US2516972A - Video signal generator - Google Patents

Description

Aug. l, 1950 R. R. GANNAWAY 2,515,972

VIDEO SIGNAL GENERATOR I Filed Nov. 12, 1947 5 Sheets-Sheet l Roberson R. Gonnowoy Aug. l, 1950 R. R. GANNAWAY VIDEO SIGNAL GENERATOR 5 Sheets-Sheet 2 Filed Nov. 12, 1947 UEE? Roberson R. Gonnowoy Aug 1, 1950 R. R. GANNAWAY I 2,516,972

VIDEO SIGNAL GENERATOR Filed Nov. 12, 1947 5 sheets-sheet s Unsque Ich Dot Pattern Generator PPS.

Advoncgd INVENTOR. Roberson R. Gunnowoy BY FIG. 3

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FIG@ Q Q Q A118 l, 1950 R. R. GANNAWAY 2,516,972

VIDEO SIGNAL GENERATOR Filed Nov. 12. 1947 S sheets-sheet 5 Q O O. @6900 INVENTOR. Robertson R. Gunnowoy Patented Aug. 1, 1950 VIDEO SIGNAL GENERATOR Robertson R. Gannaway, Oak Park, Ill., assigner to Belmont Radio Corporation, Chicago, Ill., a corporation of Illinois Application November 12, 1947, Serial No. 785,378

11 Claims. l

This invention relates t picture transmission systems, and particularly to video signal generators for use in these systems. It is especially adapted to be employed in test equipment for servicing television receivers, although not limited to such` use.

Composite video signals, such as are used in commercial television systems, for instance, include various synchronizing pulses superimposed on pedestal pulses that occur at predetermined intervals in thesignal. The pedestal pulses are of two kinds, consisting of line pedestals, which occur once for each line period to produce horizontal blanking during the retrace interval between lines, and eld pedestals which produce vertical blanking during the retrace intervals lbetween successive field scanning operations. The synchronizing signals are of several typesline synchronizing, equalizing, and field synchronizing. The line synchronizing pulses occur during thehorizontal blanking intervals between lines and are superimposed on the line pedestal pulses. They also occur during the latter portion of the vertical blanking interval, being superimposed upon the iield pedestal pulse in this instance. The equalizing pulses occur during an intial portion of the vertical blanking interval, and also during a second similar portion of the vertical blanking interval. The field synchronizing pulses occur during the interval between these two groups of equalizing pulses. The shapes, durations and timing of all these pulses have been standardized for commercial equipment. The television picture components are located intermediate the various pedestal '(blanking) pulses in the composite signal.

In generating video signals it is customary to produce the various synchronizing pulses (line, iield and equaliz'ing) and the pedestal pulses (line and eld) by wave-shaping methods in separate generating circuits, following which theser pulses are brought together in the composite video signal. According to present practice these standard recurrent-pulse portions of the composite video signal are formed from elementary signals such as sine waves, and the vtiming and shaping of the pulses proceed concurrently. This method has necessitated a ycomplex series of gating .and clipping operations. At each step in the process, waveform distortions Imust be carefully avoided. For instance, courious other precautions must be observedy as is well known in the art. Consequently, the apparatus utilized heretofore to generate video signals has been complicated, bulky and expensive, and in some instances it has been considered impractical, as for example, in service installations.

A general object of the present invention is to simplify and reduce the cost of the equipment needed to generate television video signals without impairing the accuracy of the signals produced thereby.

A specific object of the invention is to separate the functions of wave-shaping and of timing in constructing the pedestal and synchronizingv signals.

Otherobjects are to eliminate many of the disadvantages of present-day video signal generators, and to provide an improved apparatus Which facilitates the production of video signals.

