US2251966A - Television synchronizing system - Google Patents

Description

Allg. 12 1941 H. A. WHEELER IELEVISIOIIl SYNCHRONIZING SYSTEM 2 Sheets-Sheet l INVENTOR HAOLD A. WHEELER ATTORNEY Filed June 7|, m39

vA'ug. 12,1941.

A. WHEELER TELEVISION SYNCHRONIZING SYSTEM Fired June '7, 1939 2 sheets-sheet 2 aoumanag nur.;

` INVENTOR ATTORN EY Patented Aug. 12, 1941 TELEVISION sYNcHRoNlzTNG SYSTEM Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation, `a corporation of Delaware Application June 7, 1939, Serial No. 277,861

(Cl. ri-69.5)

'l Claims.

This invention relates to television/systems,

. and particularly to a television synchronizing system wherein an improved composite synchronizing signal is developed and utilized.

In accordance with present television practice, there is developed and transmitted a signal which comprises a carrier wave modulatedvduring successive intervals or trace periods by videofrequency components representative of light and shade values in an image being transmitted.

During retrace intervals between the trace periods, the carrier wave is modulated by synchronizing pulses or components which correspond to the initiations of successive lines and elds in the scanning of the image. At the receiver a beam is so deected as to scan and illuminate a target in a series of parallel lines. The videofrequency components of the received signal are utilized to control the intensity of the beam. The line-synchronizing and field-synchronizing pulses are separated from the video-frequency components and are effectively separated from eachother and utilized to synchronize the operation of the receiver scanning apparatus with similar scanning apparatus utilized at the transmitter in developing the signal. The transmitted image is thereby reconstructed on the target of the receiver.

1n scanning of the interlaced type, the linescanning and field-scanning frequencies are so related that successive fields are staggered, the lines of one field falling between or interlacing those of a preceding eld. Because of persist- `ence of vision, 'the optical effect produced is as though each frame or group of elds comprised a multiple of the actual number of lines scanned per field and the frame-scanning frequency equalled the field-scanning frequency. In such systems certain of the held-synchronizing pulses must occur between line synchronizing pulses.

In order that the line-synchronizing and fieldsynchronizing pulses may be separated from the video-frequency components and from each other for utilization at a receiver, Various types of synchronizing signals and separating apparatus have been proposed. For example, signals have been proposed in which the field-synchronizing pulses are of greater height, of longer duration, or of different wave form than the line-synchronizing pulses, and separating apparatus has been provided which comprises ldiscriminating circuits responsive to the amplitude, to the duration,y or to such arrangements, however, while being generally satisfactory,` are subject to various objections, such as giving only partial separation, requiring an undesirably large portion of the total carrier-wave amplitude, or involving relatively complicated separating apparatus.

Further, in television systems of the type described, it is desirable to control automatically various receiver operating characteristics, for example, to provide automatic amplification control, in accordance with the average intensity of the received carrier wave independent of inl tensity variations due to the light-modulation the wave form of the individual pulses, in acp l cordance with the distinguishing characteristics of the synchronizing signal utilized. Many of components. For this purpose, in systems where negatively modulated carrier waves are utilized, that is, where a vdecrease in carrier-wave amplitude corresponds to an increase in illumination, the synchronizing pulses generally appear as outward modulation peaks and the peak value of the synchronizing pulses provides a convenient measure of the carrier intensity variations independent of the light-modulation components. For various reasons, however, including the fact that the synchronizing signals utilized in the prior art have included field-synchronizing pulses of either the same or greater amplitudes than the line-synchronizing pulses and the fact that these held-synchronizing pulses are not uniformly spaced with respectto the line pulses in interlaced systems, the irregular spacing of these pulses tends to affect the control effect derived from the signal and a precise measure of the intensity variations in question has been diflicult or impossible to obtain without too great a time constant in the control circuit.

An arrangement for eliminating these lastmentioned undesirable effects is described in the instant application and is claimed in copending application Serial No. 355,442, tiled September 5, 1940, which is a divisional application of the instant application.l

It is an object ofthe present invention, therefore, to provide an improved television synchronizing system wherein a novel composite synchronizingsignal is developed and utilized.

