US2326515A - Television system - Google Patents

Description

Allg 10, 1943- "E. HQ B.` BRTELINK TELEVIS ION SYSTEM Filed Aug. s, 1940 l4 Fsheets-sheet 1 MPL/HER Mo Prog-sm /lM/fcran CAMERA T UEE wat OAMC/TY TUBE Inventor. Everhard HB.Bal"`e|r1|1,v by #www His Attorney.

1 A VERT/CIL BA/va GENE/umn MFL/nm 50 AUD/0 AMPLIFIER 456 C] 'Aug- 10 1943- E. H. B. BARTELINK I 2,326,515

TELEVISION SYSTEM Filed Aug. 3, 1940 4 Sheets-Sheet 2 Figi.

50g/:R AHFL/F/EH 60 MP2/l R 'aL-,71g o 64 Inventor: Ever-hard HB. Bar-teln k,

His Attorneg.

Aug. 10, 1943.

v E. H. B. BARTELINK TELEVIS ION SYSTEM Y Everhar'd HBartelnk,

His Attorney.

Al1g- 10, 1943- v E. H. B. BARTELINK 2,326,515

- TELEVIS ION SYSTEM Filed Aug'. 5, 1940 I 4 Sheets-Sheet 4 IPL/r00s TUNE "No Mom/Amm inl/ggg 64 Fig- 4- PULSE GENE/947W? RECEIVE/7S Inventor: Everhard H.B.Barte|ink,

Patented Aug. l0, 1943 -raLEvrsioN SYSTEM Everhard H. B. Bartellnk, Nskayuna, N. Y., assignor to General Electric Company, a corporation of New York Application August 3, 1940, Serial No. 350,643

33 Claims. (Cl. 178-5.6)

This invention relates to signalling systems and more particularly to systems in which an amplitude modulated wave is transmitted recurrently.

In the television art as it has at present been standardized in this country, each successive frame or complete picture'image is scanned in 441 lines, and-30 complete images are transmitted per secondfTh'e maximum amplitude of the wave transmitted corresponds to a black spot in the image. At the end of eachline and between each frame there are transmitted respectively horizontal and vertical pedestal and synchronizing impulses'which have respectively, intensities of 80% and 100% of the maximum carrier amplitude. Such a system requires the transmission of high frequency video signals of the order of 4 megacycles as side bands on at least one side of the carrier.` It has been found feasible to transmit a carrier wave having such a wide side band range only in the ultra-high frequency region. Even in this region, however, frequency range is not unlimited, and it is very desirable to utilize the available space Vas completely as possible. It is accordingly 'an object of my invention to provide a radio signalling system for transmitting a greater amount of intelligence perunit time within a certain frequency range. Itis a further object of my invention to provide a television system in which additional information is transmitted during transmission of the pedestal impulses. In the attainment of these objects I find it desirable'to shift the frequency of the carrier wave during a pedestal while maintaining it at maximum intensity, to produce a synchronizing impulse at the television receiver. The carrier frequency may, for example, be shifted into one band to produce a vertical synchronizing impulse and may be shifted into a different band to produce a horizontal synchronizing impulse, both bands being within the side band range produced by amplitude modulation of the wave by the video signal. It 1s an object of my invention to utilize a carrier-wave, shifted into such a plurality of different 'frequency bands, to transmit at least one channel of information, such as an audio signal, in each ing such a vertical pedestall impulse, the trans- If double inmission of horizontal synchronizing impulses is continued and vertical synchronization may be effected by a train of pulses interspersed with the horizontal synchronizing pulses. It is an object of my invention to transmit at least one signal by means of such trains of impulses.

It is a corollary object of my invention to pro.-

vide suitable mechanism for transmitting more than -one signal through such trains of pulses transmitted in a single frequency band.

In the transmission ofhorizontal synchronizing limpulses by shifting the frequency of the carrier wave into a certain range, false synchronization may be effected by means of waves of similar frequency characteristic existing in the video signal or in atmospheric disturbances. or the like. A way of reducing the possibility of vsuch false synchronization has been described in my copending application for U. S. Letters Patent S. N. 331,349, filed April 24, 1940, for Image transmission systems, and assigned to the same assignee as the present application. In that p revious' application thereV is disclosed and claimed an improved method and apparatus for transmitting and receiving a television signal having synchronizing impulses. In that application there is disclosed receiving apparatus for discriminating between a wave when its frequency is modulated and when its amplitude is modulated, Vso that substantially no energy is received except when the wave is frequency modulated. The possibility of synchronization by fortuitous frequency characteristics of the wave when amplitude modulated is therefore reduced. It is an object of my invention further to minimize the possibility of such 'false synchronization ina system such as here described. In the attainment of this object it is convenient to transmit simultaneously two separate horizontal synchronizing impulses by shifting the carrier wave into at least two individual frequency bands, within each of f which bands additional informationmay be imwith the accompanying drawings in which Fig. 1 is a simplified schematic diagram of a radio transmitter embodying my invention; Fig. 2 is a simplified schematic diagram of a radio receiver adapted to receive a wave transmitted by the transmitter of Fig. 1; Fig. 3 is a simplified schematic diagram of a more elaborate radio transmitter embodying my invention; Fig. 4 is a receiver adapted to receive a wave transmitted by the transmitter of Fig. 3; and Fig. 5 is a detailed schematic View oi' a certain portion of the transmitter of Fig. 3.

In Fig. 1 there is illustrated a television transmitter having a camera tube I connected through an amplifier andpedestal injector Il to an amplitude modulator I2. The modulator I2 modulates the amplitude of a carrier wave from a master oscillator |3 in accordance with the intensity of video impulses produced by the camera tube I0. The modulated carrier wave from the modulator I2 is radiated from an antenna I4.

Suitable apparatus is provided for controlling the horizontal and vertical scanning and framing of the camera tube I0, which apparatus comprises a horizontal and vertical deection and synchronizing signal generator l5. The generator I5 transmits horizontal and vertical deflection waves respectively to a magnetic yoke surrounding a portion of the camera tube I0 and including deflection coils I5 and I1. The generator I5 also produces horizontal and vertical pedestal impulses which are mixed in a pedestal mixer I8 and injected into 'the video signal through the amplifier and pedestal injector II. The video signal, complete with horizontal and vertical pedestals, is of usual form and need not be explained. 'I'he horizontaland vertical pedestals are also-separately transmitted to apparatus for shifting the carrier frequency during the existence of pedestals, so that the intensities of the shifted carriers are modulated distinctivel ter oscillator I3 is transmitted through the balanced modulator 2| and then through the balanced modulator 23 to an amplifier 25, which ampliiies the carrier wave and impresses it on' the amplitude modulator I2. Since each of the balanced modulators 2|, 22, 23, and 24 is identical in construction, only the first will be described in detail.

'I'he modulator 2| comprises a pair of electron discharge devices 26 and 21 which are connected to be energized in balanced or push-pull relation through a transformer 28 from the master oscillator I3. 'I'he cathodes of the devices 26 and 21 are connected together and through a source 29 of grid bias potential and a grid resistor 30 in series to the center tap of the secondary of transformer 28. The anodes of the devices 26 and 21 are connected in push-pull relation to an output transformer 3|, whose center tap is connected through asource 32 of anode potential to the cathodes of the two devices.

'Ihe source 29 of grid bias potential normally supplies a grid bias to the devices 26 and 21, suitable for amplification of the wave from the master oscillator |3 which is supplied to the voutput transformer 3|. The horizontal impulses from Y bias potential for the modulator 24 are adjustedv the generator I5 are impressed through a coupling condenser 33 across the grid resistor 30 and have such magnitude and polarity as to drive the grids of the devices 26 and 21 to cutoff.

in the balanced modulator 22 is of sufficient size and of such polarity as to maintain the discharge devices 38 and 39 in the balanced modulator 22 -at or beyond cutoff'. The horizontal pedestal impulses, which recurrently prevent transmission of the carrier wave through the modulator 2 I, act in reverse polarity on the modulator 22, so as to make the grids of the devices 38 and 39 less negative and thus allow these devices to amplify the carrlier wave from the horizontal band generator 9.

The wave from the generator I9 is transmitted through the output transformer 40 of the modulator 22, which transformer is connected in series with the output transformer 3| and with the input transformer 4| of the balanced modulator 23. The source 42 of grid bias potential for the modulator 23 and the source 43 of grid in the same ways, respectively, as the sources 29 and 31 in the modulators 2| and 22. The output transformer 44 of the modulator 23 and the output transformer 45 of the modulator 24 are connected in series with each other and with the input to the amplifier 25.

In operation, during any particular horizontal deflection of the scanning cathode beam in the camera tube I0, video impulses modulate the amplitude of the carrier wave from the master oscillator I3. The generator I5 produces no horizontal or vertical pedestal impulses, and the balanced modulators 22 and 24 Y remain in a blocked condition, so that the waves from the generators I9 and 20 are not transmitted. The balanced modulators 2| and 23, however, are in condition for transmitting the carrier wave from the master oscillator I3, first through the balanced modulator 2|, and then through the modulator 23 to the amplifier 25, and to the amplitude modulator 2.

