US2293233A

US2293233A - Television receiver

Info

Publication number: US2293233A
Application number: US317628A
Authority: US
Inventors: Harold A Wheeler
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1938-06-09
Filing date: 1940-02-07
Publication date: 1942-08-18
Anticipated expiration: 1959-08-18
Also published as: FR855820A; FR869846A; GB540590A; CH217644A; FR51519E; US2254435A; GB529320A; GB546932A; BE434800A

Description

Aug. 18, '1942. H. A. WHEELER TELEVISON RECEIVER Filed Feb. "7. 1940 2 .Sheets-Sheet l INVENTOR HAROLD A. WHEELER Bm ICQ ATTORNEY Aug. 18, 1942. H. A. WHEELER TELEVISION RECEIVER Filed Feb. 7, 1940 2 Sheets-Sheet 2 IIQEE.

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I N 'ouanbalzg Jagun Aaq Kouanbanj ouangau IN ENT R H OLSAANHEELER ATTORNEY Patented Aug. 18, 1942 TELEVISION RECEIVER.

Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltne Corporation, a corporation of Delaware Application February '1, 1940, serial No. 311,628

(ci. 11a-6.a)

Claims.

This invention relates to television receivers and is particularly concerned with the provision of an improved television receiver for receiving a carrier wave amplitude-modulated with video signals and frequency-modulated with synchronizing signals.

It has been proposed, in United States Letters Patent No. 2,254,435, granted September 2, 1941, on the application of Arthur V. Loughren, to provide a television system utilizing rectilinear scanning at the transmitter'and the receiver in which the video signals are transmitted as amplitude modulation on a carrier wave during the trace intervals of the scanning cycle and in which the synchronizing signals of the system are transmitted as frequency modulation on the same carrier wave during the retrace intervals. Such a system has the advantage of reserving the full amplitude-modulation range for the transmission of video signals and is further advantageous in that relatively simple and eliicient arrangements are available for deriving, at the receiver, the composite transmitted synchronizing signal separate from all video-signal components and for deriving the transmitted videosignal components separate from all synchronizing-signal components. However. even in such systems, the problem of separating the synchronizing signals of one type from those of another type still remains and it is, therefore, desirable to provide a receiver for reproducing a carrier wave of the type under discussion in which simple and eiective means are provided for separating line-synchronizing and field-synchronizing signals.

It is an object of the invention. therefore, to provide an improved television receiver adapted to receive a carrier wave amplitude-modulated with video-signal components and frequencymodulated with synchronizing-signal components.

It is a further object of the invention to provide a television receiver of the general type under discussion which comprises a fast-acting means for automatically controlling an operating characteristic of the receiver, suchI as the amplication, in accordance with the amplitude of the received signal. 'f

In accordancewith the invention, there is provided in a television system including a transmitter adapted to transmit a. carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration synchronizing pulses of one type, preferably line-synchronizing pulses, to a predetermined deviation and by relatively long duration synchronizing pulses of another type, preferably field-synchronizing pulses, to a deviation of lesser magnitude than the rst-mentioned deviation, a television receiver comprising, a relatively lbroadly-selective carrier-frequency selector circuit responsive to the carrier-frequency deviations by the synchronizing pulses of the one type, and a relatively narrowly-selective carrierfrequency selector circuit responsive to the carrier-frequency deviations by the synchronizing com-ponents of the other type. There is -oupled to the broadly-selective circuit means for deriving synchronizing signals of the one type for the receiver, and there is coupled to the narrowly-selective circuit means for deriving synchronizing signals of the other type for the receiver.

In accordance with a preferred embodiment of the invention, the held-synchronizing pulses occur between line-synchronizing pulses and the carrier-frequency deviations of the television signal for transmitting both line-synchronizing and field-synchronizing pulses are in the same direction. A transmitter for generating and trans- -mitting a wave of this general type is fully described in copending application of Arthur y,V. Loughren, Serial No. 317,622, led concurrently with the present application.

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.

Fig. 1 of the drawings is a schematic circuit diagram of a system including a television receiver of the superheterodyne type constructed in accordance with the invention; Figs. 2 and 3 are graphs used to illustrate certain of the operating characteristics of the receiver of Fig. 1; Fig. 4 is a circuit diagram of a portion of the line-synchronizing channel of the receiver of Fig. l; Fig. 5 is a schematic circuit diagram of a television receiver including a modiication of the synchronizing-signal channely of the receiver of Fig. 1; and Fig. 6 is-a graph utilized to explain certain of the operating characteristics of the modification of the invention illustrated in Fig. 5.

