US2468256A - Television receiver including a horizontal oscillator responsive to a predetermined fraction of transmitted synchronizing pulses - Google Patents

Description

2,468,256 TELEVISION RECEIVER INCLUDING A HORIZONTAL OSCILLAT ESPLEY April 26, 1949. D. C.

RESPONSIVE TO A PREDETERMINED FRACTION OF TRANSMITTED SYNCHRONI Z ING PULSES' 3 Sheets-Sheet 1 Filed June 22, 1945 Time-+- Time 'INVENTOR. DENNIS G. ESPLEY ATTOR EY FIG.3

Apnl 26, 1949. D. c. ESPLEY 2,468,256

TELEVISION RECEIVER INCLUDING A HORIZONTAL OSCILLATOR RESPONSIVE TO A PREDETERMINED FRACTION OF- TRANSMITTED SYNCHRONIZING vPULSES Filed June 22, 1945 s Sheets-Sheet 2- INVENTOR. DENNIS C. ESPLEY BY Zfi AT TO EY 2,468,256 AI'OR D. C. ESPLEY INCLUDING A HORIZONTAL OSCILL A PREDETERMINED FRACTION OF TELEVISION RECEIVER RESPONSIVE TO TRANSMITTED SYNGHRONIZING PULSES Filed June 22, 1945 3 Shets-Sheet'. s

FIG. 5

INVENTOR. DENNIS C. ESP

LEY,

Patented Apr. 26, 1949 UNITED STATES PATENT OFFICE Dennis G. Espley, Wembley, England, assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application June 22, 1945, Serial No. 600,868 In Great Britain October 6, 1943 Claims.

This invention relates to television receivers for utilizing the video components of a received signal during only certain ones, rather than during all, of the line-trace intervals in which video 7 components are available for reproduction. The present application is a continuation-in-part of application Serial No. 557,325, filed on October 5, 1944, now abandoned, in the name of Dennis G. Espley.

One form of television receiver well known to the art utilized a Ml-line picture signal, that is, a signal including 441 line-trace intervals per frame. Others of more recent design use a 551-line picture signal. Such receivers comprise an image-reproducing device, such as a cathoderay tube including line-scanning and fieldscanning elements, for utilizing video-frequency signal components. Line-scanning and fieldscanning generators, responsive to synchronizing-signal components usually received along with the video-frequency signal components in the retrace intervals of a composite television signal, provide scanning signals for controlling the scanning elements. The scanning signals generated have trace and contiguous retrace portions which produce corresponding traceand retrace-scanning effects within the reproducing device. These effects cause an image-reproducing area to be scanned in synchronism with the scanning of an image to be translated at the transmitter. In such a system the videofrequency signal components contained in each line-trace interval of the received signal are utilized in synthesizing the image at the receiver.

While television systems utilizing the described prior art receivers have proved to be generally satisfactory, other systems have been proposed which improve the detail of the reproduced image. Since the image definition is a function of the number of picture elements translated which, in turn, is dependent upon the number of line scansions per frame, these other systems utilize an increased line-scanning frequency both at the receiver and transmitter. For example, systems using approximately 800 and 1000 line scansions per frame have been suggested. These higher definition systems include television receivers which are generally similar to that described above, but which differ materially therefrom in the line-scanning generator. It has been found desirable in receiver systems which utilize the video-frequency signal content of each linetrace interval of a received signal, to maintain a given relationship of line-trace to line-retrace scanning intervals. Usually the retrace-scanning time is approximately equal to ten per cent. of the line-trace scanning interval. At high line-scanning frequencies this ratio may be established only through the use of costly linescanning generators of rather intricate construction which may constitute an undesirable limitation in some applications.