At the end of a horizontal deflection of the cathode ray beam in the tube I0, a horizontal pedestal impulse appears which, through the amplitude modulator I2, raises the radiated intensity of the carrier to a, maximum and thus blocks out all video signals during its existence, and at the same time changes the balanced modulator 2| to a blocked condition and the balanced modulator 22 to a condition for transmitting a Wave. The carrier wave from the master oscillator I3 is therefore no longer transmitted, while the shifted carrier wave from the horizontal band generator f I9 representing a horizontal synchronizing impulse passes first through the balanced modulator 22 and then through the balanced modulator 23 to the amplifier 25 and amplitude modulator I2.

After a single complete frame or image has been completely scanned horizontally in a succession of horizontal lines, the generator I5 produces a vertical pedestal impulse which, like the horizontal pedestal, increases the intensity of the i carrier wave passing through the modulator I2 to a maximum and blocks all video signals. The vertical pedestal at the same time changes the balanced modulator 23 to a blocked condition and renders the balanced modulator 24 capable of transmitting the carrier wave from the vertical band generator 20 to the amplifier 25` andthe amplitude modulatorl l2. The pulse of shifted carrier frequency from generator 20 represents a vertical synchronizing impulse. Since the generator 20 produces a carrier wave whose frequency is shifted to a different band than the wave produced by the generator I9, horizontal and vertical synchronizing impulses are dierent.

While the carrier wave is being produced respectively by the horizontal band generator I9 and the vertical band generator 20, additional information may be carried by impressing frequency modulation on the carrier wave within each of these two bands. For example, the audio wave, which it is usually desired to transmit along with the video signals from the camera, tube l0. may be picked up by a microphone 46, amplied by audio amplifier 41, and impressed upon a capacity tube 48, which is connected in the tuned circuit of the horizontal band generator I9. The capacity tube 48 may be any device whose capacity, or if it be desired, whose inductance changes in response to the intensity of a wave impressed thereon.V Electron discharge circuits are well known in which a discharge device is arranged to simulate either an inductancelor a capacity, the magnitude of which may be varied in accordance with a desired signal. Such a device may be used to advantage in this application. The capacity tube 48 and the horizontal band generator i9 are so adjusted that frequency modulation of the carrier wave by audio signals never causes thewave t vchange in frequency enough to leave the band assigned to the carrier wave for transmission of the horizontal synchronizing impulse.

Since in the present standard system the horizontal synchronizing impulse are seni; somewhat more than 13,000 times per second. they are of sufficiently high frequency to be modulated in response to audio signals. It has been found that audio signals may bev satisfactorily reproduced by transmission interrupted at such a rate.

Similar apparatus is provided for shifting the Y frequency of the carrier wave produced by the vertical band generator 20 to transmit a measure of -the average brightness of the picture being televised. For this purpose a photocell i9 is placed near the camera tube i0 so as to produce a voltage proportional to the average amount oi.'`

light on the camera tube. The output of the photocell 49 is amplified through an amplifier 50 and changes the capacity, or inductance, of a capacity tube 5| which is connected in the tuned circuit of the vertical band generator 20. This apparatus for transmitting a measure of average brightness is adjusted so that the carrier wave during transmission of vertical pedestals never leaves the frequency band assigned to the transmission of vertical synchronizing signals. Since the average brightness of a scene changes relatively slowly and particularly since the eye cannot distinguish changes as rapidly as thirty times per second, the transmission of a' measure of brightnessby the vertical band generator 20 and its associated apparatus once every sixtieth of a second is ample for the purpose of maintaining the received picture at a suitable degree of brightness.

Since a side band produced by amplitude modulation of an unshifted carrier may occupy a modulation band within four megacycles of the unshifted' carrier, it is desirable that a frequency band no greater than this shall be occupied by the shifted carrier wave produced by the gener- 3 ators I9 and 2 0. By the term modulation band" is meant the frequency band within which com- 'ponentsof substantiaI intensity of amodulated carrier wave may be found.

The carrier wave may be modulated either in frequency -or in amplitude within the meaning of this term. The frequency band between three and four megacycles from the unshifted carrier may be occupied by the wave from the horizontal band generator I9. `If it be assumed that the microphone 4B and the remaining parts of the audio channel are capable of transmitting audio waves up to 10,000 cycles, the frequency modulated carrier wave produced by the audio signals may have a ratio of sweep frequency to audio frequency of about 1000 to one. Satisfactory noise suppression may be obtained with a much smaller sweep ratio, and ifl such a smaller ratio be used, the carrier wave may be transmitted as several different carrier waves, each having a frequency in a different frequency band. In each of these bands the respective carrier is frequency modulated with a. smaller sweep ratio.. The manner in which this is accomplished will be set forth hereinafter in greater detail.

It may be thought-advantageous to reduce the sweep ratio by transmitting components of the audio signal or modulating wave up to a much higher frequency, rather than reducing the frequency band occupied 'by the wave. There is, however, a limitation to the maximum frequency which may be transmitted through any single frequency band. This limitation arises because the carrier ,wave is frequency modulated by audio signals during the existence of horizontal pedestals only, which occur at about the rate of 13 kilocycles per second. The audio signals are therefore effectively modulated on a 13 kilocycle carrier, and it is undesirable to transmit anaudio frequency wave which approaches 13 kilocycles. It is, in fact, preferred to transmit no audio frequency wave near or above half that frequency, namely, 61/2 kilocycles. This is in order to prevent the second harmonic of any audio signal wave from heterodyning with the 13 kilccycle horizontal synchronizing signal to produce audible hcterodyne waves.

If it be desired to transmit an audio signal vwith higher delity than that obtainable within such a 6 kilocycle band,'the carrier wave, split into two or more individual frequency bands, may be respectively frequency modulated by individual portions of .the high fidelity audio signal, For example, that portion of the carrier wave which lies within one frequency band may be modulated in frequency by components of the audio signal wave between zero and 5000 cycles; Another portion of the carrier wave which lies within a, second frequency band may be' modulated in frequency by other components of the high fidelity audio signal wave between 5000 and 10,000 cycles. The audio signal components between 5000 and 10.000 cycles, before modulating the frequency of that portion of the carrier wave in the vcorresponding frequency band, are heterodyned with a suitable wave so that their frequencies, as transmitted, lie between zero and 5000 cycles. Of course, even higher frequency components of an audio signal wave may be transmitted by provision of more of such split audio channels.

In the large majority of audio signals which it is desired to transmit, it is entirely unnecessary that any frequency components over 6000 cycles be transmitted. For most audio signals it is cycles t unnecessary to transmit frequencies over 2000 obtain good intelllsibility. Satisfactory reproduction of most music is obtained through commercial broadcasting systems, which frequently do not transmit more than 4500 or 5000 cycles of an audio signal because of the necessity of operating such commercial transmitting stations in narrow frequency bands.

The etiective suppression of noise or atmospherics in audio signals transmitted through the present systemfmakes it appear that an audio -signal of greater fidelity is transmitted than one in a range of frequencies up to 6000 cycles. With suitable limiting action in the frequency in addition to those disclosed in the above mentioned application.

A's described in that application. a grid resistor 1| and a coupling condenser 'Il of the bottom clipper 61 are proportioned so that the carrier wave of maximum intensity transmitted during horizontal and vertical pedestals is rectified and maintains a grid bias voltage on the grid of the` bottom .clipper 61. This bias is suiiicient to prevent transmission of video signals, which, as side bands of the carrier wave, can theoretically never demodulation portion of the receiver, the presi ent system using a frequency modulated wave' is capable of a high degree of noise or atmospheric suppression,

For transmission of the carrier wave from the vertical band generator '10,- frequency modulated by the measure of average brightness, a frequency band between two and three megacycles from the unshifted carrier may be employed. Since the measure of average brightness changes very slowly there-is in this case a higher degree of freedom from atmospheric disturbances than for the audio signal, discussed above.

It has been shown how a television signal, complete with video signal, horizontal and vertical synchronizing irnpulses, and brightness control, as well as an audio signal, may be transmitted entirely within the frequency band occupied by side bands produced by amplitude modulation of a carrier wave by such video sighals. 'I'he video signal and the horizontal and vertical pedestals are all amplitude modulated on the carrier wave, and the horizontal and vertical synchronizing signals, an audio signal, and a measure of average image brightness are all,

in effect, frequency modulated upon the sameA carrier Wave.

In Fig. 2 there is shown a receiver which is suitable for receiving the wave emitted by the transmitter illustratedin Fig. 1. This receiver includes an antenna 60, a tuner and amplifier 6l, an amplifier and amplitude modulation detector 62, a brightness injector 63 and a cathode ray tube 6I for reproducing television images by synthesizing the image field under control of the video signals and the synchronizing pulses. These parts oi the receiver are well known in construction and operation and they receive amplitude modulated signals which are tuned, amplified, detected, and reproduced as pictures in the usual way.

