US2171537A

US2171537A - Method and apparatus for producing composite signals

Info

Publication number: US2171537A
Application number: US282504A
Authority: US
Inventors: Frank J Bingley
Original assignee: Philco Radio and Television Corp
Current assignee: Philco Radio and Television Corp
Priority date: 1935-11-23
Filing date: 1939-07-01
Publication date: 1939-09-05
Anticipated expiration: 1956-09-05

Description

Sept. 5, 1939.

F. J. BINGLEY METHOD AND APPARATUS FOR PRODUCING COMPOSLTE SIGNALS original Filed Nov. -25, 1955 4 Sheets-Sheet l Sept, 5, 1939. F. J. BINGLEY 2,171,537

METHOD AND APPARATUS FOR PRODUCING COMPOSITE SIGNALS Original Filed Nov. 23, 1955 4 Sheets-Sheet I2 vvvvvvv IAAAA .e Sept. 5, 1939. F. J. BINGLr-:Y

METHOD AND APPARATUS FOR PRODUCING COMPOSTE SIGNALS 4 Sheets-Sheet I5 Original Filed Nov. 23, 1935 Il Illlui NlllillH llllll 1| ummm F. J. BINGLEY 2,171,537

METHOD AND APPARATUS FOR PRODUCING COMPOSITE SIGNALS Sept. 5, v1939.

Original Filed Nov. 23, 1935 4 Sheets-Sheet 4v Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR PRODUC- ING COMPOSITE SIGNALS Original application lNovember 23, 1935, Serial No. 51,324. Divided and this application July 1, 1939, Serial N0. 282,504 A 11 Claims. (Ol. P18-69.5)

This invention relates to improvements and modifications in television and like systems and has for its general object the provision of certain novel features which are particularly applicable to television systems but which may be useful in other systems wherein electrical waves are transmitted.

The present application is a division of my copending application Serial No. 51,324, illed Nov. 23, 1935.

In a conventional television receiver employing a scanning beam, two types of synchronizing signals are` usually necessary, one to synchronize the horizontal scanning of deilecting circuit f the receiver with that of the transmitter, and another to synchronize the vertical scanning or deflecting circuit of the receiver with that of the transmitter. In conventional practice, it has been found desirable to transmit these synchronizing signals through the same signal channel which carries the video or picture signal, the practice being to blank out the video signal throughout the time intervals during which the synchronizing signals are transmitted.

In such a system, it is necessary that the time relation between the horizontal and vertical deecting circuits be maintained constant with a high degree of` precision to prevent distortion of the picture due to irregular scanning.

By means of the blanking process, the video signal is arbitrarily given a value corresponding to the no-light level of the picture and the synchronizing signals are added to this blanked video signal in such a direction as to cause no light when the composite signal is applied to a picture tube. As may be readily seen, for the duration of the blanking interval no picture can be transmitted. Consequently, it is desirable to make this blanking interval as short as possible and, in general, for horizontal blanking, the time duration of the blanking interval portion should be less than percent of the duration of the horizontal line, and the vertical blanking interval should be not over 10 percent of the total scanning time. Dur ngthe vertical blanking interval, it is desirable that the horizontal scanning means at the receiver be maintained in synchronism with that at the transmitter. To accomplish this, it is necessary to so transmit the horizontal and vertical synchronizing signals that they do not interlere one with the other. Various means have been proposed by which this may be accomplished, such as that, for example, disclosed in the copending application of Richard L. Campbell for Composite signal systcm,-Serial No. 27,074, led

June 17, 1935, in which the vertical synchronizing pulse is serrated to allow the simultaneous transmission of horizontal synchronizing signals. In that system, the duration of the vertical syn- 'chronizing signal pulse may be equal to that of image showing the method of scanning; V

` Fig. 2 represents one frame of a television Fig. 3 is a block diagram showing in greater detail the seynchronizing signal generator which l forms part of the system of Fig. 1;

Figs. 4 to 6 are circuit diagrams` of certain of the units of Fig. 3;

Fig. 7 is a diagrammatic representation of electro-optical means by which some of the signals generated electrically by the system of Fig. 3, may be generated mechanically;

Fig. 8 is a face view of the disc employed in this system;

Fig. 9 shows the wave form of the composite signal obtained by combining the video signal, the background control signal, the blanking signals and the synchronizing signals;

Fig. 10 represents two portions of a carrier wave modulated with such a composite signal after the manner of the invention;

Fig. 1l is a diagram of the signal combining amplifier; and

Fig. l2 is a circuit diagram of that part of the receiver which provides for synchronized scannmg.

