US2355566A

US2355566A - Television system

Info

Publication number: US2355566A
Application number: US425015A
Authority: US
Inventors: Robert E Shelby
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-12-31
Filing date: 1941-12-31
Publication date: 1944-08-08
Anticipated expiration: 1961-08-08

Description

E Y @MQ/m T l o m5 n VT A mk 5. m km Aug. 8, 1944.`

R. E. SHELBY TELEVISION SYSTEM Filedv Dec. 51, 1941 Patented ug- 8i 1944 'i 2,355,566

vlmrri-:o 'STATE-s, PATENT ort-ics i 'retevision s rsm rgesrsssrsss mais Application December al, 19,41*. serian No.' 425,115

' transmitters.

is provided Within sitioned with limits of the s omini. (ci. 11s-5.6)

" invention relates to an improvement in televisionsystems and more particularly to tele- It is customary in television transmitting systems to transmit picture and synchronizing sigbymeans of one modulated carrier and to Y transmit the related sound ,signals by means of a second Amodulated carrier. 'Two separate carl riez-s, one for sound and the other for picture and synchronizing signals are used. These two car- .rierfrequencies are displaced from each other by 'a predetermined and fixed frequency separation. According tothe -present standards of television transmission, an otr chronlzing signals and related sound signals must be transmitted. Furthermore, according to e present standards, the picture and synchronizing signal modulated carrier is -positioned 1 .25 megacyclesabove the lower limit of the particular television band whereas the sound moduferall band of six -megacycleiiv which picture signals, synlated carrier is positioned 0.25 megacycle below the upper limit of the allotted frequency band. When the two radio frequency 'carriers are so po respect' to the lower and upper allotted band, the displacement between the two carrier frequencies is then 4.50 mesacycles.

rn the transmissin of nigh fidelity television picture signals considerable band width is required in view of the relatively high frequencies which are produced at the transmitter as a result of the scanning operation. If high Vfidelity pictures are to be reproduced at a receiver. picsignals ranging from substantially zero to frequencies of the order of from 4 to 5 megacycles mustbe transmitted. In order to conserve space in transmission, the present television standards require that a portion of the producedv side bands resulting from modulation of the picture signal carrier be suppressed so that, substantially only single side band transmission t Unaernie meseni''standardsof transmission and with a spacing of 4.50 megacycles between -the picture 'carrier' and the sound carrier, natu, rally picture -ianals'in excess of 4.25 megacycles are not ordinarilytransmitted since the selectivecharacteriitics of'the intermediate frequency portion ofthe television picture receiver cannot be made to cut ofi perpendicularly. If the picture lsignal channel of the television receiver is V-rnade wider than about 4.2 5 megacycle; for example, interference from the sound channel will cordingly it is desirable to transmit these frequencies in order to increase the definition of the picture at the receiver. Such an increase cannot be made where the sound and, picture carriers are displaced by 4.50 megacycles unless some special provisions are made. In the transmission of color images it is also frequently desirable to use a. wider band for the picture frequencies since in the transmission of color images the scanning rate and/or field repetition rate is frequently increased.

It is, therefore, one purpose of the present invention to provide a system whereby the television picture signal channel or band width may be increased "without the received image being affected in'anyg way by the related sound signals.` Y

To accomplish the above purpose the sound carrier is entirely interruptedduring' the transmission of picture signals and the sound fre- -quency modulated carrier is transmitted only I during intervals of picture signal line blanking.

vThe synchronizing signals are transmitted by the same carrier as are the picture signals but the sound signals are transmitted by an entire- 1y separate carrier frequency and, in accordance with this invention, the periods of transmission of .sound signals occur only during the transmission of horizontal or 'line blanking signals by the picture and synchronizing signal carrier.

" According to. thepresent 'United' States teleizontal deflection cycle picture signals are'transmitted. During the time that the picture signals are transmitted the sound' carrier is entirely elim-v inated whereas during the time that the horiaantal blanking signal is being transmitted the sound carrier is eifective to transmit the accom- Danying sound in the television program.

It is therefore anotherpurDOseof the present l invention to provide a system wherein the sound carrier is completely interrupted during -the transmission of signal carrier. t

Still another purpose of the present invention resides inthe provision of means whereby the sound carrier frequency `is eil'ectiveito transmit 'sound signals only during the interval when picture signals by thepicture blanking impulses are transmitted by the synchronizing and picture signall carrier.

