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Sept. 24, 1946. E.A|.AB1N I _ MULTIGHANNEL Filed Aug. 25. 1944 TIM ß m M _Z LL.n W e _Í .w 6 ...ï P ____ „_ .\ Q_EfJ1ÄIA. ÍL..1 „m a.1, e`0\ 2,4œ,077 SYSTEI 3 Sheets-S0“, 1 -l- CZIA’CW la MIXER -ll /mw „u m” _ f Ryn/. 1.6 _„_ _ \/f „fu „a ,_ _p1 5.1t 1 a LaI- „um E W n W „_||„i Am ,Sept 24, 19.46. E. LABIN 2,408,077, HULTICHANNEL SYSTEM Filed Aug. 25, 1944 3 Sheets-Sheet 2 f E . (21 D, ` y H mpmPwPs CLIP/’ER „w , / fefp.M/L „W „W î „fm mw/WwœïwwwüE n/ mmf@ ` A TT0PM'Y Sept. 24,- 1946. 2,408,077 E..- LABIN MULTI CHANNEL SYS TEM Filed Aug. 25, 1944 3 Sheets-Sheet 5 A ' n v 66 I/ l |lI. r/Jaa es H ¿WHT l BY Patented Sept. 24, 1946 # ` y 2,408,077 UNITED ' STATES PATENT OFFICE MULTICHANNEL SYSTEM » Emile Labin, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application August 25, 1944, Serial No. 551,202 15 Claims. 1 I (Cl. 179-15) » . 2 plaining the operation of the embodiments shown Thisinvention relates to multi-channel com municating system and more particularly to sys tems for transmitting in interleaved manner the in Fig. 4. time modulated pulses of a plurality of channels. One of the objects of the invention is >to pro may comprise-the Vtransmitting equipment for a two-way multi-channel communicating system or` it may be usedïas a multi-channel broadcasting , j ,_ The multi-channel transmitter shown in Fig.V 1 vide a multi-channel transmitter and method for either multi-channel transmission to a second " system for selective reception of the channels by terminalor for multi-channel broadcasting from Y individual receivers. Y In the case of multi-chan a given station for selective reception by indi nel broadcasting the transmitter, -of course, will vidual receivers. , . 10 be provided with a suitable omni-directional kan Another object of the invention is to provide a tenna. For >simplicity of illustration the system new method and means for time modulating a is shown for three transmitting channels, I, 2 train of pulses. ` and 3, although many additional channels may ' In most multi-channel communicating systems employing pulse time modulation, each channel be included, if desired. 15 , , . v The embodiment shownin Fig. 1 includes aV is provided with an individual time modulator. stable type ofpulse producer 4 of known form VAccording to one Vof the features of »my invention I provide a single time modulator for all of the for producing a train of pulses such as indicated at 5 in graph a of Fig. 2. The repetition rate of the pulses 5 is selected in this embodiment as that channels. A pulse train corresponding to the interleaved pulses vof all the channels is applied V20 pulse rate desired for a single channel. The pulses 5 are multiplied according to the number to kthe modulator and the signal energy of each of channels desired by applying the pulses to a channel is divided into spaced pulse segments -pulse multiplier 6 of known character which may timedv diiferently for the diiferent channels, the or may vnot include a pulse shaper. Preferably pulse segments of the signal energy of all the channels being applied in interleaved manner to 25 the output pulses 1 of multiplier 6 are narrow the'time modulator as the modulating energy. pulses as indicated by graph c. ~ 1 . Energy of the pulses 5 is also applied to a pulse shaper 8 to produce pulses> of a desired width as accordance with the amplitude of the correspond indicated at 9 in graph b. The pulses 9 are used ing pulse segments. 'I'his method of modulation may of course be employed for a single channel 30 for two purposes, one for selecting spaced por tions of the signal energy of each channel, and where desired, one of the advantages of such a The pulses of the train are displaced in time in system for a single channel, or even for multi the other for synchronizing receivers. channel transmission, being that the interval be tween pulse segments of any one channel may be blocked at the receiver thereby insuring a high signal-to-noise ratio. Another advantage of the system particularly in multi-channel operation The synchronizing pulses may be differently shaped, if desired by applying pulses 5 to pulse shaper 8a through connection 8b. In the present showing, however, the same pulse. width is used for synchronizing purposes and for selecting seg. ments of signal energy. The output pulses 9 Vof’ shaper 8 areapplied to a delay network I0 having output connections I I spaced'> at diiferent retarda tion points therealong whereby pulse energy may be supplied at -diñîerent time intervals correspond ing to the timing desired for pulses of the diiîer ent channels. The output connection for channel is a reduction in the number of time modulators required by such systems heretofore proposed. For a lfurther understanding of the invention, reference will be had to the following detailed description to be read in connection with the ac companying drawings, in which: ' , Fig. 1 is a block diagram of a multi-channel transmitter'in accordance with the principles of this invention; ' . ` Fig. 