US2343561A - Television broadcasting system - Google Patents

Television broadcasting system Download PDF

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Publication number
US2343561A
US2343561A US364499A US36449940A US2343561A US 2343561 A US2343561 A US 2343561A US 364499 A US364499 A US 364499A US 36449940 A US36449940 A US 36449940A US 2343561 A US2343561 A US 2343561A
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frequency
signal
synchronizing
carrier
amplitude
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US364499A
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Arthur V Loughren
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BAE Systems Aerospace Inc
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Hazeltine Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/04—Systems for the transmission of one television signal, i.e. both picture and sound, by a single carrier

Definitions

  • This invention rentes to television 'broadcasting systems and is particularly concerned with broadcasting systems of the type comprising a vreceiver which -includes signal-translatingr and utilizing apparatus designed to respond .to received carrier signals amplitude-modulated by synchronizing signals.
  • a television system including a transmitter adapted to generate and transmit, and a receiver adapted to receive, a carrier-signal 'wave amplitude-modulated in accordance with video-signal components 4and frequency-modulated in accordance with "synchronizing-signal components.
  • a carrier wave comprises video signals amplitude .modulated thereon and synchronizing signals frequencymodulated thereon.
  • the generated signal being of such a type that it is adapted also to be received on conventional television signal receivers of the type which comprises a synchronizing-signal translating and utilizing apparatus designed to respond to received carrier signals amplitudemodulated by synchronizing signals.
  • televisionbroad'casting system comprises a re ⁇ DCver which includes synchronizing-signal translating andutilizing apparatus designed to respond to received carrier signals amplitude-modulated by synchronizing signals.
  • a television transmitter is included in the system which comprises means for generating and transmitting to the receiver a modulated-carrier wave including means for generatingvideo-signal components during trace periods and synchronizingsignal components during retrace periods and means for supplyingv a carrier wave having a predetermined frequency.
  • Means are comprised in the transmitter for modulating the carrier wave in accordance with the video-signalgcomponents andmeans are also comprised in the transmitter for frequency-modulating the car-4 rier wave with the synchronizing-signal components.
  • ⁇ Means are provided inthe system having a frequency-response characteristic so related to the frequencyand frequency deviations of the carrier wave as to develop in the receiver, in response to the synchronizing-signal components, a can'ier signal amplitude-modulated by the synchronizing-signal components.
  • Fig. 1 is a cir- 4cuit; diagram, partly schematic, of a complete television transmitting system utilizedv in the broadcasting system of the present invention;
  • Fig. 2 is a schematic circuit diagram of a complete receiving system of a type which com-prises synchronizing-signal translating and utilizing apparatus designed to respond to received carrier signals frequency-modulated by synchronizing signals;
  • Figs. 3 and 4 are graphs illustrating the wave forms of signals developed by the trans- Referring now more particularly to Fig. l
  • a television transmitting system which is generally similar to that of Fig. 1 of yapplicant's above-mentioned United States Letters Patent No. 2,302,619, granted Nov. 17, 1942, and circuit elements which are similar in the two figures have identigenerator I3 with their output circuits con-- nected directly to the line-scanning and fieldscanning elements, respectively, of signal-generating device I0.
  • identigenerator I3 with their output circuits con-- nected directly to the line-scanning and fieldscanning elements, respectively, of signal-generating device I0.
  • a pedestalimpulse generator I4 having its output circuit coupled to a control electrode of signal-generating device I0.
  • an impulse generator I5 has a plurality of output circuits connected to the generators I2, I3, and I4, aswell as a plurality of output circuits coupled to a combining amplifier 9 for combining periodic pulses generated in impulse generator I5 to develop a composite synchronizing signal for transmission.
  • a modulation-frequency combining amplifier I6 is coupled to the output circuits of signalgenerating device I0 and pedestal-impulse generator I4. Connected in cascade to the output circuit of the amplifier I6, in the order named, are a video-frequency amplitude modulator I1 which is provided with a local or master oscillator I8, a single-sideband filter I9, a frequency changer 20, a heterodyne-frequency filter 2l, a power amplifier 22, and an antenna system 23,
  • the system just described-in excludes the apparatus of a television transmitting system of a conventional design, rendering a detailed description of its operation unnecessary herein.