It is a further object of the invention to provide an improved television system for utilizing this novel composite synchronizing signal for con- `trolling various operating characteristicsof the system. l 1

In accordance with the y present invention, there is provided a television system comprising vmeans for developing and transmitting a' commined critical amplitude and frequency characteristics and field-synchronizing pulses, spaced between the line-synchronizing pulses, of the same polarity as the line-synchronizing pulses and having predetermined different critical amplitude and frequency characteristics. Means are further provided for receiving and utilizing the composite signal which comprise means primarily responsive to amplitude characteristics of said composite signal for deriving therefrom separated synchronizing pulses of one type and means primarily responsive to frequency characteristics of said composite signal for deriving therefrom separated synchronizing pulsesof the other type. The expression primarily responsive, as applied to the amplitudeand frequency-responsive means, is used herein to denote a first order or intended response as distinguished from a second order or incidental response that may be unintentional or undesired. Individual synchronizing circuits are provided which are adapted to be energized individually by the separated line-synchronizing and fieldsynchronizing pulses. The means primarily responsive to the frequency characteristics of the composite signal comprises frequency-selective means. The term frequency selective, as used herein and in the appended claims, is intended to define that characteristic of the separating means whereby it is primarily and` directly responsive to frequency components in the composite signal, It is to be distinguished from the characteristics of aperiodic circuits, such as integrating and Ydifferentiating circuits, which are primarily responsive to the area or wave form characteristics of signals.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings, Fig. 1 is a schematic circuit diagram of a complete tele-- vision transmitting system embodying the present invention; Fig. 2 is a circuit diagram, partially schematic, of a complete television receiving system embodying the invention; Figs. 3 and 4 are groups of curves illustrating the wave forms of periodic waves developed at various points inthe systems of Figs. 1 and 2, respectively, to aid in the understanding of the invention; Fig. 5 is adiagram of the frequency spectrum of the composite synchronizing signal utilized; and Figs. 6 and 7 are curves illustrating certainA characteristics of the system shown in I Fie. 2.

Referring now more particularly to Fig. 1 of the drawings, there is shown.y a schematic circuit diagram of a television transmitting system comprising a video-frequency television signal generator I0 which may include the usual cathoderay signal-generating tube `and scanning and wave-shaping apparatus. Connected in cascade to the output circuit of the signal generator Il), in the order named,fare a video-frequency amplifier II, a second video-frequency amplifier I2, a modulator I3 and associated coupled carrierfrequency oscillator III, a power amplifier I5, and a radiating antenna system I6, I'I, all according to conventional practice.

For the purpose of developing an improved composite synchronizing signal in accordance with the present invention, there is provided apparatus indicated generally at I8 and including a line-frequency generator I9 and a field-frequency generator 20 having their output circuits coupled to a mixing amplifier 2|, the output circuit of which is, in turn, coupled to the vdeofrequency amplifier I2.

For the purpose of synchronizing the apparatus in the generator I0 as well as in the generators I9 and 20, there is included in the apparatus I8 a timing-impulse generator 22. The generator 22 is preferably stabilized by means of a connection 23 to a suitable source of periodic voltage, for example, to the power supply circuit or to the synchronizing voltage source of motion picture mechanism, where such is employed. Output circuits of timing-impulse generator 22 are coupled to input circuits of the scanning apparatus in the generator ID and the generators I9 and 20.

Neglecting for the moment the details of operation of the synchronizing-signal generating apparatus I8, the system just described comprises the elements of a television transmitting system of conventional design and, the various parts thereof being of any well-known construction, a detailed description of the general system and its operation is unnecessary. Briefly, the image of a scene to be transmitted is focused on the target in the signal generator IIJ and a videofrequency voltage is developed thereby in the usual manner and is applied to the video-frequency amplifier II, wherein this voltage is amplied and from which it is transmitted to the amplifier I2. The composite synchronizing signal developed by the apparatus I8, as will presently be described in more detail, is also applied to the video-frequency amplifier I2 in which it is mixed with the video-frequency voltage and further amplified, The amplified composite signal is supplied to the modulator I3, wherein it is so impressed upon the carrier wave generated by the oscillator I4 as to develop a modulatedcarrier signal. This signal is delivered to the power amplifier I5 for amplification therein and is thereafter impressed upon the antenna system I6, I'I to be radiated. Timing impulses developed by the generator 22 are applied to the generators I Il, I9, and 20 to lock the same in synchronism.