Referring now to Fig. 1, the system there illustrated comprises a receiver of the superheterodyne type constructed in accordance with the present invention and adapted to be utilized in a television system including a. transmitter 9 which maybe generally similar to that disclosed in the aforementioned Patent 2,254,435 but adapted *to develop and transmit a carrier wave amplitude-modulated by video-signal components and frequency-modulated byv relatively video-frequency amplifier I6, and an image-reproducing device I1 preferably of the cathoderay type. Preferably, as explained below, the

stages I2, I3, and I4 are designed for singlesideband reception. A line-scanning circuit I8 is also coupled to amplifier I4 by way of linesynchronizing signal-deriving apparatus 2 0', hereinafter described in more detail. A fieldscanning circuit I9 is also coupled to amplifier I4 by way of a field-synchronizing signal-deriving circuit 2I hereinafter described in more detail. 'Ihe circuits I8 and I9 are coupled tothe scanning elements of signal-reproducing device I1 in a conventional manner and preferably include conventional synchronizing circuits which are adapted to be controlled by synchronizing impulses developed by apparatuses and 2|, respectively. The elements or units IIl-IS, in-

` elusive, may all be of any conventional wellknown construction so that detailed illustraherein.

Referring briefly to the general operation of4 the receiving system, television signals are selected by antenna circuit I0, II, amplified in radio-frequency amplifier I2, and converted in frequency changer I3 into intermediate-frequency signals. The intermediate-frequency signals are, in turn, selectively amplified in the intermediate-frequency amplifier I4 and delivered to the detector I5. The video-modulation components of the signal are developed by the amplitude-modulation detector I5 and are supplied to the video-frequency amplifier I6 wherein they are amplied and from which they are supplied in the usual manner to a brightness-control electrode of signal-reproducing device I1. The intermediate-frequency signal is also supplied from the amplifier I4 to the

apparatuses

28 and 2| wherein line-synchronizing signals and field-synchronizing signals, respectively, are derived as explained hereinafter, the line-synchronizing and field-synchronizing components being applied to the control circuits of the scanning circuits I8 and I9 in a conventional manner. Saw-tooth current or voltage scanning waves are developed by the line-scanning and field-scanning circuits I8 and I9 and applied to the scanning elements of the signal-reproducing device I1 to produce electric scanning fields, thereby to deflect the intensity-modulated scanning beam in two directions normal to each other so as to trace successive fields of parallel lines on the target of the tube to reconstruct the transmitted image. y

Referring now more particularly to the portions of the system of Fig. 1 involving the present invention, and particularly to the synchronizing-signal deriving apparatuses 20 and 2l, there is comprised in apparatus 20 a line-synchronizing pulse intermediate-frequency selector 25to lesser magnitude.

-which are coupled in cascade, in the order named, a rectifier and amplitude selector 26, a line-frequency selector 21, and a. line-pulse shapcr 28. Anautomatic amplification control or A. V. C. rectifier 29 is also coupled to linefrequency selector 21 and has an output circuit coupled to one or more of the units I2, I3, and I4 to control the amplification of the receiver inversely in accordance with the'received signal amplitude. The line-pulse intermediate-frequency selector 25 comprises a band-pass selector including coupled tuned circuits 34, 35. The rectifier and amplitude selector -26 comprises a diode 36 having a load circuit including two time constants due to resistor-

condenser combinations

31 and 38. The time constant of the combination 38 is long with reference to the period of the line pulses so that a bias is provided for diode 26 to effect a proportional cutting of the applied signal in a manner understood in the art and the time constant of combination 31 is such that line-frequency components of the signal are developed thereacross for application to selector 31. Selector 31 comprises a.bandpass selector including coupled tuned

circuits

39, 39. The apparatus ZI comprises a field-pulse intervmediate-frequency lselector 30 coupledto intermediate-frequency amplifier I4 and having coupled in cascade therewith a rectifier and amplitude selector 3I, the output circuit of which is coupled to field-scanning circuit lil..A Units 38 and 3l, respectively, may comprise circuits similar to those described with reference to units 25 and 26. 2