  • the image of the scene to be transmitted is focused on the target of the cathode-ray tube of signal-generating device III, in which a cathode ray is developed, accelerated, and focused on the target.
  • Scanning or deflection waves developed by the generators I2 and I3 are supplied to the scanning elements of the signal-generating device III and serve to deflect the ray to scan successive se'ries of fields of parallel lines on the target.
  • Pedestal impulses developed by the generator I4 are applied to the control electrode of the tube of signal-generating device Ilto suppress or block-out the beam during retrace portions of the scanning cycle and are applied to the modulation-frequency amplifier I6 to suppress undesirable impulses or transients developed in the systeml during the retrace intervals to aid in obtaining the required wa've form of the video-modulation signal.
  • the photosensitive elements of the target of signal-generating device I0 being electrically affected to an extent dependent upon the varying values of light and shade at corresponding incremental areas of the image focused thereon as the cathode ray scans the target, a voltage of correspondingly varying amplitude is developed in the output circuit of the signal-generating tube and supplied to the ampliner I6.
  • Suitable timing or synchronizing impulses are applied from generator I5 to the generators I2, I3 and I4 to maintain these generators in synchronism with either the master frequency,
  • 'IheA heterodynefrequency lter ZI may be of any suitable conventional type designed to pass either the sum or difference frequencies developed in frequency changer 20.
  • the resulting modulated-carrier@ wave is amplified in the power amplifier 22 and is impressed upon the antenna system 23. 24 for radiation.
  • the generators I 2 and I3 develop scanning waves of saw-tooth form, as indicated at the left of these generators, for application to signal-generating device III for effecting desired scanning thereof.
  • Generator I5 is adapted to generate, in accordance with well-known practice, periodic waves of predetermined wave form and frequency, including rectangular-pulse key- .ing waves for keying predetermined portions of other periodic waves into the circuit of combining amplier 9.
  • the output circuit of combin- V ing amplifier 9 iscoupled to a control apparatus pulses.
  • the oscillator 29 which is provided for the purpose of shifting the frequency of the carrier wave derived from frequency changer 20 during the synchronizing Control apparatus 2! includes an oscillator indicated generally at 33 and a frequencyadjusting network indicated generally at 3
  • the oscillator is of the push-Dull type and comprises Vacuum tubes 32 and 33 having their input circuits connected inpush-pull relation by way of an inductance 34, a leak resistor 35 and a grid condenser 35a being connected in parallel between a mid-tap on inductance 34 and the cathodes of the tubes.
  • the anode circuits of tubes 32 and 33 are also connected in pushpull relation by way of an inductance 36 coupled to the inductance 34, as indicated by bracket M. a mid-tap on.
  • the inductance 35 being connected to the cathodes of the tubes by way of a suitable anode-voltage supply, such as a battery 3'I.
  • the inductance 36 is normally sharply-tuned to a fixed frequency by means of a condenser 33, or other suitable circuit arrangement such that the oscillations developed by the oscillator 3B when combined with the carrier wave developed by ol-y 'the desired carrier frequency for transmission.
  • are also connected by way of coupling condensers 4l and 46 to their respective anodes which, in turn, are connected to the terminals of an inductance 41.
  • the inductance 41 is-connected in push-pull relation in the anode circuits of the tubes, a mldtap thereof being connected to the tube cathodes by way of a suitable anode-voltage supply source. indicated by battery'48.
  • the inductance 41 is inductively coupled to the inductance 38 of the oscillator frequency-determining circuit.
  • the tubes 40 and 4l are biasedbeyond cutoff and remain so biased during the video signal or trace periods, being rendered operative only during synchronizing or retrace periods when impulses from the combining amplifier ⁇ 9 are 'applied thereto. Since the tubes 40 and 4l are'cut on during the video-signal periods, the oscillation circuit 36, 38 maintains its own natural frey quency during these periods.
  • is varied in accordance with the line-frequeney and held-frequency impulse voltages applied to the grids sf the tubes 4o and 4
  • equalizing, and field-synchronizing pulses 'of the composite synchronizing signal is preferably as shown in Fig. 3 of the drawings. in which the @out considerably longer in duration. and pref'- erably bear such relationship to the line-syn chronizing pulses -that pulses of the two types4 are not transmitted during the same time intera val.