The invention is characterized by several unique features, among which it may be noted that pip-like timing pulses derived from an elementary constant-frequency signal are converted respectively into pairs of trigger pulses (synchronizing and desynchronizing) which control the formation of the rectangular pulse components of a composite video signal. These rectangular pulses (commonly referred to as square waves) are of variable width depending upon the spacing between the pulses in each corresponding pair of trigger pulses. The spacing between individual pulses in each pair is controlled by multivibrators or equivalent devices according to the particular width of the square (i. e., rectangular) Wave whose formation they control, and the spacings between pairs of trigger pulses depend on the periods of the timing signals. Suitable square wave generators of the 'type adapted to be triggered on and triggered off are used, and I propose to allocate one such generator for the pedestal pulses and another for the synchronizing pulses in a composite video signal. Arrangements are made herein for automatically suppressing the trigger pulses in the various sets when they are not needed, so that a single generator can be used to produce pulses of different widths; that is to say, both eld and line pedestal pulses originate in one generator, and the line synchronizing, vequalizing and field synchronizing pulses originate in another generator- For ya better understanding of the invention, together with other objects, features and advantages thereof, reference is had to the following description of the invention taken in connection with the accompanying drawings which illustrate a preferred embodiment.

In the drawings,

Fig, 1 is a timing diagram to show the relations of the various trigger pulses to the composite video signal in an apparatus constructed according to theprinciples of my invention;

Fig. 2 is a block diagram of the video signal generator, indicating its essential components;

Figs. 3 and 4 together constitute a schematic wiring diagram of the apparatus, with certain conventional portions thereof being shown in simple block form or omitted;

Fig. 5 is a perspective View of the signal generator mounted in a carrying case for portability; and

Fig. 6 is an elevational view of the chassis in the portable unit.

In pursuance of the above stated objects of my invention, I provide pedestal and synchronizing pulse generators of the type adapted for thev pro'- duction of accurately shaped pulses in response to timed trigger signals. The function of timing. these pulses is performed by trigger pulse generators which are not required to produce accurately shaped pulses. I have found that the Eccles-Jordan trigger circuit is particularly wel-l' suited for the purpose of producing the pedestal and synchronizing pulses, and in accordance with the preferred embodiment of the invention disclosed herein, I provide one such circuit for generating the pedestal pulses and another for generating the synchronizing pulses. These pulse generators are accurately triggered on and on by multivibrators which are controlled by well known timing circuits, the positions and durations of the respective pulses being determined according to the functions which they will perform in the completed signal (that is, horizontal and vertical blanking, line and eld synchronizing, and equalizing).

A typical composite television video signal (with the picture signal components omitted therefrom) is illustrated diagrammatically at the top of Fig. 1. The picture is transmitted and received during those portions of the horizontal line periods (designated I-I) intervening between the regularly spaced blanking intervals, which occur while the scanning and receiving electron beams are retracing. The picture signal amplitude will, of course, vary in accordance with the image that is being received. In the usual video signal the picture component for any particular horizontal line may have an irregular appearance as indicated by the broken line 5 in Fig. 1. If desired, an artificially produced picture signal, such as a series of dots, may be provided (as is the case in the illustrated embodiment of the invention), the representation of such a signal being omitted from Fig. 1.

The picture signal variation takes place between extreme amplitudes respectively designated black and white in Fig. 1. In standard nega tive picture modulation the minimum level is white and the maximum level of the picture signal is black, as is well known. The horizontal bla'nking is produced by line pedestal pulsesy S in the video signal, which have an amplitude equal to or greater than the black level of the signal. During the horizontal blanking intervals, additional pulses known as line synchroniz ing pulses l are transmitted, these ypulses being superimposed on the line pedestal pulses 6' and extending into the blacker-than-black region Aof region, are several series of pulses comprising the Jordan type.

equalizing pulses 9, iield synchronizing pulses Eil, andv line synchronizing pulses l. The equalizing and fieldv synchronizing pulses 9 and lil occur at the rate of two per line period. The standard field pedestal pulse has a width which must be between 13H and 21H, a typical value being 18H, where l-I is a line period. In the rst 3H there is transmitted a train of six equalizing pulses 9, followed in the next 3H by an equal number of eld synchronizing pulses ld. These are succeeded by another series of six equalizing pulses El in the third 3H. The remainder of the vertical blanking interval is occupied by line synchronizing pulses l spaced apart by complete line periods. At the end of the vertical blankingv interval the scanning beam is ready to commence viewing another field, and the picture signals, line pedestal pulses, and line synchronizing pulses again cocu;1 in the previously described order.

