US2477625A - Multiplex television and pulse modulated sound system - Google Patents

Description

Aug. 2, 1949. E; LABIN MULTIPLEX TELEVISION AND PULSE MODULATED SOUND SYSTEM 3 Sheets-Sheet 1 Filed Aug. 25, 1944 Aug. 2, 1949.

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` MULTIPLEX TELEVISION AND PULSE MODULATED SOUND SYSTEM Filed Aug. 25, 1944 3 Sheets-Sheet 3 I N VEN TOR. EMIL E LHB/N Patented Aug. 2, 1949 UNITED STATES PATENT OFFICE MULTIPLX TELEVSON AND. .RULS MonULn'rnD SOUND SYSTEM Emile Labin, New `ir'o'rlr, N. Y., assigner to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application August 25, 1944, Serial No. 5515203 8 Claims. 1

This invention relates to television systems and more particularly to a multiple television systei'n and means fi for selectively receiving any desired one of the programs thereof.

In my Patent No. 2,437.300, issued on March 9, 19e-8, I disclose a television transmitting method and system for transmitting simultaneously a plurality of television programs from a single vantage point such as from the top of the highest building of a city or from a tower located at some high elevation within the area served. The picture programs are transmitted on separate carrier frequencies While the sound signals acA companying' each program are transmitted as separate channels of a multiecliannel carrier on still another frequency. synchronizing signals common to all of the picture programs are trans-` mitted as one of the channels of the multi-chene nel carrier.

It is an object of this invention to provide in combination with such transmitting method and system a television receiving method and means for selectively receiving any one of the multiple television programs transmitted.

Another object is to provide a television receiver for receiving picture signals on one carrier, and sound and/or synchronizing signals on another carrier.

Another object is to provide a method and means for obtaining certain synchronizing pulses from a multi-channel train of pulses wherein the shape and/or timing characteristics of the pulses of the train differ according to the use intended of them,

According to one of the features of the present invention the receiver is provided with directive antennas aligned with the antennas of the transmitting station.` By this arrangement substantially equal reception is had for each of the different television programs. The picture signal carriers, being distinguished by dinerent carrier frequencies, are selected by frequency tuning. The sound vsignals. accompanying each picture program being transmitted over a multiechannel carrier are selectively segregated according to the channel corresponding to a selected television program. The picture signal and sound channel selection may be coordinated so that a corresponding sound channel is obtained automatically by the tuning-in of each picture program.A

The synchronizing feature of the invention includes the provi-sionof means for segregating the channel synchronizing signals from the multi channel carrier for synchronizing the picture re production operation of the receiver regardiess graph b of Fig. 2, on a carrier frequency fc.-

2 of change in the tuningin ef different picture programs. This is made possible by employing at the transmitter the same synchronizing signals for each of the different picture programs. In addition to this use of the synchronizing signals, they may be used to synchronize arid/or stabilize 'selective reception of the sound channels.

The above and other objects and features of the invention will become more apparent upon consideration of the following detailed descripition to be read in connection with the accompanying drawings,- in which:

Fig. 1 is a block diagram of a television system incorporating the features of my invention;

Fig. 2 is a graphical illustration u-sed in explaining the operation of the system shown in Fig. 1; Y

Fig. 3 is a schematic diagram of a pulse Width discriminating circuit used in the system of Fig. 1; and

Fig. 4 is a schematic diagram o f a pulse time demodulator that may be employed in the system 0f Fig. 1; K

For simplicity o f illustration I disclose a transmitter system adapted to transmit simultaneously three picture programs, as indicated by the three. accompanying sound channels L2 and 3 in graph la of Fig. v2.- [fhe transmitter 4 shown in 1 is provided with atower 5 having antennas 6, 1,- 8 andg. Theseantennas may be of any known omnidirectional type. `Antenna ii is connected to the transmitter 4 for transmission of a multiechannelpulse traini such as illustrated in Antennas l, 8 ands are connected to thetrans'- mitter for simultaneous transmission of4 three separate picture ilpgragns each similar to the video signal of graph a, Fig. V2, over separate carrier frequencies f1, f2. and fr. The video signal of each picturevprogram such as represented by graph a of Fig. 2 includes picture signals l8 hor1f zontal blanking pulses r 'intervalswHBnand vertical lolankingY pulses or intervals While the picture signals ID are indicated as line signals such as obtained by line scanning, such showing is given by way of example only. since it is recognized that other types ofi'- television scanning may be employed without departing from the pri-nciples of thisl invention. While the transmitter system is indicated for only three `picture transmissions and 4one multi-channel trans-miseieni Ait will be clear that additional picture programs as Well as other types of broadcasts may be included.