Additional apparatus in the receiver is provided to be responsive to a carrier wave when it is shifted to either the horizontal or the vertical frequency band to transmit the respective synchronizing impulses. This synchronizing apparatus is energized from the output of the tuner and amplifier 6| and includes an asymmetrical acceptance filter 65. a carrier rejection circuit 66, la bottom clipper 61, a first limiter device 68, and a second limiter device 69 and suitable circuits for deriving respectively the horizontal and vertical synchronizing signals and the brightness measurement and audio signal. The asymmetrical acceptance filter 65, carrier wave rejection circuit 66, and bottom clipper 61 are disclosed and claimed in my previously mentioned copending application for Letters Patent S. N. 331,349, for Image transmission system. In the present application these components perform functions have more than-*half the intensity of the carrier. The bottom clipper 61 therefore acts to prevent transmission of 'any wave below a certain intensity and to allow transmission only of those portions of the wave above a predetermined intensity. The bottom clipper 61 thus constitutes an amplitude separator for segregating the line and frame synchronizing pulses from the camera or video signals'.

The carrier rejection circuit 66 is designed to prevent transmission of the carrier wave at its normal frequency to the bottom clipper 61. It acts to minimize cross talk, which might otherwise occur in the bottom clipper 61, and it also lessens the amount of frequency discrimination which it is necessary to provide in tuned circuits following the bottom clipper 61.

The asymmetrical-acceptance filter 65 is provided, as described in the above mentioned application, to guard against the possibility that side bands on opposite sides of the carrier wave might combine in intensity so as to be able to pass the bottom clipper 61. y

The grid bias for the two limiter devices 68 and 69 is so adjusted that no portion of any wave Y above a certain intensity is transmitted to the respective output circuits. This limiter action is identical with that usually provided in frequency modulation receivers. n A

The output circuit of the first limiter device 68 includes, in series, the input 14' to a band pass filter 14 and the input 15' to a frequency modulation detector circuit '15. 'I'he band pass filter circuit 14 may be of any desired form and is so adjusted as to pass every wave lying within the band assigned for transmission of the vertical synchronizing signal. That is, it is so adjusted as to accept any Wave produced by the vertical band generator 20 ol' Fig. 1. A detector 161s connected to the output of thebandfilter 14 to rectify any wave passing therethrough and to apply it as a pulse to a vertical deflection generator 11 which is connected in any convenient way to control the vertical deflection of the cathode ray in the receiving picture tube 64. Y

The frequency modulation detector circuit 'l5 is of any desired form and is adjusted to transmit and demodulate any frequency modulated wave lying within the same frequency band to which ,the band filter 'I4 is responsive and which is produced by the vertical band generator 20. The operation of such frequency modulation detector circuits is Well known. The circuit 15 produces a voltage across its output resistor 18, the magnitude of such voltages being dependent upon the frequency of the wave from the limiter device 68. which Wave was produced by the vertical band generator 20. The voltage produced across the output resistor 18 is a measure of the averagev times.

The output circuit of the second limiter device 69 passes serially through a second band pass filter circuit 19 and through a second frequency modulation detector circuit 80. The filter 19 is designed to transmit any wave within the band of frequencies produced bythe horizontal band generator I9 shown in Fig. 1. That is, it is so adjusted as to transmit the carrier wave whenever it lies in `the frequency band assigned to transmission-of a horizontal .synchronizing impulse. The output of the lter 19l is impressed upon'a detector 8l similar .to the detector 16 and which similarly produces a rectified impulse which corresponds tol-a horizontal synchronizing impulse produced in the transmitter. The impulse produced by the detector. 8l is impressed` upon a horizontal deection generator 82, which operates in well known fashion to control the horizontal deflection of the cathode ray in the receiving picture tube 64. y

The frequency modulation detectorcircuit 80 is similar to the detector circuit 15, except that it transmits and demodulates any wave whose fre'- to provide such a frequency shift of the carrier wave, which represents at least a part of one Yvertical synchronizing impulse,'at.a`

4time after a horizontal ,frequency shiftof the carrier wave equal toa quarter of, thetime be- 4 tween two consecutive .horizontalv frequency. shifts.

quency lies in the band which is passed by the filter 19 and which is generated by the horizontal band generator I9.'l The frequency modulation detector circuit Btlv includes an output resistor 83, across .which a voltage is produced whose magnitude is dependent upon the frequency-of the carrier wave produced by the horizontal band generator I9. Thus, audio signals, which have at the transmitter produced frequency modula-y tion of the carrier wave within the horizontal frequency band, appear across the output resistor 83. This audio signal is amplified through an audio amplifier 85 and is converted into a sound wave by a speaker 86. The image produced by the picture tube 6d may therefore be viewed at the same time as the sound produced by the speaker 8G is heard.

It. will thus be seen that the system described including the transmitter and receiver accomplishes transmission of a television signal including a video signal, synchronizing impulses, and image brightness control along with an accompanying sound signal, all of the transmitted waves lying entirely within the side band range produced by amplitude modulation of the carrier by-the video signal' alone. Since it is normally necessary to shift the carrier frequency, in frequency modulating a wave by a sound signal, only about five times the frequency of the sound Signal.

the horizontal frequency band assigned for operae tion of the horizontalband generator i9 need be only about 50 kilocycles wide. With the present system having a side band frequency range of about 4 megacycles, about 40 such horizontal frequency bands are available in the frequency range between 2 and 4 megacycles, which range may most conveniently be utilized. Furthermore, it is feasible to transmit a considerable number of low frequency messages, such as teletype, facsimile, or the like, by means of the vertical synchronizing channel,` as will be pointed out hereinafter. l

It is desirable that the transmitter illustrated by Fig. 1 be adjusted to maintain transmission of the horizontal synchronizing impulses at all It is therefore convenient to adjust the horizontal and vertical deflection generator l5 to transmit vertical synchronizing signals during appropriate periods interspersed between horizontal synchronizing impulses. That is, when it is desired to transmita vertical synchronizing There may actually be about 14 to 24 ,such shifts vof the carrier wave from its normal frequency'. to

the vertical frequency band, which train of shifts collectively represents one vertical synchronizing impulse. One single set or. train of these Ashifts is transmitted to produce onevertica1 synchro-v nizing impulse, while consecutive shifts ofwthe carrier wave into the horizontal frequency band are maintained. 'g Y i During the vtime when the carrier wave' is within the vertical frequency band, ybetween any two horizontal frequency shifts of the carrier, vits frequency may be modulated within the vertical frequencyband by an individual low frequency message, such as brightness measure, automatic expansion or compression control for an audio channel, or a codetelegraph message or the like. For example, during the first frequency shift to the vertical frequency band, in any single train of such shifts representing a single verticalfsynchronizing impulse, the frequency of the carrier wave" in the vertical frequency. band may be adjusted to represent a measure of the average image brightness. During the second frequency shift of the carrier in such a train, the frequency ofthe carrier may be adjusted in the vertical frequency band to represent an automatic expansion control voltage, such as may be desired to aid in producing high fidelity transmission of the sound signal accompanying the television image. The third frequency shift of the carrier in the train may be adjusted to represent a character in a code telegraph message transmitted, for example, at the rate of characters per second. That is, transmission may-be at the frequency of the vertical synchronizing impulse. The fourth frequency shift may be adjusted so that the carrier IWave frequency in the vertical frequency band represents a character in a second code l band produced' during any single train of carrier frequency shifts, which represent a single vertical synchronizing impulse.

In Fig. 3, a transmitter for transmitting Waves of such nature is illustrated in which only two main horizontal frequency bands areutilized for the transmission of audio signals and twol successive frequency shifts of the carrier representV one vertical synchronizing impulse and are utilized for the transmission of brightnessv measurement and code telegraph impulses. It is to be understood that the audio signal channels repre- Alternatively, the fourth shift may in a much longer Vtrain of such shifts, corresponding in timeto the vertical synchronizing impulse of long duration commonly used at present. Many parts of the transmitter illustrated in Fig. 3 are identical with those of Fig. 1 and are given like reference characters.

In this transmitter only the equipment for shifting the carrier wave frequency, in order to transmit horizontal and vertical synchronizing impulses, and the apparatus associated' therewith for transmitting messages frequency modulated on'the carrier wave during the carrier frequency shifts, differs from corresponding apparatus in the transmitter illustrated by Fig. 1. Only such equipment is therefore illustrated and described in detail. The balanced modulators 2| and 22 are, as they `were previously, placed respectively in a blocked and in a transmitting condition upon the production of a horizontal synchronizing impulse from the generator l5.