The time interval between the beginning of the field pedestal and the rst equalizing pulse is not critical, as is well known. A proposed value is .62H with a negative tolerance of zero and a positive tolerance of H. In the present instance, a value of 1/I-l has been chosen in order clearly to differentiate the commencement of this pulse from the rst equalizing pulse 9. This is done for convenience only, and the invention is not limited thereby.

In'accordance with the present invention I propose to generate the pedestal pulses (both eld and line) of a composite video signal in a square wave generator l2, Fig. 2, which may be of the Eccles-Jordan type. Likewise, all of the synchronizing pulses (by which term. is meant the line synchronizing, eld synchronizing, and equalizing pulses) are generated in another square wave generator M which may be of the Eccles- Details of these particular generators are shown in the schematic circuit diagrams, Figs. 3 and 4. Each of the generators i2 and |.4 has two stable states, so that the various recurrent pulses in the composite video signal can be initiated and terminated at the appropriate times by applying to the generators l2 and il! trigger pulses which are designated in Figs. 1 and 2 by the letters A, B, C and D. The trigger pulses A synchronize the pedestal pulse generator l2; the trigger pulses B desynchronize the .pedes tal pulse generator l2; trigger pulses C synchronize the synchronizing pulse generator E4, and the trigger pulses D desynchronize the synchronizing pulse generator I4. The time relations between the trigger pulses and the composite video signal are represented in Fig. l.

The terms synchronize and desynchronize as used with reference to circuits controlled by the trigger pulses and other control pulses described hereinafter are, for all practical purposes, synonymous with initiate operation oi and terminate operation of, respectively, the rst-mentioned nomenclature being extensively employed in the art bccalls'e of the particular .s manner infv'vhichmultivibrators'f-'and trigger circuits controlled by these-pulses function.l

Referring now primarily toFig.` 2, which may be'supplemented by reference to Figs.` 1,- 3 'and 4 Where necessary, the above-mentioned trigger pulses are obtained'from'various multivibrators as indicated. Themultivibrators are timedin their operations through the medium of timing pulses' which are' derived from standard timing pulse generatorsv that are-familiarito those skilled in the art: These timing pulse generators are, in

the present instance,required only to synchronize and desyn'chronize the various'fmultivibrators and have no connection whatsoever With shaping the naloutput pulses produced by the pedestal and synchronizingvk pulse generators1f|2and-I4, the shaping function ybeing performed entirely by the latter generators. y l f i Thetiming pulses whichwcontrol the multivibrators yare of tourkinds--SLEOO pulses per vsecond, 31,500: pulses per second advanced,- 31,500 pulsesy per second delayed, and f60`pulss per second (the last-mentioned pulsesfcoinciding with certain'offthe advanced pulses). In addition, a pulse signal of intermediate frequencysuch as 1500` fpulsesper second, derivedzfrom the same timer chain: is employed to synchronize the picture signal generator "I6 which preferably is of the type thatfurnishes afdot pattern'` when the equipment is being used forftest purposes.

` A line key multivibrator .l I I3 is synchronized by the l31,500 pulses per second timingsignal and is adjusted to divide the pulse repetition frequency 2 to l. This line key multivibrator synchronizes the line pedestal multivibrator 20 as indicated, the leading edge of the multivibrator output being utilized for this purpose. The terms leading edge and trailing edge denote which of the tubes in each multivibrator is effective in furnishing output. The line key multivibrator also operates an unsquelch tube 22 which per-mits the line synchronizing multivibrator 24j to operate on alternate synchronizing pulses from` the 31,500 pulses per seconddelayed'signal source. Thus, the multivibrator- s 20 and 24 normally function to supply those portions ofthe various trigger signals A, B, C and D that are instrumental in producing the line pedestal and line synchronizing pulses. l

The terms squelch tube and unsquelch tube designate tubes which enable certain multivibrators to control the operation of certain other multivibrators. A squelchr tube` becomes conducting when its controlling multivibrator res, and shunts the controlled multivibrator, preventing it from responding to synchronizingpulses. :An unsqueleh tube becomes non-conducting when its controlling multivibrator fires, thus permitting the controlled multivibrator to operate normally.