Referring now more particularly to the apparatus I8 embodying the-present invention, for the purpose of developing the line-synchronizing and field-synchronizing pulses of proper frequency and wave form characteristics, the generators I9 and 20 may comprise apparatus of any suitable type adapted to develop these required pulses. The line-frequency generator may develop periodic pulses of a suitable frequency,

such as 13,230 per second, and of narrow rectangular-pulse wave form of a predetermined amplitude. The eld-frequency generator, on the other hand, may be arranged to develop pulses of the field-scanning frequency, such as 60 cycles per second and also of narrow rectangular-pulse wave form. In accordance with the present invention, however, the field-synchronizing pulses are of lesser amplitude than the linesynchronizing pulses although they may be of comparable duration and, as stated, of substantially the same wave form, since this system does not rely on any particular wave form characteristic ofthe field-synchronizing pulses. As explained above, the input circuits of the generators I9 and 20 being coupled to the timing generator 22, the line-synchronizingand field-synchronizing pulses developed thereby are combined and amplified in the mixing amplifier 2|.

supplied to the amplifier I2 and combined therein with the video-frequency signal voltages, as explained above. f

In Fig. 3 there are illustrated .the wave forms of the signals developed at various points in the system of Fig. 1. Curve A illustrates the wave form of the continuous periodic line-synchronizing pulses developed by generator I9, while curve.

B illustrates the wave formA of the field-synchronizing pulses developed by generator 20, which are spaced between the line-synchronizing pulses, which have the same polarity as the line-synchronizingv pulses, and which have predetermined diferent critical amplitude and frequency characteristics, specifically, lesser amplitude and frequency, only one pulse being shown. The wave form of the composite synchronizing signal developed in the output circuit of the mixing amplifier 2I is illustrated by curve C, the amplitude of the line-synchronizing pulses being considerably greater than that of the fieldsynchronizing pulses, as indicated therein. Curve D illlustrates the video-frequency signal developed by the signal generator I and translated by way of the amplifier II to the amplifier I2, while curve E shows the combined video-frequency and composite synchronizing signal as it appears in the output circuit of amplifier I2. Curve F illustrates the complete carrier wave modulated by the composite video-frequency and synchronizing signal E', as it appears in the output circuit of the modulator I3, this being the wave form of the transmitted signal.

The curves A-F, inclusive, illustrate an extreme case in which the held-synchronizing pulses have the same width as the line-synchronizing pulses. Generally it will be preferable to so design the system embodying the invention as to make the field-synchronizing pulses wider than the line-synchronizing pulses and also to repeat them several times duringeach field-synchronizing period. Increasing the width or duration of the pulses, and thus increasing their areas, increases the amount of energy therein and improves the dependability of the synchronizing apparatus in the presence of noise Repeating the pulses provides additional chances for synchronizing in the event that the first pulses fail.

Referring now to Fig. 2 of the drawings, there is shown a circuit diagram, partially schematic, of a complete television receiving system of the superheterodyne type including, in cascade, an,

antenna system 30, 3l, a radio-frequency amplifier 32, an oscillator-modulator 33, an intermediate-frequency amplifier 34, a detector 35, a video-frequency amplifier 36, and an image-reproducing device 31, such as a cathode-ray signal-reproducing tube.

'A synchronizing-signal separator 38 also is coupled to the output circuit of the detector 35 and its output circuit is, in turn, coupled to linefrequency and field-frequency scanning wave generators 39 and 40 by way of synchronizingsignal separating apparatus, indicated generally at 4I and embodying the present invention. The generators 39 and 40 have their output circuits connected to the scanning elements of the device 31 in conventional manner. The-parts of the system represented schematically may be of any conventional construction and operation. There is also coupled to the output circuit of the intermediate-frequency amplifier 34 an automatic amplification control source, indicated generally at 42.

Since the system of Fig. 2 as thus far described, except the apparatus 4I and 42, is, inV general,

well understood in the art, a detailed descrip.

tionand explanation of its operation is unnecessary. Briefly, however, a television modulatedcarrier wave is intercepted by the antenna 3U, 3| and selectively amplified in the radio-frequency amplifier 32, from which it is impressed upon the oscillator-modulator 33, wherein itis converted into an intermediate-frequency signal which is thereupon further selectively amplified in the intermediate-frequency `amplifier 34. The amplified intermediate-frequency 'signal is delivered from the amplifier 34 to detector 35 in which there is developed the composite modulation signal comprising the video-frequency component and synchronizing-signal component. This modulation signal is supplied to the videofrequency amplifier 36wherein it is amplified and from which it is applied in the usual manner to' a brightness-control element of the reproducing deviceV 31. The modulation signal is also supplied to the separator 38, wherein the composite synchronizing signal is separated from thevideo-frequency components, usually by an amplitude selector, and delivered to the apparatus 4I. In the apparatus 4I, the-line-synchronizing pulses are separated from each other in accordance with 4the present invention, as presently to be further explained', and the separated pulses are applied to the generators 39 and 40 to synchronize their operations with the corresponding apparatus at the transmitter.

