US2289948A - Video-frequency signal-translating system for television receivers - Google Patents

Description

July 14, 1942.

WILSON VIDEO-FREQUENCY SIGNAL-TRANSLATING SYSTEM FOR TELEVISION RECEIVERS Filed July 25, 1940 2 Sheets-Sheet l NQFI N O s H. Y m m M 0 TC. W T l T VH mm A I Y B 6 9% 595m o .O H 05 ON 4 LF mT mywjmi c EIEE $253: 653%. 55:85. uhsouzzmhz 1054.58 99E .0 o v: a: N1 9L4 6 o m3 m k ozE3mz E EzofibzBm 6 0 a 14, 1942- J. c. WILSON 2,289,948 VIfiEOFREQUENCY SIGNALTRANSLATING SYSTEM FOR ;TELEVISION RECEIVERS Filed July 23, 1940 2 Sheets-Sheet 2 Time a.

m x K d: 0- Z I! W0 Q Q rd (2 I JWE S WILSON u. BY A ATTORNEY frequency signal-translating system the visible image, and 1 spaced parallel retrace bright seriously to impair there'produced image is ,being reproduced. The appearance of these re-' Patented July 14, 1942 uNl Eo STATE S PATEN T, OFFICE VIDEO-FREQUENCY srGNAn-TnmsnamG SYSTEM tine Corporation,

FOR TELEVISION RECEIVERS John C. Wilson, Bayside, N.

T'., assignor to Hazela corporation of Delaware Application July 23, 1940, Serial No. 346,907

. 13 Claims. (c1. inf-7.5) I

v with an automatically operating brightness control.

This invention relates an improved videoreceivers and, more particularly, t a system for translating a composite television signal including video-signal components and synchronizingsignal components. I a

The electronic television receiver of the present day conventionally employs a cathode-ray tube having a screen upon which the television image is reproduced by av signal-modulated cathode-ray beam as it lines. This pattern of lines is-composed ofa series of spaced paralleltrace lines, which form an intervening series of lines, normally invisible; The receiver conventionally is provided with a a manually adjustable brightness control by which theaveragebrightness of the reproduced image maybe adjusted; While this control may beso positioned on the receiver as to be readily accessible to the user whereby the user isable to adjust the brightness to suit his individual taste, it is occasionally positioned for adjustment from the rear'of the receiver where it is not readily accessible to'the user, I ing adjusted'only upon the initial installation of the receiver and remaining thus adjusted over a long period of receiver operation. In the event that the brightness control is adjusted either initially if inaccessible, or by the user if accessible, so as to bring out more detail in the darker portions of the reproduced image than the transmission will allow or, having once been properly adjusted, becomes improperly adjusted due to changed operating frequently happens that the reproduced image is marred by the appearance of the undesired and normally-invisible retrace lines, usually fragwhich occur during the intervals be-- tween the synchronizing pulses of each retrace period, the synchronizing pulses usually. beingmentary,

of such polarity and amplitude as to suppress the scanning beam fortheir durations. Even though the retrace lines are not sum ently ma e.

they are a distinct annoyance when no trace lines is especiallyprevalent in the cheaper television receivers in which no attempt is made to stabilize a television signal by .reinsertion of the unidirectional background components. The

objectionable appearance of the retrace lines may occur, however, even in those more elabfor television progressively scans the sur- -face of the screen in a predetermined pattern of the control normally .be-

"In accordance with the prior art practice, it

1 has been proposed automatically to eliminate the i be of the automatic r an auxiliary oscillator iliary amplifier, the latter-tends to be greatly overloaded by the highvoltage pulses derived quency response of the system and producing serious distortion of the reproduced image. ,The

conditions of the receiver, it

from the scanning system and furthertends to load the video-frequency circuit'of the receiver 3 capacitively, thereby impairing the video-freuse of an auxiliary osci lator for the purpose of extinguishing the retrace lines involves addedexpense and the addition of certain apparatus which not only involves certain additional ad- Justments but also tends to complicatethe receiver design.

