US2462874A - Multichannel electrical pulse communication system - Google Patents

Description

E. LABI'N ET A1. 2,462,874

March l, 1949.

MULTIGHANNEL ELECTRICAL PULSE COMMUNICATION SYSTEM 2 lSheets-Sheet 2 Filed Aug. 19, 1944 L/M/T OF 77/75 MOO.

0 f @92 m1/r of r/Mf Moo.

E m. 3: PUA 5E CoM/@05H5 @HRR/5R INI/ENTOR` Patented Mar. 1, 1949 MULTICHANNEL ELECTRICAL PULSE COIVIMUNICATION SYSTEM Emile Labin, New York, andDonald D. Grieg,

Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application August 19, 1944, Serial No. 550,185

2 Claims.

This invention relates to radio multi-channel communication.

An object of the invention is to provide a method and means for simultaneously transmitting and/or receiving at least two channels of intelligence modulated according to different principles of modulation on substantially the same carrier frequency or frequency band.

A feature of the invention is Ithe provision of means to modulate a carrier for one of the channels as a continuous wave, either by amplitude or frequency modulation and means to pulse modulate a second carrier according to some principle of time modulation. The tWo carriers may be mixed or intermodulated as a composite carrier before transmission or they may be transmitted at separate points and mixed in the medium of transmission. l

Another feature of the invention is the provision of means for receiving the composite carrier comprising the two channels of modulation and to separate therefrom each of the two channels for reproduction. The separation of the pulse component of the carrier is effected by clipping the received energy at a level above the maximum amplitude of the continuous wave component. The separation of the continuous Wave component is effected by clipping the received energy between two levels containing therebetween a substantial portion of the continuous wave and a minimum, if any, of the pulses.

The above and other objects and features of our invention will become more clearly understood upon consideration of the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a block diagram of a transmitter and a receiver according to the communicating principles of our invention;

Figs. 2 and 3 are graphical illustrations used in explaining the multi-channel communication lperformed by the system shown in Fig. 1; and

Fig. 4 is a block diagram illustrating a Variation of the transmitter portion of the communicating system of Fig. 1.

In Fig. 1, three sources of signal energy I, 2 and 3 are shown each coupled to a modulator. The modulator 4 with which signal source I is associated, may comprise any known form of amplitude modulator whereby the signal intelligence of source I modulates a continuous carrier wave within a given frequency band. The modulator 5 associated with signal source 2 may comprise any form of frequency modulator arranged to modulate a second continuous carrier wave according to the intelligence of signal source 2 in the same given frequency band in which modulator 4 operates. The output terminals of the two modulators and 5 are connected to a selecting switch 6 whereby one or the other of the continuous modulated waves of modulators t and 5 may be selectively applied to a coupler 'I for transmission over antenna 8.

The signal source 3 is associated with a time modulator 9 of any known form capable of displacing the pulses of a train, either produced by the modulator 9 or received from a different source, in accordance with the instantaneous Values of the intelligence received from the signal source 3. The time modulated pulses of modulator 9 are applied to a radio frequency modulator i@ for pulse modulation of a carrier wave within the same frequency band in which the modulators l and 5 operate. If the type of pulse transmission is such that a wider band width is used than the AM or FM system, several such AM or FM sysstems spread throughout the pulse frequency band may be used. The pulse modulated carrier is applied to the coupler 'l where it is mixed with the selected carrier from modulators 4 and 5 for transmission. The mixing of the two carriers results in a composite carrier due to a superposition effect of the two carriers. This superposition of the two carriers is indicated by graphs 2a and 3a of Figs. 2 and 3, respectively. Graph 2a represents a composite carrier II resulting from the superposition of the carriers produced by modulators t and I9. Graph 3a represents the composite carrier I2 resulting from the superposition of the carriers produced by modulators 5 and I Il. As shown, the composite carrier II is made up of a carrier i3 produced at modulator A and superimposed thereon are pulses I4 produced by the modulator IU. Likewise the composite carrier I2 is made up of a continuous frequency modulated wave l5 and pulses Hl from modulator I0 superimposed thereon. I

The components of composite carrier II are shown to be in phase.' They may, of course, occur out of phase, and in such instances one component may subtract from the other. To avoid loss of one or both components, the peak power of the pulse carrier is made greater than the peak power of the continuous carrier.