  • the field pulses F preferably initiate immediately after the occurrenceof theequalizingpulses D and are of a duration somewhat less than one-half a line-scanning period. It will be understood that, in a double-interlace system, the field-synchronizing pulses of the succeeding fleld-retrace interval lare displaced by one-half line, as is conventional practice.
  • the oscillator 3Q Since the oscillator 3Q is coupled to the frequency changer 20, its output is mixed with the video-modulated carrier signal from the filter I9 and the sum and difference heterodyne-frequency componentsare developed in the output circuit of the frequency changer vin a wellknown manner. Either the sum-frequency or the difference-frequency components are selected by the filter!! and delivered to power amplifier 22 to be broadcast. Therefore, the frequency of the selected heterodynelcarrler output of frequency changer 20 is maintained constant during the trace intervals, but is varied or shifted during the retrace intervals in accordance with .the frequency variations of oscillator 30, as described above. In Fig. .4 there is illustrated half of -the envelope ofthe resultant amplitude-modulated carrier wave developed by. the transmitting system.
  • the video-signal components are represented by the portion of the wave indicated at V, the .portions representing the line,- retrace and field-retrace periods during which 20 has its normal constant value, which may be of the order of 10-50 megacycles, so that the carrier frequency of the output of the frequency each line-retrace period an impulsefrom com# -bining amplifier 9 is impressed on frequency-ad- 'justing network 3l, thereby to eEect a predetermined deviation of the frequency developed bythe generator 30 and, hence. in that'of the signal developed in frequency changer 2,0,as indicated by the pulses L of Fig. 3.
  • this frethe line-synchronizing signals of the system and may be.
  • impulses from-the. combining 'amplifier 9 are applied to network-3l, thereby 5 to effect a frequency deviation corresponding to the equalizing pulses D and also to effect a dif-A ferent and lesser-predetermined frequency devia'- tion in the frequency developed by oscillator 33 corresponding to the field-synchronizing pulses F.
  • the carrier-frequency deviation during the field-synchronizing pulses is about one-half that during the line-'synchronizing pulses. for example, of the order of l megacycle for a Sil-megacycle carrier wave.
  • Line synchro-v nization of the system. as will be seen by thev the carrier is shifted or varied, as described with changer 20 is constant. During a portion ofo uency deviation is many times the frequency of curves of Fig. 3, is not interrupted during fieldretrace periods. Preferably, the direction of the carrier-frequency deviations by the synchronizing pulses is such as to bring it within thefrequency range of the transmitted sideband. ,In the signal of Fig. 3 it is seen that the total energy of the line pulses and equalizing pulses during one line-scanning period is constant.
  • the system there illustrated comprises a receiver of the superheterodyne type for receiving and utilizing the 'signal developed by the transmitter of Fig. 1.
  • This receiver includes an antenna system 50, 5l, to which are connected in cascade, in the order named, a radio-frequency amplifier and frequency changer 52, an intermediate-frequency amplier 53, an amplitude detector 54, a videofrequency equalizer 90, a. video-frequency ampliiler 55, a unidirectional or background component reinserter 9
  • the stages 52 and 53 are designed for single-sdeband reception.
  • a line-scanning generator 51 and a field-scanning generator 58 are coupled ,to the scanning elements of signal-reproducing device 56 in a conventional manner and preferably include conventional synchronizing circuits which are adapted to be controlled by synchronizing impulses developed by the apparatus 58.
  • the circuits 50-58, inclusive, may be of any conventional well-known construction. so that detailed illustrations and descriptions thereof are deemed unnecessary herein. Referring brieily to the general operation of the receiving system, however, television signals are selected and amplified and converted into intermediatefrequency signals in the radio-frequency amplifier and frequency changer 52, the intermediatefrequency signals being, in turn, selectively anipliiied in the intermediate-frequencyv amplifier 58 and delivered to the detector 54.
  • the videofrequency amplitude-modulation components of the signal are derived by the detector 54 and are supplied through equalizer 80, the operation of which will be described hereinafter, to the videofrequency amplifier 55, wherein they are amplified and from which they are supplied in the usual manner to a brilliancy-control electrode of the signal-reproducing device 55, the signals being stabilized by background reinserter 9
  • the intermediate-frequency signal is also supplied from the amplier 53 to the apparatus 59, wherein the synchronizing signals are derived, the line-synchronizing and held-synchronizing components being effectively separated from the video-frequency signal and from each other and supplied to the control circuits of generators 51 and 58, as will be hereinafter further explained.
