US2249942A - Television system and synchronizing means therefor - Google Patents

Description

July v22 19 4l- R. L. CAMPBELL 2,249,942 TELEVISION SYSTEM AND sYNcERO'NIz'INGMEANs THEEEFOR Filed oct. v 1s, lgs's s shetsfsneet 1 i l l l l l l l f I l I I i l l l lNvEN Kiel I s sheets-Sheet 2 R L CAMPBELL lFiled oct. 19, 1:9329

TELEVISIONSYSTEM AND SYNCHRONIZING MEANSv THEREFOR July 22, 1941.

July 22,:194L R L, CAMPBELL 2,249,942

' TELEVISION sxrl'sTEM AND sYNcHRoNIzING MEANSTHEEFOR Filed 00T.. 19, 1939 3 Sheets-Sheet 3 kDa-P30 lPaeiite'd'Jely A22,- 19'41 A UNITED STATES PATENT OFFICE i TELEVISION SYSTEM AND SYNCHRUNIZING MEANS THEREFOR niehara L. campbell, Hasbrenek Heights, N. J., assigner to Allen B. Dn Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Appiieatien october v19, 1939, serial No. 300,263'

1s claims. (ci. 17a-6.8)

My invention relates to improvements in television systems and synchronizing means there- By using interlaced scanning in television communication vwith cathode-ray tubes, important advantages are obtained. However, in the various systems and methods proposed heretofore to' synchronize for interlaced scanning with even the lowest interlace ratio of two, itV has been found that positive intel-lace action at the receiver is diiiicult to maintain, although operating conditions might be made as ideal aspossible. In order to obtain anydegree of satisfactory.results to maintain positive interlace action at the receiver, use of a rather complicated pulse form for the vertical synchronizing waverwhich has both low and high frequency componmts, has been resorted to heretofore. moe the frequency content of the horizontal andverticalwaves overlapinthissystemand method of the prior art, they cannot be eiiectively wanted at the receiver, with the result that the desired, positive interlace action Ais not always maintained.V Furthermore, in the prior .systems and methods, the complex synchronizing wave forum embraced such expedients as equalizing puls, serrated waves, and inten'upted horizontal: pulses. Abo, the quality of the synchronizing pulses after separation was not as goodasdedred,theverticalsynchronizingwas mectedby low frequency video transients and low-frequency surges, and there was serious distortion of the horizontal synchronizing wave train during occurrence of the vertical synchromixing pulses.

with the foregoing in mind, it is one of the objects of my invention to provide an improved' television system and synchronizing means therefor, whereby substantially more adequate separation of vertical and horizontal synchronizing mais nf attained than n possible with the various systems and methods used heretofore., and to provide a means of continuous transmissionof horizontal synchronizing signals lwithout mig the effectiveness of vertical synchronizlng. v A Y Another object. of my. invention is the provision of an improved television system and synchro'nixing means therefor, which notonly gives satisfactory synchronizing performance at the receiver, but which also makes pcwble generf-vertaal synchronizing signal etthe 'L hammitter-bymeans substantially sunoler-llmn` -1 used heretofore, for interlaced Locan- .A I I Another object of my invention is the provision of an improved television` system and synchronizing means therefor, in which there is used a vertical synchronizing signal whose frequency 5 content is such that it can be substantially entirely removed from the horizontal signal without detrimentaleftect on the horizontalsynchronizing, so that-the vertical synchronizing .does

not interfere with'horizontal vsynchronizing op 'l0 eration of the receiver.

Another object of my invention is the provision of an improved televisionsystem and synchronizi'ng means therefor, in which a vertical synchronizingpulse is transmitted in such a way l5 that it can be readily separated from the combined video and synchronizing signals and in a manner so effective that the separated horiz'ontaland vertical pulses at the receiver are so pure that they can drive the respective sweep circuits at the receiver more effectively than in ,the systems and methods used heretofore, thereby. giving exceedinglyI positive synchronization.

Another object 'oi my invention is the provision of an improved television system and synchronizing means therefor, in which the horizontal and vertical synchronizing pulses can be separated so well and effectively that no frequency adjustment is necessary at the receiver, whereby the' receiver will follow the transmitter over aconsiderable range which is not feasible in circuits using the old type of synchronizing pulses referred to.

Another oblect of my invention is4 the provision of an improved television system and syn.-

chronizing means therefor, inwhich both horizontal and vertical synchronization are so positive and effective that simplification of receiver l controls is possible to the extent that the synchronizing controls heretofore necessary at the receiver can be eliminated.