In accordance with another prior art arrangement, it has been proposed that the cathode raybe extinguished during the retrace intervals'by magnetically coupling energy from the scanningsystem of the receiver into the cathode-ray tube :55.

input circuit. This has the very serious disadvantage that it greatly aiIects the uniformity of the video-frequency response of the-system.

thereby impairing the quality of the reproduced image.

It'is an object of the present invention, therefore, to provide a new and improved video-freorate television receivers which are provided 55 quencysignal-translating system which avoids one or more of the above-mentioned disadvantages of the prior art arrangements.

, It is a further object of the present invention to provide nents of the television signal in extinguishing the retrace lines is greatly increased during a large portion of the field-retrace intervals.

It is an additional object of the invention to provide a signal-translating system wherein that level of the composite television signalwhich corresponds to black in the transmitted image is altered during at least a portion of the fieldeach retrace interval, a v

during the entire retrace' a signal-translating system wherein the effect of the synchronizing-signal compothe television signal in lines during the'fieldmodulator l3. and the 4 intermediate-frequency amplifier M in conventional manner.

Sound-signal translating and reproducing apparatus 2| is also connected to the output of the oscillator-modulator i3 and may include, connected in cascade in the order named, one or more stages of intermediate-frequency amplification, a detector, one or more stages of audio-frequency amplification, and a sound-reproducing device.

vIt will be understood that the various units thus far described may, with the exception of the field-retrace period, and means for utilizing the control potential for effectively-changing with 1 respect to the cutoff point of duc'er that level of the composite signal which ,components for the transmitted image to of the reproducer only corresponds to black in suppress the cathode ray the image repro-' during the aforesaid portion of the field-retrace with one specific embodithere is included means period. In accordance ment of theinvention;

for repeating the synchronizing-signal compov nents, means responsive primarily to the fieldsynchronizing pulses of the synchronizing-signal increasing the repeating ratio of the repeating means during at least a portion of each field-retrace period, and means for combining the repeated synchronizing-signal components with the composite signal to suppress the cathode ray of the reproducer during the aforesaid portion of the field-retrace period.

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

Referring now to the drawings, Fig. 1 is a circuit diagram, partly schematic, of a complete television receiver embodying the invention; Fig.

bodying a modified 2 is a graph representing certain related pobias derived from the A.

tentialwariations occurring at different points of the receiver and is used in explaining the operation of the invention; Fig. 3 is a circuit diagram of a portion of a form of the invention; and

, Fig. 4 is 'a graph representing certainrelated potential variations occurring at different points in the circuit arrangement of the Fig. 3 modification. Referring more particularly to Fig. 1, the system there represented comprises a'television receiver of the superheterodyne type including an antenna system l0, H connected to a radio-frequency amplifier l2, to which are connected in cascade, inthe order named, an oscillator-modulator IS, an intermediate-frequency amplifier H, a detector IS, a video-frequency signal-translating system l6, and a cathode-ray image reproducer H. A field-frequency and line-frequency scanning unit I8 is also coupled to the output of the video-frequency signal-translating system through suitable synchronizing-signal separating apparatus [9.

An automatic amplification control or A. V. C. system 20 is coupled to the output circuit of the intermediate-frequency amplifier ll and the output circuit of the A. V. C. system the input circuits of one or more of the tubes of the radio-frequency amplifier l2, the oscillatortelevision receiver emvideo-frequency signal-translating system I, be of a conventional construction and operation,

--the details of which are well known in the art, rendering further description thereof unneces sary. Considering briefiy the operation of the receiver as a whole, however, and neglecting for the moment the operation of the video-freqency signal-translating system i6 presently to be described, a vision-signal modulated-carrier wave is intercepted by the antenna system III, N, selected and amplified in the radio-frequency amplifier i2, and applied to .the oscillator-module tor l3 wherein it is converted to an intermediatefrequency signal. The vision-signal modulated intermediate-frequency carrier selectively amplified in, quency amplifier ll andis detected by the detector l5 to derive the modulation components thereof. The modulation components, which comprise a composite television signal including synchronizing-signal components and video-signal components, are applied to the video-frequency signal-translating system cation and are thereafter applied in the usual manner to a brilliancy-control electrode of the cathode-ray image reproducer II to modulate the intensity of the electron beam of the tube 11 in accordance with the video-signal components.

