US2236501A - Television-telephone system - Google Patents

Description

April 1, 1941 A. N. GOLDSMITH- TELEVISION-TELEPHONE SYSTEM Filed Dec. 27, 1937 3 Sheets-Sheet 2 Euwba Wm mm INVENTOR. I ALFRED N. GOLDSMITH 7 I M ATTORNEY.

TESL Patented Apr. 1, 1941 water UNITED STATES PATENT OFFICE TELEVISION-TELEPHONE SYSTEM Alfred N. Goldsmith, New York, N. Y.

Application December 27, 1937, Serial No. 181,853

Claims.

This invention relates to a television system and more particularly to a television system wherein telephone transmission constitutes a part thereof.

In the transmission of television image signals it has been customary to transmit with the television or video signals also audio signals which,

when reproduced with the video signals, provide an'observer with both the sight and sound conditions obtaining at the point of transmission, However, up to the present time it has been practically a universal custom to combine on the carrier frequency upon which the video signals are transmitted all of the various signals or signal components appertaining thereto. Consequently,

' there have been transmitted along with the video The present invention has for its purpose that of providing a system for transmission of both sound and picture signals and, in addition, the provision of a suitable arrangement by which the picture or video signals which are the most difficult to transmit, due to the wide frequency band required, for example, will be grouped about a chosen carrier frequency, known as the video carrier and wherein the sound signals will be grouped about the audio carrier and with these latter signals will be combined all auxiliary television indicia. It has already been established in the art that while the sound transmission channel itself is very narrow, as compared with the video channel, it, nevertheless, must be separated for circuit and other reasons from the television channel by a relatively wide frequency band and this portion of the unused frequency band may be used conveniently and efficiently for the incorporation therein of all auxiliary television indicia.

Briefly, the present invention provides for a combined television-telephone transmission and reception system where there is separate trans-v mission of the television signal (that is, the videofrequency picture modulation alone or, insome instances, with some of its associated auxiliary picture-control signals) and the transmission of the telephone signal in association with anyor all of the remaining picture-controlling signal.

Thus it is apparent that the picture-controlling signals, last referred to, include, for example, the line synchronizing signal and the line return blocking, the frame synchronizing signal and the line return blocking and, in addition, the background control signal. In television systems, as has already been proposed by Carlson in reissue Patent #20,?00 dated April 19, 1938, a fixed separation between the video and audio carrier is maintained and in receiving the transmitted sig- I nals it is customary in turning the receiver to tune to the sound signal whereupon, because of the fixed separation, between the two transmitted carriers, the video signal is also properly tuned. Reference herein is made to the Carlson patent.

above'referred mm such portions thereof as are applicable to an understanding of this dis closure. Accordingly the present invention has for its primary object that of providing a television system With accompanying sound wherein the width of the sound and the picture frequency bands shallbe more nearly equalized and the power requirementsmore evenly distributed, and wherein any interaction between the television or video-modulation signal and the signals corresponding to the other television indicia will be minimized.

Other advantages and objects of this invention are to provide a system for transmitting both picture and sound signalswherein the stability of operation of the television receiver will be improved, as well as to provide a simplification of.

the selective circuits by which the different signals are separated one from the other in the receiver in order to become efiective for the purposes desired.

Still other objects and advantages will become apparent and at once suggest themselves to those skilled in the art by reading the following specification and claims in connection with the accompanylng drawings wherein Figure 1 is a schematic diagram of a combined television and sound transmission system;

Figure 2 is a schematic diagram of a receiver for receiving the transmissions from the transmitterof Fig. 1;

FigureBis a schematic diagram indicating the relative .lband widths of the several different transmitted signals Figure 4 is a diagrammatic representation closely analogous to that of Fig. 3; and

Figures 5 and 6 are expanded schematic diagrams of a portion of Fig. 4 illustrating respectively systems wherein background signal is arranged to modulate a sub-audible carrier which in turn modulates the sound carrier and wherein the background signal modulates the sound carrier directly.

Referring now to the drawings for a further understanding of this invention the complete system has been shown in block diagram for the purpose of simplification since each and every element thereof, except insofar as these elements are combined one with the other and used in combination in a manner which, so far as is known, is new and novel in the art, is known and has been used.

