US2480582A

US2480582A - Synchronizing pulse gating system

Info

Publication number: US2480582A
Application number: US623127A
Authority: US
Inventors: William D Houghton
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1945-10-18
Filing date: 1945-10-18
Publication date: 1949-08-30
Anticipated expiration: 1966-08-30
Also published as: NL76845C; GB628833A; FR1000353A; FR934838A

Description

VlDro Aug. 30, 1949. w, D. HOUGHTON 2,480,582

SYNCHRONIZING PULSE GATING SYSTEM Filed oct. 18, 1945 2 sheets-sheet 1 GATD B PULSE SYNC S Ag @swf R7- Cl ls/Nc PULSE :simu-mpg GATE GEERAWR PULSE g R P R5 R6 28' 9 lo Scmpul E l (sync Purse swam-rang @A1-E @msnm-0R13 @g5 A t1curn'uv` +B f v -3 GTED RL 1 2g 26 I @Las min l y vlnso Puig? n l s `l V7 INPUT l l y l j li- 0 6 I L T sync Puuse -E lag' 4 sEPARAToR GATE NERMW INVENTOR.

` g Um/AMD Haz/@MON BY rg/WM irme/wy ug- 30 1949. w. D. HOUGHTON 2,480,582

SYNCHRONIZING PULSE GATING SYSTEM Filed Oct. 18, 1945 2 Sheets-Sheet 2 T: M E

cHANNEL PuLsss Two sYNC PULSES CHANNEL PULES PULSE mrur Y /2 f-f" To GATED AMR g 10 l+.

2P' l l) l MT5 F/ ji@ 2a,

MODULATI 0N E AMPL.

- IN VEN TOR. (f/z MM .Z2 wwf/raw me/Vix Patented ug. 30, 1,949

12,480,582.. srNonnoNIziNG PULSE Gli'riNG SYSTEM i.

` signor to RadioCorpo poration ofnDela'ware -Application October 18, 1945,@Serial No. 623,127

. This invention relates ratusfor gating orselecting .periodicallyrecurring synchronizing pulses and-*rejecting` all .other .pulses present during the interval between said synchronizingv pulses. l 1 l In pulse receivingr systems it is known tofcon'- trol the time during which va desiredvsignal pulse is permitted. to pass through-a vacuum tube. This voperationl is usually'achieved by biasing-a tube to cut-off a vcondition during which no anode current flows) except forcertaintime intervals during which the signal pulse is expected toarrive.A The tube may normally be cut-ofi and conditioned-to lpass the desired sig-nal pulsebysupplyingto its. control electrode a pulse' of su'icient magnitude and polaritytc overcome the cut-oir bias, or in the alternative, 'thetube may normally be conductive and biased-'to cut-off during those intervals when signalsV arenot to be passed. Stated inl other words, the lvacuumtuloe vfunctions in a manner which is analogous to aigate orfshutter? and is keyed or gatedwat a desired rate'. One'such method of gatingma receiving system, -given -by way "of exampld'is described in'U. S. Patent 2,361,437 granted'October 31,-'1944 to B. Trevor.` l Another method is described in copending U. S.application-SerfNo. 517,814 filed-'January 8,' 1944 by H. O.'Peterson,

now U. S. Patent No. 2,463,094, granted March The present invention is. designedfor use in those systems which utilize'trains of recurring pulses separated-by periodically recurring -controlling or synchronizingpulses. -The invention nds particular appl-ication'at the receivingend of a time division multiplex `communication system. s j