The automatic amplification control or A. V. C.-

signal is, in turn.

tive to control the amplification of one or more 'of theunits l2, l3, and H to maintain the signal input to the detector l5 within a relatively narrow range for a wide range of received signal int'ensities. v

The sound-signal modulated-carrier wave accompanying the desired vision-signal modulated-carrier wave is also intercepted by the-antenna system. In, H, selected and amplified in the radio-frequency amplifier l2, and applied to is connected to the oscillator-modulator I3 whereinit is converted to a sound-signal modulated intermediate-frequency signal of the sound signal translating apparatus 1|.

Here the sound-signal modulatedintermediatefrequency carrier signal is, in turn, amplified and detected to derive the modulation components which are further amplified and reproduced by the sound-reproducing device of the apparatus 2|.

The synchronizing-signal components are separated from the video-signal components of the composite television signal, in a manner presently to be considered in detail, and applied to the inter-synchronizing-signal separating ap- .paratus I9. The field-synchronizing and the line-synchronizing pulses are effectively separated from each other by the separating apparatus i9 and are applied to the respective fieldfrequency and line-frequency scanning systems of the scanning unit IS. The field-frequency and line-frequency scanning systems generate periodic scanning currents of saw-tooth wave form, the frequencies of which are controlledthe intermediate-fre-- V. C. system iii-is eflecand applied to the input synchronizing-signal aasaees by the respective field-frequency and line-irequency synchronizing components the received television Si nal. These scannin tern oi parallel lines on the screen of the tube, a thereby toreproduce the transmitted image.

Referring now more particularly to the portion 01' the system embodying the present invention, the video-frequency signal-translating. system It comprises a video-frequency ampli-' iler tube 22 having an input circuit, which in- I cludesa grid-leak resistor 23, coupled through a condenser 24 to the load resistor 25 of the detector IS. The tube 22 has an anode which is connected through a load resistor "to the, positive terminal of a source or operating potential +3. The anode or tube 22 is also coupled througha blocking condenser- 21 to the raycontrol electrode of the cathode-ray image reproducer l1; Connected in series between the ray-control electrode and cathode otthe oath: ode-ray tube l I is a resistor 28 and, a source of,

- biasing potential 30, apotentiometer It being connected across the biasing potential 30 to provide a manually adjustable brilliancy control. Connected between an adjustable tap on the maybe or the diode vacuum-tube type. a resistor 33, and-a condenser 32, the cathodeot-the diode rectifier being connected to the adjustable tap on the resistor 2'6. The anode of the diode rectifier is also connected to the positive terminal 01' a source oi'bias'potential +0. The voltage condenser 34 isapplied through ajcoupling conthrough a resistor; 36

:developed across the denser 32 to an anode 28 or tube, ll. This anode may be the suppressor electrode of. a pentode type of cathode-ray tube andis eifective tomodulate the cathode-ray. beam of tube II inac- ,cordance with potentials applied to the anode. In considering the operation or the circuit just described, it will be assumed that a composite I television signalpa' portion otthe field-synchro nizing component otwhichis illustrated graphically bycurve a of Fig. 2, is applied from the diode load resistor 25 of the. detector I! through, the video-frequency amplifier 22 to the ray-.

control electrode or the cathode-ray tube IT.

This composite' television signal includes video- A signal components, not shown. in Fig. 2, and

components comprising pulsesd' and line-synchrofield-synchronizing nizing pulses e. I

The condenser 24 and resistor 23 in the input circuit oi the amplifier tube22 provide an operating bias for tube 22 by peak-grid rectification of the synchronizing-signal components of the composite television signal applied from the detector I! to the input circuit oftube-22 and thus stabilize the peaks of'the synchronizingsignal components at a uniform level of the television signal, represented by the broken .line 7', 7' of Fig. 2, in the output circuit of tube 22 even though diflerent television signals, or even the same televisionsignals, may vary somewhat in the intensity with which'they are received.