  • Saw-tooth current or voltage-scanningwaves are developed in the line-scanning and field-scanning generators 51 and 58 and applied to the scanamate;
  • line-frequency selector 8l may be constructed in accordance with the correspondingly numbered unit of Fig. 2 of applicant's United States Letters Patent No. 2,302,619 granted-.Nom 1'1, 1942, and
  • the selected line-synchronizing pulses and equalizing pulses as applied to the input circuit of generator 51 are of a wave form as represented by the curve of Fig. '1.
  • field-frequency selector 82 is effective to pass primarily the carrier wave when deviated to a different frequency by the field-synchronizing pulses F of Fig. 3 and the selected wave pulses are rectified byrectifler and amplitude selector 84. Only the peaks of the rectified output of the amplitude selector unit 84 are utilized to synchronize field-canning generator 58 and such peaks comprise substantially only fieldsynchronizing information as illustrated by the wave form of Fig. -8.
  • both the single-sideband filter I8 of Fig. 1 and the selector of intermediate-frequency amplier 58 of Fig. 2, which may be of any suitable well-known design, have response-frequency characteristics such as that shown by curve A of Fig. 5, wherein relative gain is plotted against frequency,
  • Each selector is designed to have a response characteristic which is substantially level or uniform over a wide frequency band and a mean frening elements of the signal-reproducing device to produce electric scanning fields, thereby to deilect the intensity-modulated cathode ray in two directions normal to each other so as to trace successive series of fields of parallel lines on the target of the tube to reconstruct the transmitted image.
  • the synchronizing-signal deriving apparatus 59 there is comprised therein an intermediate-frequency amplifier 60 to which line-scanning vgenerator 51 is coupled through a line-frequency selector quency so related to the carrier frequency of the signal to be translated that this carrier frequency is located on the uniform portions thereof, as indicated by X in Fig. 5.
  • the selectors thus pass the carrier wave, one complete sideband of its modulation components, the vestigial portion of the other sideband components not suppressed at the transmitter, and, in case the carrier-frequency is deviated within the normally ltransmitted sideband, such carrier-frequency deviations.
  • is effective to stabilize the signal input to signal-reproducing device 55 at a predetermined shade value within the amplitude range ofl the actual transmitted signal, rather than on the peaks of synchronizing pulses which correspond to signal amplitudes outside of the range of the transmitted shade values as in conventional television systems.
  • may be effective to stabilize the signal input to signal-reproducing device 56 directly at an amplitude level thereof corresponding to the black level of the transmitted signal, rather than at some infra-black level, as in conventionaltelevision systems.
  • is effective to stablize the signal input to signal-reproducing device 56 at an amplitude level corresponding to the white shade value of the transmitted signal. Ii the receiver is adapted to receive such a positively modulated video signal, in some cases, it
  • may be of the form disclosed in the correspondingly numbered unit of Fig. 2 of apwhere they are converted Iinto intermediate-frequency signals which, ,in turn, are selectively amfrequency amplifier IIB wherein they are amplif ed and from which they are supplied in the usualmanner to a brilliancy-control electrode of H1; Detected modulation-signal components are also supplied to synchronizing-control elements of generators II8 and IIS through synchronizing-signal separator I20. The intensity ofthe scanning ray of device II'I is thus modulated or controlled in accordance with the video-frequency voltages impressed on the control electrode in the usual plicants United States Letters Patent No.
  • the equalizer 90 may, therefore, be constructed in accordance with the disclosure of applicants 'United states Letters Patet No. 2,302,619, granted Nov. 1'?, 1942. l i
  • vA receiver of this type is illustrated in Fig. 9 and includes an antenna system IIB, III connected to a radio-frequency amplier II2, to which are connected in cascade, in the order named, an oscillator-modulator II3, an intermediate-frequency amplifier IM, a detector II5, a video-frequency amplii-lerv II6, and an image-reproducing device III.