The intensity of the beam of the reproducing device 31 is modulated or controlled in accordance with the video-frequency voltages impressed on its control electrode in the usual manner. Scanning waves, developed by the generators 39 and 40 controlled by the synchronizing components supplied from the apparatus 4I, are utii lized in the conventional manner to deflect the scanning beam of the image-reproducing device 31, for example, by producing electric fields of saw-tooth wave form which deect the cathode ray of a signal-reproducing tube in two directions normal to each other, so as to trace the usual rectilinear scanning pattern upon the target of the reproducing device, thereby to reconstruct the transmitted picture.

Referring now more particularly to the portion of the system of Fig. 2 embodying the present invention, the separating apparatus 4I preferably comprises a pair of vacuum-tube amplifiers 43 and 44 having theirinput circuits coupled in parallel to the output circuit of separator 38 by way of coupling condensers 45, 45 and leak resistors 46, 46 connected in series with biasing batteries 41, 41. Operating potentials are supplied to the screens of the tubes 43, 44 from suitable sources indicated at -l-Sc, while anode potentials are supplied to these tubes from sources indicated at |B by way of high resistors 48, or choke coils.`

For the purpose of separating theline-synchronizing pulses from the composite synchronizing signal, the tube 43 is so biased that it 0perates considerably beyond grid-voltage cutoff, repeating in its output circuit only the portion of the impressed composite signal above the peak-amplitude value of the field-synchronizing pulses, To this end, the line-synchronizing pulses are applied t0 the grid with positive polarity and may be allowed to draw some grid current to stabilize the grid bias. The anode circuit of vtube 43 is coupled by Way of a blocking condenser 49 to the input or synchronizing circuit of the line-frequency generator 39.

For the purpose of separating the field-synchronizing pulses from the composite synchronizing signal, filter-delay apparatus comprising a. single dead-end filter circuit, indicated generally at 50, is coupled across the resistor 48 of the tube 44 by way of a blocking condenser 5l. The circuit 50 comprises a low-pass filter including input terminals across which a terminating resistor 52 is connected and to which is coupled an m-derived half-section including as a mid-shunt arm the series-connected inductance 54 and condenser 55; a. series of constant-7c Whole sections, each comprising a series-inductance arm 56 and a shunt-condenser arm 5l; and a terminating series-inductance arm 56a. Series arm 53 comprises the mid-series arms of the adjoining halfsections. The filter is short-circuited at the remote terminals, as indicated by the connection 58.

The amplification control circuit 42 may comprise a conventional diode rectifier 59 connected across a transformer secondary winding 50 by way of a load circuit including a parallel-connected .resistor 6| and by-pass condenser 52. The winding 60 is coupled to a transformer primary winding 63 which is connected to the output circuit of the intermediate-frequency amplier 34. The negative terminal of the load resistor 6l is connected by way of a suitable filter, including series resistors 64 and shunt condensers 65, to the control electrodes of one or more of the signal-translatingtubes in the stages 32, 33, and 34.

In the operation of the separating apparatus of Fig. 2, thecombined video signal and synchronizing signal is delivered from the detector 35 to the separator 38, wherein the composite synchronizing signal is separated from the video signal in a conventional manner. The composite synchronizing signal is impressed upon the input circuits of the tubes 43 and 44 with such polarity that the synchronizing components extend in the positive direction. The tube 43 is so biased that only the portions of the line-synchronizing pulses of the composite signal which are of greater amplitude than, or extend beyond, the peak amplitude of the eld-synchronizing pulses are repeated by the tube and appear in its output circuit, the arrangement thus being primarily responsive to the amplitude characteristics of the composite synchronizing signal. These separated line-synchronizing pulses are thereupon impressed upon the input or synchronizing circuit of the generator 39 to synchronize the operation of this generator.