The balanced modulator 22 serves to transmit three shifted portions of the carrier wave from three generators 90, 9| and 92, frequency modulated by threerespective audio signals. All three Waveportions from the generators 90, 9| and 92 lie` at all times in a single main horizontal frequency band which may, as was explained previously, be about 50 kilocycles wide. The shifted carrier wave portion from .the generator 90 is so adjusted in mean'frequency that it lies always in a sub-channel, which may be designated as No. 1, and which occupies only one third of the main horizontal frequency band assigned to the three .generators The generator 9| produces a similar wave, and is so adjusted that the corresponding shifted carrier wave portion lies in av secondl sub-channel No. 2, which occupies a different third of the 50 kilocycle band assigned for this main channel. The generator 92 is adjusted to produce a shifted wave portion in a third sub-channel No. 3, occupying the remaining third of this main horizontal frequency band.

Microphones 93, 94, and 95 are associated respectively with. the generators 90, 9|, and 92 in the same Way as is the microphone 46 in Fig. 1 associated, through the audio amplifier 41 and capacity tube 48, with the horizontal band generator I9. The audio signal fromy the microphone 93 modulates the frequency of the wave produced by the generator 90 within the subchannel No. 1. Correspondingly the audio signals from microphones 94 and 95 modulate the frequencies of the wave produced by generators 9| and 92 only within the respective sub-channels Nos. 2 and 3.

Entirely satisfactory audio signals may be transmitted through such an arrangement, even though such a high degree of noise and atmospheric suppression as may be attained by the apparatus illustrated by Fig. 1 is lnot present. For ordinary telephone communication purposes it is unnecessary to transmit the high frequency components of audio signals above 2000 or 3000 cycles and even in commercial broadcasting very of Fig. 1.

and satisfactory telephone channels are avail-,

Such frequency limits and other exact able. quantities as are given in this specification are exemplary andare not to be taken as delimiting applicants invention. l

Additional shifted carrier wave portions in a second main horizontal frequency band of 50 kilocycles Width may be transmitted from generators 96, 91, and 98 through a balanced modulator 99 to the amplifier 25. Each shifted carrier wave generatedby the generators 96, 91, and 98 is adjusted to remain respectively in subchannels Nos. 4, 5, and 6. The carrier wave portion within each of thesesub-channels is modulated in frequency by an audiosignal respectively from microphones |00, |0|, and |02. The balanced modulator 99 operates identically with the balanced modulator 22 and is placed in condition for transmission of shifted carrier Wave'portions in response to the same horizontal synchronizing impulse, which is reversed in phase by the tube 34.

The generators 90, 9|, 92, 96, 91, 98.and their associated audio signal sources, along with the balanced modulators 22 and 99, may be multiplied many times in number so that additional main horizontal channels are available, each including if desired one or several sub-channels. If only two main channels, as shown, are utilized, it may be of advantage to assign to each channel a frequencygband of greater width in order to obtain a higher degree of noise suppression.

The balanced modulators 23 and 24, which are identical with those shown in Fig. l, are placed respectively in blocked and transmitting condition by a vertical synchronizing impulse from the generator I5, as was the case with the transmitter However, the vertical synchronizing impulses are applied to the balanced modulators Y 23 and 24 through a channel selector switch |03,

to be described in detail hereafter, which operates to apply only the first vertical synchronizing impulse, in a train of such impulses collectively representing a vertical synchronizing signal, to the balanced modulators 23 and 24, and to apply the second vertical synchronizing impulse in such a train to avpairof additional balanced modulators |04 and |05.

It is assumed with the circuits illustrated that only three successive shifts of the frequency of the carrier wave into the vertical synchronizing band are produced in a single train of such shifts. which corresponds to one complete vertical synchronizing signal. Usually many more individual shifts of the carrier frequency into the vertical synchronizing frequency band are necessary, or at least desirable, in one vertical synchronizing signal, and in such case additional pairs of balanced modulators such as modulators 23, 24, and |04, |05 may be provided, corresponding to additional low frequency information channels.

There is a slight diierence between the transmitters of Figs. 1 and 3 in connections through the balanced modulators 2h22, 23, and 24 to the amplifier 25; in that the carrier Wave transmitted through the balanced modulator 22 is transmitted directly to theamplier 25, rather than first through the balanced modulator 23. If a system be used, as explained above. in which the carrier wave is shifted in frequency to the vertical frequency band during different periods from those when it is shifted to the horizontal band or bands, it is unnecessary to transmit the output of the balanced modulator 22 through the modulator 23.. In such a system the balanced-modulator 22 is never conditioned for transmission of waves, when the balanced modulator 23 is in blocked condition.

Only one vertical frequency band need be assigned for transmission of the several low frequency message channel carrier wave portions respectively through the balanced modulators |04, |05, and through other similar modulations,

if they are used. This is true because the vertical frequency band is occupied byshifted carrier wave portions in the same frequency band but passing through the balanced modulators in turn and thus modulated in frequency successively by diiferent message characters.

Only a rather small frequency band need be assigned for transmission of the vertical synchronizing signals, since the low frequency information channels transmitted through the vertical frequency band have a satisfactory degree of atmospheric suppression with only a small sweep frequency of the shifted carrier Wave portions. This small channel for the vertical synchronizing impulses may be allocated at either extreme of the horizontal frequency bands, which carry horifrequency message.

Vtical frequency band, during transmission of the nrst vertical synchronizing impulse in a train of such impulses. This generator produces a wave f whose frequency is' modulated by a second low Three addmenai generators me, nu, and m are provided, which generate shifted carrier wave portions respectively within the same' three parts zontal synchronizing impulses and sound signals,

or the like.

Three individual generators |06, |01, and |08 are adjusted to produce individual, shifted carrier Wave portions within the vertical frequency band, and are connected to transmit these carrier waves through the balanced modulator 24 to the amplifier 25. Each of these generators is adjusted to operate in an individual portion of the vertical frequency band, in a manner similar y to the three generators 90, 9|, and 02 Which operate in individual portions of their corresponding horizontal frequency band. For example,A the generator |00 may be adjusted so that the shifted carrier wave portion which it produces lies a1- Ways Within a first part of the frequency band assigned for transmission of the vertical Vsynchronizing impulse.

The first part of this Vertical frequency band, during transmission of the first synchronizing impulse in a train of such impulses, may be conveniently termed the brightness measurement sub-channel. As illustrated, the wave generated by the generator |00 is modulated in frequency, within this brightness measurement sub-channel, in accordance with a voltage produced by the photocell 09 and amplified through the amplier 50.

The generator |01 may be adjusted to produce a shifted carrier wave portion lying, in a similar 'manner, within a second part of the frequency quency modulation is, for example, a signal such Y as is utilized in transmitting messages by commercial teletype machines. Another low freof the Vertical frequency band as the generators |06, |01, and |08, but'during transmission of the second vertical synchronizlng'impulse in a train of suchv impulses. There is no interference between the waves produced by these two sets of generators, since their output signal-s are transmitted to the amplifier 25 sequentially., and never at the same time. The channel selector switch I |03, acting through the balanced modulators 24k.

ciatd with apparatus for modulating the-frequency of the wave portion produced by it within its respective portion of the vertical frequency band. This frequency modulation is in accordance with corresponding code telegraph messages or the like. Since the Waves produced-by vthe two sets of generators |06, |01., |08', an-d |09, ||0, do not mutually interfere, the frequency modulated Waves produced by the generators |09, I0, may be respectively designated 'as lying in sub-channels Nos. 3, 4, and 5.

Additional sub-channelssimil-ar to those Just described may be made available in .the system by a change in the channel selector switch |03 to select more channels periodically and successively and by the addition, for each additional set of one or more sub-channels, of another pair of balanced modulators similar to modulators |04 and |05 and their associated generators |09, ||0, and

It may be noted that the generators which produce carrier wave portions frequency modulated by vaudio signals, such as generators 90, 9|, 92. 00, 0l, and 90, all operate simultaneously but in different and individual portions of the total available frequency range, which preferably corresponds roughly to the side band range produced by amplitude modulation of the carrier wave by the video signal. If, as shown, six such generators are utilized, it is preferred that the shifted carrier wave portion produced by each is, when radiated from the antenna l0, of `about one sixth the intensity of the unshifted carrier wave which originates in the master oscillator I3 and is impressed on the antenna I0.

For a similar reason, each of the generators |06, |01, and 08, which operate simultaneously, and also each of the generators |00, ||0, and l l, which also operate simultaneously -and separately Ifrom other generators, should .produce radiation at the antenna l0 of their respective shifted carrier frequencies, which for each wave portion is about one third of the intensity of the normal frequency carrier wave controlled by the master oscillator i3.

By thus providing that theme'ans for shifting the frequency of the carrier wave shall maintain the total intensity of all radiation from the antenna I4 substantially constant and maximum during pedestal periods, the amplifier 25 and the amplitude modulator |-2 are operated during the transmission of horizontal and vertical pedestals and 'synchronizing signals at full load and at maximum carrier intensity. Therefore, emcient transmission of a frequency modulated wave is achieved, and at the receiver the maximum intensity of the received wave is available to maint-ain horizontal and vertical synchronization, as Well as to reproduce any other intelligence, such as audio signals, applied to the carrier wave during pedestal periods, when horizontal and vertical synchronization is effected.