The stabilized signal output of tube 22 is applied directly to the control grid of image-reproducing tube ll through the relatively large couthe bottom toward the top of the fluorescent resistor and ground is a series circuitcomprising, inthe order named, arrectitler 35 which television receivers of Fig. 1, do not'attempt to reinsert the unidi- 40 the diode rectifier as v currence oi synchronizingpulses.

the opposite side of the electrical or equal-area level I, f of the television signal, the video-signal components modulate the cathode-ray beam durcathode .ray both during the line-retrace and ray tube IT with the peaks of the synchronizing on the stabilizedtelevision signal 3 pling condenser 21. Assuming that the image to be reproduced has substantial areas of white therein, the composite television signal has large amplitude values in the white direction and. the level of the television signal corresponding to black consequently is considerably displaced on axis 0-0 or the signal, as indicated in curve a of Fig. 2, the black level being indicated at !-f.

It the manual brightness control 3| is adjusted to bias the cathode-ray tube I I to cutoff at the inglthe trace intervals. whereby the cathodeeray tube reproduces the transmitted image, while the synchronizing-signal components d, e bias the. tubexbeyond cutoff, thereby to extinguish the frame-retrace intervals. In using the manually adjustable brightness controlill, however, it is diflicult accurately to ascertain the optimum ad- 1 Justment for best definition in the reproduced image and the control i'requently'is adjusted to operatethe cathode-ray tube H to cutofl at a level 01' the television signal which provides a brighter image as, for example, that level indicated by tnebroken l e a, a or 2. Thus, during the field-retrace interval h between the completion of'onefiel'd and the beginning of a successive field, the cathode ray,as it moves from screen oi',the tube, or vice versa, produces a-visibleilluminated spot upon the occurrence of each serration i of the field-synchronizing pulses d and l a visible fragmentary retrace line during each,- interval it between successive line-synchronizing pulsese, especially-true in the cheaper which, as in the arrangement rectional background components of the television signal, thereby toapply the television signal to the ray-control electrode of the cathodepulses stabilized at a uniform level,but rather apply the television signal to the ray-control electrode 'as an unstabllized altemating potential varying aboveland below its electrical axis.

In order, to eliminate this efiect. the anode of .is so biased with relation. to the potential of theitap on the resistor," to which the cathode is connected that current flows through the diode rectifier only during the oc- The synchronizing-signal components are thus separated from the composite televislonsignal by clipping the synchronizing pulses at a predeterminedlevel displaced from the peaks oi the pulses, whereby only the synchronizing-signal components appear in the anode circuit of the diode-rectifier. These synchronizing-signal components are applied to an integrating means responsive primarily to the duration of the ileld-synchronizing pulses and comprising the resistor 33 and the condenser 34 to produce across the condenser 34 a negative unidirectional control potential during at least a portion of eachvfield-retrace period following each group of field-synchronizing broad pulses which varies in accordance with curb b of Fig.

,2. The time constant of this integrating circuit is so proportioned that the potential across the condenser 34 rises rapidly to its maximum value a during each group of field-synchronizing broad pulses. The time constant of the condenser discharge circuit, comprising the resistors 33 and 36, 1

is so proportioned that the potential appearing -returns to the relatively constant value across the condenser 34 from the integration of the synchronizing-signal components decays more slowly, whereby at least two andpreferably five orsix line-scanning periods elapse after the termination of the field-synchronizing broad pulses before the potential "of the condenser 34 of the potential of the source +0.

Since the potential of the condenser 34 is applied through the condenser 32' to the anode 29 of the cathode-ray-tube 11, the resultant in- 'stantaneous potential effective to modulate the cathode-ray beam during the field-retrace period is the combined potentials applied to the ray-- control electrode and to'anode 29 as represented bypurve c. It is at once evident that the potential developed across the condenser 34 primarily from the field-synchronizing pulses of the synchronizing-signal components effectively changes,

insofar as the modulation of the cathode-ray beam is concerned, that level of the composite television signal which corresponds to black in the transmitted image. The above-mentioned control potential is thus utilized for efiectively changing or increasing in the black direction with respect to the cutoff point ofthe image mit the appearance of the fragmentary retrace lines during the field-retrace interval.

