the repeater system is avoided.

"Since channels A and B are identical and symmetrically "connected with respect to each other and the transmission line, channel B will nectedfto'theincoming line from direction W,

and- 1112 of transformer I0 is connected to the line from the'opp'osite direction E. Coils I4 and- H! of 'theftransformers are connected to in- "put stages A2 and Bi,respectively. Coils l6 and I6 are connected to output stages A0 and Bo respectively.

A signal arriving from direction W will be induced into coil l4 and a portion of the signal energy, as determined by adjustment of potensistor 32 between its grid and cathode, the signals.

impressed thereon are not. as yet transmitted. Resistor 32 is also in the plate circuit of the normally conducting triode section of diode.- f

triode tube 34 in control stage Ac, so that the steady plate current through said resistor causes the voltage drop which is applied as a .cutqff bias to the grid of tube 30. Voltage-dividing resistors 36 and 38, bypassed by the suitable capacitors, are connected in series across a B-voltage source (not shown) for supplying suitable plate potentials to tubes 30 and 3d.

The signal voltage across secondary 2.6 is also rectified in a circuit including diode-anode A9 of tube 3%, the cathode of said tube to ground; and from ground through resistor .4-2',1shunted by a capacitor 44, in the grid circuit of. tube 26' of input amplifier Bi, and then back tosecondary 25 through lead 100.

Another circuit from ground back to the secondary extends through resistor 56, shunted by capacitor .48, and through resistor 50. The voltage drop across resistor :42 biases tube 20* to cutoff, so that signals which might arrive from direction E, will not .betransmitted.

A short interval later, .due to the additional delay provided the series resistor 5. a volta e is developed across resistor 46 which renders ,gr-id .52 sufficiently negative to drive the triode section oftube 3.4 to cutoff. The resulting drop inupla'te current through resistor 32 Will remove .thecutofi .bias from the grid of tube'St', whereby said tubeis rendered operative to amplify signals;v from secondary 2d and transmit them over the line through transformer it. Since .tube. 20 .of

channel B is not conducting, no feedback to the to the normal, no-signal condition during said intervals. Said time constants arealso such that, after signal transmission ceaseaoutput stage A0 (will be cut off slightly before inputstage Bibecomes operative.

Channel B is, in every respect, identical -..With

channel A, and functions for signals "from-the 1E direction in the same manner as channel A vfunctions for signals in the .W direction. {Ihe,com-

ponents of both channels are symmetricallyconnected with respect to each other and to the line.

Components of channel B whichare. identical in structure and function asthe corresponding corn,-

ponents in channel A,,are identifiedbylthe same reference numerals, but Witha prime markadded. Thus signalsarriving from direction E, will first cause a bias Voltage to-be developed ,acrossmesistor 42 to block input amplifier-A1, .and thendepair" of channels.

velop a voltage across resistor 46 which then causes output amplifier B0 to become inoperative. Many changes may be made in the circuits above described. Instead of using potentiometers I8 and I8 to adjust the average levels of the incoming signals, conventional AVC' circuits may be used for this purpose. {The repeater may be adapted for use with a sin le transmission channel in one direction and a pair of transmission channels in the opposite direction, by using separate input and output transformers for said It will be obvious to those skilled; theart that various other changes and modifications may be made Without departing from the true spirit and scope of the invention asdefined in the appended claims.

I claim: I -13 a-I'two-may signal repeater system comprising apair of'amplifying channels; each channel having first and second amplifier stages, said first stage being. normal y zop ra iye and s id s end stage bein ne ma ly ncnera re; meanslto couple the fi st sta e of each chann l. and I'll? second stage of the other channel to a common s cti n or a twmv ay tra s iss qndine; and means in each channel responsive to a. irl the output of the first stagein channel-to provide a bias voltage torender inoperative the first stage of the other channel, atiirre delay circuit respo sive to said bia vo a e t provi s delayed bias volta e to render thesecond stagger said channel operative :to amplify and transmit .saidsignd-ls from one to' the other seotionotsaid transmissionline, 1H1

2. A 17W0-WaY signal repeater system com; i ing pairo am l f inegchanne s; .ea h.qhan.- nel having a normally operative first amplifier stage, a second electron-tube amplifier Stagaaand an electron-tube control stage coupled QO thEgQHP: put of said firststage; means to couple the first sta e of one channel and the second stageotthe other channel to eachother and 3 aqqqmniqn section of .a two-way t' a Sm-i siQm 'I nm .ens responsive to normal lat -curren fl 11- the electron tuloe in the control sta e ofeachphannel :to bias the electron tube in the. second stage of aid channel to cutoff and means responsilfi to a signal in the o tput of the first-s a e inane h ne sfo develop n a bia volta o se o the first stage of the other channel, ,andatime dela ir ui responsive osai bi s-v ta o p -.;v. .i a .delavedbias y ltagetdcut on theelectro .tube of the control stage in said. one channel to T l 1S3'. Q m l p ate-cu re f ew suliiient y tor mev ai utmensi o thee o qntube in the second stage of said 10 6 channel, thereby re d rin s d s qn st e o erat v eampl an t a mi s id s n l fr m l n .t membe ,s .e@ti. n.cis idt nsm o li e- I f. RAN 13. J :B LTBZ- serge The followingreferences are of record in the of this'patent: 7

NI D STAF A EN :Date

.Number Name 2,141,553 :Ravut .Dec. .217, .1938 125,164,185

rBertnolli etzal. June 2.7, .1939

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