Briefly, a television system, as such is now customarily used in the United States and/or Great Britain comprises a camera or pick-up tube whose output is fed to a video pre-amplifier from which the signal feeds into a video amplifier and a mixer. In the mixer stage shading control produced from the shading adjustment generator, may be introduced. The output from the video amplifier and the mixer is then fed to a video amplifier and black-level control device into which is fed the output of a suitable form of pedestal generator. This combined output is then fed to a video amplifier wherein are incorporated suitable means for introducing the synchronizing signals which are produced from a synchronizing signal generator. The combined output of all of these stages is then fed to a video amplifier and a modulator which is used to modulate a suitable source of radio-frequency carrier energy. In the pick-up or camera end of the system the line and frame scanning generators are caused to control the scanning in substantially the same manner as the control would be effective in the receiver. Likewise upon the camera tube, if it is a storage type of device such as Zworykin has disclosed in many publications,

for example, a suitable blocked-out source of energy is applied to a control electrode to blank during return line periods. All of the blockingout generators, line scanning generators, the frame scanning generator, the pedestal generator and the synchronizing signal generator are interlocked by a suitable form of timing arrangement. In order that the direct current component of the transmitted view may be introduced this component is obtained at the camera tube, for example, by means of a separate pickup light or in connection with film transmission by determining the average density of the film to be scanned just prior to the time when it is. scanned and then introducing this direct current component into the video amplifier and the blacklevel control, above referred to, or by introducing the control directly into the modulator. In connection with film transmission, due to the rapidity with which the film moves, the control of the background is usually introduced automatically by feeding the output from the photoelectric means which covers the average density of a film frame, as disclosed by Beverage, for example, through a D. C. amplifier and obtaining this direct current component from the film to be scanned at a number of frames prior to the ac tual scanning corresponding substantially to the lag period of the D. C. amplifier. In connection with studio transmission, however, the D. C. component may be introduced by virtue of a manual control operated in accordance with the actual view seen on a monitor of the transmitted image, or the control of the background may be in accordance with methods already described by Holmes, for exmaple, in United States Patent 112,109,618, granted. March 1, 1938.

Accordingly, in the system herein shown the system is of general utility and applicable to studio pick-up, outdoor pick-up or motion picture film pick-up of the view of which the image is to be reproduced at points of reception. By the drawings there has been conventionally illustrated a pick-up device or a camera I wherein is incorporated either a storage type cathode ray type scanning tube 2 of the general nature shown by Zworykin or a non-storage type tube of well known character. This tube is for the purpose of providing a light image translation means and to accomplish this objective there is directed up on the mosaic electrode of this tube the view or subject for transmission. The view or light image is focussed upon the light resistive electrode of the scanning tube by a suitable form of optical means 3. Scanning deflection means for causing scanning action within the tube in well known manner, and which may comprise either electromagnetic or electrostatic means, or a combination of both, have been shown only schematically by the coils 5 and I for the purpose of simplicity because the detailed arrangements thereof are well known in the art. Likewise, connections to control the development and blanking during return line periods of the scanning beam which is developed within the neck portion of the tube have been omitted since such controls are well known in the art and, per se, form no part of the present invention. The output energy from the scanning tube 2 is fed from the signal plate 9 of the mosaic electrode I l to a video pre-amplifier l3 and through other suitable amplifiers (not specifically shown herein) wherein the shading adjustments which compensate for the so-called dark spot condition, for example, have been introduced and thence through any desired number of additional video frequency amplifiers (not shown) to the modulator l5 wherein the carrier frequency developed by the oscillator I1 is modulated and the resultant modulated carrier carrying only the video modulation is transmitted from the antenna [9.

Similarly the sound end of the system sound signal energy is picked up in a suitable form of sound pick-up or microphone device 25 and fed through a sound amplifier 21 to a modulator 29 wherein the radio frequency carrier energy developed from the oscillator 31 is modulated and the resultant signal is transmitted from the antenna 33. The oscillators for the sound and the video signal carrier frequencies are spaced apart by fixed frequency separations, as disclosed by the Carlson patent above mentioned, for example, for the purpose of maintaining a substantially constant spectral separation of the desired frequency band width between the audio and the video carriers.

The line synchronizing generator 31 and the frame synchronizing generator 39 which control the deflection of the cathode ray beam of the scanning tube 2 are suitably interlocked with a synchronizing signal generator and the source of A. C. power supply (not shown) where necessary. The output energy developed by each of these generators 31 and 39 is fed respectively to modulate in two oscillator modulator devices 41 and 49 the super-audible frequencies developed from the oscillator portion of each. Similarly, the background control signal source whose output signal indicates the general picture level or brightness which is to be produced at the receiver is suitably amplified and caused to modulate in the oscillator modulator combination 55 the super-audible or sub-audible subcarrier frequency energy developed by the oscillator portion thereof. The output from the several oscillator- modulator devices 41, 49 and 55 wherein the super-audible sub-carrier frequencies are modulated respectively by the line synchronizing signal and the frame synchronizing signal, as well as the super or sub-audible frequency are fed to the combined modulator 29 for the sound, the line synchronizing signal, the frame synchronizing signal and the background control signal. This resultant signal energy is then transmitted from the antenna 33 to accompany the video transmission sent out from th television antenna l9.