Referring particularly tc Fig. 1 of the drawings, there is illustrated a complete television transmitting system embodying the invention. The arrow heads indicate the directions of ilow of energy between the various units. This illustration is schematic in form and is intended only to enable a general understanding of the complete transmitting system.

As shown in Fig. 1, the transmitting system includes a video signal generator which supplies yinclude intelligence by which background control maybe obtained at the receiver. The horizontal synchronizing signal,l the vertical synchronizing signal, and the corresponding blanking signals are supplied to the composite 'signal amplifier by a synchronizing signal generator.

The horizontal and vertical synchronizing signals are also used respectively toenergize the horizontal and vertical scanning means at the video l 'signal generator.

'Ihe composite signal is supplied to a transmission line which extends between the studio and the transmitting station. I'he composite signal is transferred to a modulated stage or amplifier. 'I'his amplier, which is also energized by an oscillator, produces a modulated carrier wave in which the modulation is in accordance with the composite signal. may be supplied directly to a radiating system, but it is preferably amplified first by a linear R. F. power amplifier and then radiated..

For a clear understanding of how the vertical and horizontal synchronizing signals should be co-related, reference may be had to Fig. 2 of the drawings `which illustrates the method of interlaced scanning. The scanning beam may start at Aand move downward to the right following the dot-and-dash path. At B, the video` signal yis blanked and the beam is returned to point D finition requires that each i'rameI be subdivided into a large number of lines which are scanned successively by the scanning apparatus. The

' second and a horizontal scanning signal of 10,350

pulses per second. The time required to scan the entire frame once in such case would be of y the order of magnitude of 33,300 micro-seconds,

this being the time required for the scanning beam to move fromy A to G. 'Ihe time required to scan one horizontal line would be about 9'( microseconds. For purposes` oi' illustration, the

'invention will be described with respect to such a particular system. It will be understood, however, the invention is in no wise to be limited to these particular values but is applicable to other systems.

According to the present invention, narrow vertical synchronizingpulses, together with the horizontal synchronizing signal and the blanking signals, are generated by the s ynchronizingsig- 'Ihe modulated carrier wavek nal generator oi'Fig. l. which may take various forms as described hereinafter. 'By combining the said signals, the composite signal which may be of the form shown in Figs. 9 and 10 is formed. In these figures, showing respectively thecomposlte signal and the modulated carrier, the horizontal synchronizing pulses are shown at I while the narrow vertical pulse is shown at 2, these signals occurring during the intervals when the video signal is blanked.

Broadly the method of the present invention contemplates the provision of two synchronizing signals which may be combined, transmitted as a combined signal, and then used to synchronize separate means without interfering with the continuity of operation of these means. As shown in Figs. 9 and 10, the synchronizing signals, which comprise pulses of brief duration, are positioned on one side of a voltage level Ai-Az which level .is established at the transmitter and reproduced at the receiver. By virtue of this transmittable reference, if desired, the synchronizing signals may be separated from the video by amplitude selection. Furthermore, one synchronizing signal may be separated from the other by removing the other by amplitude selection. A preferred form of this method contemplates the use of a narrow vertical synchronizing pulse having an amplitude greater than that of the horizontal synchronizing signaLpulse so that by amplitude selection a signal free from horizontal pulses and including only the vertical synchronizing signal may be obtained. A signal containing only the horizontal synchronizing pulses and from which the vertical pulses have been removed may be i obtained by the use of wave shape or frequency selective networks as will be pointed out more clearly below. It will be understood. of course, that wave shape or frequency selective means may be employed in both instances in lieu of the amplitude and wave shape lselection of the preferred form.

The fundamental requirements of a synchronizing system for television use are as follows:

(l) Positive and precise synchronization must .be effected.