The tube 44 repeats the entire composite synchronzing signal, this signal being developed across its output circuit and applied to the input terminals of the filter 50. As a result of the reflecting termination or mismatching at the end of the filter remote from the input terminals, an electrical wave which is the inverted image of the applied wave isreflected from the shortcircuited terminals and appears, after a predetermined time delay, across the input terminals. The time delay of the filter in each direction is made one-half of thev desired delay, for example, one-half of a line-scanning period to effect a desired delay of one line-scanning period in the reflected wave. Since the filter is short-circuited at its remote terminals, the reflected wave is of polarity opposite to that of the original wave and, hence, the combined applied and delayed waves constitute a resultant wave across the re. sistor 52 from which the line-synchronizing pulses are suppressed. In other Words, when the delayed wave of reversed polarity is combined with the undelayed wave, certain synchronizing signal components, that is, the line-synchronizing components, coincide and neutralize each other, The resultant wave across resistor 52, therefore, comprises only the separated fieldsynchronizing pulses, the arrangement being primarily responsive to the frequency characteristics of the composite synchronizing signal, and it is applied directly to the synchronizing-input circuit of the field-frequency generator i0 to synchronize the operation thereof.

In Fig. 4 there are illustrated the wave forms of the signals developed at .various points in the system of Fig. 2. Thus, curve G illustrates the wave form of the detected signal, which is like the modulation envelope of the received carrier wave, as it appears in the output circuit of the detector 35 and is impressed on the synchronizing-signal separator 48. Curve H shows the wave form of the composite synchronizing signal after it has been separated from the video signal by the separator 38 and as it is impressed on the input electrodes of the tubes 43 and 44. Curve I illustrates the separated line-synchronizing pulses derived bypassing only the peaks of the composite synchronizing signal in the tube 43, which pulses are impressed on the input circuit of the line-frequency generator 39. Curve J shows again the composite synchronizing signal as it appears in the output circuit of the tube 44 and is applied to the input terminals of the lter 50, while curve K illustrates the wave form of the synchronizing signal reflected from they short-circuited remote terminals of the filter back to the input terminals thereof reversed in polarity and delayed by one line-scanning period. Curve L illustrates the wave form of the resultant of the combined delayed and undelayed signals appearing across the resistor 52, comprising only the separated field-synchronizing pulses, which are applied to the synchronizing-input circuit of the field-frequency generator 40.

The operation of the filter 50 of Fig. 2 may be considered from another point of view with reference to Figs. 5, 6, land 7. It will be appreciated that each of the line-frequency and fieldfrequency series of synchronizing pulses of the composite synchronizing signal is represented by frequency components including a fundamental and many harmonic components. The field-frequency pulses, for example may have a fundamental frequency component of cycles, as well as harmonic components of 120 cycles, 180 cycles,

240 cycles, etc. The line-frequency pulses have components of, for example, 13,230 cycles fundamental, 26,460 cycles, etc. Fig. 5 is a frequencyspectrum chart, indicating at fv the fundamental frequency of a field-synchronizing pulse; at 2fv, 3fv, etc., its progressively higher harmonic frequencies; and indicating at fu the fundamental frequency of a related line-synchronizing pulse and at 2f, 3fu, etc., its progressively higher harmonic frequencies. ity, Fig, 5 indicates only 71/2 lines per field. whereas in the actual system there would be n much greater relative number of lines, say 2201/5.

The circuit 50 of Fig. 2 is essentially a two-terminal impedance network which couples the out.. put circuit of tube 44 to the synchronizing-input For the purpose of simplici intended to show critical points.

circuit of the field-frequency generator 4l). In the absence of the resistor 52, the input imped; ance of the circuit 5 0 is a pure reactance which Vvaries with frequency between plus and minus infinity', as illustrated bythe curve of Fig. 6. This figure is not drawn to scale, but is merely Such a system inherently has zero reactance at a particular fundamental frequency and multiples thereof, and it behaves as a family of series-resonant traps connected in parallel branches. The network shown, or such a system of traps, is a wellknown equivalent of a reflecting transmission line. With the resistor 52 connected across the input circuit of filter 50, the impedance charac teristic of the circuit assumes the form illus* trated by the curve of Fig. 7. The circuit thus behaves as a multiple band-pass filter which attenuates, suppresses, oreliminates a particular fundamental frequency component, in the present case the line-synchronizing fundamental component, and its harmonic components.