2 is a graphical illustration useful in ex plaining the operation of the transmitter of 1 I is applied to an amplifier I2V which is normally blocked. The signal source I3 for channel I is also applied to the amplifier I2 but the blocking potential for the Yamplifier is so chosen that ythe signal energy _remains blocked regardless of its Fig. 3 isa schematic Vwiring diagram of a pulse 50 variations in amplitude.L The retarded or keying pulses from output connection Ilaunblock the time modulator that may be yused in the system amplifier for the duration of-each of the pulses. of Fig. 1; i e _ . `This 'passes a segment of the signalv energy, -or Y Fig. 4 is a block diagram of a further embodi Fig. 1; ' ' ment of the invention, and , Y ` . Fig. 5 is a -graphical illustration used inex rather producesin effect an output pulse lwhich 55 is amplitude modulated in accordance with the 2,408,077 3 4 segment of signal energy coincident with each signal pulses of graph d which vary in amplitude keying pulse. in accordance with segments of the signal energy are applied over connection I8 to the anode cir cuit 29 of an amplifier 30 to Which is applied over connection BI the pulses 'I' from pulse multiplier 5. The source of anode voltage is applied through the resistor 32 and the retardation circuit 25. In graph b, for example, the pulses I4, I5 and I6 represent three successive output pulses from ~ amplifier i2 which are representative segments 0f the signal envelope I'I. These signal pulses thus define points along the signal envelope I1 Should the impedance of coil 26 be sufficient the as indicated. The output pulses of each of the amplifiers of the different channels are applied over connec tion I8 to a time modulator I9 to which is also applied the pulses l, graph c. The signal pulses resistor 32 may be omitted. The instantaneous signal value of the signal envelope Il at the occurrence of pulse I5 is reater than the minimum value at the occur of the dii-ferent channels are interleaved in` ac rence of pulse I4, and therefore produces greater cordance with the retardation applied thereto in delay device le. Pulses I4, .I5 and I6 are shown to be retarded an amount t1 causing them to Coin cide with the pulses of channel I. For channel 2 retardation eiîect on pulse Ib by a total amount -equal to T`-|-./_\.t. This greater retardation of the pulses I b over pulses Ia is produced by a change in permeability of the core of coil 26, which alters the pulses 9 are retarded an amount t2 for coin the inductance of the circuit 25. The still greater signal value represented by pulse Iâ produces a therefore, that the amplitude modulated pulses 20 still greater retardation for pulses ic which equal cidence with pulses of channel 2. It will be clear, to T-1-2At. From the foregoing it is believed clear that as the signal energy increases still further, the greater the time displacement Will be for the corresponding pulses of channel I. The time dis character capable of displacing in time the pulses ‘I in accordance with the amplitude 4of the corre 25 placement according to this method of modula tion is of course small but small displacements sponding pulses applied over connection I8. Two are of advantage in multi-channel communica examples of time modulators of this character tion since a larger number of pulses is possible for are hereinafter described in connection With Figs. of each channel coincide in time With pulses of the pulse train 1 of graph c. The time modulator I9 _may be of any desired 3 and 4. v Graph e of Fig. 2 illustrates the time displace ment produced on the pulses of channel I by the pulses I 4, I5 and. I6 of graph d. The loW or minimum amplitude of pulse I 4, which may be regarded as corresponding to the maximum nega tive signal value, is indicated as having retarded pulse Ia of channel I an amount T. This mini mum amount of retardation for pulse I4 may be regarded as always present in the time modula tor. The amplitudes of pulses I5 and I6 are shown to time displace the pulses Ib and Ic amounts T-l-At and T-1-2At respectively, since they are of successively greater signal values. It will be clear that the time displacements of the pulses of the several channels vary in amounts according to the instantaneous values of the cor responding signal energies, and that the displace ments are relative to the pulse positions of train 'I in the absence of modulation or with respect to the positions of the pulses S of the synchroniz ing channel (graphs f and g). The pulse energy 9 from Shaper 3 is applied over connection 29 to a clipper mixer 2l to which is also applied the time modulated pulse output of modulator I8. The synchronizing pulses being a given time interval. For a further discussion of this principle of time modulation reference may be had to my copending application Serial No. 546,378 filed July 24, 1944. In Fig. Ll ï show an embodiment of the inven tion wherein pulse producer 33 is arranged to produce pulses .at the repetition frequency desired for all of the channels