.deleteriously affect the performance of the system.

In the specific case of a 345 line frame' per second, interlaced system, the horizontal synchronizing signal may comprise'pulses of 4 to 'l microseconds'duration occurring` at a rate 4of 10,350 pulses per second. Ihe vertical synchronizing signal may comprise pulses of30 to 45 microseconds duration occurring 60 times per second. As may be seen in Fig. 9 these signals are established in an output circuit of an ampliiler on one side of a reference axis. If simple rather than interlaced scanning were used, the duration of the vertical synchronizing pulse might be doubled.

An important feature of the present method is that the transmission of horizontal synchronizing pulses is continuous-and the vertical synchronizing pulses so timed that they do not interfere with the former signal. Thus, the horizontal scanning means can at all times be maintained in synchronization with the synchronizing signal and the departure from synchronization sometimes occasioned by the presence of the vertical signal of systems of the prior art avoided.

Another important advantage of this narrow impulse method is that while the slope of the narrow vertical pulse is suiciently different from that of the horizontal synchronizing signals to permit discrimination by means of wave front selective circuits, still the slope of the vertical pulse is suiiciently steep to permit very accurate synchronization of the vertical scanning means. The slope of such a pulse will be approximately 25 times greater than `that of the broad vertical pulse disclosed in the above-mentioned Campbell application and, consequently synchronization I may be made 25 times more accurately. For example, if the time error due to pulse-slope or amplitude various, or both, of the Campbell system were as large as 50 microseconds. using the arrow pulse system this might be reduced to as low as 2 microseconds.

While the wave shape of the narrow pulse resembles that of the horizontal synchronizing signals. more closely than does the broader vertical pulse of the prior art, there is still adequate difference to permit easy separation by wave front or frequency selective networks. For the case of an interlaced picture such as that disclosed in Fig. 2, it is necessary that the duration of the narrow vertical pulse be less than one-half the duration of one line. Due to the interlacing, the narrow pulse will at one time follow .immediately after a horizontal synchronizing pulse and the next consecutivevtime will appear immediately in front of a horizontal synchronizing pulse. For this reason there will be less symmetry between the synchronizing signals which return the scanning beam to the point A of Fig. 2, and the signals which would return it to point F than there would be between the corresponding signals in the case wherein the broad vertical pulse is used. On the other hand. when using the Campbell system, it is necessary to blank the video signal for a time duration of about 16 lines to permit the scanning beam to return from the bottom of the picture to the top. In the device of my invention, the narrow impulse may occur between say, the second and third horizontal pulses',` occurring during this vertical blanking period, thus leaving a time interval corresponding to, say, 13 lines during which the picture is blanked, and the horizontal scanningr means may recover from any transient introduced by the vertical pulse. In the corresponding case wherein a broad vertical pulse is used. this pulse may 'exten'd from, say the second or third to the sixth or seventh horizontal pulse of the blanked period. leaving a shorter time for the horizontal scanning meansl to recover from the transients introduced by this broad vertical pulse. Alternatively. for

certain types of television reproduction; the

blanking period may be reduced thus permitting the reproduction of a more detailed picture. In addition, the greater energy of the broad vertical pulse tends to introduce a larger transient than that of the narrow pulse, even though the latter may be of greater amplitude than the former. In general, it has been found that the circuit which discriminates between the horizontal and vertical signals, in the case wherein the narrow vertical pulse is used, may be so adjusted as to enable it to recover from any transient disturbance in less than the time of one horizontal line.

As will be readily apparent, if the vertical pulse is of greater than one line duration, it is necessary either to omit some of the horizontal pulses, or to provide serrations in the vertical pulse in which the horizontal pulses may be positioned. The former condition is undesirable due to t-he lack of synchronization occasioned by the presence of the vertical pulse. The latter method oiers some disadvantages by virtue of the fact that some frequency components within the range of the horizontal synchronizing signal may be introduced by the serrations in the vertical pulse. In this respect the use of the narrow vertical pulse offers the advantage that little transient signal is introduced in the horizontal signal separatorby the vertical pulse and yet thel continuity of the horizontal synchronizing signal is not interrupted.

synchronizing signals including the narrow vvertical pulse may be generated by an electronic generator, as shown in Fig. 3 or by an electromechanical system as shown in Figs. 7 and 8 or bia combination of the two. It will be understood that such signals may also be generated by other means but the generators shown have been found very satisfactory.