Fig. 3 represents schematically the manner in which these several signals distribute themselves in the ether and on Fig. 4 the abscissa separation indicates schematically relative frequency separations between the sevenal carrier frequencies which are each identified by suitable legends.

By Fig, 3 the spectral space required for the transmission of each of the signals has been conventionally shown, although it is to be understood that the lower side bands representing the background control, the frame synchronizing control and the line synchronizing control have been omitted both for the sake of clearness of illustration and for the reason that in practice it is usually unnecessary to transmit both the upper and lower side bands for these controlling signals which are grouped on either side of the audio carrier. As indicated schematically by Fig. 3, the sound signal carrier 62 is also modulated by three separate sub-carriers 63a, 64a and 65a which are, in turn, modulated by the background control signals 4|, the frame synchronizing control signals 42 and the line synchronizing control signals 43. It should be understood, however, that this sound carrier is modulated by the audio signal 4!! as well. In this way, as shown by Fig. 3, the frequency increase is in the direction looking from left to right and while the side bands occupied by the modulation of the video carrier have been shown as extending from a maximum to zero, it is, of course, obvious that zero video frequency need not be transmitted unless desired because of the fact that a separate signal is provided for controlling background, Further, it should be understood that the contour of the side bands shown as grouped around each of the carriers and sub-carriers referred to is purely schematic and in no sense intended to represent the energy distribution but rather must be considered as representative of the frequency band actually or effectively occupied for the transmission, and this is particularly true with respect to the background control where, from what will be pointed out herein in further detail, the band width required for control is relatively narrow compared even with the frame frequency.

It will be seen from an examination of the schematic representation of Fig. 3 that the video carrier is modulated by the video signals so that the side bands resulting extendfor an appreciable distance in the frequency spectrum either side of the carrier. Where desired one of these side bands may be suppressed or both side bands may be simultaneously transmitted. As indicated on Fig. '3 a substantially fixed spectral separation FS is maintained between the audio or telephone carrier and the video or television carrier. About the audio carrier the super or sub-audible sub-carrier frequencies for the line synchronizing signals, the frame synchronizing signals and the background control signals are grouped as conventionally illustrated, and the transmission of all of these are physically associated.

Referring now for a further understanding of the invention to Fig. 4, this figure also illustrates schematically substantially the same arrangement as shown by Fig. 3 with the background signal, however, serving to modulate a subaudible sub-carrier which in turn modulates the sound or telephone carrier, It can be appreciated that it is easily possible and proper to modulate a sub-audible sub-carrier by the background signal since the frequency of such a signal is extremely low, due to the fact that background values of the subject for transmission do not change by appreciable amounts instantaneously or from one moment to another. As shown by Fig. 4 symmetrical side bands for both the frame synchronizing and the line synchronizing signals extend either side of the super-audible sub-carrier frequencies which modulate the sound carrier and it is, of course, Within the scope of this disclosure to wholly or partially eliminate either of these symmetrical side bands, as is the case with video side bands.

The arrangement of Fig. 5 illustrates schematically inexpanded form the general relationship between the sound side bands actually grouped about the sound carrier and the side bands resulting from background modulation (omitting herein any synchronizing control signals) where the background modulation is placed upon a subaudible sub-carrier which in turn modulates the sound carrier.

Fig, 6 illustrates a still further alternative where the background signal modulates the sound carrier directly and sub-audibly. In connection with the modulation which results'from the frame and line synchronizing signals it will, of course, be appreciated that these side bands, in general, extend for the frame synchronizing signals approximately cycles either side 'of the frame synchronizing modulated intermediate frequency carrier and that the side bands, due to the line frequency modulation, extend for a distancevof slightly more than 13 kilocycles either side of the line synchronizing signal modulated intermediate frequency carrier, assuming of course, that the transmission i concerned with a 441 line picture interlaced at 30 repetitions per second with a field frequency of 60 which is the form on which the greater portion of the experimental transmissions in this country have been carried forward.