  • a line-frequency generator IISand a field-frequency gen'- erator IIB are coupled to the output circuit of the detector II5 through a synchronizing-signal separator
  • 20, inclusive, may all be of conventional well-known construction so that detailed illustations and descriptions thereof are deemed unnecessary herein. y
  • Scanning waves are generated in the line-frequency and field-frequencyv generators I I8, I I9 and are controlled by synchronizing-voltage pulses supplied from ldetector I I5 and supplied to the scanning elements of image-reproducing device II'I to produce deflecting fields,
  • FIG. 10 there is shown aportion of the responsefrequency characteristics of one of the band-pass circuits of the television receiver of Fig. 9. This may, for instance, be a portion of the characteristic of the intermediate-frequency amplifier Ill.
  • the received intermediate-frequency,signal is applied to the selector having the characteristic of Fig. 10 so that the carrier frequency thereof, during thev time when video signals are being translated, that is, during the time when the received carrier is only amplitude-modulated, falls
  • the selector i's so designed that equalization of single-sideband components and double-sideband components ⁇ is obtained. Therefore, during intervals of reception of frequency-modulated.
  • the frequency deviation of the carrier signal shifts it beyond the sloping portion of the curve a, b and on the straight or uniform-response part b, c of the curve for all translated synchronizing sighals; that is, even the translated field-synchronizing pulses F are effective to shift the carrier frequency to the point b of the curve a, b.
  • the output of intermediate-frequency amplifier III during the synchronizing intervals and in response to the synchronizing signal components a carrier-frequency signal which is lamplitudemodulated by the synchronizing-signal components.
  • the selector comprises means having a frequency-response characteristic so related -to the frequency and frequency variations of the carrier wave as to develop in the lected and amplie'd in radio-frequency amplifier lll and coupled'to the oscillator-modulator II3 receiver in response to the synchronizing-signal components a carrier signal amplitude-modulated thereby.
  • a signal may be translated and utilized by the receiver in the same manner that conventional amplitude-modulation/signals are Atranslated and utilized.
  • a television broadcasting system comprising, a receiver which includes synchronizingsignal translating and utilizing apparatus de-. signed to respond to received carrier signals amplitude-modulated by synchronizing signals, a television transmitter including, means for developing and transmitting to said receiver a modulated-carrier wave including means for developing video-signal components during trace periods and synchronizing-signal components of, a predetermined wave form during retrace periods, means for supplying a carrier wave having a predetermined frequency, means for modulating said carrier wave in accordance with said video-signal components, means for frequencymodulating said carrier wave with said synchronizing-signal components, and means in said system having a frequency-response character ⁇ istic so related to the frequency and frequency deviations of said carrier wave as to develop in said receiver in response to said synchronizingsignal components a carrier signal amplitudemodulated in response to said synchronizingsignal components with amplitude-modulation assasei 'p1itude-modulated by synchronizing signals, a
  • a modulated-carrier wave including means for developing video-signal components during trace periods and line-synchronizing signal components of a predetermined wave form during lineretrace periods and heid-synchronizing components of a predetermined wave form during field-retrace periods, means for supplying a carrier wave having a predetermined frequency, means for modulating said carrier wave in accordance with said video-signal components, means for frequency-modulating said carrier wave with said synchronizing-signal components, and means in said system having a frequencyresponse characteristic so related to the frequency and frequency deviations of said carrier Waveas to develop in said receiver in response to said synchronizing-signal components a carrier wave amplitude-modulated by said synchronlzing-signal components and comprising amplitude-modulation components of wave forms similar to the wave forms of said synchronizing-signal components.
  • a television broadcasting system comprising, a receiver which includes synchronizingsignal translating and utilizing apparatus designed to respond to received carrier signals amplitude-modulated by synchronizing signals, a television transmitter including, means for de- "veloplng and transmitting to said receiver a modulated-carrier wave including means for developing video-signal components during trace periods and synchronizing-signal components during retrace periods, means for supplying a carrier wave having a predetermined frequency1 means for amplitude-modulating said carrier wave in accordance with said video-signal cornponents, means for frequency-modulating said Wave with said synchonizing-signal components.