Even though it may ultimately be determined that the fidelity of the reproduced image warrants extensive use of systems of 800 or 1000 lines per frame, or systems having a still greater number of line scansions per frame, there will remain installations in which the detail of a lower order line system is adequate. In these installations line-scanning generators of simplified construction may be used, materially reducing the equipment cost. However, the firstdescribed prior art receivers designed for use in present day 441-line or 525-line systems and including comparatively inexpensive line-scanning arrangements are not adapted to translate the television signal utilized in higher definition systems. Hence, these prior art receivers cannot readily be employed in such remaining installations.

It is an object of the invention, therefore, to provide a television receiver which avoids the aforementioned limitations of prior art arrangements.

It is another object of the invention to provide a simplified television receiver for utilizing the video components of a received signal during only certain ones, rather than during all, of the line-trace intervals in which video components are available for reproduction.

It is a specific object of the invention to provide an improved television receiver featuring a simplified and inexpensive line-scanning arrangement and adapted to utilize a television signal including well over 400 line-trace intervals per frame.

In accordance with the invention, a television receiver for utilizing a signal including videofrequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-retrace intervals comprises an image reproducing device for utilizing video-frequency signal components and including line-scanning elements. The receiver also comprises a signal generator for controlling the linescanning elements of the reproducing device to produce line-trace scanning effects only during separated time intervals corresponding in total time to a preselected fractional portion of the plurality of line-trace intervals of the received video-frequency signal to the-reproducing device to effect image reproduction duringtheaforesaid" separated time intervals and" for preventingimage reproduction throughout the periods b tween such separated time intervals; I

For a better understanding of thep'r'esentinvention, together with other and further objectsthereof, 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.

In the drawings, Figs-1 and 2 comprise curves usedin explaining the present invention; Fig. 3 is'a schematic circuit diagram of a signal genera'torfor inclusion in a television receiver in accordance with the invention; Fig. 4 represents a complete television receiver embodying the invention in modified form; and Fig. 5 comprises graphs used in explaining" the operationof the Figs-4 arrangement.

In Fig; 1," curve A indicates the line-scanning signal of potential or current conventionally supplied'by the lin'e scanning signal generator of a television receiver. Where, as in the usual'case, the receiver is toutilize the video components of each-line-traceinterval of a received composite television signal, the line-scanning signal of curve}; has a frequency corresponding to the repetition frequency of the line-trace intervals of the received signal. befdesigned for operation in an 800 or 1,000-line system', the line-scanning signal of curve A has a corresponding frequency of 800 or 1,000 cycles for e'ach frame period which means an operating frequency of 20,000 or 25,000 cycles per second where'the frame frequency is'taken as 25 per second. Curve B of Fig. 1 shows a synchronizing signal of" negative polarity and pulse waveform used to synchronize the line-scanning generator of the receiver and to paralyze or block the cathode-ray image-reproducing tube in conventional manner during the line-retrace intervals. For the 800 line system the rise or trace portion to oftheline' -scanning signal has a duration of approximately 45 microseconds while the fly-back or retrace portion '61 has a duration approximately of only 5 microseconds. As mentioned above, where the fiy-back or retrace interval is of such a; short duration, the line-scanning signal generator is both complicated and expensive.

In'one embodiment of the invention, the complexity of the line-scanning signal generator is reduced by having the fly-back or retrace intervals of the line-scanning signal correspond substantially with those intervals occupied by alternate line-scanning periods of the received signal. This will be apparent from Fig. 2 in which curve J shows the wave form of the desired line-scanning signal. It includes a trace portion tq and a fiy-back or retrace portion (/1 each of which has a duration of approximately 50 micro seconds corresponding to the line-scanninginterval of the received 800-line signal. The remaining curves of Fig. 2 are to be identified-and explained in connection with the signal-generating arrangement of Fig. 3.

Assuming the receiver to The arrangement of Fig. 3 includes a primary line-scanning generator for producing a signal of saw-tooth wave form. This generator comprises a condenser l0 having one terminal connected through a charging resistor H to a unidirectional potential source +B. The other terminal of condenser I0 is connected to ground to complete a charging circuit. This connection is provided by a resistor 12 in series with a resister-condenser combination of elements 13 and I4. The'parameters of the charging circuit are selected to obtain a. linear variation of potential between the high-potential terminal of condenser l0 and ground during the charging interval.