The present system is essentially different from filter systems of the types which heretofore have been utilized for somewhat analogous purposes, as exemplified by low-pass filters having an upper cutoff frequency slightly less than the line frequency for attenuating the line frequency and its harmonic components. Such systems necessarily have suppressed the higher harmonic components of the field-synchronizing pulses which are essential to maintain the desired sharpness of rectangular wave form. The filter arrangement of Fig. 2, while attenuating the fundamentaly as well as the harmonic-frequency components of the line-synchronizing pulses, translates all of the higher harmonic-frequency components as well as the fundamental frequency component of the field-synchronizing pulses, except the few which may be coincident with certain of the line-synchronizing components. Therefore, in accordance with the invention, separation of the field-frequency synchronizing pulses is obtained by a frequency-selective filter circuit and the wave form of the separated pulses is substantially unimpaired -in its sharpness, though accompanied by a reflected pulse which has no detrimental effect.

'The-automatic amplification control circuit 42, per se, is constructed and operates in substantially conventional manner, an improved result being obtained by virtue of a modification of design with the novel wave form of the signal of the present invention which is supplied thereto from the intermediate-frequency amplifier 34. This circuit, including the diode rectifier 59, peakrectifies the applied signal to derive across its load impedance 6I, 62 a unidirectional negativebias voltage which increases in proportion to the amplitude of the received signal carrier independent of its light-modulation components. It will be appreciated that, since the field-synchronizing pulses of the novel composite signal are of considerably lesser amplitude than the line-synchronizing pulses and since the time constant of the rectifier load circuit 6I, 62 is substantially greater than the period of the linesynchronizing pulses, they do not undesirably affect the operation of the rectifier circuit as they do in the case of similar systems of the prior art, -as explained above. That is, only the peaks of the line-synchronizing pulses are rectified and these peaks provide a precise measure of the intensity variations of the signal carrier wave. yThe unidirectional control-bias voltage thus developed across the load' circuit 6I, 62 is illustrated by curve G1 in Fig. 4. Such a volt age is readily smoothed out by the filter elements 64, 65 of the A. V. C. system, thereby providing a steady unidirectional control-bias voltage oi the exact required amplitude. This voltage, being applied negatively to the control electrodes of one or more tubes in the stages 32, 33, and 34, serves to vary the amplification in these stages inversely in accordance with the variations in received carrier intensity and independent of variations corresponding to light modula tion, so as to provide a signal output for the system having rel-atively small variations in amplitude for a wide range of received signal carrier-wave variations, according to conventional A. V. C. practice.

In suchv control systems of the prior art, where the field-synchronizing pulses affected the control, it was necessary that the time constant of the control circuit have ai value much greater than that of the field period. In the system of the present invention, however, the control is independent of the eld-synchronizing pulses and the time constant of the control rectifier and filter circuits 6|, 62, 64, 65 may be made much smaller without irregularity of control. The smaller time constant is advantageous in that it minimizes the duration of the effect of strong transient disturbances, such as static. The greatest benefit in minimizing the effect of such a disturbance is obtained if the time comstant of the control circuit is of a value somewhat less than that of the field period, although its value is still much greater than the line period. The

single requirement of the system of the present 1 invention is that the time constant of the control circuit have a value'much greater than the line period. It may be 'of the same order of magnitude or even less than the field period, although such rapid control is ordinarily not necessary. In general, it will be satisfactory if it is somewhat greater than the field period but yet not nearly great enough to smooth o ut disturbances such as caused by field, pulses in systems of the prior art.

From the foregoing explanations, it will be apparent that the novel composite synchronizing signal'provided in accordance with the present invention, has numerous characteristics which are highly desirable for various reasons. These desirable characteristics include the fact that from the novel composite synchronizing signal both the line-synchronizing pulses and field-sym chromzing pulses may be completely separated from the composite signal prior to utilization for synchronizing the scanning-Wave generators. Further, when this novel composite synchronizing signal is used with a negativelymodulatedcarrier Wave, as described in the instant case, a control-bias voltage may be readily developed in accordance with variationsin peak values of the line-synchronizing pulses alone, for effecting a precise automatic control in the system, such as automatic amplification control, in accordance with variations in the received carrier-wave intensity and independent of light-modulation components. AIt will be readily apparent that various other` improved automatic controls, such as automatic selectivity control, automatic signal level adjusting, etc., may be obtained by utilizing the composite television signal of the present invention with suitable control apparatus.