Another object of my invention is the provisionotanimprovedtelevisionsystemandsynehrenmpgmeens therefor, in which it is pessime to use at the receiver aperiodic sweep circuits 'which canbe made to synchronize automatictnlyoverawiderangeofscanningtrequencles, whereby the receiverwill respond toatelevision transmittingsystemwhichisiiexibleinthesense that the respectiveh'equencies 0I the pulses transmitted for horizontal andrve'rtical synchroniaingmishtbechansedasoccaslonorrequirementsmightarlse.

Citheroblcctsandadvimtaseswlllhereinafterl maccordancewithmyinvcntiomnulselofa high; radio-frequency wave are used for vertical synchronizing. This wave, which. may have an approximate frequency of 529 k. c., for example, is electronically keyed during the intervals for vertical synchronizing, and these pulses are, mixed with the horizontal synchronizing signals and-transmitted along with the video signals in much the same manner as commonly used in the present television systems. At the receiver, the pulses of the radio-frequency wave for vertical synchronizing are separated out by employing a tuned" stage, responsive to the frequency of this wave, to select the vertical synchronizing signals or pulses which are then applied to the vertical synchronizing circuit. The video and horizontal synchronizing components in the receivedcomposite signal are'thus effectively excluded from the vertical synchronizing circuit. The pulses of the wave at radio-frequency, for vertical synchronizing, are removed from the signals applied to the horizontal synchronizing circuit by means of a wave trap, so that only the horizontal synchronizing signals are applied to the horizontal synchronizing circuit.

My inventionI resides in the improved system and method of the character hereinafter described and claimed.A

For the purpose of illustrating my invention, an embodiment thereof is shown inthe drawings, wherein Figure 1 is a simplified, diagrammatic view of a television transmitting system constructed and operating in accordance with my invention;

Fig. 1a is a. graphical view illustrative of the principle ofoperation in Fig. 1; i

Fig. 2 is a simplied diagrammatic view of I8, the output signal I1 from the ampliiier tube I5 is mixed with the horizontal synchronizing pulses I4, to obtain in the output line I3 the composite` synchronizing signal represented in Fig. 1a. yIn the radio transmitter 20, this composite signal is mixed in the well known manner with the video signals from the amplifier 2|,.to form a composite television signal. In the transmitter, that part of the vertical synchronizing pulses, represented by the lighter portions 22 in Fig. 1a, is clipped or saturated off in the well known manner.

From the foregoing it will be seen that in my improved system and method, the horizontal synchronizing pulses or signals I 4 are not interrup'ted to permit insertion of the vertical synchronizing pulses I2, as in `the.various systems proposed heretofore, but are allowed to and actually do remain on continuously. Therefore,A the pulses I4 at the horizontal scanningl frequency of 13,230, are simplyobtained from the frequency dividerunit of the synchronizing generator I0,

`and mixed with the'vertical synchronizing pulses 0 control tube 31 is adjusted to draw sufficient plate television receiving system for intercepting and usin'fthe signals transmitted from a system such as is shown in Fig. 1;-

Fig. 3 is a view similar to Fig. 1, showing a modication; and

' Figs. 4, 4a and 5 are graphical views illustrative of the principle of operation in Fig. 3.`

With reference to Fig. 1, there is employed a synchronizing generator I0 which'is of the usual, conventionall construction, with the exception of omission of `the complicated circuit used heretofore to form the complex synchronizing wave forms ofthe prior art systems and methods referred to'.

The carrier source II for the vertical synchronizing pulses or signals, represented at I2 in y Fig. la, comprises' a frequency multiplier, which is driven from the master oscillator of the irequency divider in the synchronizing generator I0, and which provides a 529.2 k. c. wave, represented at I3, which is synchronous with the horizontal Vsynchronizing pulses supplied from the generator I0 at the rate of 13,230 per second, as. represented at I l. A constant phase relation is therefore maintained between the wave I3 forl vertical synchronizing and the horizontal synchronizing-pulses Il.

Thecarrier I3 is fed to `a tuned 'amplifier I5 which is modulated by pulses, represented at I6 and supplied from tha synchronizing" generator I0, and Whichvoccur at the desired vertical scanning frequency of 60. The output-of the amplifier I5, represented at I1, is therefore a ser-ies of the vertical synchronizing pulses I2. taken from the radio-frequency wave I3, and these vertical synchronizing pulses or signals I2 occur at the A desired vertical pulse or iield frequency of 60.

current so that tube I5 is biased off -at times or intervals when there is no signal on the grid of the tube 31. When the vertical signals I6 are applied to \the grid of tube 31 in negative polarity, the current in the common cathode resistor 38 decreases to where tube I5 becomes operative to allow a puise of carrier frequency to appear in the plate transformer 39 oftube I 5. from whence it is applied to the grid of tube 35 for mixing with the. horizontal synchronizing pulses Il from the tube 36.