A still further purpose of the present invention resides in the provision andthe use of a rst radio frequency carrier for sound and a second radio frequency carrier for picture and synchronizing signals, with the picture and synchronizing signals transmitted sequentially by the second carrier and with the sound signals transmitted only during transmission of line blanking signals.

A still further purpose of the present invention resides in the provision of means whereby the sound signals are transmitted alternately with respect to picture signals and concurrently with respect to the line blanking signals, the synchronizing signal carrier and the picture signal carrier being identical.

Still other purposes and advantages of the present invention will become more apparent to those skilled in the art from the following detailed specification particularly when considered in connection with the drawing wherein the single figure represetns by way of example a preferred form of the present invention.

Referring now to the drawing and particularly to the figure, there is shown a television picture transmitting tube II) which includes a mosaic or light responsive electrode I2 and an electron gun structure I4. The electron gun structure includes at least a cathode I6, a control electrode IB, a first accelerating anode 20 and a second accelerating anode 22. The second accelerating anode is connected to terminal 24 to which is applied a relatively high positive potential. A potentiometer resstance 26 is connected between the positive terminal 24 and ground or the negative terminal of the source of potential in order that varying potentials may be obtained. The first accelerating anode 20 is connected to a point along the potentiometer 26, the point o'f c onnection being 'responsive electrode I2 signal load circuit including resistance erators 32 and respectively, the generated cathode ray beam is caused to scan the light in bilateral directions in order to produce picture signals in theupictie voltage which is available from the signal plate of the light responsive electrode I2 is then transadjustable in order to focus' the produced cathode ray beam. The cathode IE is connected to a point on the potentiometer 26 negative with respect to the first accelerating anode whereas the control electrode I8 is connected by means of grid resistance 28 to a point along the potentiometer 26 that is negative with respect to the point where the cathode I6 is connected. This connection is also preferably made adjustable in order that the average beam intensity may be controlled. Whenproper operating potentials are applied to the electrodes of the .electron gun structure a focused cathode ray beam is produced.

In order to control the television transmitting system a master oscillator 30 is provided. This oscillator may be of any desired form and may operate at any appropriate frequency. The master oscillator supplies impulses corresponding to its frequency of operation to the horizontal deflection generator 32 which, .in turn, supplies energy to the horizontal defiecting coils 34. The masteroscillator 30 also supplies impulses to a frequency divider 36 and the output frequency of the frequency divider corresponds to a predetermined sub-harmonicof the master oscillator frequency. The frequency divider'then supplies control impulses to the vertical-decction generator 38. The vertical deflection generator then supplies the desired voltage variations to the vertical deflecting coils 40.

When the

deflecting coils

34 and 40 are ener- Sized-by voltage variations of proper wave form from the horizontal and vertical deflection genmitted to a picture s'ignal amplifier 44 by way of coupling condenser .46. The picture signal amplifier may be of .any desired form and preferably should have a band width capableof transmitting frequencies from substantially zero to frequencies of the order of at least five megacycles.

In order that the television receivers may be held in synchronous operation with the operation of the television transmitting tube, synchronizing signals must be transmitted for controlling horizontal'and vertical deflection generators at the receiver. These synchronizing imp ses are transmitted on the same carrier as are /he picture signals and are interspersed with the picture signals. The synchronizing signals, according to the present standards, are transmitted in a direction corresponding to black in the picture so that they may be used at the receiver for automatic blanking of the return beam. The master oscillator 30, therefore, supplies impulses to the horizontal blanking and synchronizing signal generator 48 and the horizontal blanking and synchronizing signal generator produces voltage variations of the-desired wave form which may be used for picture signal blanking and for synchronizing.. Likewise, the frequency divider 36 supplies impulses to the vertical blanking and synchronizing signal generator 50 which, in turn,

produces vertical blanking and synchronizing signals of the desired wave form. The energy from the horizontal and vertical blanking andsynchronizing signal generators and 50 is then applied to an amplifier or mixer 52 in order that the picture signals may be suppressed or blanked during intervals of synchronization and in order that both the horizontal -and vertical synchronizing signals may be interspersed with the picture signals. At the output of the amplifier and mixer 52, therefore, is derived a series of signals representative of the picture signals and including both the horizontal and vertical blanking pedestal and,

the horizontal and vertical synchronizing signals. For the purpose of simplicity in so far as this application is concerned, specific details of the blanking pedestal and the so called super-sync impulses are not considered because they do not in any way affect the merits of this invention.