Even though the pedestals, during which a shift of carrier frequency effects transmission of synchronizing impulses, exist during only about per cent of the total time of transmission, the audio signals reprod-uced at the receiver are satisfactory because carrier intensity is maintained at its maximum value during transmission of such signals, as it is in convention-al systems of transmission by frequency modulation. It is known that conventional frequency modulation transmitters may be low powered .to produce the same received signal strength as a higher powered amplitude modulated transmitter whose side-band intensity is only a small fraction of its maximum carrier intensity. e

It is Ia great advantage in the use of such a transmitter as is described herein that, not only the audio' sign-al accompanying the television image is transmitted Without the necessity for any extra carrier wave, but that a large number of additional audio signals as well as low frequency signals, are also transmitted. All these signals are transmitted on the same carrier wave as .the television signal, and in a frequency range preferably not greater than that occupied by the side bands arising Ifrom amplitude modulation of the carrier wave by the video signal. It is, of course, highly desirable to dispense with the extra carrier normally used to transmit sound accompaniment for a television picture, not only to save the space which it takes up in the available frequency range, but to effect very substantial simplification of the receiver and savings in the cost of building and operating an extra transmitter. i

More important yet, in a transmitter rsuch as accompanying sound, and may also transmit 8 or 10 commercial broadcast sound signals. On the remaining audio channels may be transmitted service telephone messages or the like and, on the low frequency message channels, signals such as teletype transmissions. A receiver may be installed in a home, which receiver is capable yof receiving and reproducing the television image with its accompanying sound, or alternatively is capable of reproducing any of the eight for ten commercial broadcast sound signals.

oi' these signals to a nearby relay transmitter. This relay transmitter may be of the same nature as that illustratedv in Fig. 3.

A receiver suitable for receiving the carrier waveetransmitted by the apparatus illustrated by Fig. 3, and for reproducing all the signals impressed thereon, is illustrated in Fig; 4. Many of the components of this receiver are identical with those described in connection with the rehave a single frequency, but is in effect split up into portions which are individually shifted into a number of frequency bands.

It has` been found that a bottom clipper, such as the clipper 61, when adjusted to transmit only portions of a wave of greater than a predetermined intensity, will transmit portions of several waves of different frequencies, none of whose individual intensities are as great as the predetermined intensity, but the sum of Whose intensities exceeds the predetermined intensity even by a slightI amount. It has been found, further, that the wave portions transmitted by such a bottom clipper are easily distinguishable according to their frequencies.

As a particular example of the operation of bottom clippers 61, let it be assumed that the six generators 98, 9|, 92, 8B, 91, and 98 in the transmitter of Fig. 3 are controlling the radiation o-f a carrier from the antenna I4. The carrier therefore has six component parts, each of a different frequency, and each of about one sixth the total carrier intensity. Let it also be assumed that the bottom clipper 61 is adjusted to reject 'any wave or combined waves, whose intensity is less than nine tenths of the total intensity of the carrier radiated by the antenna H. The output of the bottom clipper 61 under such conditions contains six component parts whose respective frequencies are the same as the several frequencies at which the six generators 80, 8|, 92, 86, 91, and 98 operate. These several frequencies can be readilyseparated by means oi' suitably tuned frequency discriminating circuits.

In the receiver illustrated, which is arranged ators 9B, 81, and 98. Filter |22 is designed to At some distance from such a transmitter there may be placed a commercially operated receiver which may be designed to receive the signals described above and to supply all or part transmit Waves from any of the generators |06 through controlling the wave portions AWithin the vertical frequency band, assigned to transmission of vertical synchronizing impulses.

These three lters |20, 12|, and |22 are'respectively energized from the output of the bottom clipper 61 through limiter devices |23, |24, and |25, which are so adjusted as totransmit to their respective filter a fixed portion of the output of the bottom clipper 61, except when the Wave received by the antennaill decreases to a value near or below the threshold of the bottom clipper 61. The function of apparatus such as 9|, and 92 of Fig. 3. Apparatus, which will be explained in some detail, is connected to the output ofthe filter 20 for initiating a horizontal deflection of the cathode ray in the receiving picture tube 64, whenever energy appears in the corresponding frequency band. Additional audio reproducing apparatus is connected to the output of the filter |20 respectively to convert the frequency variations of the three waves from the generators 90, 9|, and 92 in the transmitter of Fig. 3 into three corresponding audio signals.

The audio reproducing apparatus comprises three frequency discriminator circuits |26, |21, and |26 of anyv suitable form which are energized lthrough a buffer amplifier |29 from the filter |20.

The frequency discriminator circuits |26, |21, and |28 are respectively connected throughaudio amplifiers |30, |3|, and |32 to speakers |33, |34, and |35. The speaker |33 reproduces audio signais which were originally converted into electrical impulses through the microphone 93 of Fig. 3. Correspondingly the speakers |34 and |35 respectively reproduce audio signals from microphones 94 and 95.

Although it may be provided that horizontal deflection of the cathode ray in the tube 64 is initiated in response to any wave lying within a single main horizontal frequency band, it is preferred to employ apparatus to initiate such horizontal deflection only when wave energy exists simultaneously in at least two different main hiorizontal frequency bands whose frequencies are preferably widely separated. By provision of two separate main horizontal frequency bands w for interlocked synchronization, the possibility that video signals or atmosphericV disturbances, having an appropriate' frequency characteristic, may produce false synchronization, is substantially eliminated.V y

Such interlocked synchronization is provided as follows. The band pass filter 2|, designed to transmit only waves inthe same frequency band as waves generated by the generators 96, 91, and 98 of Fig. 3, is connected through a buffer amplifier |36 to a detector diode |31. This diode has an output circuit including a load resistor |39. Waves are similarly transmitted through the band'pass filter |20 and through the buffer amplifier |29 to be rectied by a detector diode |39 which has an output circuit including a load resistor |40. The load resistors |38 and 40 are by the horizontal and vertical Adeflectionand` synchronizing signal generator I5 in Fig. 3, r'

proper synchronization is maintained between generators I5 and 82. However, if for somecau'sey. a voltage appears across the resistor |4 0lrwhich lhas no counterpart in the voltage from; the:

generator I5, false synchronization maybegef# fected. The chances are great vthat suclriVex-Sk Y, traneous voltages cannot ever appear sin'iu'ltaefV` neously uponthe resistors |38 and |'40."11||Ieansr.- I is therefore providedA to prevent synchronization? 'of the generator 82 through the voltagewaye' appearing across the resistor |40, except whe an identical Voltage Wave appears across ithe vvre, sistor |38. .Y

nofcorresponding voltage appears on the resistorV las. when the diode |43 is conducting, sumcient I. 'Y current passes through the resistor |42 so thatr I' the voltage whichexistson the resistor |40 and not on the resistor |38 Vis not repeated through the buffer amplifier|4| to the generator 82.

The horizont-a1 synchronizing circuits in the reiceiver therefore act to maintain horizontal syn-A chronization only Ywhen'energy simultaneously appears in atA least. two individual main horizontal frequency bands. It is tobe understood thatthe circuit illustrated for performing this function is exemplary 'and thatother circuitsV within the scope' of the invention may be ar-l ranged to perform the same function.

The band pass lter |2|, in addition to being connected through the diode |31 to impress a` voltage-across the resistor |38, also energizes Y three demodulatingicircuits |44, |45, and |46, which are arranged to demodulate the frequency modulated wave passing through the' filter |2I. These three demodulating circuits |44, |45, and |46 correspond in` their own main horizontal' frequency band to the de'modulating circuits |26,

` |21, and |28 in theirrespective horizontal freconnected'end to end with such polarity that .f

mitted simultaneously through the lters |20 and 2|, substantially no voltage exists across their free ends. Suitable apparatus responsive to the voltage across either resistor, but only responsive when no voltage appears across their free ends, is arranged to initiate operation of the horizontal deflection generator'BZ. y

Such apparatus for initiating synchronization of th'e generator 82 comprises a buffer amplifier |4| which is connected to be energized from the voltage across the resistor |40 through a resistor |42 and is arranged to amplify that voltage and apply it to the horizontal deflection generator 82 to initiate production of a horizontal deflection wave for the picture tube 64. So long as the voltage across the resistor |40 corresponds tothe horizontal deiiection impulses produced quency band. Each of the circuits |44, |45, and

|46 is adjusted respectively to respond to a wave from a corresponding one of the generators 96, V 91, and 99 of Fig. 3and they are provided with audio signal is reproduced by its associated.'

speaker. Y

If the generators 91 and '98 of Fig.V 3 be omitted and the demodulating circuits |45 and |46 of frequency components of the audio signal. 'Like-V wise, the demodulating circuit |44 `should be de signed to demodulatea frequency modulated. wave occupying the corresponding entire mainhorizontal frequency band.