Referring now to Fig. 3, there is shown a block diagram of a generator which may be employed t generate all the necessary synchronizing and blanking signals for the transmitter in a 345 line double interlaced system as described above. A 60 cycle signal is derived from a master source (e. g. a power main) which also may supply energy to a movie projector unit #16 or similar device which must be correlated with the scanning system. The 60 cycle signal is filtered and its phase correlated with unit #1b by unit #1. The signal is then squared inunit #2a and the 15th harmonic (900 c. p. s.) is selected in unit #3. This 900 cycle signal may be used to coordinate the vertical and horizontal synchronizing and blanking signals.

Squared 900 cycle signals, from unit #3 are supplied to unit #4 in which the 17th harmonic may be selected, and vthis is supplied to a frequency halving circuit unit #5 which produces the required horizontal pulses. Horizontal blank ing pulses may be derived by unit #6 from the horizontal synchronizing signal.

60 cycle signals are also supplied 'to unit #9 from unit #1. In unit #9, two 60 cycle signals are formed, slightly displaced in phase. Both signals are passed through independent ampli-4 tude limiting circuits to produce rectangular pulses which are then combined in opposed relation to form a narrow 60 cycle pulse. 'I'his pulse may be used to select one or more 900 cycle pulses from unit #3, thus producing vertical blanking pulses occurring at the rate of 60 per second but timed by the intermediate frequency and thus tied-in in time relation with the horizontal signals.

The above-mentioned circuits are more fully described and claimed in the above-mentioned parent application. Such circuits do not require detailed description here. Those circuits of Fig. 3 which are directly pertinent to the present invention will now be decribed in detail.

To generate the narrow vertical synchronizing signal, 60 cycle signals lfrom unit #l are supplied to unit #25, shown in detail in Fig. 4. Two sinusoidal'signals displaced in phase are formed by the phase shifting network 3, reduced to rectangular pulses slightly displaced in time relation by independent amplitude limiting devices I, l, I, 1, and combined in opposed relation by the common load l to produce a narrow 60 cycle impulse.

A 900 cycle signal from unit #3 is treated in similar fashion by the narrow impulse generator kunit #7, shown in Fig. 5. In this unit, the tube 8 and its output circuits provide the phase shifting, and tubes il, il, li2 and Il are the amplitude limiting devices. These narrow 900 cycle pulses are-then supplied vto biased amplifier I4 (see Fig. `4) via tube Il, in addition to the narrow 60 cycle impulse, which raises every 15th narrow 900 cycle v pulse to on level. The output of unit above.

#2b is then a narrow vertical pulse occurring at the rate of 80 persecond but timed by theintermediate frequency and hence with the horizontal synchronizing signal.

"Thisnarrow vertical signal may be combined directly'with the horizontal synchronizing signal, but preferably it is passed through a serrating unit #8 (see Fig. 6) This unit, which is energized by unit #5, comprises a yfrequency doubling and pulse producingnetwork including elements II to 23 inclusive, vwhich forms a series of pulses of slightly greater duration than the horizontal synchronizing signals and occurring at twice their rate. The circuits are similar to those described 'lllese pulses are added to the narrow vertical pulse in tube 24 in opposed relation so as to cut oi! any portion of the vertical pulse which might overlap the horizontal pulses.

The thus formed narrow verticalsignal. is then added to the horizontal synchronizing signal and the two are supplied to the combining amplifier via tube 2l (see Fig. ll). Blanking and other control signals may alsobe inserted at this point. The synchronizing signals are also supplied to the scanning circuits at the transmitter as shown in In Figs. 'l andi! is shown a second method of obtaining the narrow' vertical synchronizing pulses, in combination with the horizontal synchronizing signals and with the horizontal and vertical blanking signals, b'y means of a conventional light-chopper disk. This disk may have apertures VS, HS. HB and VB corresponding to the narrow vertical synchronizing impulse. the horizontal synchronizing impulses, the horizontal blanking pulses, and the vertical blanking pulses.