The receiver H includes .two receiving antennas I2 and I3, preferably of the directive character arranged for alignment with respect to the antennas 6 to 9 of the transmitting tower 5. Associated with the antenna I2 and I3 are the usual R.F. and I.F. amplifier converter units I4 and I tunable for reception of the appropriate carriers. The unit I4 'maybe tuned to either of the carriers f1, f2, or fs, for selective reception of any one of the picture programs. It will be understood, of course, that the amplier units I4 and I5 may be made tunable for receiving other broadcasts as well, and the directive antennas I2 and I3 may also be made adjustable if desired. The output of the amplier I4 is appliedto a detector I6 for translation of the intermediate frequency signals into a video signal such as shown in graph a. The video signal is applied to a picture reproducer I1 whereby the picture is reproduced according to known methods.

The multi-channel carrier received by antenna I3 and amplier I5 is detected at I8 to produce a train of channel pulses such'as indicated by graph b. For three sound channels the train includes three different series of signal pulses I, 2 and 3, and a fourth channelv comprising horizontal and vertical synchronizing pulses H and V. The horizontal synchronizing pulses H are of a width greater than the signal pulses l, 2 and 3 while the vertical synchronizing pulses V are of still greater width. If desired, pulse shapecharacteristics other than width may be used for distinguishing the horizontal land verticalsynchronizing pulses from each other and from the pulses of the other channels.

The multi-channel signals are applied over connection I8a to pulse width discriminator IQ which may be of any suitable character capable of distinguishing between the signal pulses and the horizontal and vertical synchronizing pulses. A suitable width discriminating circuit for this purpose is illustrated in Fig. 3. The circuit includes limit clipping stage 23 as an input coupler which limits all input pulses to substantially the same amplitude, and also inverts the input pulses from a positive polarity to negative polarity. The output pulse energy from stage is applied through a resistor R to a shock excitable L.C. circuit ZI. Connected across the tunable circuit 2| is a Vacuum tube 22, the cathode 23 of which is connected to the input side of the circuit ZI, while the anode 24 is connected to the opposite side 25 of the tunable circuit. The side 25 is also connected to a source of anode potential 25. The pulse energy from the anode connection 21 is applied to the control grid 28 of the tube 22 so as tooblook the conduction between the cathode 23 and the anode 24 while the pulse energy is applied to the circuit 2 I. The undulations produced in the circuit 2l in response to pulse energy over anode connection 21 are taken off through a connection 29 for application to a threshold clipping amplifier 3U and through a connection 3I to a second threshold clipping amplifier 32,

Graph c of Fig. 2 illustrates the pulse width discriminating function of the circuit I9. When the leading edge 33 of a horizontal synchronizing pulse H, for example, reaches the L.C. circuit 2I it shock excites the circuit into an oscillatory condition as-indicated by the undulation 34 of graph c, Where the circuit 2l is tuned to a resonant frequency one-half the period of which corresponds to the duration of the wider pulse V, graph b, it will be apparent that the trailing edge 35 of the pulse H occurs before the undulation 34 has gone through its normal duration. The edge CII 4 35 accordingly shock excites the circuit 2I in theopposite polarity direction thereby producing an oscillatory condition 36 out of step with undulation 34. This results in an average oscillatory condition as represented by the positive undulation 31.

When the vertical synchronizing pulse is applied to the circuit 2l, the leading and trailing edges thereof are separated by an interval corresponding exactly to one-half the period of resonant frequency so that when the trailing edge 38 is applied to the circuit 2l the shock effect thereof occurs at the point where the initial undulation 34 is crossing the zero axis thus adding to the oscillatory eiect produced by the leading edge. This results in a maximum undulation 39 greater than the undulation 31. As regards tne effects of the pulses of the signal channels I, 2 and 3 it will be readily apparent that these pulses being much narrower in width will only produce a small ripple effect as indicated at 45, graph c. This clearly is due to the fact that the leading and trailing edges operate substantially in opposition one to the other in their action upon circuit 2|.

The oscillatory condition established in the circuit 2i would normally continue as a damped wave except for the action of tube 22, The pulse energy applied to the circuit ZI is negative in polarity, as hereinbefore stated, and by applying this negative energy to grid 28 the tube 22 is maintained opened for the duration of the pulse. Since the pulse energy is dissipated the blocking energy on grid 28 is removed .permitting the tube to conduct as soon as the oscillatory energy again goes negative. This condition permits the tube to absorb the oscillatory energy of the oscillation when the positive undulation reaches the zero axis thereby preventing a carry over of oscillatory energy from one pulse to the next. For a further discussion of the width .discriminating circuit reference may be had to the Patent to E. Labin and D. Grieg, No. 2,440,278, issued April 2'?, 1948.