In the receiver end of the system, as shown by Fig. 2, the signals transmitted upon the two separate audio and video carrier frequencies, and which include, on the one hand, the video signals and, on the other hand, the audio signals and all or substantially all control signals for the video, are received upon any suitable receiving antenna system 6| usually a di-pole, as is known in the art. The received signals (combining video :andgaudio as well as the control signals) are directed through suitable selector circuits E3 and if desirable amplifiers into a common receiver and heterodyne detector circuit to which the frequency output of the local oscillator 61 is supplied. As was disclosed by the above,

mentioned Carlson patent, it is possible, in view of the substantially fixed separation between .the video and the audio carrier frequencies to tune the receiver to the sound signal only in order to receive both the audio and the video signals properly selected, The output from the receiver and detector 65 which is signal energy at the desired intermediate frequencies is then fed through filters to separate the video intermediate frequency from the audio intermediate frequency resulting upon detection by detector 65, as well as the auxiliary signals accompanying the audio signal. In practice, it has been customary to transmit the audio signals on a higher carrier frequency than the video and, therefore, the selection and separation of the video intermediate frequencies is preferably taken care of by a low pass filter 61, while the audio intermediate frequencies and the accompanying control signals for controlling the video end of the system are separated by way of a high pass filter 69.

In the video end of the system as is the usual custom the output signals from the low pass filter 61 are fed through an intermediate frequency amplifier 1| and a detector 13 to the image reproducing tube 15. For the audio signals the output of the high pass filter 69 is amplified in the intermediate frequency amplifier 11 and then detected by detector 19. In view of the fact that the control signals for the video end of the system accompany the audio signals there is connected to the output of the audio intermediate frequency detector 19 a high pass filter 8| which separates from the composite intermediate frequency energy output of the detector 19 the complete group of signals representing the line synchronizing signal energy. These signals are then detected in a heterodyne detector 83 to the input of which is applied the output from the oscillator 85 and after suitably controlling the synchronizing signal and deflecting circuit control arrangement 81, of the type known in the art and described, for example, by Tolson, Bedford and Vance and others, is caused to deflect the cathode ray beam developed within the cathode ray receiver tube and also caused where necessary or desirable to produce blanking in the receiver tube.

Similarly, by way of a bandpass filter selection means 89 whose output is fed to the heterodyne detector 9| the frame synchronizing signals are separated and these signals then serve to control the deflection of the cathode ray beam in a manner closely analogous to the line deflection so that the cathode ray beam of the receiver tube 15 is deflecting in the vertical direction. Kny background control signals which are transmitted to accommpany the audio carrier are separated by way of the low pass filter 93 which preferably has a cut-off frequency at approximately to cycles. Thence the separated background control signals are impressed upon the input of the heterodyne detector 95 and amplifier 91 so that the output from this amplifier serves to bias in known manner the control elec trode of the image reproducing tube 15.

It will be noted that by virtue of the fact that the low pass filter 93 has a cut-off at sub-audible frequency of approximately 20 to 25 cycles that this serves also the additional purpose of limiting the'rate of change of field brightness in the receiver so that on conditions when the transmission scene changes from a very bright picture to a dark portion the abruptness of the change will not be objectionably apparent but will be integrated slightly over a short period of time In this way substantially the effect of a gradual changing background effect can be obtained.

The audio signals, like the frame synchonizing signals, are preferably selected in a bandpass filter 94 which selects from the lowest audio-frequency of about 30 cycles up to the frequency corresponding to the maximum fidelity of the system, which is usually a frequency of about 10 kc., and the audio signals are then detected in the heterodyne detector 95 and further amplified in the amplifier 96 and then supplied to the sound reproducer 99.

Since all the foregoing individual sections of the complete apparatus are substantially of standard form reference is made to the prior art and particularly to the form of installation now being used experimentally in the United States for a complete description of the individual units of the receiver as well as the transmitter.

It should be appreciated also that while the schematic diagram of the receiver system does not show automatic volume control arrangements, such arrangements are fully Within the scope of this disclosure and for this portion of the system, like other portions, reference also may be had to the aforementioned Carlson patent.

Many and various modifications of the system herein disclosed are, naturally, possible and within the scope of this disclosure and it is to be understood that I am free to make and use any and all of these modifications provided they fall fairly within the spirit and scope of the hereinafter appended claims.

What I claim is:

1. In a television system, means for producing carrier frequency energy, means for developing video signals and means for modulating the produced carrier frequency energy by the developed video signals, means for producing a plurality of controlling signals for controlling the reproduction of the produced video signals at all points of reception, means for producing sound signals accompanying the produced video signals, means for producing a second carrier frequency having a predetermined frequency spacing from the first produced carrier frequency energy, means for producing auxiliary sub-carrier frequencies of a number corresponding to the number of auxiliary controlling signals produced for controlling the reproduction of video signals at reception points therefor, means for modulating each of the produced auxiliary sub-carrier frequencies by individual controlling signals, and means for modulating the second produced carrier frequency by both the sound signals and the control signal modulated auxiliary submarrier frequencies.