It is to be understood that'many more than Y two main horizontal frequency bands may -be provided within the side band range produced by I `frequency apparatus |54 and Y| 55.

amplitude modulation of the carrier wave by the video signal, as has been pointed out above, so that accordingly additional band pass filters similar to lters |20 and |2| withtheir associated apparatus may be provided, one for each of the main horizontal frequency bands.

duces a pulse simultaneously with the occurrence The output of the band pass lter 122, which comprises all waves in the vertical frequency band, is transmitted serially through a buffer amplifier |41, through three frequency demodulating circuits |48, |49, and |50, and through the switching device |62. The wave from the amplifier |41 also passes to a diode |5| to be rectified to form a vertical synchronizing signal, which is applied to the vertical deflection generator 11 to maintain its synchronization with the vertical deflection generator i in the transmitter of Fig. 3.

The three frequency demodulating circuits |48, |49, and |50 are respectively adjusted to reproduce signals which are frequency modulated upon carrier waves within the first, second, and third portions of the vertical frequency band, which three Waves are respectively controlled by the generators |06, |01, and |08, in Fig. 3. The frequency demodulating circuit |48 includes a load resistor |52 across which a voltage is produced, which is a measure of the average picture brightness as viewed by the photocell 49 of Fig. 3.

The brightness measurement voltage across the resistor |52 is transmitted through an amplier |53 to the brightness injector 63, where it performs a function explained in connection with the receiver of Fig. 2. Such a low frequency control circuit may similarly be used to control volurne compression or expansion or the like in any of the circuits associated with the speakers |33, |34, |35, etc., or for other similar purposes. The frequency demodulating circuits |49 and |50 reproduce low frequency pulses, which control low v Such apparatus may be,.as explained above, printing teletype machines or facsimile receivers.

The three frequency demodulating circuits |48, |49, and |50 are arranged to respond only to the first pulse of carrier Wave energy, or more accu! rately, only to the first shift of carrier wave frequency, within the vertical frequency band in a single train of such pulses o'r shifts representing a vertical synchronizing signal. Means are provided to prevent the energy of later pulses in a single train from affecting these circuits, and for applying these later arriving pulses to other successive circuits. In the apparatus illustrated only two successive pulses of energy in the vertical frequency band have been utilized, so that a shift from the circuits |48, |49, and |50 t0 only one other set of circuits is necessary during each train of pulses. If, however, as is usually desirable, there are a large number of successive pulses in each train of pulses forming a vertical pedestal, the apparatus illustrated may be duplicated to respond to additional pulses and to provide additional sub-channels in the vertical frequency band.

The apparatus for deenergizing the circuits |48, |49, and |50 after the rst pulse in each vertical pedestal comprises a short circuiting device |-56 connected across the circuits to by-pass energy therearound. A control bias for the device |56 is provided which maintains it in normally nonconductive condition. A pulse generator |51 is provided which is energized by the initial pulse in a vertical pedestal applied to the vertical deflection generator 11 so that it proof the second pulse of' energy in each vertical pedestal. This pulse produced by the generator |51 is transmitted through a transformer |50 to control the shortA circuiting device |56 so that it bypasses current around the frequency demodulating circuits |48, |49, and |50.

Three additional telegraph receivers |59, |60, and |6| are provided, each of which is similar to the telegraph receiver including the frequency demodulating circuit |49 and the low frequency` apparatus |54. These receivers are connected serially with the frequency discriminating circuits l|48, |49, and |50 so as to receive' energy from the filter |22. Current is normally bypassed around them by the switching device |62 whose control bia-s is normally such that it remains in a conducting condition. The pulse from the pulse generator |51, which makes the 4device |56 conducting, is applied'to the switching device |62 through a transformer |63 in such polarity as vto render it non-conducting. 'Ihe second pulse in each train which appears through the band pass filter |22 therefore is transmitted through the buffer amplifier |41 and through the short leireuiting device lss, to the receivers |59, lso,

and 6| which then operate to demodulate and reproduce their respective low frequency characters.

The particular switching apparatus which is i1- lustrated as controlling the energization of the telegraph receivers and the brightness measurement receiver from successive pulses in each vertical pedestal is a relatively simple mechanism when only two successive pulses are utilized. However, if about 15 to 25 pulses in each pedestal be employed to transmit separate messages, the switching apparatus becomes bulky and it may be desirable to utilize some other form of switching means, such. for example, as the channel selector switch |03 illustrated in connection with the transmitter of Fig. 3.

In Fig. 5 this channel selector switch |03 is schematically illustrated in some detail. This switch comprises a cathode ray tube |10 which has a defiecting electrode |1| arranged to sweep the cathode ray successively over three separate anodes |12, |13, and |14 as its potential becomes less positive. To keep the defiecting electrode |1| at a suitable positive potential for maintaining the cathode ray upon the anode |12, connection is made through a resistor |15 to a source |16 of operating potential. Apparatus is provided to reduce the potential of the electrode |1| in steps in response to successive pulses in a single train representing a vertical pedestal or synchronizing signal.

This apparatus comprises a condenser |11 which is charged through a diode |18 and a variable resistor |19 by verticall synchronizing pulses which originated at the generator |5 to which the diode |18 may be coupled through a coupling condenser |80. The condenser |11, which before the beginning of each trainl of pulses is discharged, is charged in successive increments as each pulse from the generator |5 passes through e the diode |16.

A direct current amplifier |8| is arranged to amplify the voltage across the condenser |11, and to reduce the voltage of the defiecting electrode |1| as the charge is stored in condenser |11 and builds up in increments. The potential of the defiecting electrode |1| becomes less positive in corresponding increments, each of which, by adjusting resistor |19, is made to be of such magnitude that the cathode ray moves in steps from the anode |12 to. the anode |13, and then to the anode |14, and'then to additional anodes if such be provided. The number of anodes pro vided corresponds to' the `number of diderent main vertical channelsj to be transmitted, plus one. It 'also corresponds to the number of pulses produced by the vertical synchronizing generator I in each vertical pedestal. f

The anodes-l12, |13, and |14`fare maintained atpositive potential byconnections respectively through load Vresistors |82, |83, and |84. The

. anodes |12 and |13 are connected vrespectively to two exterior circuits.which, as illustrated in Fig.

3, lead to the balanced modulators 23 and 24, and to balanced-nfodulators:l04 and |85, to control their successiveY operatioxr.

. The anode |14 is notconnected to anyV exterior circuit, but is utilized to remove thechargefrom thecondenser; |11 at the'end of each 'train-of pulses from the generator I5, so as to return the cathode ray to the anode-n i12an d to condition ferent modifications may be made both in the circuit arrangement and instrumentalitiesemployed, and I aim Vin the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new Vand desire to secure by ,Y Letters Patent of the United States is:

Y of which wave is determined by a second signal,

the apparatus as a whole to be ready for a later train of pulses in a succeedingver'tical; pedestal. To accomplish this the-anode |11! is connected through a resistor |85 to a direct current amplifier |86, which in yturn is connected so that anY amplified impulse from anode I14'operates-a short circuiting device |81, arranged in shunt to the condenser |11. Condensers |88 and |89 are connected respectively from the two ends'of the resistor |85 to ground.

'Ihese two condensers |88 and |89 are soV proportioned relative to the magnitude of the resistors |84 and |85that, when the cathoderay lmpinges on the anode |14 and its positive potential accordingly is-reduced,l the grid oftheamplifier |86 remains long enough ata sufficiently reduced positive potential as to allow its anode to rise in potential from a highly negative, or cut-off, value for a certain time,

ode of the amplifier |88 rises in potential,l theV short circuiting device |81 becomes Conducting and, due to the resistors |84 and |85 andthe condensers |88 and |88,` remains in lconducting condition long enough to discharge the condenser |11 substantially completely. I

As suggested in connection with Figs. 3 and 4, the generator I5 maybe adjusted to produce additional pulses in each train forming a vertical pedestal, thus allowing additional low frequency messages to be transmitted, if the balanced modulators 23, 2li, I 04, and |85 and other equipment be duplicated. It is then only necessary, in the channel selector switchl03 illustrated in Fig. 5, to provide additional anodes similar Yto the anodes |12 and |13 with their accompanying cirthat in actual commercial practice, as such appa- Y ratus as I have described is further developed,V

necessary, and in fact'it is even undesirable, tov

include' all vthe apparatus illustrated by Fig. 4.

Conversely, in a receiver adapted for Vuse in relaying, many of the circuits designed for utilization in home receivers may be undesirable.

While I have shown particular embodiments of my invention, it will, of course, be understood and concurrently modulating the frequency of said carrier wave within said band in response to a third signal.