In considering the operation of' the portion of the receiver of Fig. 1 constituting the present invention, it will be assumed that the received modulated-carrier wave is of the type illustrated in Figs. 2 and 3`=of the drawings. A transmitter for generating and transmitting a modulated-carrier wave of this type is fully described in the above-mentioned application of A. V. Loughren. Thel transmitted signal comprises a modulated-carrier wave amplitude-modulated by video-signal components during the trace portions of the scanning cycle and frequencymodulated by relatively short duration line-synchronizing pulses, during line-retrace intervals,

to a predetermined deviation and by relatively long duration field-synchronizing pulses, during field-retrace intervals and between line-synchronizing pulses, to a deviation in the same direction as the predetermined deviation but of One-half of the amplitudemodulation envelope of the received carrier is illustrated in Fig. 2 wherein the transmitted signal is represented as having a predetermined peak or unmodulated amplitude L duringthe 'line-retrace intervals during which line synchronizing pulses are transmitted and an amplitude F during the field-retrace intervals during which field-synchronizing pulses are transmitted, the amplitudes L and F being equal. The amplitude of the transmitted carrier wave is varied or modulated during trace intervals in accordance with the video-signal components being transmitted, as indicated by the portions V of the curve of Fig. 2.

The frequency deviation of the carrier wave during the occurrence of line-synchronizing pulses is indicated by pulses L of Fig. 3 while the frequency deviation of the carrier wave during the occurrence of eld-synchronzing signals is indicated by the pulse F of Fig. 3. It is thus seen that, during line-synchronizing pulses, the

which is excited from unit 2l, may be designed received carrier wave has a frequency deviation or modulation of two units as referred to Fig. 3 and that, during held-synchronizing pulses, the received carrier wave has a deviation or modulation of one unit. It is furthermore seen that the field-synchronizing pulse F occurs between line-synchronizing pulses so that there is no interruption of the line-synchronizing pulses during the field-synchronizing pulses. It is further noted that the deviation of the carrier frequency representing the line-synchronizing pulses is in the same direction as the deviation representing the Held-synchronizing pulses. In case a. double interlaced scanning cycle is utilized in the system, the field-synchronizing pulse succeeding pulse F4 preferably has a relationship to pulses as illustrated by the line-synchronizing the dotted pulse F'.

The band-pass characteristics of certain portions of the'receiver circuit of Fig. 1 are illustrated by the band-pass curves to the left in Fig. 3. Thus, the units I2, I3, and I4 preferably have band-pass characteristics of the shape of curve A, the carrier frequency of the system during` the interval when video-signal components are being transmitted being located at the half-amplitude point on the slope of the characteristic A in a conventional manner, as indicated by the line fe. 'I'he over-all selective characteristic of 25, 26, and 21 is illustrated by curve B, the unit 25 thus effectively comprising a, relatively broadly-selective can'ier-frequency selector, while the over-all selective characteristic of the units and 3l is illustrated by curve C, the unit 3G thus eifectively comprising arelatively narrowly-selective carrier-frequency selector circuit.

It is thus seen that the receiver of Fig. l is eifective to operateas a conventional amplitudemodulation receiver insofar as the transmitted video-signal components are concerned. In considering the line-synchronizing channel of the system, it will be seen that, since the carrier wave is deviated by two units, with reference to Fig. 3, during the line-synchronizing pulses, the

selective properties of units 25, 2i, and 2l, as represented bycurve B, are elfe'ctive to separate the line-synchronizing components from the transmitted wave. Rectifier 26 is a conventional re'ctier and comprises means for amplitude-selecting only amplitude values above a predetermined value'in order to derive line-synchronizing signals for the receiver substantially free of all other signal components. It isapparent that video-signal components, as well as noise components, may lie within the frequency range of the response characteristic of curve B. However, the amplitude of these components is small with reference to the peak-amplitude carrier wave of the line-synchronizing pulses -s o that, due to the amplitude-selecting properties of unit 26, substantially only line-synchronizing pulses are fed to unit 21, wherein they are further selected, and afterwards shaped in the unit 28 for application to the line-scanning circuit II. The

units

26 and 21 thus comprise amplitude-selecting means coupled to the above-mentioned relatively broadly-selective carrier-frequency selector for deriving line-synchronizing components. Inasmuch as the amplitude of the signal transmitted by unit 2l varies in accordance with the peak amplitude of thereceived signal and contains substantially no components of the transmitted signal other than line-synchronizing components, the A. V. C. rectiner 2S,

tude, in a manner which will be band width of curve C of with a time constant which only need be long compared to the period of the line-synchronizing pulses so that it is effective t@ provide a fast-acting automatic `amplification control bias, or control effect, for the receiver for controlling the amplification of the receiver inversely in accordance with the received Signal ampliunderstood by those skilled in the art.