-In a vtime division multiplex system, itis customary. to generate' at -the transmitting endv of the system-short pulses of radio frequency energy and to transmit these pulses at constant" amplitude and atla xed average repetition rate. 1 The pulses in the different-channels are transmitted consecutively.` These pulses mayfhave their occurrence time or phase y'modulated within pretermined limits. Thus, a pulse occurs from each channel once for eachcycle of operation -or synchronizing period, and this pulse is advancedfor retarded from itsnormal timevof` occurrence by an amount proportional -to :the `instantaneous amplitude vof the modulation.w During veach cycle of operation or synchronizing period,.there are transmitted pulsesirom all ofthe channels followedby a single. synchronizing pulse of longer duration thanthe channel pulses or byvtwo or f feciaimfsl (Grits-15) to amel-,hedor and'appa- .more short 4synchronizing pulses more closely spaced in time than the consecutively occurring .channel pulses. Asfanfillustration, let it be assumed-that there are eight channels; Thenduring each. cycle .of operation Aor synchronizingiperind, Athere will occurei-ght constant .amplitude pulses. (one for eachchannel) followed by one'or more synchronizing pulses This cycle of `operation repeats -itself continuously'. at. the synchronizing period.` i l At. thereceivinglendfoi .the multiplex system,

it is necessaryto .provide a` circuit for distinguishing `between the channel pulses and thesynchronizing pulses. The present invention is a pulse selective system which achieves this purpose and enables the utilization f of synchronizing pulses.

One of the objects of the present -inventionis to provide a gating system for the synchronizing pulses in order to :prevent interference or missynchronizing'ldue to noise, ignition radiation,

Briefly stated, the present invention providesat the `receiving Vend of a vpulse -communicationfsystem,A a pulse-selective system which distinguishes between synchronizing pulses and channel pulses, and which is open -orfv receptive .to the synchronizingpulses for only a short-period 'of time compared to the synchronizing period. This open or receptiveinterval occurs at* about the time the synchronizing pulse is due to arrive at the receiver station.1"*Because the pulse selective system of the invention is"-c1`osed" or-non-receptive in the intervals betweenfopen intervals, noise pulsesare prevented from interfering withfthe synchronizing circuit, and vhence, the signal-tonoiseratio is increased ycompared to' other sysvtems wherethe synchronizing pulseselector is open for 'the lentire synchronizing` period. v

more detailed description of the invention follows in conjunctionwith a drawing, whereinv 1 Figs. 1,3 and- 4- illustratethreedifferent circuitembodiments ofthe present invention;r A'and Figs.*2a.to 2ev are graphical Yrepresentz'altio'ns of voltage waveforms Y.in-'different parts of the'system,=fgiven to aid in an understanding ofthe operation-oftheinvention. Y j

Throughoutv theflgures ofthe drawing, the same parts 'are represented bythe same reference characters/f v' 'K Referring. to Fig. 1, there isrshownv onecircuit embodiment of `a pulse` selective'and gating system of theinventionpcomprisinga gated pulse vacuum tube amplifier I0 (pentode or mixer type) to whosefcontrol'electrode the channel andy synchronizingr pulsesare applied; a synchronizing 3 pulse separator il, and a gate generator I3.

The pulses supplied to input terminal 9, which is connected to the control electrode of amplifier tube Iii are video pulses of positive polarity and of fixed peak amplitude. It should be understood that these video pulses are unidirectional in character 'and constitute the output of a superheterodyne or other type radio receiver, not shown.

The amplifier I comprises a pentocle but may be a mixer type tube such as an RCA 6L7. Amplifier I is gated or keyed by pulses applied to its second grid over lead 8 from the output of gate generator I3. If desired, amplifier tube III may be a pentode vacuurn tube with. the screen grid connected as shown in Fig. 3.

The synchronizing pulse; separator I IA comprises a dual diode V2 having two diode sections a and b, a normally conductive triodevacuum tube V3 forming part oi a sawtooth generator, and, a normally non-conductive (cut-off) triode vacuum tube V4. y

The gate generator I3 comprises an electronic trigger. C ircuit in the forrn onfY two regeneratively conncctedvacuum tube triodes V5 and Vs having a, common cathode bias resistor R11. Tube V5 is normally Conductingv and tube Vs, is normally non-conductingin thestable state. The application. Qf; a. negative. pulse to. the. grid; of tube. V5

trips or triggers the circuit into its active state in whichv the current passing conditions of the two tubesl'are reversed. The time during which the trigger circuit remains its active state is determined by the time constants of condenser Cjand resistor Re.4 The trigger circuit restores itself fto the stablestate after the charge on condenser; @has leaked Olii Output fronl the trigger circuit in the form of a.r pulse. o i negative polarity; is taken via couplingcondenser Ca and fed to amplifier i8 over 1.1

lead 8 in order to bias the amplifier to the anode current cut-.offv condition.