taken together. The pulse output of producer 33 is represented by the pulse train 34 in Vgraph m of Fig. 5. To obtain the pulses for each channel, the pulse train 34 is 40 applied t0 a pulse divider 35 whereby pulses 36, graph 11, are produced. These pulses are then applied through a pulse shaper 31 to a delay net Work 38 similar to the device I0 in Fig. l. The pulse energy 3S is thus shaped and delayed for channel I as indicated by the pulses 39, 40 and 4I of graph o. These Wider delayed pulses are applied to channel amplifier 42 for selecting a segment of signal energy from source 43 in the manner hereinbefore described. The output pulses 39, 49, 4I of amplifier 42 are thereafter applied to a clipper gate 44, for translation of the amplitude modulation thereof into time modula tion. ` If a time modulator of the character shown in Fig. 3 were employed in the system of Fig. 4, the pulses 34 would be applied directly thereto as hereinbefore described in connection with Fig. l. Before application of pulse energy 34 to clipper gate 44, it is desirable to reshape the pulses into chronizing pulses S, the resulting train of pulses 60 pulses each having at least one inclined edge cor for transmission being as shown by graph g. responding in time to one of the pulses of the These pulses are applied to transmitter 23 for several channels. The energy of the pulse train transmission at a given carrier frequency over 34 is therefore applied t0 a Wave producer 45 of the type capable of producing a zig-Zag shaped antenna 24 which may be of a directional or omni-directional type. Wave 4B, the undulations of which are shown in graph p, symmetrically shaped. The wave, of Referring to Fig. 3 a pulse time modulator is course, may be varied considerably, and if desired shown that may be employed as the time modu may be of the saw-tooth form having one edge of lator I9 in Fig, 1. The time modulator comprises each tooth inclined and the other edge thereof a retardation circuit 25 having an inductance the same as pulses 9 in graph b as to Width and timing coincide with pulses of a fourth chan nel in the train of pulses l. By providing the mixer 2l With a limit clipping level indicated at 22 in graph f the pulses 4 are replaced by syn coil 26 with a core of iron or other permeable material, and condensers 21, 28. The minimum retardation characteristic of the substantially vertical. Various types of clipper gates may be employed at 44, the example shown being of a type having circuit 25 may be represented by the time inter two dry rectiiiers 47 and 48. The two rectiñers val T of graph e, Fig. 2 for a maximum negative are connected back to back and a small positive signal value such as indicated by pulse I4. The 75 voltage is applied over resistor 49 to the inter " '2,408,077 5 ~ mediate point 50. The resistor 49 is -preferably at least several times larger than the low “for ward” resistance of the rectiñers, although it . for Vusein deblocking circuits of` the> receiving channels. ' 1 t For a more complete discussion of the time should be low in comparison with'the high “back” ‘_ modulating principles of the clipper gate type of resistance thereof. The input wave 46, graph p r5 VmodulatorV and of variations thereof, reference is applied through coupling *condenserk 5|` to re may be had to the copending- application of D. D. Grieg and myself, Serial No. 455,898, filed August sistor 52 which is preferably several times smaller 24, 1942. f ' ` thanA resistor 49. The output of the circuitV is delivered across resistor 53 which maybe of the same order of magnitude as resistor 52, For modulating the clipping action the am plitude modulated pulses such as 39, 40, 4|,- etc., of channel I are applied through resistorY 52 to From the foregoing description it is clear that ' 10 I have disclosed a multi-channel communicating system requiring a single time modulator for a plurality of channels. Also, I have shown two diiîerent methods of producing the train of pulsesA rectifier 41. The relationship between clipping to vbe time modulated and - a second train of levels 41a, 48a of the clipper gate vand wave 46 k15 pulses, energy of’which is used for each of the shown in alignment with the pulses of the fourth channels to obtain segments of the signal energy channel, graphs m and p, Fig. 5, represents the of the different channels. While I have indicated condition when the amplitude modulated pulse ' a base pulse producer from which these two trains input- is of- an amplitude corresponding to the are obtained it will be clear that in the'place of maximum negative value of the signal energy for 20 a base pulse producer I may use a stableY oscil such channel. The action of the two rectiñers lator for producing a sinusoidal wave havingthe Y is that of limiting the passage of input wave 46 frequency desired for either train of pulses. By between levels 41a and 48a. The application of using a frequency multiplier or divider a wave of energy to -the circuit through resistor 52 operates the frequencydesired for the 4otherrpulseftrain