In considering the operation of the el'd-synchronizing channel of the receiver of Fig. l, itlb will be seen that the field-synchronizing pulses F are selected by field-pulse'selector 30 with an amplitude equal to the peak amplitude of the ca-in'ier wave. While video-frequency components are present within the frequency pass band of selector 30, which is represented by curve C of Fig. 3, the amplitudes of these components are small with respect to thev peak amplituderof the transmitted carrier wavey representing the field-synchronizing pulses. Also. while 'linesynchronizing components are present within the frequency pass band represented by curve C, these components are within such pass band only for the extremely short intervals requiredto sweep the carrier frequency through this pass band, ,which is dependent on the steepness of the edgessof the line-synchronizing pulses. Therefore, only an extremely small amount of energy is applied to the field-synchronizing channel during such intervals, while the field-synchronizing pulse F is of appreciable duration and supplies considerable energy tothe field-synchronizing channel. Amplitude selection is also provided in lmit 3| in a manner similar to that described above for unit 26 so that only signal-components above a predetermined amplitude value are supplied to field-scanning circuit I9 and the input thereto thus comprises substantially only eld-synchronizing pulses. The unit 3l thus effectively comprises amplitude-selecting means coupled to the above-mentioned narrowlyselective circuit for deriving field-synchronizing signals for the receiver.

Preferably, the frequency deviation'of the carrier wave represented by the pulses L of Fig. 3, which is used to transmit the line-synchronizing f pulses, is many times the line-scanning frequency of the system. for example, 500 kilocycles, which is many times 13 kilocycles. Also,

' the band width of curve B of Fig. 3 is prefer- ,ably many times the line-scanning frequency of 500 kilocycles. The Figs.l and 3 is at least as great as the line-scanning frequency of the System and preferably greater,-for example. kilocycles.

In Fig. 4 there is illustrated a' modification of the line-synchronizing channel of Fig. l which can be substituted-in th'e receiver of Fig. 1 by connecting points X, X and Y, Y to correspondingly marked terminals of the circuit of Fig. l. The circuit o f Fig. 4 comprises a line-pulse intermediate-frequency selector :including vacuum tube 4l having input electrodes coupled to terminals X, X and output electrodes coupled through band-pass selector 4I, 42 to' the detector and amplitude selector 44. Detector M is a diode having a load network including seriesconnected resistors R1 and Ra, by-passed, respectively, by condensers C1 and C3, theresistor R1 being shunted by series-connected resistor Rz an'd condenser Cz, and the resistor R3 being shunted by series-connected resistor R4 and condenser C4.

the system, for example,

The operation of the circuitlof Fig. 4 will be readily apparent when considered in connection with the description given above with reference to corresponding 'portions of Fig. 1, and it will be understood that the line-pulse intermediatefrequency selector including vacuum tube 40 and selector circuit Il, 42 may have a characteristic generally as indicated by curve B of Fig. 3. Detector 44 is thus effective to detect components of these frequencies and, by proper selection of the time constants of the branches of its load network, may be made to providean output at terminals Y, Y-which is limited to amplitude values above a predetermined value so that linesynchronizing components are effectively selected from noise components and video-signal components which may appear within the frequency range of the band-pass characteristic B.

Preferably, thecircuit of Fig. 3 is so proportioned` that R1 is much less than Rz; Ci,Ri is much' less than C3,R3; C1,R1+Cz,Rz is much less than a linescanning period; C3.R3 and C4,R4 are much greater than a line-scanning period; C1,R1 and C2',Rz are much greater than the period of the intei-mediate frequency of the` receiver; and C:,R3+C4,R4 is greater than the period of the zfield-synchronizing pulses of the system. The

diode 44 is thus eiective to operate as a multiple time-constant 'device and to-eiect-a proportional cutting of the signal applied thereto.

While applicant does not intend to be limited to any specific circuit values, the following constants are suggested for-the circuit of Fig. 4 and are particularly applicable for a system in which CO-cycle field-synchronizing pulses and 13,230- cycle .line-synchronizing pulses are utilized:

in accordance with the invention and adapted ther assumed that the over-all band-pass characteristic of units I2, |13, and Il of Fig. 5 is of the form illustrated by curve E; that the relationship of the carrier frequency of the received signal thereto is as illustrated by the'line je of Fig. 6; and that the over-all band-pass characteristic of the line-synchronizing channel of Fig. 5 is exactly similar to that of Fig. 1 and is represented by the band-pass characteristic of curve B of Fig. 6. However, the over-all band-pass characteristic of' the field-synchronizing channel, that is, of units 30 and 3| of Fig. l5, is as illustrated by curve G of Fig. 6, in order to provide a selective response to the carrier wave when deviated in frequency in th'e direction herein arbitrarily chosen as negative, which is utilized to transmit field-synchronizing pulses.