Their wave form, naturally, should be such as will conform to the required standards.

The signals which are derived from the amplifier and mixer 52 are then fed to a modulator 54 in order that oscillations'derived from a radio frequency oscillator 56 may be amplitude modu- `I lated thereby. The amplitude modulated carrier is then applied to a vestigial side band illter 51 and the output from the filter is impressed upon the television transmitting antenna 58 for trans-` mission. If desired, frequency modulation may be employed.

The gure also shows a microphone or sound responsive device SII which is normally positioned in the television studio and which responds to the sound or aural part vof the television program. 'I'he audio signals which are available from the microphone or sound responsive device SII are then applied to an amplifier 62 in order that the 'amplitude of the audio frequency voltages variations may be increased. c y

the picture and synchronizing signal carrier. is amplitude modulated by the picture and syn' chronizing signals whereas the sound frequency carrier is frequency modulated bythe sound signals. Accordingly, the outputfrom the amplifier 6 2 is then supplied to a frequency modulated oscillator 64 in order that the voltage variations produced by the oscillator contained therein may be frequency modulated. In so far as this invention is concerned, it is immaterial what type of frequency modulation is used and a frequency modulating system such as-that shown in Crosby application, Serial No. 136,578, illed April 13, 1937, (D-12019) may be used. The frequency modulated oscillations that are derived from the oscillator and frequency modulating device 8| are then applied to an amplifier and/or frequency multiplier 86. This device. may be used to increase the amplitude of the signals or to increase 3 pas un'ough the tube n and be applied to the amplifier and/or frequency multiplier 88. Durthe frequency as well as the frequency deviation caused by frequency modulation.

The output from the amplifier and/or frequency. multiplier 66 is then supplied by way of condenser 88 to the controlelectrode of tube 10. 'Ihis tube includes, in addition to the control electrode, at least a cathode and an anode. The cathode is connected to ground by way of resistance 'l2 and by-passed condenser 'M while the anode is connected to thesource of positive potential by means of anode load resistance 16. In order that the control electrode may be maintained ing other intervals, the tube I0 is blocked so that no radio frequency energy is available at the input ofthe amplifier or frequency multiplier 86. rThe carrier is therefore completely eliminated between intervals of horizontal blanking and synchronization, during which time picture signals are transmitted.

Through the use of the above described system it is,ltherefore, possible to transmit sound by frequency modulating an oscillator, the radio frequency energy being transmitted only during the intervals when the horizontal blanking and synchronizing impulse occurs. At all other times the sound carrier is completely eliminated so that the picture signal carrier may then be modulated by picture signals over a band such as will produce side band frequencies of the order of 4.75 megacycles from the picture signal carrier \fre quency and the receiver may be made responsive to this band of frequencies without resulting in interference from the sound channel.

Inasmuch as the synchronizing signals do not produce side bands that are as extensive as the side bands produced by the picture signals, there is no` possibility of interference between the syn-A at its proper.' operating potential withv respect to A the cathode, a potentiometer "Il is provided, one end of thepotentiometer resistance being connected to ground and the other end of the po'- tentiometer resistance being suppliedv with a negative potential. The control electrode of tube 10 is connected tothe movable contact on thel potentiometer by means-of radio frequency choke coil or inductance 88 and resistance 82.

The potential of the control electrode of tube? 'I0 with respect to its cathode. is normally suchv 'chronizing signals andV the sound signals during their simultaneous transmission.` In view of the fact that the sides of the synchronizing signals, when transmitted in accordance with present standards, are quite steep, frequencies of the order of 3.0 to 3.5 megacycles may be produced, however,- these Afrequencies do not com pletely illl the space between the picture signal and synchronizing signal .carrier and the sound signal carrier.

connection maybe included a wave shaping clrcuit85 if such va circuit is necessary. Amplification may also be included ify the intensity of the signals is not suiilcient to produce the desired keying. A wave form of the' voltage variations appearing at condenser 84 is shown at 15, the blanking or keying signals extending in a posito the control electrode of tube 10 by means of condenser 84, the tube l0 is rendered conductive only during the line blanking signal intervals. During these intervals the output from the amplier 66 is effective to modulate' the electron stream in the tube 10. This produces a voltage variation at the anode of the tube and these voltage variations are applied to a ilnal amplifier and/or frequency multiplier 85 denser 88. The output from the amplifier 88 is then .supplied to a sound transmitting antenna 88.