At the receiver the composite wave I I or I2, as the case may be, is received over antenna I6 and preferably, although not necessarily at this point, reduced to an intermediate frequency by the usual R. F. and I. F. amplifier stages I1. For separation of a desired channel, the output energy of amplifier I'I is applied through a pulse clipper I8 for clipping along a level such as indicated at I9 and I9a in graphs 2a, and 3o, respectively.'

the threshold clipping -type in which case the clipped energy from graphs Zaand 3a will appear substantially as indicated in graphs 2band 3b, respectively. Where the pulse energy occurs as shown in 2b, the pulse energy maybe limitedto a given amplitude by suitably biasing the detector to which the pulse energy is applied from clipper I8. Such a limit level is shown at 2i in graph 2b. The pulse output of the detectorrZ- is then applied to a known vform of time demodulator 22 depending, of course, upon the principle of the time modulation at modulator I0. By way of example only, a suitable time modulator and deoutput energy of amplifier II is applied to a clipper gate 23 arranged to clip energy between two levels 24 and 25, as indicated in graph 2a, or levels 24a and v25a as indicated in graph 3a. Where the composite carrier is of the type shown in graph -2a,jthe output of clipper gate 23 is selectively applied through switch 25 to an AM-detector 1.27. The output of such detector is indicated in graph 2c,whereby the signal envelope of the amplitude modulated continuous wave I3 is shown at Ila together with portions of the pulses M as indicated at Ma. The output of the detector 2'? is preferably provided with a low pass filter While we have shown and described particular apparatus of the invention, it should be understood that such is given by way of illustrationr of the invention only andnot as restricting the invention as set forth in the object and the appending claims.

W e claim:

1. A method of multichannel lcommunication comprising amplitude modulating a carrier wave of a given frequency with a continuous wave sig.

nal representing the intelligence from one signal source, modulating a second carrier wave of substantially the same frequency with a train of time modulated pulses representing the intelligence from a second signal source, superposing and simultaneously transmitting both modulated carrier waves, receiving the superposedV carrier waves on a single receiving channel, separating the vpulses from the received. energy by clipping the received energy at ailevel above the maximum amplitude of the continuous wave modulation, and separating the continuous wave modulation from the received energy by clipping the received energy between two levels containing ,a substantial portion of the continuous wave modulation and a minimum, if any, of said pulses.

y2. A system for multichannelv communication comprising a source of continuous wave signals representing intelligence, a `source of time modullated pulses representing other intelligence,

, means for simultaneously producing a plurality of carrier waves oi substantially the same irequency, means for amplitude modulating oney of said carrier Waves with said'continuous wave whereby the pulses Ida are substantially removed from the envelope thereby resulting in a substan .tially true reproduction I3?) of the intelligence transmitted from source I graph 2d.

W'here the composite carrier according to graph 3a is received, the output of the clipper gate 23 is applied through switch 26 to an FM demodulator 29 of known character whereby the intellias indicated by `gence of source 2 is obtained from the clipped energy 3l), graph 3c.

The outputs of the demodulators 22, 28 and 29 are applied to their respective reproducers.

While the two carriers produced in the system shown in Fig. 1 are mixed before transmission, it

`Will be clear to those skilled in the art that the mixing may take place in the transmitting me dium such as the ether, or if a line communication is used, atinbranching points along the line. `To

vmake this clear, Fig. 4 has been added showing Tand. appear at receivers as a superposition composite carrier as indicated by graphs 2a and 3a.

signal, means for modulating a second of saidcarrier waves with a train of saidtime modulated pulses, means for superposing and simultaneously transmitting both modulated carrier waves, a receiver for receiving the superposed carrier waves on a single receiving channel, a clipper biased to clip the received energy at a level above the maximum amplitude of the continuous wave modulation, and a gate clipper biasedA to clip the received energy between two levels containing a substantial portion of the continuous wave modulation and a minimum, if any, of said pulses.

' `EMILE LABIN.

DONALD D. GRIEG.`

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

UNITED STATES PATENTS

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