Cil

respectively, cut in an annular section of the disk. 'Ihe disk may be driven at synchronous speed by a synchronous motor SM and light from sources IS may bepermitted to pass through' -the Proper apertures and then to fall on photo electric cells PE so as to produce a signal in the output of each photo electric cell amplifier corresponding to the holes cut inthe disk. These signals may then be used in the same way as those described in the electronic generator.

I art," it is deemed unnecessary to desire it further,

As the light chopper disk is well known in the except to point out' that while it ls relatively easy to obtain holes of the proper size, it is diiilcult to accurately space holes in the disk. Consequently, the several methods of eliminating. periodic frequency variations from a periodic signal, which have been describedin my parent application, may advantageously be used with such a mechanical-electrical system.

In general, the signal forming aperturesfmay separating circuit described hereinafter used to separate the several signals.

Separation of the horizontal synchronizing signal from the vertical signal at the receiver may be obtained by wave shape or frequencyI selective means, as described in greater detail below. One such circuit is shown in Fig. 12 which illustrates in detail the portion of the receiver subsequent to and including the detector. The receivin'g system may comprise an antenna, and a conventional carrier frequency amplifier (not shown) which may or may not include a detector-oscillator and an intermediate frequency amplifying system, following the conventional superheterodyne practice.- In either case,l tile carrier frequency amplifier will be followed by a linear detector 2l which is energized by a modulated carrier signal and the output of which comprises the composite signal above mentioned (see Fig. 9). The output of the linear detector may be supplied to a video signal amplifier and picture tube (not shown).

The output of the linear detector or preferably that of the ilrst video frequency amplifier stage is also supplied to a synchronizing signal selector stage 2l which separates the combined synchronizing signals from the video signal. 'Ihis may conveniently be accomplished by amplitude selection; that is, the selector tube 28 is biased to pass only that portion of the composite signal .greater thanthe no-light level which portion includes only the synchronizing signals.

The output of the selector stage is supplied to two separator stages 2! and 30 one of which separates. the vertical synchronizing signal. and the second the horizontal signal. 'I'he vertical synchronizing signal separator may comprise a further amplitude ,limiting stage 3l which passes only that portion of the combined signal having an amplitude greater than the horizontal synchronizing signal.

Thehorizontal synchronizing signal separator may comprise a wave shape or frequency selective network and amplifier which discriminates between the abrupt wave front of the horizontal synchronizing pulses and Ithe less abrupt wave front of the vertical synchronizing pulses, permitting the former to pass through substantially unaffected while markedly attenuating and modifying the latter. For example, synchronizing sig- -nal separation may be accomplished by the vresistance and

capacitancecombination

32 and 33. When the voltage across resistance 32 changes, a voltage will appear across the condenser which will result in a charging or discharging current in resistance 32. The signal supplied to the following stage will be determined by the differential voltage across resistance 32 occasioned by this charging or discharging current. If the voltage output of stage 34 changes quickly as will be the case for horizontal pulses, a large charging current will be drawn through resistance 32 and the signal will be transferred without marked attenuation. If the voltage changes slowly, as in the case of the longer vertical pulses, the rate of charge will be much less, and the signal transferred more highly attenuated. The time constant of this circuit may be of the order of one line or 9'1 microseconds. Under these conditions,

any transient voltage introduced in this circuit by the vertical synchronizing signal would decay in a period equivalent to one line.

Having thus separated the synchronizing signals, each may be applied to a separate scanning signal generator. This generator, in response to the pulse synchronizing signal, forms a signal which may be used with the defiecting coils or deflecting plates of the picture tube or camera tube to obtain the desired scanning motion of the electron beam.

It is unnecessary 'to describe here in greater detail the elements of Fig. 12 which areffully described in the above-mentioned parent application.