The tubes 35 and 36 are mixer tubes, of the vertical and horizontal synchronizing pulses I2 and Il, respectively. There isa continuous train of the horizontal synchronizing pulses I4 applied to tube 36, and these pulses are mixed with the vertical carrier pulses I2 in this form, in the common resistor 40, from whence these mixed pulses are applied to the grid of tube 4I which may be a cathode load stage for low impedance output. The mixed synchronizing pulses or composite synchronizing signal, shown in Fig. 1a, is fed by line I9 from tube 4I to the transmitter 20, where it is superimposed on or added to the video signal, as explained.

The basic composite synchronizing signal as represented in Fig. 1a, is comprised of a continuvous train of the horizontal pulses I4 and the pulses I2 of the radio-frequency wave I3.

The negative half-cycles' of the vertical synchronizing pulses I2 extend considerably below the axis. as shown in Fig. la. These negative half-cycles also extend considerably below the negative portion of the horizontal pulses. The equal positive and negative portions of the carrier are not the best type of synchronizing signal,

. because the negative loop of the carrieris visible on the received picture. Therefore, it might be desirable to "clip off this negative loop and obtain a resulting signalsuch as is shown in Figs. 4. and 4a. I

For the above purpose, there may be used a circuit such as'isshown' in Fig. Y3, in which parts which correspond to andserve the same purpose a more continuous train of pulses is applied to the horizontal sweep circuit, and thereforel no transient such as mentioned above can occur.

From the foregoing it will be seen that in my improved method for synchronizing the respective scanning devices at the transmitting and receiving stations, there are mixed the synchronizing signals il occurring continuously at the given line frequency with a wave I3 ata radio frequency and which occurs only during intervals at the given field frequency, to obtain thereby the composite synchronizing signal as illustrated in Fig. `1a. Considering the broader aspect of my invention, this lresides in use of the source of synchronizing signals Il occurring continuously at the given line frequency, use of the wave at radio frequency and which occurs only during field intervals as illustrated at I2 in Fig. 1, and

-horizontal sweep circuit Lwould be responsive to frequencies from 5000 cycles to 20,000 cycles. An aperiodic sweep circuit, as called for in the claims, is intended to be a sweep circuit which is' responsive to control pulses or signals which might vary in frequency over a substantial range i. e., a frequency range, of which 'the highest frequency is from four to five times the lowest frequency; and which has such a characteristic of frequency-response without requiring synchronization or tuning adjustments.

The feasibility of using aperiodic sweep circuits, as in `my improved system and method, results in a vvery important advantage, which is that the entire system is flexible in the sense that the respective frequencies of the pulses transmitted for horizontal and vertical synchronizing might be changed as occasions or requirements A might arise, andthe sweep circuits at the receiver would still respond 'satisfactorily without, requiry A more detailed showing of a television receiving'system, for intercepting and using the signals transmitted from a system such as is shown in `Fig. 1, is disclosed in my copending application filed December 22, 1939 and bearing SeriallNo.

It will be understood that various modifica-l tions, within the conception of those skilled in' the art, are possible without departing from Athe spirit of my invention' or the scope of the claims.

I claim as my invention:

1. Inthe art of television communicatio between two stations, the steps in the method of holding in synchronism therespective scanning devices at said stations, which consist in generating pulses occurring continuously at a given line frequency and pulses at a given eldnfrequency. said pulses at line frequency lasting longer than the interval between line pulses generating a wave at a frequency that is an integral multiple greater than two of the line frequency, utilizing the pulses at the field frequency to obtain synchronizing pulses of said wave occurring at the same rate and at the same intervals as thepulses at the field frequency, mixing the pulses occurring continuously at the line frel quency and the pulses of said wave to obtain aV composite synchronizing signal having a component consisting of pulses occurring continuously at the line frequency, and utilizing said composite synchronizing signal for the purpose set forth.

2. In the art of television communication between two stations, the steps in the method of holding in synchronism the respective scanning devices at said stations, which consist in generating synchronizing signals at a given line frequency, generating from the'same source as said line frequency a signal at a frequencygreater than twice said line frequency and which is an even multiple of said line frequency, and using said wavefto obtain a source of pulses of said wave for synchronization at a given eld frequency said. pulses lasting longer than the interval between signals at line frequency.

3.- An electronic synchronizing system for television communication, comprising a source of synchronizing signals occurring at a given line frequency, a source of signals occurring at a given field frequency, a source of supply of a wave at a frequency greater than twice the line frequency, and means for applying said signals at the field frequency to key said wave to obtain synchronizing pulses of said wave occurring at the field frequency and occurring only during the field periods, said keyed signal lasting longer than theinterv'al between signals at line frequency.