The anode electrode of a gas-filled triode i5 is connected to the junction of condenser 10 and resistor ll. The cathode is connected to the junction of resistor l2 and the resistor-condenser combination l3, M to complete a discharging circuit for condenser iii. The discharging circuit is proportioned to have a time constant which is short with reference to that of the charging circuit. Tube I5 is controlled in order to time the generation of the primary line-scanning signal by means of synchronizing pulses applied to terminals l3, iii. The synchronizing terminals are coupled to the input circuit of tube l5 through a condenser il, a resistor If; connected in series therewith to the control electrode of tube l5 and an additional resistor l9 connected in shunt relation thereto. Condenser I7 and resistor [9 have such values as to provide a differentiating circuit in the input circuit of tube l5.

A wave-shaping stage, including an amplifying triode 20, has an input circuit coupled across the high-potential terminal of condenser i0 and ground. The potential source +13 is connected to the anode electrode of tube 20 through a series peaking coil 2| and a resistor 22. The cathode of tube 20 is grounded while its control electrode is coupled through a resistor 23 and coupling condenser 24 to the high-potential terminal of condenser l0. Resistors 25 and 26 in conjunction with potential source +13 constitute a biasing circuit for establishing an operating bias for tube 20. The operating potentials applied to this tube are selected to obtain symmetrical limiting of the signal applied thereto from condenser N2, in a manner described more fully hereinafter. An output terminal 21 is coupled to the anode of tube 20 for deriving an output signal therefrom.

The output signal of the wave-shaping stage is also applied tothe input circuit of an integrating and amplifying unit, including a triode tube 30. The coupling between the input circuit of tube 30 and'the output circuit of the preceding tube is provided by a condenser 31, a series resistor 32 and a shunt resistor 33. A cathode resistor 34 and a by-pass condenser 35 constitute a selfbiasing arrangement for tube 30, and a condenser 36 is coupled from the anode to the control electrode thereof for a purpose to be made clear presently. An anode resistor 37 couples the potential source +B with the anode of tube 30 and a condenser 38 supplies the signal translated therethrough to an output terminal 39. The signal from tube 30, after translation through a triode vacuum-tube repeater 40, is also supplied to a second output terminal ii coupled through a condenser 42 to the anode of tube 48. Potential source +B is also coupled to the anode through a resistor 43. Cathode resistor 44 provides a selfbiasing arrangement. The output circuit of tube 30 is coupled to the input circuit of tube 40 through a voltage-dividing arrangement including resistors 45 and 45 and coupling condenser 41. A condenser 48, arranged in parallel with the resistor 45, is provided to compensate the capacitance to ground of the control electrode of tube 40.

The generating arrangement of Fig. 3 includes three output terminals designated 21, 39, and 4|. The first of these supplies a control voltage from tube 20 which may be utilized to suppress the cathode-ray beam of the image-reproducing tube of the receiver during fiy-back or retrace intervals of the line-scanning operation. The remaining terminals 39 and 4| provide balanced linescanning signals which may be applied to electrostatic deflecting plates to control the linescanning operation in the receiver.

In considering the operation of the generating arrangement of Fig. 3, reference is made to the curves of Fig. 2. Curve C represents a synchronizing signal applied to terminals I6, Hi. It includes spaced line-synchronizing pulses of positive polarity derived from a received composite television signal having approximately 800 line intervals per frame. These pulses individually correspond with the line-retrace portion of the received signal and are separated by the line-trace portion. The synchronizing signal of curve C, after difierentiation in the input circuit of tube I5, is applied to the control electrode thereof with the wave form of curve D. Assume that upon the arrival of the first differentiated line-synchronizing pulse condenser I is fully charged. At this instant, the positive component occurring at the leading edge of the differentiated synchronizing pulse initiates an electron discharge in tube l5, rapidly discharging condenser I0 therethrough. As a consequence, the potential across condenser l0 and tube l5 falls rapidly, in the manner indicated in curve G. The slow charging time constant of condenser l0 permits deionization to take place, extinguishing the electron discharge in tube l5. Thereafter, condenser I0 is recharged from the source +B, increasing the anode voltage of tube I5 in a positive direction and in a linear manner as shown in curve G.