Speaking generally of the narrow pulse system of this invention, it will be noted that by means of this system I have provided a method by which accurate synchronization of the vertical synchronizing means at the transmitter and receiver may be obtained, and, in addition, the horizontal scanning means may be kept in accurate synchronization without requiring the two to miss a cycle or so during the duration of the vertical synchronizing signal. Furthermore, additional time is allowed the horizontal scanning means to recover from any transient which may have been introduced by the occurrence of the vertical synchronizing pulse, and the system is so arranged that the introduction of transients is minimized.

It will be apparent that the invention is not limited to the specific devices illustrated and de-- scribed but is capable of modification within the scope of the appended claims.

I claim:

1. In an electrical system, means for generating a signal comprising pulses of predetermined frequency and duration; means for generating a second signal comprising pulses of predetermined frequency and duration, the frequency of said sec- -ond signal being less than the frequency of said rst signal and of fixed relation thereto, the duration of pulses of said second signal being less than the period of said ,first signal and the pulses of said second signal occurring between certain consecutive pulses of said first signal and noncoincident therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal; means for combining said signals to form a composite signal; and means for transmitting said composite signal.

2. In an electrical system for producing and transmitting synchronizing signals, means for generating a signal comprising pulses of predetermined frequency and duration; means for generating a second signal comprising pulses of predetermined frequency and duration, the frequency of said second signal being less than the frequency of said first signal and of fixed relation thereto, the duration of pulses of said second signal being less than the period of said first signal frequency and the pulses of said second signal occurring between 'certain consecutive pulses of said first signal and non-coincident therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal; synchronized means at said transmitter energized by signals derived from said first and said second generator means; means for combining said generated signals to form a composite signal; and means for transmitting said composite signal.

3. A method of producing and transmitting a plurality of timing signals, which comprises generating a timing signal comprising pulses of predetermined requency and duration; generating a second timing signal comprising pulses of pre-A determined frequency and duration; the frequency of said second signal being less than the frequency of said first signal and of fixed relation thereto, the duration of pulses of said second signal and non-coincident therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal; combining said signals to form a composite signal; and transmitting said composite signal.

4. In an electrical system for effecting synchronization of a plurality of means in a transmitter and a receiver, the method of synchronization which comprises generating a pulse signal comprising pulses of predetermined frequency and duration, and a signal of fixed'time relation with said pulse signal for synchronizing one of said transmitter means; generating another pulse signal comprising pulses of predetermined frequency and duration, the frequency of said second pulse signal being less than the frequency of said first pulse signal and of fixed relation thereto, the duration of pulses of said second pulse signal being less than the period of said first pulse signal, and the pulses of said second pulse signal occurring between certain consecutive pulses of said first pulse signal and non-coincident therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal, and al second signal of fixed time relation with said second pulse signal for synchronizing another of said transmitter means; combining said pulse signals to form a composite signal; and transmitting said composite signal for utilization to synchronize said receiver means.

5. In a television system utilizing two directional scanning, a method of effecting synchronization of transmitting and receiving scanning means, which comprises generating a synchronizing signal comprising pulses of predetermined frequency and duration; generating a second synchronizing signal comprising pulses of predetermined frequency and duration; the frequency of said second signal being less than the frequency of said first signal and of fixed relation thereto, the duration of pulses of said second signal being less than the period of said first signal frequency, and the pulses of said second signal occurring between certain consecutive pulses of said first signal and non-coincident therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal; utilizing said' respective signals to synchronize said transmitter scanningfmeans; combining said signals to form a composite signal; and transmitting said composite signal for utilization to synchronize said receiver scanning means.

46. In a television system utilizing two directional scanning, a method of eecting synchronization of transmitting and receiving scanning means which comprises generating a synchronizlng signal comprising pulses of predetermined frequency, wave shape, and duration; generating a second synchronizing signal comprising pulses of predetermined frequency, wave shape, and duration; the frequency of said second signal being less than the frequency of said first signal and of fixed relation thereto, the slope of the wave front of pulses of said second signal being less than the slope of the wave front of pulses of said first signal, the duration of pulses of said second signal being less than the period of said first signal frequency, and the pulses of said second signal occurring between certain consecutive pulses of said first signal and non-coincident therewith, there beinga plurality of pulses said first signal andl of iixed relation thereto, the

posite signal; and transmitting said composite signal for utilization to synchronize said receiver scanning means.