  • a television broadcasting system comprising, a receiver which includes synchronizings'gnai translating and utilizing apparatus designed to respond to received carrier signals amplitude-modulated by synchronizing signals, a television transmitter including, means for developing and transmitting to said receiver a modulated-carrier wave including means for developing video-signal components during trace periods and a composite synchronizing signal including line-synchronizing components and eldsynchronizing components, means for supplying a '.carrier wave having a predetermined frequency, means for modulating said carrier wave in accordance with said video-signal components, means for frequency-modulating said wave with said composite synchronizing signal so that said line-synchronizing components and said field-synchronizing ⁇ components eect different frequency deviations of said wave, and means. in said system having a frequency-response characteristic so related to the frequency assassi plitude-modulated by synchronizing signals., a modulated-carrier wave including means for developing video-signal components during trace periods and a composite synchronizing signal including line-synchronizing
  • television transmitter including, means for developing and transmitting to said receiver a modulated-carrier wave including means for developing video-signal components during trace periods and synchronizing-signal components during retrace periods, means for supplying a carrier wave having a predeterminedfrequency, means for modulating said carrier wave in accordance with said video-signal components, means for frequency-modulating said wave with said synchronizing signal components, and means in said receiver having a frequency-response characteristic so related to the frequency and frequency deviations of said carrier wave as to develop in response to said synchronizing-signal components a carrier signal amplitude-modulated by said synchronizing-signal components.
  • a television broadcasting system comprising, a receiver which includes.' synchronizingsignal translating and utilizing apparatus designed to respond to received carrier signals amplitude-modulated by synchronizing signals, a television transmitter including, means for developing and transmitting to said receiver a carrier wave including'means for developing videoignal components vvduring trace periods and ynchronizing-signal components during retrace periods, means for supplying a carrier wave having a predetermined frequency, means for modulating said carrier wave in accordance with said video-signal components, lmeans for frequency-modulating said carrier, wave with said synchronizing-signal components.
  • a television broadcasting system comprising.
  • a receiver whichl includes signal translating and utilhing apparatus delned to'respond to signals Il amplitude-modulated by synchronizing signals
  • a television transmitter including, means for developing and transmitting to said receiver a carrier wave includingmeans' for developingv video-signal components during trace periods and synchronizing-signal components during retrace periods, means for modulating said carrier'l wave in accordance with said video-signal components, means for frequency-modulating said carrier wave with said synchronizmg-signal components, and means in said receiver having a frequency-response characteristic with a sloping portion and a uniform-response por'tion so related to the frequency and the frequency deu viations of said carrier wave as to develop in said receiver in response to said synchronizing-signal components a carrier signal amplitude-modulated to a substantially uniform degree by said synchronizing-signal components.
  • a television system including a transmitter and a receiver designed to receive an amplitude-modulated carrier-frequency televission signal.
  • the method of operation of which comprises generating and transmitting a carries-frequency signal which is modulated by ⁇ video-frequency components and frequencymodulated by synchronizing-signal components, receiving the transmitted signal, translating the received carrier-frequency signal to develop a u" carrier-frequency signal having amplitude variatlons corresponding to the frequency variations of the received carrier signal, utilizing only said amplitude variations of said developed 'carner-frequency signal to synchronize the operau tion of the receiver, and utilizing the developed carrier-frequency signal also to lreproduce the transmitted picture.
  • av receiver designed to receive an amplitude- 40 modulated carrier-frequency television signal
  • the method of operation of which comprises revcelving a carrier-frequency signal. which is modulated by video-frequency components and frequency-modulated by synchronizing-signal components, translating the received carrier-fre- .quency signal to develop a carrier-frequency signal having amplitude variationsl corresponding. to the frequency variations of the received carrier-frequency signal, utilizing only said amplitude variations of the developed carrier-frequency 8181181 to synchronize.. the operation o f the receiver, and utilizing the developed carrierfrequency signal also to reproduce mitted picture.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
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US364499A 1940-11-06 1940-11-06 Television broadcasting system Expired - Lifetime US2343561A (en)

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BE443400D BE443400A (US08197722-20120612-C00042.png) 1940-11-06
US364499A US2343561A (en) 1940-11-06 1940-11-06 Television broadcasting system
FR876686D FR876686A (fr) 1940-11-06 1941-11-11 Disposition et procédé pour la télévision

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2921127A (en) * 1953-01-26 1960-01-12 Pye Ltd Television distribution system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2921127A (en) * 1953-01-26 1960-01-12 Pye Ltd Television distribution system

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FR876686A (fr) 1942-11-12

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