to vary the location'of these two levels relative 25 may be obtained. The pulses may thereafterbe to the amplitude Yof the wave 46. ' , produced from'these two waves according to well This double limit clipping results in Va rec tangular or trapezoidal wave form suchv as in dicated in graph q. This rectangular wave is applied to a diiïerentiator 54 which converts each rectangular pulse portion of the wave into alter nately positive and negative pulses as indicated by graph r. It will be noted that the rectangular pulse portion 55 corresponding to the clipping of known methods. - ' While I have shown and described particular embodiments of the present invention, it is’recê ognized, of course, that many variations and dif ferent embodiments may be made without de parting from my invention. It is therefore to be understood that this description is given by way wave 46 in alignment ywith channel 4 produces a of example only and not as a limitation on the scope of the invention as set forth in the objects narrow pulse which, when generated, producesY thereof and the accompanying claims. positive and negative pulse 55a and 55h. The am plitude modulatedrpulse 39 of channel I shifts the clipping levels of gate 44 to a lower portion 56 on Wave 46. This produces a wider pulse 51 than the pulse 55. Thegincreased width of pulse I claim: ' ' l. A method of multi-channel transmissie comprising producing a train of pulses, segregat ing spacedsegments from the signal energies of a plurality of channels, differently timing the 51 over pulse 55 corresponds to the increased segments of the different channels to interleave signal value represented by the amplitude of , them together into a series of segments wherein pulse 39. Accordingly, the pulses 51a and 51h . each segment corresponds to a pulse of said train., :are separated by a time interval corresponding to ' 45 and time modulatingr the pulses of said train ac the width of pulse 51. Likewise pulses 58d and cording to the amplitude of the corresponding 58h resulting from pulse 58 are displaced a greater signal segments. 7 time interval corresponding to the greater am 2. A method of multi-channelV transmission plitude of pulse 46, and the still greater pulse comprising producing. a plurality of` series of width 59 resulting from> the clipping produced by 50 vpulses differently timed so that the pulses of the pulse 4| produces pulses 59a and 59h having a diñ‘erent series interleavein time, -producing a wcorresponding greater time displacement. 'I'he trainof pulses corresponding to said plurality of pulses of graph r are applied to a threshold clip series taken together, translating `the pulses of per circuit 6B by which pulses 551), 51h, 58h, each series into signal pulses the amplitude of etc., are clipped at level 6l. Of course, pulses 55 which Vary according to the instantaneousvalues 55a, 51a, 58a, etc., may instead be clipped where of the signal energy of a corresponding'channel, by the time displacement of the output pulses and timemodulating the pulses of said train ac~' will be in the opposite direction. , cording to the amplitude of the corresponding The output of the clipper 60 is applied to a signal pulses. mixer 62 to which is also applied synchronizing 60 3. A method of multi-channel transmission pulses 64 obtained by shaping the pulse output comprising producing a train of pulses of a given of pulse divider 35 at shaper 63. The synchroniz repetition frequency, dividing the pulse energy ing pulses 64 are shown in graph s to coincide of said train to obtain a series of pulses of a lower repetition rate such as may be desired for chan with pulses 55h produced from the pulses of channel 4, and since the mixer 62 is preferably 65 nel communication,V retarding by diiîerent amounts the energy of said series of pulses to ob- , of the character having a limit clipping level 65, the synchronizing pulses 64 replacethe pulses , 55b. This results in a train of pulses indicated by tain a plurality of series of Vpulses of different timing so that they interleave in time similarly `as the pulses of said train, translating .the pulses graph t in which the synchronizing pulses 64 70 of each series into signal pulses the amplitudes ‘ are of a width greater than the pulses of the of which vary according to the instantaneous channels I, 2 and >3. This greater width of the valuesof the signal energy of the corresponding synchronizing pulses >makes it possible for the channel, and time modulating the pulses of said receiver to segregate the synchronizing pulses train VVaccording to the amplitude of the corre from the channel pulses by width discrimination 75 sponding signal pulses. 2,408,077 7 4.'A method of multi-channel transmission comprising producing a series a pulses of a repe tition rate desired for channel communication, multiplying the pulse energy of said series to ob tain a train of pulses having a repetition fre quency corresponding to a given plurality of ' 8 position of the pulses and means for applying the signal pulses of varying amplitude to said delay means to vary the retardation effect thereof on the pulses of said train. 