In order to obtain horizontal synchronizing pulses corresponding to the leading edges of the pulses H and V the output energy of the circuit I9, graph c, is applied to the threshold clipper 3l] biased to clip the negative undulations of the output energy at a level 4I which clears the ripple eiect 48 produced by the signal channels. By applying the clipper output to a shaper 42 which may comprise a differentiator circuit only or additional pulse shaping circuit, output pulses 43, graph d, are obtained timed substantially to the leading edge of the pulses H and V. These pulses 43 are then applied over connection 44 to the picture reproducer I1 to control the horizontal sweep circuit of the reproducer.

To obtain a vertical synchronizing pulsefcorresponding to substantially the occurrence of pulses V, graph b, the output energy of the circuit !9 is applied to the threshold clipper 32 which is adjusted for a clipping operation at level 45 which clears the positive undulation 31 but clip`s the maximum undulation 33 produced from pulses V. By shaping the clipped portions at 46 pulses 41 are obtained, as indicated in graph e, for application over connection 48 to the reproducer I1, While the timing of the pulses 41 is slightly delayed with respect to the pulses V, it will be noted that each pulse 41 occurs shortly after the occurrence of the leading edge of each vertical blanking pulse VB of graph a so, that the vertical retrace period is initiated during the blanked out portion which of course is provided of adeso chosen as to occur at the peak of the Wavepotential produced by the bench mark pulses or those channel pulses in the position indicated for pulse la. This clipping level is indicated at 16 and produces an output of pulses as indicated by graph fi, the amplitude variations of which define the envelope 11 of the original modulated signal wave.

For a further discussion of the demodulating features of the type of demodulator circuit shown in Fig. 4 reference may be had to the Patent to D. Grieg No. 2,416,306, issued February 25, 1947.

From the foregoing description it will be clear that in accordance with my invention the receiver of Fig. 1 is capable of selecting by tuning of the amplier I4 any of the picture programs broadcast from the tower 5. By ganging the tuning control indicated at 18 for amplifier I4 with the adjustment control 19 of the delay device 53 the sound channel corresponding to the selected picture carrier will be automatically segregated from the multi-channel transmission received by amplifier i5. In this connection it will be clear to those skilled in the art that the multi-channel transmission may include broadcasts other than sound signals for the picture programs. In other Words, sound signals may be included for other sound programs for radio transmission and in addition other channels may be provided for facsimile transmission. The gang connection 80 between the control 18 and 19 may therefore be interrupted to provide independent adjustment of the delay device for reception of broadcasts other than television.

While I have shown and described my invention in connection with specific apparatus it will be understood that the illustration is given by way of example only and not as limiting the scope of the invention as set forth in the objects and the appended claims.

I claim:

1. In a television system wherein a plurality of picture programs are transmitted on separate carriers and the sound signals corresponding to each program are transmitted as one of the channels in a multi-channel carrier separate from the picture carriers; a method of selectively receiving one of the transmitted picture and sound programs comprising detecting the picture carrier having the desired picture program, detecting the #i multi-channel carrier, deriving from the multichannel carrier energy common to the picture and sound programs, applying the derived energy to the multi-channel carrier, and under control of said derived energy, segregating from the channel signals the sound signals corresponding to the selected picture program and reproducing from said detected picture signals, said derived energy and the segregated sound signals, the desired picture and sound program.

2. In a television system wherein a plurality of picture programs are transmitted on separate carriers and the sound signals corresponding to each program are transmitted as one of the channels of a multi-channel carrier different from the picture carriers, one of the channels of said multi-channel carrier comprising synchronizing pulses common to all of the picture programs, a method of selectively receiving one of the -picture and sound programs comprising detecting the carrier modulated with picture signais of the desired picture program, detecting the multichannel carrier, selecting from the multichannels the channel having the synchronizing pulses'segregating, under control of the synchronizing pulses, from the multichannels, the channel having the sound signals corresponding to the selected picture program, reproducing under control of said synchronizing pulses the picture program transmitted by said picture signals, and reproducing the sound transmitted by the segregated sound signals.

3. A television receiver for receiving a picture program wherein the picture signals thereof are transmitted over one carrier and the accompanying sound signals and synchronizing signals are transmitted by different channels over a second multiplexed carrier, comprising means for detecting said one carrier to obtain the picture signals, means for detecting said second carrier to obtain the sound and synchronizing signal energy, means for separating out the synchronizing signals, means for deriving the multi-channel carrier energy common to the picture and sound programs, and under control of said derived energy for segregating from the channel signals the sound signals corresponding to the selected picture program, a picture reproducing device, means to apply said synchronizing signals to said device to control the reproduction of said picture program, and means for reproducing the sound of the picture from said sound signals.