For producing the eld pedestal pulses there is provided a multivibrator 26 that is synchronized by the 60 pulses per 'second signal and desynchronized by the `31,500 pulses per second advanced signal. While each multivibrator is to be adjusted to a certain period of operation as indicated in Fig. 2, the length of this period maybe made to Vary step-Wise by applying a desynchronizing signal to such a multivibrator. The trailing edge of the multivibrator thenoccurs coincidentally with Ione of the desynchronizing pulses so that theperiod of .the multivibrator operation will vary'in steps rather than continuously as` would otherwise occur.. VThe leading edge pulsesv from the eld pedestal and line pedestal multivibratorslZIi and'20 ,are appliedto an amplifier 28', having separate amplifying sections struction as shown.

forl the two pulses, and a combined output circuit through which the trigger signal A 'is applied to the pedestal pulse generator I2 for synchronizing this generator." The trailing edge pulses from the multivibrators 26 and 20 are fed to an amplier 30 which furnishes awcombined desynchronizing trigger signal B to the pedestal generator I2. The eld pedestal multivibrator 26 controls a squelch tube 32 for squelching the line pedestal multivibrator during the vertical blank'r ing interval. Hence, line pedestal triggerpuls'es are not generated While eld pedestal trigger pulses are being generated. The pedestal pulse generator I 2 has a rst com ponent, including the left-hand tube in the rectangle I2, Fig. 3, to which are applied the sync triggers A (Figs. l and 2) from the amplifier 28 for initiating thevarious pedestal pulses. Similarly, the generator `I2 has a second'component, including the right-hand tube in the rectangle |22, Fig. 3, to which are applied the desync triggers B (Figs. l and 2) for terminating the various pedestal pulses. These two tubes actually are enclosed by a single envelope in the con'- -Each tube has an abrupt action so as to impart steep leading and trailing edges to `the generated pulses. The manner in which these tubes are coupled together for providing an Eccles-Jordan type of trigger circuit is clearly illustrated in Fig. 3 and is Well understood by those skilled in the art.

; During the rst portion of the vertical blanking interval it is essential that the line synchronizing multivibrator 24 be prevented from functioning. This is accomplished by the key No. 1 multivibrator 34 which is synchronized by the 60 pulses per second timing signal and desynchronized by the 31,500 pulses per second timing signal. The multivibrator 34 has a period of operation equal to 9H during which time it operates the squelch tube 36 for suppressing the line synchronizing multivibrator 24, vand thejunsquelch tube 38 to condition the equalizing pulse multi--V vibrator 40 for operation. The key delay multivibrator 42 synchronizes the key No. 2 multivibrator 44 which commences operation when the period of the key delay multivibrator ends. However, inasmuch as the key delay multivibrator operates for approximately the first 3H of the vertical blanking interval, the key No. 2 -multivibrator 44 is inactive during that time. There- Afore, the equalizing pulse multivibrator t0 is effective to feed synchronizing and desynchronizing trigger pulses respectively to the amplifiers 46 and 48, the outputs of which are applied to the synchronizing pulse generator I4. f The synchronizing pulse generator I4 shown in Fig. 3 has essentially the same construction als the pedestal. pulse generator I2 previously described. fSync triggers C (Figs. l and 2r) areapplied by the amplifier 46 (Fig. 4) to the left-hand tube in the rectangle I4 for initiating the respective synchronizing pulses, Desync triggers D are applied by the amplifier 48 to the right-hand tube in the rectangle I4 forterminating the respective synchronizing pulses. y