2. In a television system wherein video signals are transmitted upon one carrier frequency and wherein sound signals accompanying the video signals and the control signals for the video reproduction are concomitantly transmitted upon a separate carrier frequency spaced by a predetermined frequency separation from the video carrier, a signal receiving means for receiving all of the transmitted signals, a common heterodyne detecting means for detecting all of the received signals and converting all of the received signals into intermediate frequency signals, means for separating the produced video modulated intermediate frequency signals from the produced sound modulated intermediate frequency signals and the video control signal modulated intermediate frequency signals accompanying the sound, means for amplifying the video modulated intermediate frequency signals subsequent to separation from the remaining received signals, means for detecting the amplified video modulated intermediate frequency signals, means to produce visible signal indications from the resultant detected video signals, means for amplifying the separated intermediate frequencies modulated by the sound and the video control signals, means for detecting said last named amplified signals, a plurality of filter means for separating the sound and the video control signals from each other, and independent means for converting the separated sound signals into audible signals and for controlling the production of the video signals in accordance with the separated video control signals.

3. In a television system wherein video signals are transmitted upon one carrier frequency and sound signals accompanying the video signals and a plurality of control signals for the video reproduction are each transmitted upon a separate carrier frequency spaced by a predetermined frequency separation from the video carrier, a single receiving means for receiving all of the transmitted signals, a common heterodyne detecting means for detecting all of the received signals and for converting all of the received signals into signals occupying an intermediate frequency range, means for separating the video modulated intermediate frequency signals from the intermediate frequency signals modulated by the sound signals and the video control signals, means for amplifying the video modulated intermediate frequency signals subsequent to the separation thereof from the remaining signals, means for detecting the amplified video modulated intermediate frequency signals, means to produce visible signal indications from the resultant detected video signals, a plurality of separating circuits for separating the sound modulated intermediate frequency signals and the video control signal modulated intermediate frequency signals, means for detecting said separated sound signals, means comprising a plurality of filters for separating the plurality of video control signals from each other, means for converting the separated sound signals into audible signals and means for controlling the production of the video signals in accordance with the separated video control signals.

4. In a television system means for producing a first main carrier frequency energy, means for developing video signals and means for modulating the produced carrier frequency energy by the developed video signals, means for producing controlling signals for controlling the reproduction of the produced video signals at all points of reception, means for producing signals representative of the sound accompanying the produced video signals, means for developing a second main carrier frequency spaced by a predetermined frequency spacing from the first produced carrier frequency, means for producing auxiliary sub-carrier frequencies of a number corresponding to the number of auxiliary control signals produced for controlling the reproduction of the video signals at reception points, means for independently modulating each of the produced auxiliary sub-carrier frequencies by individual controlling signals, means for developing background control frequencies at a sub-audible rate for controlling the video signal reproduction levels, and means for modulating the second produced main carrier frequency directly by the produced sound and background control signals and by the previously modulated auxiliary sub-carrier frequencies for transmitting the second produced main carrier frequency modulation simultaneously with the first produced main carrier frequency modulation.

5. In a television system, means for producing a first main carrier frequency, means for develop-' ing video signals, means for modulating said produced first main carrier frequency by the developed video signals, means for developing a second main carrier frequency spaced at a predetermined frequency separation from the first main carrier frequency, means for developing signals representative of the sound accompanying the produced video signals, means for modulating the second produced main carrier frequency directly by the produced sound signals, means for producing a plurality of separate synchronizing signals for controlling the reproduction of the produced video signals at points of reception, means for developing a background control signal for controlling the reproduction of the produced video signals at points of reception, means for producing a plurality of auxiliary sub-carrier frequencies of a number corresponding to the number of developed synchronizing signals and background control signals, each of said auxiliary subcarrier frequencies being of different frequency and each being of a frequency sufiiciently different from that of the maximum side-band frequency developed by the sound signal modulation of the second main carrier frequency as to be external to the frequency spectrum developed by sound signal modulation of the second main carrier frequency, and each of said auxiliary subcarrier frequencies being spaced apart from all other auxiliary sub-carrier frequencies by a frequency separation such that the frequency spectra of auxiliary sub-carriers and generated sidebands resulting from modulation of the said auxiliary sub-carrier frequencies shall be noncontiguous, means for independently modulating a number of the auxiliary sub-carrier frequencies equal to the number of independent synchronizing signals individually by individual ones of said produced synchronizing signals, means for modulating one of the auxiliary sub-carrier frequencies 'by the produced background control signals only, and means for modulating the second produced main carrier frequencies by the plurality of modulated auxiliary sub-carrier frequencies.

ALFRED N. GOLDSMITH.

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