The second differentiated line-synchronizing pulse is applied to the control electrode of tube I5 when the charging process of condenser I0 is approximately half completed. At this instant, the anode potential of tube l5 has a relatively low value. Also, the charging current for condenser H], in traversing resistor l3, establishes a bias potential which tends to maintain the tube in a nonconductive state. These effects of anode potential and bias potential are such that the second differentiated line-synchronizing pulse is ineffective and tube l5 remains in its nonconductive state so that the recharging of condenser It continues uninterruptedly.

When the third difierentiated line-synchronizing pulse arrives, condenser Ill is charged to the extent desired, the anode of tube I '5 has a relatively high value, and the charging current and resulting biasing potential developed thereby across resistor l3 are much reduced. Consequently, the third differentiated line-synchronizing pulse initiates an electrode discharge in tube l5, discharging condenser I0 and completing a cycle of the primary saw-tooth line-scanning signal generator. The line-scanning signal thus produced by the primary generator has the wave form of a curve G. It has a frequency equal to half that of the line-scanning synchronizing pulses of curve C. I

The saw-tooth line-scanning signal of curve G is applied to the input circuit-of the wave shaping or limiting stage. The potentials applied to tube 20 of this stage establish two critical potential levels. The first, designated by horizontal broken-line curve e1, corresponds with a condition of anode current cutoff. The other, represented by broken-line curve 62, designates a condition of anode current maximum. In view of these critical potential levels, the portion of the applied signal of curve G below line (:1 is eliminated in the translation through tube 20 by Way of anode current cutofi phenomenon. The portion of curve G which lies above line ez is also eliminated but through anode current limiting phenomenon. As a consequence, the output signal of the limiter has the wave form of curve H. This signal of approximately rectangular wave form is available at output terminal 27 and is also supplied to the input circuit of tube 30.

The condenser 36, bridged between the anode and control electrodes of tube 30, causes the impedance measured between its control electrode and cathode terminals to be highly capacitive.

This capacitive reactance, in junction with the preceding series resistor 32, constitutes an integrating circuit in the input of tube 30. Therefore, the input signal of curve H is first integrated then, after amplification in tube 30, appears at output terminal 39 with the wave form of curve J. This output signal of tube 30 is repeated by tube 40 and also appears at the remaining output terminal 4| with the same wave form but opposite polarity.

From a comparison of curves C and J of Fig. 2, it is apparent that the generating arrangement of Fig. 3 produces line-scanning signals for controlling a television receiver to utilize only a portion of the video components contained in a received composite television signal. More particularly, the trace portions t'o of the line-scanning signals are effective to produce line-scanning efiects only during separated time intervals corresponding in total time to approximately half of the line-trace intervals of the received signal. Each trace portion t'c of the line-scanning signal will be seen to have a duration at least equal to and a time coincidence with one of the line-trace intervals of the received signal. The fly-back or retrace portion #1 of the line-scanning signal is substantially equal to the trace portion t'o. Hence, the line-trace scanning efiect occurs during alternate line-trace intervals of the received signal while the retrace scanning effect occupies the intervening line-trace intervals of the received signal. The signal of curve H, which is available at output terminal 27, may be utilized to suppress the image-reproducing device of the receiver during line-retrace scanning intervals ti. It will be noted that for the duration of such intervals, the control signal has negative polarity.