During the second 3H'of the vertical blanking interval thekey No. 2 multivibrator operates the squelch tube 50 for suppressing the equalizing pulse multivibrator -40 and it also operates the 'insquelch tube 52 for exciting the eldvsynchronizing multivibrator 54. vThe multivibrator 54 is effective to supply those trigger pulses in the signals C and D for producing the wide iield Synchronizing pulses I0 of Fig. 1. When the key No. Zmultivibrator 24 ceases operating,f`the`unsquel'ch tube 52 again suppresses the field lsynchronizing multivibrator 54', while the equalizing pulse multivibrator 4B is again unsquelched. This causes equ'alizing pulses S to be resumed throughout the third 3H of the vertical blanring interval, at the end of which time the key No. 1 multivibrator 34 'ceases operating and the multiv-ibrator di) is squelched.

During the latter portion of the vertical blankin'g interval the line synchronizing multivibrator 24 is free to operate to produce the line synchronizing pulses l through the medium of the synchronizing pulse generator Hl.

The picture signal generator l of Fig. 2 is illustrated schematically at the bottom of Fig. 3. The 1500 pulses per lsecond timing signal is used to synchronize a multivibrator G@ whose width is adjusted to about 2H. The multivibrator 6B cuts off a normally conducting starting tube E2 thereby interrupting the flow of current in the coil of a tank circuit '54. When the tube 62 is cut off, a train of oscillations is set up in the tanlr circuit 64 at the resonant frequency of this circuit. A keep-alive oscillator 66 prevents the amplitude of the oscillations from decreasing until the starter tube 62 again becomes conducting as the multivibrator 60 returns to its normal state to terminate the oscillations. The frequency of the tank circuit 64 is adjusted to be an even multiple of the line frequency. e. the /l-Oth multiple, or 630 kc. The result is a series of chains of sine waves of 630 kiloc'ycles frequency, these chains occurring 1500 times per second, or 25 times per ii'eld, and lasting for about tvvo horizontal lines of the scanning, depending upon the adjustment. These Waves 'are passed through an amplifier ES to a pulse shaping circuit 'le that forms the waves into pulses for use as a dot pattern in the video signal. These dot pattern pulses are combined with the pedestal pulses in the 'mixer '12, into whose plate circuit are also fed the synchronizing pulses, and the combined signal is fed to the out-- put amplifier T4. The composite video signal then appears at the terminals 16 and 'I8 which are alternatively selectable depending upon whether a lpositive or negative composite signal is desired. In Fig. 2 the mixer T2 and output amplifier 14 are designated generally by the numeral 80. The picture signal appears on the viewing screen as 25 horizontal rows of dots with 4i) dots in each row. Choice of a particular number of rows and dots per row is arbitrary, 'and the invention is not restricted thereby.

The television video signal generator disclosed herein is of considerably simpler construction than the prior types of apparatus for this purpose. It is ideally suited for use in test equipment to service television receivers. However, it may be employed in television transmitters as well. To this end there are provided terminals 82 and84, Fig. 3, in the held pedestal and line key multivibrator circuits 26 and I8, respectively, whereby the operation of the illustrated pedestal and synchronizing pulse generating equipment may be correlated with that of a television camera or other picture signal source, and the grid of the mixer 72 to which the dot pattern signal normally is applied may be switched instead to a terminal 86 so that signals from the picture source will appear in the output of the mixer to replace the dot pattern.

The video signal generator herein disclosed is especially suited for portable use. In Figs. 5 and 6 there is illustrated a portable unit complete with power supply and all of the components illustrated schematically in Figs. 3 and Ll. The generator chassis is mounted vertically in a carrying case 92 havinga handle 94, feet 9S and a detachable cover or lid 9B. InlFig. 6 the chassis is shown `exposed to View after removal of the cover 98,.the various tubes and other circuit elements being represented by circles and rectangles for simplicity. The entire unit measures approximately 24 inches by 16 inches by 7 inches.