2.A In a television system utilizing an assigned communication channel Within a predetermined frequency bandthe method comprising transmitting a-carrier wave of predetermined frequency modulated in amplitude in response to a video V signal during separate recurrent periods, the frequencies of said carrier wave and the side bands resulting from amplitude 'modulation thereof lying Within said predetermined frequency band, transmitting a carrier wave whose frequency dif- .fers from said predetermined frequency and lies within said `band during periods intervening between said recurrent periods, one characteristic of which wave is determined by a. second signal, and, concurrently modulating the frequency of said carrier wave within said band in response to .a third signal only during said intervening periods.

3.` Ina television system the method comprisingtransmitting a carrier wave'modulated in amplitude in response to a video signal during separate regularly recurrent periods, the frequencies of said carrier wave and the side bands resulting-from amplitude modulation thereof lying Within a predetermined frequency band,

, transmitting a carrier wave whose frequency differs from the frequency of said first carrier wave and lies within said band during all periods intervening between Asaid recurrent periods and concurrently modulating a characteristic of said carrier Wave of different frequency in response to a second signal only during said intervening periods, said periodsrecurring at a frequency which is higher than the frequencyof said second signal. f y

v4. In a carrier television system, the method including transmitting-a carrier-wave only during separate recurrent periods, said carrier wave being modulated in response to a video signal, transmitting a. carrier wave whose frequency dif fers from the frequencyof said first carrierv wave only-during periods intervening between `said recurrent periods, andV modulating a characteristic of ksaid second carrier 'wave during said intervening periods.

5. In a carrier television system,' the methodV said carrier wave and the side bands resulting that I do not wish to be limited thereto, since diffrom amplitude modulation thereof lying within a predetermined frequency band, transmitting a carrier wave whose frequency differs from the frequenty of said first wave and lies within said band during periods intervening between said recurrent periods, and concurrently modulating the frequency of said second carrier wave in response to a second signal during said intervening periods,

6. In combination in a signalling system, a rst signal source, means responsive thereto for modulating the amplitude of a carrier wave during recurrent periods, whereby a side band is produced having frequencies extending over a predetermined frequency range, a second signal source, means to modulate the frequency of a carrier wave during periods alternating with said recurrent periods over a frequency band within said predetermined frequency range in accordance with signals from said second signal source, l

a third signal source, and means to modulate the frequency of a carrier wave during said alternating periods over a second different frequency band within said predetermined frequency range in accordance with signals from said third signal source said periods recurring at a frequency which is higher than the frequency of signals from at least one of said sources.

7. In combination in a signaling system, a first signal source, means responsive thereto for modulating a characteristic of a'carrier wave, whereby a side band is produced having frequencies extending over a predetermined frequency range, means to make said characteristic of said carrier wave constant during recurrent periods, means to shift the frequency of said carrier wave duri-ng said periods to a frequency within a second frequency range in the range of said side band, a second signal source, means to modulate the frequency of said carrier Wave over said second frequency range in accordance with signals from said second signal source, and means for producing distinguishable responses corresponding respectively to the modulation of said characteristic, the frequency shift and the frequency modulation of said carrier waves, whereby the transmission of signals from said sources utilizes a minimum frequency range.

8. In combination in a. television signaling system, a Video signal source, means` responsive thereto for modulating a characteristic of a carrier wave, whereby a side band is produced having frequencies extending over a predetermined frequency range, means to transmit said carrier wave without modulation during recurrent periods, a synchronizing signal source, means responsive thereto to shift the frequency of said carrier wave during said periods to a frequency within a second frequency range in the range of said side band, a third signal source, means to modulate the frequency of-.said carrier wave during said periods over said second frequency range in accordance with signals from said third signal source, and means for reproducing the signals from said sources in response respectively to the modulation of said characteristic, the frequency shift, and the frequency modulationof said carrier wave, whereby the transmission of said signals utilizes a minimum frequency range.

9. In combination i-n a signalling system, a carrier wave source, a first signal source, means responsive thereto to modulate a characteristic of said carrier wave, whereby a side band is produced having frequencies extending over a predetermined frequency range, means to transmit said carrier wave without modulation of said characteristic during regularly recurrent periods, a second signal source, means to modulate the frequency of said carrier wave during said periods over a frequency range of predetermined width in accordance with signals from said second signal source, said period having a frequency of recurrence higher than the frequency of at least one of the signals from said signal sources, and means to shift the frequency of said carrier wave during said periods to a frequency within the range of said side band such that said frequency range of predetermined width lies entirely within the predetermined frequency range of said side band.

10. In combination in a television signalling system, a carrier wave source, a video signal source, means responsive thereto to modulate the amplitude of said carrier wave, whereby a side band is produced having frequencies extending over a predetermined frequency range, means to increase the amplitude of said carrier wave to a constant value during regularly recurrent periods, an audio signal source, means to modulate the frequency of said carrier wave during said periods over a frequency range of predetermined width in accordance with signals from said audio signal source, said periods having a frequency of recurrence higher than the frequency of signals from said audio signal source, and means to shift the frequency of said carrier wave during said periods to a frequency within the range of said side band such that said frequency range of predetermined width lies entirely within the predetermined frequency range of said side band.

11. In a television signalling system, a carrier Wave source, a video signal source, means responsive thereto to modulate the amplitude of said carrier wave, whereby a side band is produced having frequencies extending over a predetermined frequency range, 4means to increase the amplitude of said carrier wave to a constant maximum value during recurrent periods, a synchronizing signal source, means responsive thereto during said periods to shift the frequency of said carrier wave to a frequency within the range of said side band, an audio signal source, and means to modulate the frequency of said carrier wave during said periods over a range within the range 0f said side band in accordance with signals from said audio signal source.

12. In a signal transmission system, a signal channel, means to transmit through said channel a signal modulated carrier wave during regularly recurrent intervals, and means to transmit through said chan-nel a plurality of signal modulated carrier Waves during intervals alternating with said recurrent intervals, said recurrent intervals being substantially shorter in duration than a cycle of the highest frequency of modulation of said plurality of carrier waves.

13. In a signal transmission system, means to transmit a signal modulated carrier wave during regularly recurrent intervals, and means to transmit a plurality of signal modulated carrier waves during intervals alternating with said recurrent intervals, the frequencies of said plurality of waves bei-ng spaced apart in the modulation band of said first Wave by amounts comparable with the respective modulation bands of said plurality of waves and said recurrent intervals being substantially shorter in duration than a cycle of the highest frequency of modulation of said plurality of waves.

14. In a signal transmission system, means to during regularly recurrent intervals, and means to transmit a plurality of frequency modulated carrier waves during intervals alternating with said recurrent intervals, the frequencies of said plurality of waves being spaced apart in the modulation band of said amplitude modulated wave by amounts comparable with the respective modulation bands of said frequency modulated waves and said recurrent intervals being substantially Vshorter in duration than a cycle of the highest frequency of modulation of said plurality of waves.

. 15. In a television system, a video signal source, means to transmit a carrier wave amplitude modulated with signals from said source during regularly recurrent intervals, means to ,transmit a plurality of carrier waves during intervals alternatins.r with said recurrent intervals, the total intensity of said plurality of waves being substantially equal to the unmodulated intensity of said transmit an amplitude modulated carrier wave rst carrier wave, means to modulate the frequency of each of said plurality of carrier waves, the frequencies of said plurality of waves being spaced apart in the modulation band of said first wave by amounts comparable with the respective modulation bands of said plurality of waves and Ymeans responsive only to portions of said waves above a predetermined intensity less than said unmodulated intensity and greater than the intensity of any one of said plurality of waves for demodulating said plurality of frequency modulated waves.

16. In a television system in which video impulses and synchronizing impulses are produced, means to transmit a carrier wave modulated with said video impulses during regularly recurrent intervals, means responsive to said synchronizing impulses to transmit a plurality of carrier waves during intervals alternating with said recurrent intervals, and means to reproduce said synchronizing impulses from said plurality of carrier waves.

17. In a signal transmission system in which a signal modulated carrier wave is generated only during recurrent intervals and a plurality of signal modulated carrier waves are simultaneously generated only during intervals alternating with said recurrent intervals, the method which includes utilizing only portions of said Waves above a predetermined intensity greater than the intensity of any of said plurality of waves.

18. In a signal transmission system in which an amplitude modulated carrier wave is generated only during recurrent intervals, and a plurality of frequency modulated carrier waves are simultaneously generated only during intervals alternating with said recurrent intervals, the method which includes utilizing only portions of said waves above a predetermined intensity greater than the intensity of one side band of said amplitude modulated carrier wave, whereby transmission of said frequency modulated carrier waves is maintained during the simultaneous transmission 'thereof and transmission of said side band is minimized.

19. In combination in signalling apparatus,

A means for transmitting a plurality of Waves each lying in an individual frequency band, means individually responsive to each of said waves, and means to transmit to said responsive means only portions of said waves above a predetermined intensity less than the total intensity of said Waves, whereby said `responsive means is unresponsive to any wave when the total intensity of said waves is less than said predetermined intensityV and the response of said responsive means is minimized for waves whose total intensity is less than predetermined intensity during the absence of said plurality of waves.