When blanking or keying signals, such-as 'are shown at the curve 15, are applied to the con trol electrode of tube 10, the tube is rendered conductive or operative during intervals of picture line blanking. Only at this time are the tive direction. When these signals are applied The present 'system has certain limitations which are inherent in the system. Since the sound signals are transmitted at intervals which occur at horizontal synchronizing frequency naturally the highest audio frequency that can be transmitted will correspond to approximately one-half the horizontal synchronizing signal frequency. In present television systems transmission is carried out at.5,25 lines per frame. The frame repitation rate being 30. The horizontal synchronizing and blanking frequency has therefore 15,750 cycles per second. In sequential color television, however, the transmission may be at the' rate of 405 lines per frame, and a frame frequency of cycles per second (120 flelds'inl l terlaced two to one). Under these conditions the horizontal blanking and synchronizing frequency would be 24,300 cycles per second.

It is desirable also that the harmonics which are transmitted in the sound channel be limited so that they will not interfere with signals in V thenext adjacent television band. To reduce by way of confrequency modulated oscillations permitted to 1I these harmonics itis preferable that the wave form of the control impulses 'l5 that are applied to the control electrode of tube 10 be somewhat rounded.- Any slight attenuation of the high frequencies, however, will be entirely sufllcient since the sound carrier is positioned 250,000 cycles below the upper limit ofthe particular television band.- A limitation of all harmonics above the tenthharmonic of the controlling frequency of 15,750 cycles persecond (the sixth harmonic in the above example of color tele.

vision) would therefore 'be completely adequate to eliminate any possibility of interference with the next adjacent television channel. For eliminating all harmonics above the tenth harmonic of the line repitation rate a small condenser '82 may be employed. In many cases the distributed capacity of the conductor connecting the horizontal blanking and synchronizing signal channel with the control tube 'I0 will be sufficient to eliminate any such interference..

Although the system is described as being apcerned it is immaterial whether frequency or amplitude modulation is employed for the transmission of sound. If amplitude modulation is employed then naturally 'amplitude modulators will be used in place of a frequency modulated oscillator, however, a control tube similar to that shown in the figure may as conveniently be used to permit or prevent the transmission of amplitude modulated radio frequency energy to the final radio -frequency amplifier.

Although'the present invention is described as applicable to a transmitting tube of the Iconoscope type, naturally the present invention may also be applied to any type television transmitting tube since it is immaterial where the particular picture signals are derived. Furthermore, the picture signals and synchronizing signals may be used to amplitude or frequency modulate the carrier used for such transmission.

The present invention has the particular ad `a source of picture signals and a source of synchronizi'ngsignals, means for combining the picture and synchronizing signals to produce a comvantage that it may be exercised or put into -1 practice without causing any undesired effects in so far as television receivers which are at present in use are concerned since no change need be made in such receivers. The same picture and sound carriers are used and the carriers are displaced by the same amount.

In television receivers that are designed .to receive sound transmitted as a frequency modula- 'tion of a carrier and wherein aJimiter is used.

it may be desirable under some circumstances to provide a limiter which will not only remove noise from the top of the frequency modulated carrier envelope but also provide a limiter or cir'- `cuit arrangementwhereby low levels of amplitudeI modulation could also be removed. Since the frel quency modulated carrier is available only at spaced intervals, noise which appears as an amplitude modulation might, in some instances, be eective to produce noise at the sound receiver unless some means were provided to remove the noise between sound transmission intervals. Noise, winch is superimposed upon the frequency modulated sound carrier (during intervals of transmission) is naturallyremoved by the limiter in its usual method of operation.

Various alterations and modifications of the present invention may become apparent to those skilled. in the art and it is desirable that any and all such vmodifications and alterations be considered within the purview of the present invention except ,as vlimited by the hereinafter appended claims.

' I claim:

' 1..A television transmitting system comprising a source of picture signals, a source -of synchronizing signals, means for combining the plcture signals and synchronizing signals, a source of radio frequency carrier energy, means for modulating the source of radio frequency carrier by the combined picture and synchronizing signals, a source of audio signals related to the picture' signals,I a second source of radio frequency carrier energy of a frequency differing from the frequency of the first radio' frequency carrier by 75 of synchronizingsignals only.