While the invention as described in connection with the arrangement of Fig. 3 is particularly suited for obtaining line-scanning signals to control electrostatic deflections of the image-reproducing tube, it has equal application to arrangements employing electromagnetic deflections. Such an arrangement is disclosed in Fig. 4 and the invention will be more fully described with reference thereto,

Referring now more particularly to Fig. 4, the television receiver there represented is of the superheterodyne type and is adapted to utilize a received signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals and separated by line-retrace intervals. This receiver ineludes an antenna system 50, connected toa radio-frequency amplifier 52 of one or .more stages. There are connected to amplifier 52 in cascade and in the order named an oscillatormodulator .53, an intermediate-frequency amplifier ,54 of one or more stages, a detector and automatic volume control or A. V. C. supply 55, a video-frequency amplifier 56 of one or more stages. and a cathode-ray type image-reproducing device 5]. The image-reproducing device is provided with a conventional electron-gun structure and accelerating electrodes for forming an electron beam and for focusing the beam on an image-reproducing area. The input circuit of tube5l, including a brilliancy-control electrode 65, is coupled through a condenser 66 to the output circuit of video-frequency amplifier 56, thereby providing means for applying video frequency signals to the image-reproducing device for utilization. A stabilizing diode 51 having a load-resistor- 68 is associated with the input circuit of tube 51 for thepurpose of stabilizing applied television signals in well-known manner. A source of bias potential, indicated E0, is coupled to control electrode 65, establishing a predetermined cutoff amplitude level, defined more particularly hereinafter, and rendering tube 5'! responsive only to applied video-frequency signal components having an amplitude exceeding its cutofi level. The image-reproducing device also includes the usual line-scanning elements 10, H and fieldscanning elements 12, T3.

A line-scanning generator arrangement 5i, particularly described hereinafter, and a fieldscanning generator 58 are coupled to an output circuit of detector 55 through a synchronizingsignal separator 59. They have output circuits coupled, respectively, to line-scanning elements 10,- "H and field- scanning elements 72, 73 of tube 51. A conductor labelled A. V. C. applies a unidirectional voltage derived from detector and A. V. C. supply'55 to one or more of the tubes of radio-frequency amplifier 52, oscillator-modulator 53, and intermediate-frequency amplifier 54 to control the amplification of the signal-translating channel of the receiver. A sound-signal reproducer at is coupled to an output circuit of intermediate-frequency amplifier 54 for translating and reproducing sound signals accompanying the received television program. The stages or units 50-50, inclusive, may all be of conventional well-known construction so that a detailed illustration and-description thereof are unnecessary herein.

Referring briefly, however, to the operation of the-described receiver and momentarily assuming unit 6| to be a conventional line-scanning arrangement, television signals intercepted by antenna system 563, 5| are selected and amplifiedin radio-frequency amplifier 52 and applied to oscillator-modulator 53 wherein they are .converted into intermediate-frequency signals. The intermediate-frequency signals, inturn, are selectively amplified inintermediate-frequency amplifier 54 and delivered to detector 55. The modulation components of the signal are-derived by detector 55 and supplied to video-frequency amplifier 56, wherein they are amplified and from which they are supplied in the usual manner to the, brilliancy-control electrode 95 of image-reproducing device 51,. The intensity of the electron beam of device 51 is thus modulated or controlledinaccordance with the video-frequency voltages im pressed uponits control electrode. Line andfield synchronizing-signal components derived; in detector 55 are separated from the video-frequency components of thedetected signal and from one another in synchronizing-signal separator 59 and areapplied to synchronizing-control elements of units 61 and58, respectively. Scanning signals are generatedin units 58 and 6! underthe control of the applied synchronizing-signal components and are supplied to the scanning elements of tube 51 to produce scanning fields, thereby to deflect theelectron beam in two directions normal to each other so as to trace a rectilinear scanning pattern and reconstruct the reproduced image. A unidirectional control potential, derived from unit 55 and applied .to one or more tubes of the preceding stages, serves to maintain the amplitude of the signal input to detector 55 Within a relatively narrow amplitude range for a wide range of received signal intensities. Sound signals accompanying the received television program are reproduced in sound-signal reproducer 69 in conventional fashion.