Numerous advantages of the disclosed system will be apparent to those skilled in the art. Electrically, the apparatus is much simplerin design and easier to maintain than prior video signal generators. Almost all of the tubes may be of a uniform type, preferably double trlodes. The apparatus also has improved mechanical features such as relatively small size and weight. The cost of the generator is suiiiciently moderate so that it will be a profitable addition to servicemens equipment. The circuit design is highly adaptable for locating trouble in television receivers. The various components of the test apparatus can be operated independently, if desired, so that only those components of the receiver which respond, for example, tothe pedestal pulses or the synchronizing pulses are tested. A variety of other uses willreadily suggest themselves.

While a preferred embodiment of the invention has been illustrated and described, it will be obvious that modifications and variations can be made therein without departing from the spirit of the invention as set forth in the appended claims.

I claim:

l. vIn an apparatus for generating a composite video signal including 'synchronizing pulses of various durations and pedestal pulses 'of various durations, all of) said pulses occurring respectiveiy at predetermined times in the video signal, thc 'combination comprising a iirst trigger circuit adapt'ed to be triggered back and forth be'- tween two stable states i' respectively initiating and terminating each f the various synchronizing pulses ccurring in the video signal, a second trigger circuit adapted to be triggered back and forth between two 'stable states for respectively initiating and terminating each of the Various pedestal pulses 'occurring in the video signal, a plurality of multivibrators. one for each of the various kinds of synchronizing pulses and pedestal pulses included in the composite video signal, eacli lf said multivibrators being elfective intermittently to produce pairs of triggolf pulses in which the pulses of each pair are separated Athe time interval occupied by a pulse of a particular kind in the composite video signal, timing controlmeans effective to 'space the successivehoperations f each multivibrator to coincide with' the successive occurrences of a particular kind of pulse in the video signal, and a plurality of pulse-handling devices peratively interposed between said multivibrators and said trigger circuits whereby all of the trigger pulses corresponding to the various synchronizing pulses in theA video signal are applied to said lirst trigger c'zirfc'suitI and all of the trigger ,pulses corresponding to the various pedestal pulses in the video signal are applied lto said second trier ger circuit. Y y

2. In a videol signal generator, a trigger circuit including a pair of electron tubes for generating pulses to be included inthe video signal, the 'first of said tubes being effective when operated to initiate a pulse, and the second of said tubes being effective when operated to terminate the pulse, saidtrigger ,being so ,arrangedthat perati've' 'in' response" to a `momentary trigger ap lse'appli'ed thereto, trigger pulse' generators/,each being 'adapted' intermitftently'togeneratevpairs of trigger pulses, wherein 5 leach pair consists fof f ing pulse', a pulse ingall 'off the leadingA pulses from leading puise andI a trailndlii'igdevice for applysaid trigger pulse generators to said tube in lsaid trigger circuit, asecndpulse-handling',device forI pllo 'plying 'all of the trailing pulses from said'trig r pulse generators to said Asecond electro'nftube of 3. In a 'video :signal"'gent-irator,` pedestal'pulse generatingmeans*A comprising atrigger'circuit having a rst electrontube effective in responsemgo to a momentary synchrnizing, trigger fpulse toU initiate a pedestal pulse,"'an"d Aa second 'electron tube effective iurespo'lrisetona inomentary'dej synchronizing trigger pulse' to 4`terminate the pedestal pulse initiated by s'aid` first electronw25 tube, a first multivibrator adapte'dt'o furnishr* lalternate synchronizing and desynchroniz'ing trigger pulses, a' second" multivibrator adapted to vfurnish alternate synchronizing and desynchronizing'trig'ger pulses, 'pulse-handling means for 30 applying all of said synchronizing trigger 'pulsesw fromboth of said"multivibrators to said rst electron tube, other pulse-handling means for applying all ofthe desynchronizing trigger pulses from both ofy said multivibrators to said secondm35 electron tube, and timing means to effect oper-t" ation ofsaid multivibrators coincidentally with the respective occurrences of horizontal and verticalblanking intervals in the voutputvideo sig- 4. In combination with thepedestal pulse generatingv means set forth` in the'preceding claim 3, squelclu `means to prevent operation'of one'of i"said multivibrators when the 'other of said multivibrators is operating.