While it was assumed in the foregoing descripthe cathode-ray tube l1 and includes in its input circuit a coupling condenser 40 and a grid-leak resistor 42 which reinsert the unidirectional background-illumination component of the composite television signal.

Connected to an adJustable tap on the resistor 26 is the anode of a diode rectifier tube 43 the cathode of which is connected through a resistor 44 to a source of positive-bias potential +C. Connected across the resistor 44 is an integrating circuit comprising a resistor 45 and a condenser 46. The input circuit of a vacuum-tube repeater 41 is connected across the resistor 44, a source of biasing potential 48 providing a normal oper- I ating bias for the control electrode. Connected to the junction between the resistor 45 and the condenser 46 is an auxiliary control electrode 48 of the repeater tube 41. Operating potentials are applied from a source of operating potential +B through a load resistor 50 to the anode of tube 41 and to the screen from the source +80. The anode of tube 41 is coupled through a condenser 5| to an auxiliary control electrode of the video-frequency amplifier tube 39.

In considering the operation of this modification of the invention, it will be assumed thata composite television signal is applied from the detector 15 through the video-frequency ampli- I the input circuit of the video-frequency amplifier fiers 22 and 39 to the input circuit of the cathoderay tube I! and would appear therein, were it not modified in a manner presently to be considered, as a potential having the wave form graphically illustrated by curve a of Fig. 4. As in Fig. 2, this composite signal includes video-signal components, not shown, and synchronizing-signal components d and e. v

The composite television signal is applied to 22 with negative polarity and appears inthe'output circuit thereof with positive polarity as represented by the curve b of Fig. 4. The diode rectifier 43 is so biased by the positive potential tion of the operation of the Fig. 1 arrangement that the image to be reproduced had appreciable areas of white therein, the operation of this 5 modification of the invention is essentially the same in the case where the image to be reproduced contains only areas of grey and black. In

this event, the voltage developed across the condenser 34 from thebroad field-synchronizing pulses still has the same value, as represented by the curve b of Fig. 2, and is efiective to suppress the cathode ray of the image reproducer l1 during the greater portion of the field-retrace period.

A modification of the video-frequency signaltranslating system of the invention is represented in Fig. 3 in which circuit elements corresponding to similar circuit elements of Fig. 1 are designated by similar reference characters. In this modification, the composite television signal is applied to the input circuit of the video-treapplied through the resistor that the synchronizing-signal components are separated from the video-signal components by the diode rectifier 43 and the synchronizing-signal components are applied'to an integrating circuit comprising the quency amplifier 22 with negative polarity and it is, therefore, necessary to provide across the video-frequency amplifier 39 is connected between the output circuit of the video-frequency amplifier 22 and the input circuit of the oathode-ray image reproducer II. This amplifier is direct-connected to the ray-control electrode of resistor 45 and condenser ,46. The. integrating circuit integrates the synchronizing-signal comconstant equal to at least two and preferably five or six line periods, whereby the potential developed across the condenser 46 persists over a rela-- tively long time interval following each group of field-synchronizing broad pulses.

The synchronizing-signal components are like- A wise applied directly to the control grid of the vacuum-tube repeater 41 from resistor 44. The amplification or repeating ratio of this tube, however, is controlled by the potential appearing,

across the condenser 46 and applied to its auxiliary control electrode and is thus responsive primarily to the synchronizing-signal components, the amplification increasing during at least a portion of each field-retrace period as the poten- I I aaeaoce tial across the condenser 46 increases in a posi-' tive direction. Thus, the amplified synchronizing-signal components appearing in the output circuit the vacuum-tube repeater 41 have larger amplitudes during, and shortly after the occurrence of, each group of field-synchronizing broad pulses as represented by curve m of Fig-4.