It will further be appreciated that a controlbias voltage for automatically controlling the various characteristics of the system may be obtained by peak-detecting the modulation signal developed by the detector 35 as well as by rectifying the signal carrier wave itself, as explained above. In this case, as in the arrangement illustrated, a quick and highly accurate control is obtained by reason of the fact that the peaks of the line-synchronizing pulsesare available for rectication without interference from'the iieldsynchronizing pulses.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What isv claimed is:

1. A television synchronizing system comprising means for developing aY composite synchronizing signal including continuous line-synchronizing pulses having predetermined critical amplitude and frequency characteristics and eldsynchronizingpulses spaced between said linesynchronizing vfpulses, of the same polarity as said line-synchronizing pulses'and having predetermined different critical amplitude and frequency characteristics, and means for receiving and utilizing said composite signal comprising means responsive primarily to amplitude characteristics of said composite signal for deriving therefrom separated line-synchronizing pulses and means responsive primarily to frequency characteristics of said composite signal for deriving therefrom separated field-synchronizing pulses.

2. A television synchronizing system comprising means for developing and transmitting a composite synchronizing signal including continuous line-synchronizing pulses of a predetermined amplitude and field-synchronizing pulses spaced between said line-synchronizing pulses, of the same polarity as said line-synchronizing pulses and of amplitude substantially different from that of said line-synchronizing pulses, and means for receiving and utilizing said composite signal comprising primarily amplitude-selective means for deriving from said composite signal separated synchronizing pulses of the type having the greater amplitude and primarily frequency-selective means for deriving from said composite signal separated synchronizing pulses of the other of said types.

3. A television synchronizing system comprising means for developing and transmitting a composite synchronizing signal including continuous line-synchronizing pulses of a predetermined amplitude and field-synchronizing pulses spaced between said line-synchronizing pulses, of the same polarity as said line-synchronizing pulses and of amplitude substantially less than that of said line-synchronizing pulses, and means for receiving and utilizing said composite signal comprising primarily amplitude-responsive means for deriving from said composite signal separated line-synchronizing pulses and primarily frequency-selective means for deriving from said composite signal separated eld-synchronizing pulses. l

4. A television synchronizing system comprisving means for developing line--synchronizing pulses of a predetermined amplitude which continue through the field-retract intervals, means for developing eld-synchronizing pulses spaced between said line-synchronizing pulses, of the same polarity as said line-synchronizing pulses and of a predetermined amplitude substantially less than the amplitude of said line-synchronizing pulses, and means for combining said linesynchronizing and field-synchronizing pulses to develop a composite synchronizing signal.

5. A television synchronizing system comprising an input circuit adapted to have impressed thereon a composite synchronizing signal including continuous line-synchronizing pulses of a predetermined amplitude' and held-synchronizing pulses spaced between said line-synchronizing pulses, of the same polarity as said linesyn-chronizing pulses and of a predetermined amplitude substantially different from the amplitude of said line-synchronizing pulses, primarily amplitude-responsive means coupled to said input circuit for dering from said composite signal separated synchronizing pulses of the type having the greater amplitude, primarily frequency-selective means coupled to said input circuit for deriving from said composite signal separated synchronizing pulses of the other of said types, and individual line-scanning and fieldscanning. synchronizing circuits couplel to said two separating means and adapted to be energized by the respective synchronizing pulses separated thereby.

6. A television synchronizing system comprisving an input circuit adapted to have impressed scanning synchronizing circuits coupled to said amplitude-responsiveseparating means and frequency-responsive separating means, respectively.

7. A television synchronizing system comprising an input circuit adapted to be energized by a composite synchronizing signal including continuous line-synchronizing pulses of a predete mined amplitude and field-synchronizing puls s spaced between said lineynchronizing pulses, of the same polarity as said line-synchronizing pulses and of a substantially lesser amplitude than the amplitude of said line-synchronizing pulses, a. first synchronizing circuit adapted to be energized by said line-synchronizing pulses, a second synchronizing circuit adapted to be energized by said field-synchronizing pulses, primarily amplitude-responsive means coupling said first synchronizing circuit to said input circuit for deriving from said composite signal separated linesynchronizing pulses, and primarily frequencyresponsive means coupling said second synchronizing circuit to said input circuit for deriving from said composite signal separated field-synchronizing pulses.

HAROLD A. WHEELER.

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