10. A system according to claim 7 wherein the means for time modulating the pulses of said train includes means for producing a zig-zag channels, retarding by diiîerent amounts the en shaped wave from said train thereby providing ergy of said series of pulses to obtain a plurality triangularly shaped undulation having at least of series of pulses of different timing so that they interleave in time 'similarly as the pulses of said 10 one inclined edge to correspond to each pulse of said train, means for gate clipping the undula train, translating the pulses of each series into tions between two levels, means for varying the signal pulses the amplitude of which Vary accord clipping levels of the gate clipping means rela~ ing to the instantaneous v‘alues of the signal en tive to the amplitude of eac‘n undulation accord ergy of a corresponding channel, and time modu lating the pulses of said train according to the 15 ing to the amplitude of the corresponding signal pulse, and means for differentiating the clipped »amplitude of the corresponding signal pulses pro portions of the undulations to obtain pulses, the duced from said plurality of series. time positions of which represent the time posi 5. A method of time modulating pulses com tion of the clipped portion of .the corresponding prising producing a ñrst train of pulses varying inclined edges of said undulations. in amplitude according to the instantaneous val 11. A multi-channel transmission system com ues of ` a given signal energy, producing a second prising means for producing a ñrst train of pulses, train of pulses having a repetition frequency cor means for producing a second train of pulses the responding to the repetition frequency of the repetition frequency of which is a multiple of the amplitude modulated pulses, and time modulat ing the pulses of said second train according to 25 repetition frequency of said iirst train of pulses, retardation means for retarding the pulse energy the amplitude values of the corresponding pulses of said first train 0i pulses to produce a plurality of said ñrst train. of 'series of pulses diiîerently timedl so that the 6. A system for time modulating pulses Corn pulses taken together correspond to the pulses of prising means for producing a train of signal pulses of a given repetition frequency, the pulses 30 said second train, separate means for varying the amplitude of the pulses of each series according of which vary in amplitude according to instan~ to the instantaneous values of the signal wave of taneous values of a given signal wave, means for a corresponding channel, and means to time producing a second train of pulses having said modulate the pulses of said second train accord >repetition frequency, and means for varying the ing to the amplitude values of the pulses of said time positions of the pulses of said train in ac plurality of series. cordance with the amplitude values of the corre 12. A system according to claim 11 wherein the sponding signal pulses. means Íor'producing the pulses of the second 7. A multi-channel transmission system com train includes means for multiplying the pulses prising means for producing the plurality of »series of pulses differently timed so that the pulses of 40 of said ñrst train. 13. A system according to claim 11 wherein the said plurality of 'series interleave in time, means means for producing the pulses of said first train for producing a train of pulses corresponding to includes means for dividing the pulses of said said plurality of series taken together, means for translating the pulses of each series into signal pulses the amplitudes of which vary according to the instantaneous values of the signal energy of a corresponding channel, and means for time modulating the pulses of said train according to second train. » 14. A system according to claim 1l wherein the means for varying the amplitude of the pulses of each series includes a normally blocked ampliñer for the signal energy of each channel and means to apply one of said series of pulses to unblock 8. A system according to claim '7 wherein the 50 each said ampliñer for the duration of each pulse of such series. . means for translating the pulses of each series 15. A system according to claim 1l further in into signal pulses includes a normally blocked cluding means to produce a synchronizing pulse ampliñer for the signal energy of each channel channel comprising means for mixing the pulses and means to apply one of said series of pulses of said first train with the time modulated pulses to unblock each said amplifier for the duration of said second train, the pulses of said first train of each pulse of such series. being distinguished in width from said time 9. A system according to claim '7 wherein the modulated pulses. means for time modulating the pulses of said EMILE LABIN. train includes delay means for retarding the time the amplitude o1“ the corresponding signal pulses.