y Theanodes of theditferent tubes in amplier Impulse separator Il and gate generator I3-are Vindividually supplied with anode polarizing poftentialsover separatev resistors R2, R5, Re, R9 and R19, respectively, lfrom 'the positive terminal -i-B Qfa'source of unidirectional potential. Y

Ini the" operationof Fig, fl, the normal bias on tube V1 oigthe'pulse amplifier IB Vis set by the values of Ri and C2v in the cathode circuit. In theab'sence offa negative pulse on the second {(#l of tube. V1 supplied byv thegate generator I3, anodefcurrent will now in this amplifierl whenfthernagnitude of thepositive video pulse'sexce'eds the cathode bias developed by R1 and=Cz. These video pulses are of fixed peak amplitude exceeding this cathode bias. In practice, tube V1 is biased to a negative value by elements-R1 and C2 so that it conducts at about half amplitude on the incoming pulses. In the normaloperation of this amplifier, the voltage onfthe second grid is reduced during the synchronizing periodby the negative pulse on lead 8,.supipliled from generator I3, to avalue which prevents anode currentirom flowing in tube V1. By selecting suitable values `fo'r-thecircuit constantsof the` electronic ftrigger circuit of generator I3, this negative pulse on lead 8 terminates inmediately beforethe arrivalof a video synchronizing pulse on input terminal 9. The termination of the negative pulse onlead 8 causes thevoltag'e on the second Ygrid of tube-V1 to be raised to zero (value-which permitsanodecurrent-to owjn amplifier. IB when an input pulse 4 is present on the control grid of tube V1. After the amplier lil has passed the synchronizing pulse or pulses, the voltage on the second grid of tube V1 is again reduced by a negative pulse on lead 3 to the same low value which prevents anode current from flowing in tube V1.

The invention will first be described in connection with a pulse type multiplex system utilizingtwo closely' spaced synchronizing pulses which recur periodically. Pulses from such a multiplex system are represented in Fig. 2a which shows a series of channel pulses followed by two 'synchronizing pulses for each cycle of operation or synchronizing period. These synchronizing pulses are more closely spaced in time than any two adjacent channel pulses in extremes of modulation. In iirst starting up the system of Fig. 1, let us assume the absence of a negative pulse on lead 8 for the full synchronizing period since no synchronizing pulse has previously arrived to trip) gate generator I3. Before the synchronizing pulseA is applied, to input terminal 3,v tube V1 will pass. anode current each time a channel pulse is applied toits control grid. The flow of anode current in V1 causes a negative pulse of voltage to be developed across anode resistor R2 each time a channel pulse isapplied to V1 and this negative pulse is appliedY to;V dual. diode V2 through coupling condenser C1. The leading (falling) edge of each negative pulse causes the cathode of diode section b of dual diode V2 to become negative as a result of which current flows in diode section b and produces a negative charge on condenser C3. On the trailing (rising) edge oi each negative pulse of voltage developed across R2, current will flow through section a of dual diode Vzinto condenser C1, thus restoring the` charge on condenser C1 to its normal value.

The negative voltages developed across condenser C3. are shown in Fig. 2b. Condenser Ca isshunted by a resistor R4, and the values of these two elements are such that the negative charge on C3 leaks. oi to a low value between channel pulses, as shown in Fig. 2b. However, when` two. closely spaced synchronizing pulses occur, there are developed two correspondingly closely spaced negative voltages across resistor R2A which produce cuniulatively added negative charges on condenser Ca. Stated in other Words, the negative charge on condenser C3 due to the rst. synchronizing pulse does not have an opportunity to leak off to a low enough value to cause anode current flow in tube V3 before there is addedanother negative charge on condenser Cacaused by the closely spaced second synchronizirigv p ulser This is shown in Fig. 2b at position A.