3. A television transmitting system including a source of picture signals and a source of synchronizing signals, means for combining the picture and synchronizing signals to produce a composite series of signals, a first sou'rce of radio frequency energy, means for modulating the first source of radio frequency energy by the combined picture and synchronizing signals, a Asource of audio frequency, a secondsource of radio frequency energy, means to modulate said second source ofradio frequency energy by said audio frequencies, and means to interrupt the modulation of said second radio frequency energy during. the modulation of said first radio frequency energy by picture signals and to modulate said second radio frequency energy during synchronizing signal modulationof said first radio frequency carrier. f

4. A television transmitting system wherein picture and synchronizing signals are transmitted as a modulation of one carrier frequency and wherein the related sound signals are transmitted as a modulation of` a second radio frequency carrier, comprising a combined series of picture and synchronizing signals, a first radio frequency carrier, means to 'modulate said first radio frequency carrier by said combined picture and synchronizing signals, a second adio frequency carrier, a source of related sound signals, means tov modulate said second radio frequency carrier by :the sound signals during modulation 'ofgsaid first radio frequency carrier by synchronizing signals only, and means to pre-- vent themodulation of said second radio frequency carrier during periods of modulation of said -flrst radio frequencyv carrier by said picture signals.

5. A television transmitting system wherein picture and synchronizing signals are transmitted as a modulation of one carrier frequency and'wherein the related sound signals are transmittedas a modulation of a second radio frequency carrier, comprising a combined series of picture and synchronizing signals, a-first radio frequency carrier, means to modulate said first radio frequency carrier by said combined picture and synchronizing signals, a'second radio frequency carrier, a source of related sound signals, means to modulate said second radio frequency carrier by said related sound signals, means to transmit said modulatedsecond radio frequency carrier only during transmission of said first radio frequency carrier when modulated by synchronizing signals and means to prevent the transmission of said second radio frequency carrier during transmission of said first radio frequency carrier when modulated by picture signals.

6. A television transmitting system including a source of picture signals, a source of synchronizing signals, a source of radio frequency energy, means to modulate said source of radio frequency energy alternately by said picture and synchronizing signals. a source of related sound signals, a second source of radio frequency energy, means to modulate said second source of radio frequency energy by said sound signals,

' ysaid second sourcel of radio frequency energy by and means to transmit said modulated second l radio frequency energy only during intervals of modulation of said first radio frequency energy l y by said synchronizing signals.

'7. A television transmitting system including `a source of picture signals, a source of synchronizing signals, means to combine the picture and synchronizing signals to produce a composite se- I ries of signals, a source of radio frequency carrier energy, means to modulate said source of radio frequency carrier energy alternately by said combined picture and synchronizing signals, a source of related sound signals, a second source of radio frequency carrier energy, means to modulate said second source of radio frequency carrier energy by said sound signals, and means to cause transmission of said modulated secondradio frequency carrier only during intervals of modulation of said first radio frequency carrier by said synchronizing signals.

8. A television transmitting system including a source of picture signals, a source of synchroy nizing signals, means to combine the picture and synchronizing signals, a first source of radio frequency energy, means to alternately modulate said first source of radio frequency energy by said combined picture and synchronizing signals, a

'source of relatedsound signals, a second source said sound signals, an electron discharge tube including a cathode, a control electrode and an output electrode, means to maintain the output electrode positive with respect to its associated cathode, means to apply said sound modulated radio frequencyd energy to said control electrode, means to bias the potential of said control electrode relativeto the cathode by an amount sunlcient to prevent electronic conduction through said tube, and means to apply control impulses of synchronizing signal frequency to said control electrode to render said tube conductive at predetermined intervals, whereby sound signal modsaid sound signals,'an .electron discharge tube including a cathode, a control electrode and an output electrode, means including a load circuit to maintain the-output electrode positive with respect to its associated cathode, means to apply said sound modulated radio frequency energy to said control electrode, means to normally prevent electronic conduction through said tube, and

Q means to apply control impulses of synchronizing signal frequency to said control electrode to render said tube conductive at predetermined intervals, whereby sound signal modulated radio frequency energy is available from the output electrode of said tube only during such intervals.

ROBERT E. SHELBY.

of radio frequency energy. means to modulate I