7. In a television system utilizing two directional interlaced scanning, a method. of effecting synchronization of transmitting and receiving scanning means, which comprises generating a synchronizing signal comprising pulses of predetermined frequency and duration; generating a second synchronizing signal comprising pulses of predetermined frequency and duration; the frequency of said second signal being less than the frequency of said first signal and of iixed relation thereto, the duration of pulses of said second signal being less than one-half the period of said first signal frequency, and the pulses of said second signal occurring between certain consecutive pulses of said iirst signal and non-coincident therewith, there being a plurality of pulses of said iirst signal between consecutive pulses of said second signal, utilizing said respective signals to synchronize said transmittter scanning means, combining said signals to form a composite signal; and transmitting said composite signal for utilization to synchronize said receiver scanning means,

8. In a television system utilizing-two directional interlaced scanning, a method of eifecting synchronization of transmitting and receiving scanning means, which comprises generating a synchronizing signal comprising pulses of predetermined frequency, wave shape, and-duration; generating a second synchronizing signal comprising pulses ,of predetermined frequency, wave shape, and duration; the frequencyoi said second signal being less than vthe frequency, of

slope of the wave front of pulses of said second signal being less than the'slope of the wave iront of pulses of said ilrst signal, theduration of pulses of said second signal being less than onehalf the period of said rst signal frequency. and the pulses of said second signal occurring betweenA certain consecutive pulses of said first signal and noncincldent therewith, there being a plurality of pulses of said first signal between consecutive pulses of said second signal: utilizing said respective signals to synchronize said transmitter scanning means; combining said signals to form acomposite signal; and transmitting said composite signal for utilization to synchronize said receiver scanning means.

9. In s television system utilizing two directional scanning, a method of effecting synchronization of transmitting and receiving scanning means. which comprises generating a synchronizing signal comprising pulses of predetermined frequency `and duration; generating a second synchronizing signal comprising pulses oi predetermined irequency and duration: the frequency of said second signal being less than the frequency of said first signal and of xed relation thereto, the duration of pulses of-said secondsignalbeinglessthantheperiodofsaidrst signal frequency, and the pulses of said second signal occurring between ,certain consecutive pulses ot said first signal and non-coincident therewith, there being a plurality of pulses of said Vfirst signal between consecutive pulses of said second signal; modifying said second signal to insure a finite time interval between the occurrenceofapulseofoneoisaidsignalsanda. pulseoi the other ofsaid signals; utilizing said respective signals to synchronize said transmitter scanning means; combining said signals to form a composite signal; and transmitting said composite signal for utilization to synchronize said receiver scanning means.

10. In a television system utilizing two directional scanning, a method of effecting synchronization of transmitting and receiving means, which compris generating a synchronizing signal comprising pulses of predetermined frequency and duration; generating a second synchronizing signal comprising pulses of .predetermined frequency and duration; the frequency of said second signal being less than the frequency of said first signal and of fixed relation thereto, the duration of pulses of said second signal being less than one-half the period of said first signal frequency,.and the pulses oi' said second signal occurring between certain consecutive pulses of said first signal and non-coincident therewith, there being a plurality of pulses of said iirst signal between consecutive pulses of said second signal; modifying. said second signal to insure a finite time interval between the occurrence of a pulse of one of said signals and a pulse of the other 'of saidsignals; utilizing 4said respective signals to synchronize said transmitter scanning means; combining said signals to form a composite signal; and transmitting said composite signal for utilization to synchronize .said receiver scanning means.

11. In a television system utilizing two directional. scanning, a method of effecting synchronization of transmitting and receiving scanning means, which comprises generating a synchronizing signal comprising pulses of predetermined frequency. amplitude, and duration; generating a second synchronizing signal comprising pulses of predetermined frequency, amplitude, and duration; the frequency oi said second signal being less than the frequency of said iirst signal and of fixed relation thereto, the amplitude of said second signal pulse being different from the amplitude of said first signal pulses, the duration of pulses of said second signal being lessvthan the period of said iirst signal frequency, and the' 'posite signal for utilization to synchronize said receiver scanning means.

FRANK J. BINGLEY.