'I'.riode V3 is normally conductive. The anode current cut-off value of tubeVs is shown by the n horizontal dash vline in Fig. 2b. It should be observed that tube rV3 is cut-oli each time a negative charge is built upon condenser C3, but that the duration-of cut-on` of. tube V3 is over a longer period of time when the two synchronizing pulses are present than when the channel'pulses are present. Tube V3A and condenser C4 in its anode circuitlconstitute a; sawtooth waveform generator. When V3 is; cutoff, a.,positive charge builds up linearly onycondenser C4 through resistor R5, resulting-in a Vvoltage as shown inFig, 2c. The small fpulses; in Fig. 2c represent the voltage charges 4.builtup on condenserCi dueto 'the presenceiofchannel 'fpulses Thelarger 'voltage pulse in-.Fig. 2c represents. the voltage charge built up on condenser Cfidue tothe. presence. of fthe V'two closely spaced synchronizing pulses which causes ftube Vs to be cutv off for a longer period oftime. Upon the dissipation of the negative` charge on .condenser C3, tube Vs again conducts and provides a low impedance path to ground for the coupling condenser C5 and is used to trip the electronic trigger. circuit V5, Vs of the gategenerator I3. from its stable to its active state. As mentioned before, tube V5 is normally conducting and ytube E normally non-conducting. Tube Vais normally non-conducting due tothe voltage developed across the common cathode resistor R11 by the current flowing therein. Current'normally flows in tube V5 because its grid is connected to +B through resistor R3. The application of va negative pulse, Fig. 2d, to the grid of V5 causes tube Vsfto out off and allows tube Vs to conduct. When tube kVe' starts torconduct, therev is produced a negative voltageacross resistor R which further biases tube V5 below 'c ut off, by virtue of the regenerative coupling condenserV Cv. The trigger circuitY remains inthe active state until' the charge on condenser C7 leaks off through resist/or Rs. Af 'lube'Varemains kcut off, therefore, for a time interval determined by the time constants of condenser C7 and resistor Rav` The values of condenserC'z and resistor Re 'are' so chosen that the trigger circuit restores itself to the normal stable state after a time slightly less than the synchronizing period.

'As a result of this operation, a negative pulse A is developed `across resistor R10 having aduration slightly shorter than the synchronizing period. This negative pulse is coupled via condenser Cs and lead' tothe second or number 2 grid of tube VVV1 of the amplifier lil and keys or gates amplifier I0 so that tube V1 is cut off during the major part of the synchronizing period or for thedurajtion of thenegative pulse on lead 8. Hence, am'- plifier IB isV cut-off duringl that portion of the synchronizing period when the channel pulses are present. Any noise' or ignition interference which might be present on input terminal '9 during the time V1 is cut off can have no elect on the amplifier [D of the pulse selective system of the invention yand cannot cause mis-synchronization. Obviously, mis-synchronization due to noise' jis thus conined to the interval when amplier vIl) vis open or responsive, which occurs just preceding the arrival of the synchronizing pulses. Since noise israndom incharacter and doesl not recur at the same rate and timeas the synchronizing pulses it Will be evident 'that the present invention results in an increase in the signal-tonoise ratio in multiplex systems using pulse type synchronization. v i c Output pulses from the system of the invention are taken from terminal I4 which is connected to the anode of tube V4. These output pulses are of negative voltage as shown in Fig. 2d, and are repeated once for each `synchronizing period. and can be utilized tol synchronize or control the re;- Aceiving channelselectors, not shown.

Fig. 2e represents the Wave form appearing at -the anode of tube V5'.