4. An electronic synchronizing system for television communication, comprising a ,source of synchronizing signals occurring at a given line frequency, a source of signals occurring at a given field frequency, a source of supply of a wave at a frequency greater than twice the line frequency, means for applying said signals at the field frequency to key said wave to obtain synchronizing pulses of said wave occurring at the field frequency and occurring only during the field periods, said keyed pulse lasting longer than the interval betwen signals at line frequency, means for mixing said signals occurring at the line frequency and the -pulses of said wave to obtain a composite synchronizing signal, and a transmitter embodying a source of a carrier wave and means for modulating said carrier -wave by said composite synchronizing signal.

5. In a television transmitting system, a transmitter, a scanning device for generating video,

an electronic source of signals occurring at 'a' -given field frequency, a source of supply of a 'wave at a frequency greaterr than twice the line frequency, means for applying said signals at the field frequency to key said wave to obtain syn- -chronizing pulses of said wave occurring'at-the field frequency and only during the field synchronizing period, said pulse lasting longer than the interval between line synchronizing signals, and means for mixing said signals occurring at the line frequency and the lpulses of said wave to obtain a composite synchronizing signal, said transmitter embodying a source of a carrier wave and means for modulating said carrier wave by the video signals and by s'aid composite synchronizing signal.

6. An .electronic synchronizing system for television communication, comprising a source of supply of synchronizing signals occurring at a given line frequency, a source of supply of signals at a desired field frequency, a source of supply of a wave at a frequency greater than twice the line frequency, an amplifier having an output resonant circuit responsive only to said thirdnamed frequency and comprising a tube having a grid to which said wave is applied, a control tube for said amplifier tube having a grid and adjusted to draw normally sufficient plate current to bias off said amplifier tube, and means for applying said signals at the eld frequency in negative polarity to the grid of said control tube whereby the plate current drawn by said control tube decreases at leastto a value whereat said amplifier tub'e becomes operative to allow a pulse duration of at least one horizontal line interval,

and means for mixing said keyed carrier wave with said synchronizing signals that are at line frequency.

8. An electronic synchronizing system for television communication, comprising a source of Vsynchronizing signals at line frequency, a source of field synchronizing signals, a source ofsupply of a wave having a frequency greater than twice said line frequency synchronizing signals, means for modulating said wave to key it in only during pulse intervals of eld synchronizing signals in a manner so as to produce a field carrier wave of duration of at least one horizontal line interval, means formixing said keyed carrier wave with said synchronizing signals that are at line frequency and means for clipping off the composite pulsesof said mixed signals and wave to a.

fiat level. y

9. An electronic synchronizing system for television communication, comprising a source of vsynchronizing signals at line frequency, a source of field synchronizing signals, a source of supply of a wave having a frequency greater than twice said line frequency synchronizing signals, means for modulating said wave to key it in only during pulse intervals of field synchronizing signals lin a manner soas to produce a eld carrier wave of slow rise and duration of at least one horizontal line interval, and means for mixing said keyed carrier wave with said synchronizing signals that are at,` line frequency.

l0. In a televisionA transmitting system, apparatus for producing a composite television synchronizing wave form, comprising means for producing uniform horizontal synchronizing pulses recurrent at picture line frequency, means for producing a burst of a high frequency carrier lasting longer than one line period, said ,carrier being more than twice the frequency of. said line frequency, means for integrally relating said horizontal synchronizing pulse frequency and said carrier, and means for mixing said horizontal pulses and4 said burst of high frequency carner.

11. In a television transmitting system, apparatus for producing a composite television synchronizing wave form, comprising means for producing uniform horizontal synchronizing pulses recurrent at picture line frequency, means for producing vertical synchronizing signals, means for producing a burst of a high frequency carrier lastinglonger than one line period, said carrier beingmore than twice the frequency of said line frequency, means for integrally relating said horizontal synchronizing pulse frequency and said carrier, and means for mixing said horizontal pulses and said burst of high frequency carrier.

l2. An electronic synchronizing system for television communication, comprising a master signal l, oscillator, synchronizing signals at line frequency derived from said oscillator, means for deriving from said master oscillator a wave train having a frequency higher than said oscillator, a source of pulses at field frequency, means for electronically A keying said wave train by said pulses to provide said synchronizing signals at line frequency.

13. An electronic television transmitting system comprising a transmitter, a scanning device for generatingI video signals, means for controlling scanning action of said device, a sourceof synchronizing pulses occurring at a given line frequency, a source of synchronizing'pulses occurring at substantially uniformly spaced intervals and at a rate corresponding to the desired field frequency, each of said pulses being comprised of electrical pulsations occurring uniformly 'and only during the field synchronizing interval and said electrical pulses occurring at a rate greater thanl twice'said line frequency, and means for supplying to said transmitter said signals at theline frequency and said synchronizing pulses at field frequency.`

g RICHARD L. CAIWPBELL.

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