20. In a signalling system, a. carrier wave source producing a carrierwave in a predetermined frequency band, means to produce a succession of frequency shifts of said carrier wave during each of a series of recurrent`periods to a different frequency band, a signal source, and means to modulate the frequency of said carrier Wave during a respective frequency shift in each of said periods in accordance with signals from said signal source.

21. In a television signalling system, aqcarrier wave source, a synchronizing signal source, means responsive to synchronizing signalsfrom said source thereof to produce a succession of frequency shifts of said carrier wave to a frequency different from the initial frequency of said carrier wave in each of a series of recurrent periods, a signal source, and means to modulate the frequency of said carrier wave during a respective frequency shift in each of said periods in accordance with signals from said signal source.

22. In combination in a signal receiver,I means for transmitting a plurality of waves in different frequency bands simultaneously, a plurality of circuits tuned respectively to said frequency bands, and means to transmit saidwavesto said circuits, said last means transmitting portions of said waves when their total intensity is greater than a predetermined amount and'blocking said waves when their total intensity is less than said predetermined amount, whereby the transmission of waves whose intensity is less than said predetermined amount is minimized during the absence of said plurality of waves.

v23. In combination ina signal receiver, means to transmit a plurality of waves in individualfrequency bands, a plurality of circuits respectively tuned to each of said frequency bands, and means to transmit said waves to said circuits, said last means comprising limiting means blocking transmission of portions of said waves above a predetermined intensity, and means transmitting portions of said waves when their total intensity is greater than a second predetermined intensity less than said first intensity, said last means blocking transmission of said waves when their total intensity is less than said second intensity, whereby transmission of waves whose total intensity is less than said second predetermined intensity is minimized during the absence of said plurality of waves.

24. In combination ina television receiver, means for transmitting a carrier wave having a video signal amplitude modulated thereon, said carrier wave being subject to recurrentvshifts in frequency to a predetermined frequency band and being frequency modulated thereover in accordance with an audio signal, an image forming device, means for energizing said image forming device in accordance with the amplitude modulation of said carrier wave, means to synchronize operation of said image forming device with said frequency shifts of'said carrier Wave, and means to reproduce said audio signal in response to the frequency modulation of 'said carrier wave.

25. In combination, in a television system having a transmitter of television images, a receiver therefor, a plurality of devices connected 'With said receiver to be operated from said transmitter, means in said transmitter for transmitting a train of impulses between transmission of each successive pair of images, each of said trains being effective to cause synchronization of image formation by said receiver with image transmission by said transmittenmeans in said receiver to store the impulses of each of said trains, and means responsive to the successive storage of each impulse of each train for initiating the operation of a corresponding one of said devices, said last means being eflective to initiate operation of said devices successively as the impulses of each train are stored by said storage means, whereby each of said devices is caused to operate repeatedly in response to corresponding impulses in the successive trains.

26. In combination, in a television system having a transmitter of television images, a receiver therefor, a plurality of devices connected with saidreceiver to be operated from said transmitter, means in lsaid transmitter for transmitting a train of impulses between transmission of each successive pair of images, each of said trains being effective to cause synchronization of image reproduction by said receiver with image transmission by said transmitter, means in said receiver to store the impulses of each of said trains, means responsive to the successive storage of each impulse of each train for initiating the operation of a corresponding one of said devices, said last means being effective to initiate operation of said devices successively as the impulses of each train are stored by said storage means, and means responsive to termination of each of said trains to restoie said storage means to its condition at the beginning of any train, whereby each of said devices is caused to operate repeatedly in response to corresponding impulses in the successive trains.

27. Apparatus for reproducing images and sound accompaniments from transmitted carrier wave energies of a rst frequency amplitudemodulated by Video signals and interspersed with line synchronizing and frame synchronizing signals of a second and a third frequency respectively, said second frequency being frequency modulated by sound signals, comprising means for receiving the transmitted carriers, means for demodulating the received carriers, means for segregating the video signals from the line synchronizing, frame synchronizing, and audio signals, means for segregating the line synchronizing signals from the frame synchronizing signals, means for limiting the segregated line synchronizing signals, means for frequency-demodulating the limited signals, means for producing sound under the control of the frequency demodulated signals, and means for synthesizing the image field under the control of the segregated video signals and both the line synchronizing and frame synchronizing pulses.

28. Apparatus for reproducing images and sound accompaniments comprising means for producing video signals representative of the image to be reproduced, means for generating carrier oscillations of a predetermined frequency, means for amplitude-modulating the produced carrier oscillations by said video signals, means for generating line synchronizing pulses and frame synchronizing pulses, means for generating -signal energy representative of the sound accompanying the video signals, means for interrupting the video signal modulation of the carrier frequency under the control of the line synchronizing pulses, means for shifting the generated carrier frequencyto a different value during the intervals of interruption of video signal modulation, means for frequency-modulating the shifted frequency carrier by the ,sound signal energy, means for periodically shifting the predetermined frequency to a second different value under the control of the frame synchronizing signals, means for transmitting all of said modulated and frequency shifted carrier frequency oscillations, means for receiving the transmitted carriers, means for demodulating the received carriers, means for segregating the video signals from the line synchronizing, frame synchronizing, and audio signals, means for segregating the line synchronizing signals from the frame synchronizing signals, means for limiting the separated line synchronizing signals, means for frequency-demodulating the limited signals, means for producing sound under the control of the frequency demodulated signals, and means for synthesizing the image field under the control of the segregated video signals and both the line synchronizing and frame synchronizing pulses.

29'. Apparatus for transmitting video, line synchronizirg, frame synchronizing and audio signals from a single transmitter comprising means for generating carrier oscillations of a predetermined frequency, means for producing video signals, means for producing audio signals, means for amplitude-modulating the carrier oscillation by the produced video signals, means for periodically interrupting said modulation, means for shifting said predetermined frequency to a different value during the intervals of interruption of modulation, means for frequency-modulating the shifted carrier by said audio signals, means for periodically shifting the predetermined carrier frequency to a second different value, said last named periodicity occurring at a lower rate than said first named periodicity, means for modulating distinctively the intensity of both of said shifted carriers, and means for transmitting all of said modulated carriers.

30. Apparatus for transmitting video, line synchronizing, frame synchronizing and audio signals from a single transmitter comprising means for generating carrier oscillations of a predetermined frequency, means for producing Video signals, means for producing audio signals, means for amplitude modulating the carrier oscillation by the produced video signals, means for periodically interrupting said modulation under the control of line synchronizing signals, means for shifting said predetermined frequency to a different value during the intervals of interruption of modulation, means for frequency modulating the shifted frequency carrier .by said audio signals, means for periodically shifting the predetermined carrier frequency to a second different value under the control of the frame synchronizing signals, and means for transmitting all of said modulated carriers.

31. Apparatusfor transmitting video, line synchronizing, frame synchronizing and audio signals from a single transmitter comprising means for generating carrier oscillations of a predetermined frequency, means for producing video signals, means for producing audio signals, means for amplitude-modulating the carrier oscillation by the produced video signals, means for periodically interrupting said modulation, means for shifting said predetermined frequency to a diierent value during the intervals of interruption of modulation, means for frequency modulating the shifted frequency carrier by said audio signals, means for periodically shifting the predetermined carrier frequency to a second different value, said last-named periodicity occurring at a lower rate than said first named periodicity, and means for transmitting all of said modulated carriers.

32. Apparatus for transmitting signals repre- Y sentative of images and sound accompaniments comprising means for producing video signals representative .of the image to be reproduced, means for generating carrier oscillations of a predetermined frequency, means for modulating the produced carrier oscillations by said video signals, means for generating line synchronizing pulses and frame synchronizing pulses, means for generating signal energy representative of the sound accompanying the Video signals, means for interrupting the video signal modulation of the carrier frequency under the control of the line synchronizing pulses, means for shifting the generated carrier frequency.I to a diierent value during the intervals of interruption of-A video signal modulation, means for frequency-modulating the shifted frequency carrier by the sound signal energy, means for periodically shifting the predetermined frequency to a second diierent value under the control of the frame synchronizing signals. and means for transmitting all of said modulated and 'frequency shifted carrier frequency oscillations.

33. A receiver comprising means to receive transmitted 'Wave energy modulated by the signals from a television camera interspersed with frequency modulated sound signals and shifted carrier signals representative of line and frame synchronized pulses, means to detect the received signals, amplitude separator means to segregate the line and frame synchronizing pulses from the camera signals, lter means to separate the line synchronizing pulses from the frame synchronizing pulses, means to control vertical deflection of a cathode ray. tube by the separated frame synchronizing pulses, means to control thel horizontal deflection of said cathode ray tube by the separated line synchronizing pulses, meansy

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