This is a negative pulse csinceVs isfcut-off and its anode potential is there fore equal to +B up to a time just prior to the arrival of the synchronizing. pulse, at which time the gate generator circuit returns to its normal or'fstable condition. The arriving synchronizing .pulse causes tube V5 to again cut-off and thus drive the flip-flop circuitto its unstable condi- ,.tion. It remains in this state for aperiod of time 'slightly shorter than the synchronizing period. 10

, torily in pulse multiplex systems wherein only a single synchronizing pulse of longerr duration than the channel operation.

The system of Fig. 1 can also be used satisfacpulses is used foreach cycle rof Fig. s'shcws a modincauoncf the'system of i Fig. l, for 'use at the receiving end of a pulse multiplex system using a single synchronizing pulse Lwhich is of longerv duration than the channel pulses.v 'This longer duration l synchronizing pulse takes the place of the two closely spaced 1 v synchronizing pulsesv of Fig. 2a,`and occurs once Fig. 3, the negative pulses developed across -sistor R2 are coupled to the grid ofnormally con- -ducting tube V3 via condenser C1.

for` each cycle of operationv or synchronizing The'systemiof Fig. 3 is similar to that of Fig., 1

Fig. 1 iseliminatedin Fig. 3 and ,the amplifier tube I0" is va pentode vacuum tube .connected somewhatdifferentlyfrom that of'v Fig. .1., In

Eachnegativepulse carries tube'Vs to cut 01T, and as a result causes condenser C4 to chargeup through Vresistor R5.

fC4 form a sawtooth waveform generator. Con- As in Figi, tube V3 and condenser denser C4 chargesup to a higher value when the ylongerduration synchronizing pulse is present because tube V3 is then cut oi for a longer period wjof time than in the presence of channel pulses.

The rest Aof the system of Fig. 3 operates -in'the vsame manner as Fig. 1.

' Fig-4 illustrates another-embodiment of the inventionin which only triode tubes are employed.

This embodiment is also designed for use in" such pulse multiplex systems which use a single synfchronizing pulse -of longer duration than the channel pulses, although by the'addition of a diode as in Fig. 1, this embodiment canbe used for either system. Fig. 4 includes an additional-tube V7 which is normally" biased 'to' the anode current cut-off condition and controlled by a positive output pulse from the trigger circuit V5. Vs via coupling condenser C9' and lead 1. The grid "of tube 1 is supplied with a negative' bias via resistorRnandthe negative terminal of a uni- 'directional source of potential-E. rlhis negative bias'is of such magnitude as to prevent 'the flow of current through the tube.

The'gate generator I3 supplies a positive pulse to the' gridof tube Vv of such magnitude as to overcome the negatii/'e bias on tube Vr; and cause this tube to conduct. j When tube V7 conducts, it develops a positive voltage across resistor Riaan'd vthis positive voltage is supplied via ylead 6 to the cathode of tube V1', and biases tube V1' below cut-off for the duration of this positive pulse regardless ofthe maximum peak amplitude of.v the video pulses lsuppliedfto thev grid of Vi. lhe video pulses are passed throughlimiters before being'applied to the grid of tube V1', hence all pulses are constantamplitude. The duration of this positive pulse` (applied tothe cathodeof tube Vi) is for the major part of the synchronizing period, as in the case of Figs. 1 and 3.v The remaining portions of Fig. 4 operate in the same manner as corresponding portions of Fig. 1.

What is claimed is: l

l. In a time division pulse multiplex communication system wherein a plurality of intelligence carrying channel pulses and one or more synchronizing pulses are transmitted during each synchronizing period, a receiving station having apparatus thereat for producing from said received synchronizing pulses other pulses which occur once each synchronizing period, said appa- Vra'tus including an amplifier multi-electrode tube Vmagnitude and polarity as to prevent the flow or current in said amplifier for the major portion of the succeeding synchronizing period.