The amplified synchronizing-signal components are applied through the condenser to the auxiliary control electrode .of the video-frequency amplifier 39, thecondenser 5| causing the synchronizing-signal wave to center about its alternating current axis n, n as represented by curve 0 of Fig. 4. The amplified synchronizing-signal components applied to the auxiliary control electrode of tube 39 (curve o) are electronically added to or combined withthe composite telethat level of said composite signal which corresponds to black in the transmitted image to suppress the cathode ray of said reproducer only during said portion oi! said field-retrace period.

2. A video-frequency signal-translating system for a television receiver including a cathode-ray image reproducer comprising, a video-frequency signal-translating device having an input circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signalcomponents to be visually re-- produced by said image reproducer, integrating means responsive primarily to the duration of the field-synchronizing pulses of said synchronizlug-signal components for deriving a control potential during at least a portion of each fieldvision signals applied to the input circuit thereof (curve b) and, after reversal of their polarity by amplifier 39, there is thus applied to the ray-'- control electrode of the cathode-ray tube H a composite television signal 01' modified wave form as represented by curve p of Fig. 4, wherein that level of the composite signal which corresponds to black in the transmitted image has been altered by increasing the black level in the black direc-- tion. It is evident that the ray-control electrodeof the cathode-ray image reproducer i1 is biased beyond cutofl, and the cathode ray thereby extinguished, by the changed black level of the composite television signal during the greater .portion of the field-retrace interval even though the brightness control 3! may have been improp-- erly adjusted to the level of the television signal at which the retracelines otherwise would appear. 'Whlle the intervals i of the television signal between the fleld-synchronizingbroad pulses dmay produce luminous spots during the fieldretrace'interval, the spots are either out of the picture field orare. near one edge thereof and, therefore, are not objectionable.

Instead oi electronically adding or combining in retrace period, and means for utilizing said .control potential for eifectively changing with respect to the cutoff point of said image reproducer that level of said composite signal which corresponds to black in the transmitted image to sup press the cathode ray of said reproducer onlyduring said portion of said field-retrace period.

3. A video-frequency signal-translating system for a television receiver including a cathode-ray image reproducer comprising, a video-frequency signal-translating device having an input circuit adapted to have applied thereto a composite sig nal including synchronizing-signal components and video-signal components to be visually re-' produced by saidimage reproducer, integrating means responsive primarily to the field-synchronizing pulses of said synchronizing-signal components for deriving a control potentialduring an interval of each field-retrace period equiv I alent to several line periods following each group tube l9 the composite signals and the amplified synchronizing-signal components. substantially the same result can be accomplished by efl'ecting the addition or combination directly in the input circuit of tube ll as by applying with proper polarity the amplified synchronizing-signal components across a resistor positioned in the cathode circuit of tube ll.

-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 modiflcations 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 is claimed'is;

1'. A video-frequency signal-translating system for a television receiver including a cathode-ray image reproducer comprising, a video-frequency signal-translating device having an input circuit adapted to have applied thereto a composite sig- 'nal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, integrating means responsive primarily to the field-synchronizing pulses of said, synchronizing-signal components for deriving a control potential during at least a portion of each fieldretrace period, and means for utilizing said put circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, integrating means responsive primarily to the field-synchronizing pulses of said synchronizingsignal components for deriving a control potential during at least a portion of each field-retrace period, and means for utilizing to said control potential for effectively increasing in the I black direction that level of said composite signal which corresponds to black in the trans-.

mitted image to suppress the cathode ray of said reproducer only during said portion of said fieldretrace period.