Returning now to a consideration of unit 61, this unit of the receiver is a modification of the generator arrangement of- Fig. 3. It constitutes means for controlling the line-scanning elements lo, I l .of the image-reproducing device to produce line-trace scanning effects only during separated time intervals which correspond in total time to a preselected fractional .portion of the plurality of line-trace intervals included in the received television signal. Further, the line-trace scanning effects produced under the control of this unit individuallyhave a duration equal to, and a time coincidence with, at least a substantial portion of one of the line-trace intervals of the received signal, as will be made clear in the following description.

Unit 6| includes a line-scanning signal generator for generating line-scanning signals having trace portions and contiguous retrace portions for controlling the line-scanning elements of tube 51 to produce line-trace and line-retrace scanning effects, respectively. This generator includes a pentode-type vacuum tube Bil having an output circuit which includes the primary Winding8| of a transformer 81, 82. Winding it! is shunted by a resistor 83, while winding 82 is directly coupled to the line-scanning elements of tube 5?. Tube has an input circuit including a coupling condenser 84 and grid resistor 85 for coupling the described generator to a trigger circuit through the agency of which the scanning generator is controlled or synchronized by at least predetermined ones, but preferably by all, of the synchronizing-signal components customarily received along with the video-frequency signals during the line-retrace intervals. The trigger circuit is provided by a pair of cathode-driVen electron-discharge devices 99 and 9! having a common cathode impedance 92. These devices are cross-coupled by means of a pair of resistorcondenser circuits individually coupling the control electrode of one such device to the anode of the other; One resistor-condenser circuit includes a resistor 88 and a condenser 89 and the other includes a resistor 88' and condenser 89'. Grid resistors 93. and 9 as Well as plate resistors 95 and-96, are provided for tubes 90 and 9|, respectively. A suitable source of space current, indicated +13, is coupled to the anode electrode of each tube,as illustrated. Cathode impedance 92 iscoupled to anoutput circuit of synchronizingsignal separator 59 so that synchronizing-signal components supplied therefrom may excite the trigger circuit. A control effect or control signal 9 is derived in the anode-cathode circuit of tube 9| for application to the input circuit of tube 80. This control signal is also applied from a tap on anode resistor 96 through a condenser 91 to the control electrode of image-reproducing device for a purpose to be stated hereinafter.

In considering the operation of unit BI and its effect on the described operation of the receiver of Fig. 4, reference is made to the curves of Fig. 5. Curve K represents one-half the modulation envelope of a fragmentary portion of a received composite television signal of familiar wave form, this signal appearing in the output circuit of detector 55. This signal includes video-frequency signal components having a maximum amplitude limited to a predetermined percentage of the peak amplitude of the carrier signal, occurring during a plurality of substantially identical linetrace intervals t2, t2 and separated by line-scanning synchronizing-signals L occurring during line-retrace intervals t3, is. The signal also includes double line-frequency equalizing pulses E and serrated field pulses F, occurring during fieldretrace intervals. Let it be assumed that the received signal is generated in a high definition television transmitter and that approximately 1000-line s-cansions take place in a given fieldtrace interval. In other words, 1000 line-trace intervals, each including the video-frequency signal components V, intervene between succeeding field pulses F. The signal of curve K is applied directly to control electrode 65 of tube 51 and to :the input circuit of synchronizing-signal separator 59, as already indicated. Unit 59 derives and applies to cathode impedance 92 of the trigger circuit line-scanning synchronizing-signal components, equalizing pulses and serrated field pulses, represented by the full-line curve M. In deriving such signals, unit 59 removes the videofrequency signal components V of the signal input thereto through an amplitude-limiting process. The limited signal is then differentiated and the resulting amplitude variations of positive 100- larity, shown in broken-line construction in curve M, are removed through a second amplitude-limiting step. Thus, only signal variations of negative polarity, representing the line-scanning synchronizing-signal components, equalizing pulses and serrated field pulses of the received signal, are applied to unit 6l. The response of the trigger circuit to this applied signal of curve M is represented by curve N and will be clear from the following consideration.