5. An apparatus for supplying the synchronizing pulses of a composite video signal, comprising a trigger circuit having a first electron tube component effective when operated to initiate a synchronizing pulse and a second electron tube component effective when operated to terminate the synchronizing pulse, a first multivibrator effective when operated to apply intermittent pairs of trigger pulses to said trigger circuit, a second multivibrator effective when operated to apply intermittentpairs of trigger pulses to said trigger circuit, control means including a third multivibrator for causing said first and second multivibrators to operate at different times, and pulse-handling devices operatively interposed between said trigger circuit and said multivibrators for feeding the first trigger pulse of each pair of pulses furnished by said first and second multivibrators to said rst component and the second trigger pulse of each pair of pulses furnished by said first and second multivib-rators to said second component.

6. An apparatus as set forth in the preceding claim 5, wherein said control means includes a squelch tube operatively interposed between said third and rst multivibrators, and an unsquelch tube operatively interposed between said third and second multivibrators.

7. In a picture transmission system, a composite video signal generating means compriseine , ing a pedestal pulseg nerator, a synchronizing pulse generator, each 'of i i ld pulse generators being of thetype that'inclu'des a rst electron tube component eiective, when operated toinitiate a rectangular pulse' and a second electron tube component effective when operatedzto' terminate the rectangular pulse, a picture signal generator, meansfor combining the respective outputs of all of the aforesaid generators to furnish the composite video signal, iield pedestal and line pedestal multivibrators for triggering said pedestal pulse` generator; line synchronizing, equalizing and 'el'cl'synchronizing multivi- `brators for triggering said synchronizing pulse generator; eachof the aforesaid multivibrators being adapted when" operated to furnish a pair l of trigger pulses'for vexciting the` respective one of said pulse generators, pulse-handling devices whereby the first triggerypulsein each 'pair is applied to the rst component of the respective pulse generator and' the second' triggerpulse of each pair is applied to the second component thereof, timing control means for operating all of said multivibrators in aipredetermined timed relation, including key multivibrators squelch tubes, unsquelch tubes and a source of timing signals, all arranged to govern the sequence and manner in which the various trigger pulses are generated to correspond with the respective occurrences of the various pedestal and synchronizing pulses in the composite video signal.

8. An apparatus for generating a composite video signal including recurrent 'pulses of various types having different time durations, such apparatus comprising a plurality of trigger pulse generators Veach operative to furnish synchronizing and desynchronizingtrigger pulses in alternate sequence coincidentally with the respective times at which the'recurrent pulses of a particular type start andstop, pulse generating means including a rst portion for initiating a pulse and a second portion f or'terminating such pulse, bothvof' said portonsbeing responsive to trigger pulses applied thereto, pulse handling means for applying to said first portion said synchronizing trigger pulses as the same are generated by said plurality of trigger pulse generators, other pulse handling means for applying to said second portion said desynchronizing trigger pulses as the same are generated by said plurality of trigger pulse generators, with said pulse generating means being operative to generate the recurrent pulses of the various types in response to said trigger pulses, and output means for incorporating the pulses generated by said pulse generating means in a video signal wave.

9. An apparatus for generating a composite video signal including rectangular pulses of various durations occurring at different times in the signal, such apparatus comprising a plurality of trigger pulse generators each operative to furnish synchronizing and desynchronizing trigger pulses in alternate sequence, control means timing the operation of said trigger pulse generators for causing the synchronizing and desynchronizing trigger pulses furnished by each of said trigger pulse generators to coincide with the respective times at which rectangular pulses of a given duration are initiated and terminated in the video signal, a rectangular pulse generator capable of being triggered back and forth between two stable states for respectively initiating and terminating a rectangular pulse, pulse handling means for applying all of the synchronizing trigger pulses from said trigger pulse gen-

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