4. A television receiver for receiving a desired one of a plurality of picture programs wherein the picture signals of the different programs are transmitted on separate carriers and the sound signals accompanying each program are transmitted as one of the channels in a multi-channel carrier, comprising means for detecting the carrier of the desired picture program to obtain the picture signals thereof, means for detecting the multi-channel carrier, means for deriving from the multi-channel carrier energy common to the picture and sound programs, and means under control of said derived energy means for segregating from the multi-channel carrier the sound channel corresponding to the selected picture program and for reproducing the picture from the picture signals, and means for reproducing the sound for the picture program from said sound signals.

5. A television receiver comprising means for receiving picture signals transmitted on a given carrier, means for receiving a multi-channel carrier, one channel of which includes the sound signals of said picture signals and another channel of which includes synchronizing signals for said picture signals, means to segregate the synchronizing signals from the received channels, means for reproducing the picture conveyed by said picture signals under control of said synchronzing signals, means controlled by said synchronizing signals for segregating from the received `channels the sound channel corresponding to the received picture signals, means for reproducing the sound from the signals of the segregated sound channel, and means coordinating said sound channel segregating means with the picture signal receiving means.

6. A television system comprising means for transmitting a plurality of picture programs on separate carriers, means for transmitting as separate channels on a multi-channel carrier the sound signals corresponding to the separate picture programs, said last named mean-s including means for transmitting synchronizing signals common to all of said picture programs as one of the channels of said multi-channel carrier, and means for radiating the picture carriers and said multi-channel carrier; a receiver for simultaneously receiving a desired one of said picture carriers and said multi-channel carrier, means for segregating from said multi-channel carrier the pulses of the synchronizing channel, means for reproducing the picture from the received picture signals under control of said synchronizing signals, means for receiving and ren producing from the multi-channel carrier under control of said synchronizing signals the sound signals corresponding to the selected picture program.

7. In a television receiver having means for receiving a desired one of a plurality of picture programs transmitted on separate carriers and means for receiving a train of synchronizing pulses common to all of said picture programs transmitted on a carrier separate from said picture carrier-s, the synchronizing pulses being timed according to line scanning of the picture signals with certain of the pulses differing in width from others to represent the timing of successive frame scanning intervals; means for obtaining line and frame synchronizing pulses from said train comprising a pulse width discrminator to produce an undulation of a given polarity in response to the leading edge of each pulse and to produce an undulation of opposite polarity in response to the combined action of the leading and trailing-edges of each pulse, said discriminator being arranged to vary the amplitude of said undulations of opposite polarity according to the width of the pulses, whereby the undulations responsive to said certain pulses are of greater amplitude, means to pass energy of said undulations of given polarity for use as line scanning synchronizing pulses and means to clip the undulations of said greater amplitude for use as frame scanning synchronizing pulses,

8. In a television receiving system having means for receiving a multi-channel train of pulses, one channel of which comprises pulses of width greater than the pulses of other channels, the pulses of said one channel being timed according to line scanning, with certain of the pulses thereof differing in width from others to represent the timing of successive frame scanning intervals; means for obtaining line and frame synchronizing pulses from the train of pulses comprising a pulse width discriminator to produce an undulation of a given polarity initi- 10 ated by the leading edge of each pulse of said train and to produce a maximum undulation of opposite polarity in response to the combined action of the leading and trailing edges of each pulse, said discriminator being arranged to cause the amplitude of the undulations produced from the pulses of said other channels to be small in comparison with the undulations produced from the pulses of said one channel, and those maximum undulations of said opposite polarity resulting from the pulses of said one channel are of greatest amplitude for said certain pulses, means to clip the undulations of said given polarity at a level beyond the amplitude of the undulations resulting from the pulsesl of said other channels to obtain pulses for use as line scanning synchronizing pulses, and means to clip those undulations of said opposite polarity that are of greatest amplitude for use as frame scanning synchronizing pulses.

EMILE LABIN.

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

UNITED STATES PATENTS Number Name Date 1,975,055 Weinberger Sept. 25, 1934 2,089,639 Bedford Aug. 10, 1937 2,198,969 Lewis Apr. 30, 1940 2,227,045 Urtel Dec. 31, 1940 2,231,971 Tubbs Feb. 18, 1941 2,282,046 Goldsmith May 5, 1942 2,329,339 De Baun Sept. 14, 1943 2,391,776 Fredendall Dec. 25, 1945 2,401,384 Young June 4, 1946 2,408,063 Grieg Sept. 24, 1946 2,408,077 Labin Sept. 24, 1946 2,414,453 De France Jan. 21, 1947 2,416,330 Labin Feb. 25, 1947 2,421,017 Deloraine May 27, 1947 2,437,300 Labin Mar. 9, 1948 FOREIGN PATENTS Number Country Date 322,025 Great Britain Nov. 28, 1929 397,681 Great Britain Aug. 31, 1933 421,937 Great Britain Jan. 2, 1935

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