Y 2. In a time division pulse multiplex communi- .cation system wherein a plurality oi intelligence carrying channel pulses and one or more synd chronizing pulses are transmitted each synchronizing period, a receiving station having apparatus thereat for producing from said received synchronizing pulses other pulses which occur onceeach synchronizing period, said apparatus including a multi-electrode amplifier tube and means for supplying to said amplifier tube pulses -representative of the receivedintelligence carrying channel pulses and the synchronizing pulses, a circuit coupled to the output of said amplifier for producing voltages of one amplitude in response to the channelpulses and voltages of a higher amplitude in response to the synchronizing pulses, an electron discharge tube coupled to the 'output of said last circuit and normally biased to be non-conductive, said tube being responsive only to voltages of said higher amplitude in order to pass current, an electronic trigger circuit coupled to. and responsive to the ow of current in vsaid electron discharge tube ior producing a pulse, and a feed-back circuit from said trigger circuit to an electrodeof said amplier, the pulse produced by saidA trigger circuit having such duration, magnitude and polarity as to prevent the `flow of current in said amplifier for the major portion of the succeeding synchronizing period.

3. In a time division pulse multiplex communication system wherein a plurality of` intelligence carrying channel pulses and cneor more synchronizing pulses are transmitted each synchronizing period, a receivi'ngstation having apparatus thereat `for producing from said received synchronizing pulses other pulses which occur once each synchronizing period, said apparatus including a multi-electrode amplifier tube and means for supplying to said amplifier tube pulses representative of the reved intelligence carrying channel pulses and the Vsynchronizing pulses, a circuit coupled to the output of said amplifier for producing voltages of one amplitude in response to the channel pnlses'and voltages of a higher amplitude in response to the synchronizing pulses, an, electron discharge' device coupledto the output ci said last circuit and normally biased tobe nonconductive.: said tube being responsive only to (voltages of saidhigher amplitude in order to pass current, a self-restoring electronic trigger circuit coupled to and responsive to the flow of current in said electron discharge device for producing a pulse, and a feed-back circuit from said trigger circuit to an electrode of said amplifer for feeding back to said amplifier a pulse which prevents the now of current in said ampliiier, the time constants ci said trigger circuit being such that it supplies said feed-back circuit with a pulse whose duration extends over the major portion of the synchronizing period.

4. In a time division multiplex system for receiving periodically recurring controlling or synchronizing pulses between which are positioned intelligence carrying pulses, apparatus Ifor conver-ting said synchronizing pulses to other pulses which occur once each synchronizing period, said apparatus including a multi-electrode vacuum tube and means for supplying to said tube pulses representative or" the received intelligence carrying pulses and the synchronizing pulses, a triangular waveform generator coupled to the output of said tube for producing triangular-shaped `voltage waves oi one amplitude in response to the intelligence carrying pulses and triangularshaped voltage waves of a higher amplitude in response to the synchronizing pulses, a pulse generator circuit responsive solely to the voltage waves of said higher amplitude for producing substantially flat-top pulses, and a feed-back circuit from said pulse generator circuit to an electrode oi said tube for feeding back to said tube a pulse which prevents the flow of current in said tube, the time constants of said pulse generator being such that it supplies said feedback circuit with a pulse whose duration extends over the major portion of the synchronizing period.

5. In a time division multiplex system for receiving periodically recurring synchronizing pulses between which are positioned intelligence carrying pulses, apparatus for converting said synchronizing pulses to other pulses which occur once each synchronizing period, said apparatus including a multi-electrode vacuum tube and means for supplying to said tube pulses representative of the received intelligence carrying pulses and the synchronizing pulses, a triangular waveform generator coupled to the output of said tube for producing triangular-shaped voltage waves of one amplitude in response to the intelligence carrying pulses and triangular-shaped voltage `'waves of a higher amplitude in response to the synchronizing pulses, a pulse generator, and elecltronic means responsive to each wave of higher amplitude produced by said triangular waveform generator for tripping said pulse generator, and a feed-back coupling, the output of said pulse generator to an electrode of said tube, the pulses produced by said pulse generator having such duration as to extend over the major portion of the synchronizing period.