The operation of the receiver of Flg 5 will be readily apparent to those skilled in the art from the above description of the .operation of the receiver of Fig. 1 when it is pointed out that the added circuit element or intermediate-frequency limiter 50 is eifective substantially to eliminate all amplitude-modulation components from the input circuits of units 25 and 30. The system of Fig. 5 has the desirable characteristic th'at only the transmitted line-synchronizing signals are eiective to energize units 30 and 3l having the band-pass characteristic illustrated by G of Fig. 6 for the reason that the frequency deviation utilized for transmitting line pulses is in the opposite direction and because video-signal sideband components are effectively eliminated by the amplitude limiting effected in limiter 50.

to receive a double-sideband carrier signal amplitude-modulated with video signals during trace intervals and in which' line-synchronizing pulses are represented by a frequency modulation or deviation of the carrier frequency in one direction during line-retrace intervals and in which field-synchronizing pulses are represented by a deviation of the carrier frequency in the opposite direction during field-retrace intervals. The receiver of Fig. 5 is generally similar to that of Fig. l and similar circuit elements have identical reference numerals. The circuit of' Fig. 5

diiers from that of Fig. 1 primarily in that units 25 and 30 of Fig. -5 are coupled tothe intermediate-frequency amplifier N .through an intermediate-frequency limiter rather than directly as in Fig. 1.

In considering the operation of th'e circuit of Fig. 5, it will be assumed that the received carrer wave is amplitude-modulated-by video-frequency signals; that both sidebands are transmitted; that the frequency deviation for transmitting line-.synchronizing pulses is two units in one direction, as illustrated in Fig. 6; and that the frequency deviation for' transmitting eldsynchronizing pulses is one unit in the opposite direction, as illustrated in Fig. 6. It will be fur- The receiver of Fig. 6 is subject to the limitation that an over-all increased band width is required for the transmission of a given television signal with a given fidelity.

While 'there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modications 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 truevspirit and scope of the invention.

What is claimed is:

1. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration synchronizing pulses of one type to a predetermined deviation and by relatively long duration synchronizing pulses of another type to a deviation of lesser magnitude than said predetermined deviation. a television receiver comprising; a relatively broadly-selective carrier-frequency selector circuit responsive to said carrierfrequency deviation by synchronizing components of said one type, a relatively narrowly-'selective carrier-frequency selector circuit responsive to said carrier-frequency deviation by synchronizing components of said other type, means couleser magnitude than said predetermined deviation, a television receiver comprising, a relatively broadly-selective carrier-frequency selector circuit responsive to 'said line-synchronizing carlier-frequency deviations, a relatively narrowlyselective carrier-frequency selector circuit responsive Yto said field-synchronizing carrier-frequency deviations, means coupled to said broadly-selective circuit for deriving line-synchronizing signals for said receiver, and means coupled to said narrowly-selective circuit for deriving field-synchronizing signals for said receiver.

3. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration line-synchronizing pulses to a predetermined deviation many times the frequency of said line-synchronizing pulses and by relatively long duration iield-synchronizing pulses to a deviation of lesser magnitude than said predetermined deviation, a television receiver comprising. a relatively broadly-selective carrierfrequency selector circuit having a band width many times the frequency of said line-synchronizing pulses and responsive to said line-synchronizing carrier-frequency deviations, a relativelynarrowly-selective carrier-frequency selector circuit having a band width at least greater than the frequency of said line-synchronizing pulses and responsive to said field-synchronizing carrier-frequency deviations, means coupled tosaid broadly-selective circuit for deriving linesynchronizing signals for said receiver, and means coupled to said narrowly-selective circuit for deriving field-synchronizing signals for said receiver.

4. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal corn-v ponents and frequency-modulated by relatively short duration line-synchronizing pulses to a predetermined deviation and by relatively long duration held-synchronizing pulses between line-synchronizing pulses to a deviation of lesser magnitude than said predetermined deviation, a television receiver comprising, a relatively broadly-selective carrier-frequency selector circuit responsive to said line-synchronizing carrier-frequency deviations, a relatively narrowly-selective carrierfrequency selector circuit responsive to said eldsynchronizing carrier-frequency deviations, amplitude-selecting means coupled to said broadlyselective circuit for selecting therefrom only amplitude values above a predeterminedvalue to derive line-synchronizing signals for said receiver,

and ,amplitude-selecting means coupled to said narrowly-selective circuit for selecting therefrom only amplitude values above a predetermined value to derive iield-synchronizing signals for said receiver.

5. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively long duration Held-synchronizing pulses to a predetermined deviation and by -relatively short duration line-synchronizing pulses to a deviation including values outside said predetermined deviatiom a television receiver comprising, a cartier-frequency selector circuit selectively responsive to said line-synchronizing carrier-frequency leviations outside said predetermined deviation, means coupled to said selective circuit for derivfor utilizing saidlcontrol effect for controlling an operating characteristic oi'said` receiver in response to changes in said characteristic of `said received signal.

6.-In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration line-synchronizing pulses to a predetermined deviation and by'relatively long duration field-synchronizing pulses between linesynchronizing pulses to a deviation of lesser magnitude than said predetermined deviation, a television receiver comprising, a relatively broadlyselective circuit responsive to said line-synchronizing carrier-frequency deviations, a relatively narrowly-selective circuit responsive to said field-synchronizing carrier-frequency deviations, means coupled to said broadly-selective circuit '.for deriving a control'effect responsive to variations` in a characteristic of the received signal, and means for utilizing said control eii'ect for controlling an operating characteristic of said receiver.

,7. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration. line-synchronizing pulses to a predetermined deviation and by relatively long duration eld-synchronizing pulses between linesynchronizingl pulses to a deviation of lesser magnitude than said predetermined deviation, a television receiver comprising, a relatively broadly-selective circuit responsive to said linesynchronizing carrier-frequency deviations, a relatively narrowly-selective circuit responsive to said ield-synchronizing carrier-frequency deviations, means coupled to said broadlyselective circuit for deriving a control eiect responsive to the amplitude of the received signal, and means for utilizing said control effect for controlling the ampliication of said receiver inversely in accordance with the received signal amplitude.

8. In a television system including a transmitter adapted to transmit a single-sideband modulated-carrier wave amplitude-modulatedV by videosignal components and frequency-modulated by relatively short duration line-synchronizing pulses to a predetermined deviation within said amplitude-modulation sideband and by relatively long duration iield-synchronizing pulses to a deviation in the same direction as said predetermined deviation but of lesser magnitude, a television receiver comprising, a relatively broadly-selective carrierfrequency selector circuit responsive to said line-synchronizing carrier-frequency deviations, a relatively narrowly-selective carrier-frequency selector circuit responsive to said eld-synchronizing carrier-frequency deviations, means coupled to said broadly-selective circuit for deriving line-synchronizing signals for said receiver, means coupled to said narrowly-selective circuit for deriving held-synchronizing signals for said receiver, and means for selecting and reproducing said single-sideband video-signal components of said carrier wave.

9. In a television system including a transmitter adapted to transmit a modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relatively short duration line-synchronizing components to a predetermined deviation and by relatively long duration ileld-synchronizing pulses to a deviation in the opposite direction from said predetermined deviation, a television receiver comprising, a relatively broadly-selective carrierfrequency selector circuit responsive to said linesynchronizing carrier-frequency z ieviations, a relatively narrowly-selective carrier-frequency selector circuit responsive to said eld-synchronzing carrier-frequency deviation. means coupled to said broadly-selective circuit for deriving line-synchronizing signals for said receiver, means coupled to said narrowly-selective circuit for deriving ield-synchronizing signals for said receiver, and means for reproducing said video-signal components of a vreceived carrier wave.

10. In a television system including a transmit-,ter adapted to transmit a double-sideband modulated-carrier wave amplitude-modulated by video-signal components and frequency-modulated by relativelyshort duration line-synchronizing components to apredetermined deviation and by relatively long duration field-synchronizing pulses to a deviation in the opposite direction from said predetermined deviation. a television receiver comprising, a relatively broadly-selective carrier-frequency selector circuit responsive to said vline-synchronizing carrier-frequency deviations, a relatively narrowly-selective carrierfrequency selector circuit responsive to said fieldsynchronizing carrier-frequency deviation. means coupled to said broadly-selective circuit for devriving line-synchronizing signals for said receiver, means coupledr to said narrowly-selective circuit for deriving mld-synchronizing signals Iorsaid receiver, and means for reproducing said J Y double-sideband video-signal components of a re-