5. A video-frequency signal-translating system for a television receiver including a cathoderay image reproducer comprising, a video-frequency signal-translating device having an input circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, means for integrating said synchronizing-signal Y components to derive primarily from the fieldcontrol potential for effectively changing with respect to the cutoff point of said image reproducer synchronizing pulses of said synchronizing-signal components a control potential during at least a portion of each field-retrace period, and means for utilizing said control potential for, effectively changing with respect to the cutoff point of said image reproducer that level of said composite signal which corresponds to black in the transmitted image to suppress the cathode ray of said components to derive primarily from the fieldsynchronizing pulses of sa d nchronizing-signalcomponents a control potential during at least a portion of each field-retrace period, said means comprising an energy-storage element, a charg ingcircuit for said element having a timeconstant short compared to the duration of said field-synchronizing pulses, a discharge circuit for said element having a time constant long compared to the period of line-synchronizing pulses of said synchronizing-signal components, and means for utilizing said control potential for effectively changing with respect to'the cutofl point of said image reproducer that level of said composite signal which corresponds to black in the transmitted image to suppress the cathode ray of said reproducer only during said portion of said field-retrace period.

7. A video-frequency signal-translating sysfield-synchronizing pulses of said synchronizing-.

signal components for deriving a control potential during at least a portion of each field-retrace period, and means for combining said con-' reproducer only during said portion of said field of said image reproducer that level of said composite signal which corresponds to black in the transmitted image to suppress the cathode ray of said reproducer only during said portion of said field-retrace period.

9. A video-frequency signal-translating system for a television receiver including a cathoderay image reproducer comprising, a video-Irequency signal-translating device having an input circuit adapted to have applied thereto a composite signal including retrace period, and means for applying said com-' said derived potential to rayposite signal and control electrodes of said image reproducer etfectively to suppress the cathode ray of said reproducer only during said portion of said fleldretrace period.

10. A video-frequency signal-translating system for a television receiver including a cathode-ray image reproducer comprising, a. videofrequency signal-translating device having an input circuit adapted to have applied thereto a j tem for a television receiver including a cathodetrol potential and said composite signal eflectively to change with respect to the cutoff point of said image reproducer that level of said composite signal which corresponds to black in the transmitted image to suppress the cathode ray of said reproducer only during said portion of said field-retrace period.

8. A video-frequency signal-translating system for a television receiver including a cathode-. ray image reproducer comprising, avideo-frequency signal-translating device having an input circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, means for stabilizing at a predetermined signal level the peaks of the field-synchronizing pulses of said synchronizing-signal components, means for clipping at a second predetermined signal level said field-synchronizing pulses to separate said pulses from said composite signal, integrating means responsive primarily to the field-synchronizing pulses of said synchronizing-signal comcomposite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, means for repeating said synchronizing-signal components, means responsive primarily to the field-synchronizing pulses of said synchronizingsignal components for increasing the repeating ratio of said repeating means during at least a portion of each field-retrace period, and means for combining said repeated synchronizing-signal components with said composite signal .to sup press the cathode ray of said reproducer during said portion of said field-retrace period.

11. A video-frequency signal-translating system for a television receiver including a cathode-ray image reproducer comprising, a videofrequency signal-translating device having an input circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer,

said repeated synchronizing signal components with said composite signal to suppress the oath-- ode ray of said reproducer during said portion.

of said field-retrace period.

12. A video-frequency signal-translating system for a television receiver comprising, a cathode-ray imageireproducer having an input circuit adapted to have applied thereto a composite signal including synchronizing-signal components and video-signal components to be visually reproduced by said image reproducer, means for repeating said synchronizing-signal compoponents for deriving a control potential during at least a portion of each field-retrace period, and means for utilizing said control potential for eiiectively changing with respect to the cutoff point lug-signal components to suppress the nents, means responsive primarily to the fieldsynchronizing pulses of said synchronizing-signal components for increasing the repeating ratio of said repeating means during at least a portion of each field-retrace period, and means for applying to said input. circuit repeated synchronizsynchronizing-signal components and video-signal components to be ray of said rcproducer during said portion of said field-retrace period.

13. A video-frequency signal-translating sys tem for a television receiver including a cathode-ray image reproducer comprising, a videofrequency signal-translating device having an input circuit adapted to have applied thereto field-synchronizing pulses or said synchronizing-' signal components for increasing the repeating ratio of said repeating means during at least a portion of each field-retrace period, and means for combining said composite signal with said repeated synchronizing-signal components the JOHN C. WILSON.

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