6. In a pulse selective system, a multi-electrode amplier tube, means for supplying to the input ci said tube recurring trains of pulses in each train of which at least one pulse is of different character than the others in that train, a diode having its cathode coupled to the output of said amplifier tube, a condenser connected between the anode of said diode and ground, a resistor in shunt to said condenser, a normally conducting triode having its grid connected to the anode of said diode and its cathode connected to ground, a resistor connecting the anode of said triode to the positive terminal of a source of unidirectional potential, a condenser connected between the anode of said triode and ground, said triode and last condenser forming a sawtooth generator, another triode normally biased to the anode current cut-01T condition, a resistor connecting the anode of said last triode to said positive terminal, a connection from the grid of said last triode to the anode of said rst triode, a pulse generator coupled to the anode of said last triode, and a feed-back circuit from the output of said pulse generator to an electrode of said amplifler for supplying said amplifier with pulses of such magnitude and polarity as to cut oi the flow of current in said amplier, the duration of the pulse produced by said pulse generator extending over the major part of the time occupied by said train of pulses.

7. In a time division pulse multiplex receiving system, an amplifier tube, means for supplying to the input of said tube recurring trains of pulses in each train of which there are a plurality of intelligence carrying pulses and a synchronizing pulse of different character than said intelligence carrying pulses, a triangular waveform generator means coupled to the output of said amplifier, means for causing said triangular waveform generator to produce a triangular-shaped voltage wave of higher amplitude for each said synchronizing pulse in the train than for the intelligence carrying pulses in the train, an electronic circuit responsive solely to the triangular voltage wave of higher amplitude for producing a substantially flat-top wave pulse, and a feed-back circuit from said electronic circuit to said amplifier tube, the pulse in said feed-back circuit having such magnitude, polarity and duration as to prevent the flow of anode current in said amplifier tube for the major part of the period occupied by a train of pulses.

8. In a time division pulse multiplex communication system wherein a plurality of intelligence carrying channel pulses and one or more synchronizing pulses are transmitted each synchronizing period and are repeated, a receiving station having apparatus thereat for producing from said received synchronizing pulses other pulses which occur once each synchronizing period, said apparatus including a multi-electrode amplifier tube having a screen grid and means for supplying to said tube pulses representative of the received intelligence carrying channel pulses and the synchronizing pulses, a circuit coupled to the output of said ampliiier for producing voltages of one amplitude in response to the channel pulses and voltages of a higher amplitude in response to the synchronizing pulses, a pulse generator responsive to pulses solely of said higher amplitude for producing correspondingly positioned pulses, and a feed-back circuit coupling the output of said pulse generator to the screen grid electrode of said amplifier tube, each pulse produced by said pulse generator being of negative polarity and of such duration as to prevent the flow of current in said amplifier tube for the major portion of the succeeding synchronizing period.

9. In a pulse multiplex communication system wherein a plurality of channel pulses and one or more synchronizing pulses are transmitted each synchronizing period and are repeated, a receiving station having apparatus thereat for producing from said received synchronizing pulses other pulses which occur once each synchronizing period, said apparatus including a multi-electrode amplifier tube to which are applied pulses representative of the received pulses, said amplier tube including a cathode, a circuit coupled to the output of said amplifier for producing voltages of one amplitude in response to the channel pulses and voltages of a higher amplitude in response to the synchronizing pulses, a pulse generator responsive to pulses solely of said higher amplitude, and a feed-back circuit coupling the output of said pulse generator to an electrode of said amplifier, said feed-back circuit including a triode Whose cathode is connected to the cathode of said amplifier for supplying to said amplifier a pulse of positive polarity and of such magnitude and duration as to prevent the ilow of current in said amplifier for the major portion of the succeeding synchronizing period.

WILLIAM D. HOUGHTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,113,011 White Apr. 5, 1938 2,141,343 Campbell Dec. 27, 1938 2,199,634 Koch May 7, 1940 2,300,999 Williams Nov. 3, 1942 2,359,447 Seeley Oct. 3, 1944 2,399,135 Miller et a1 Apr. 23, 1946 2,406,019 Labln Aug. 20, 1946 2,416,305 Grieg Feb. 25, 1947