The trigger circuit is a modified form of a wellknown circuit. Assume an instantaneous operating condition in which tubes 90 and 9| are equally conductive. If, for any reason, one of the tubes, say tube 90, should be rendered even slightly more conductive, the potential at its anode electrode decreases, applying a negative potential to the control electrode of the opposite tube, tube 9! for the assumed case, to decrease the conductivity thereof. As the conductivity of the second tube decreases, a positive signal variation islapplied from its anode circuit to the control electrode of the first tube, increasing the conductivity of the latter still further. This regenerative effect endures until the first tube is rendered fully conductive, while the alternate one is biased to anode current cutoff by the combination of grid and cathode potentials. Thus, the normal condi tion of the tubes is such that one operates at a condition of anode current saturation, while the other is cut off.

When a synchronizing signal of negative po- "1o larity is applied to the common cathode impedance 92, it has substantially no eifect on the tube operating at anode current saturation. However, the applied pulse renders the alternate tube conductive, thereby to apply a negative potential to the control electrode of the first-mentioned tube. A regenerative cycle, similar to that already described, follows and reverses the conductive states of the tubes. Thus, it will be seen that the succeeding synchronizing signal components of curve M produce a so-called flip-flop action in the trigger circuit, first rendering tube 90 conductive and biasing tube 9| to anode current cutoif, and then reversing their conductive states. The resulting control effect or control signal of curve N derived from the anode-cathode circuit of tube 9| by means of condenser 84 is an alternating current signal of substantially rectangular wave form having a reference amplitude level corresponding to its alternating current axis 60. This control signal has amplitude variations in a given direction from its reference amplitude level, or of positive polarity, and alternate amplitude variations in an opposite direction, or of negative polarity, and has a peak-to-peak amplitude value which is at least equal to, but preferably greater than, the maximum amplitude value of the video-frequency signal components V of the received signal.

From a comparison of curves K and N, it will be evident that the amplitude variations of positive polarity of the control signal produced during any given field-trace interval of the received signal occur only during separated time intervals t4, t4 corresponding in total time to a preselected fractional portion of the plurality of line-trace intervals t2, t2 include within the particular fieldtrace interval. More specifically, for the illustrated arrangement such positive polarity amplitude variations of the control signal occur during alternate line-trace intervals of the received signal or, expressed differently, occur only during uniformly separated time intervals corresponding in total time to approximately one-half of the plurality of line-trace intervals of the received signal. It will also be evident from a comparison of curves K and N that these positive polarity amplitude variations of the control signal individually have a duration at least equal to, and a time coincidence with, one of the line-trace intervals is, while the negative polarity amplitude variations have a duration t5 which is equal to the separation of the above-mentioned uniformly separated time intervals ii. The portion of the control signal generated by the double-line-frequency pulses E and the serrated field pulse F is generally similar to that described, except that the durations #4 and t5 of its positive and negative polarity amplitude variations are approximately half of the corresponding portions of the control signal obtained during field-trace intervals of the received signal.

The positive and negative polarity amplitude variations of the control signal are effective to render tube of the line-scanning generator alternately conductive and nonconductive, in order to generate line-scannin signals. When tube 80 is energized, its anode-cathode circuit has a time constant proportional to and Rp is the plate-cathode resistance of tube 80 plus the resistance of winding 8|. When tube 80 is biased to cutoff, the current through winding 8i decays in accordance with a time constant proportional to ale where R is the-value of resistor 83 which is se lected to be much larger than the resistance Rp. The parameters of the generator are so selected that the described time constants result in the generation of line-scanning signals having a sawtooth waveform, as represented by curve P. The scanning signals generated during field-trace intervals of the received signal have substantially linear trace portions 11- and contiguous retrace portions b for controlling the line-scanning elements (0, H of tube 51 to produce corresponding line-trace and line-retrace scanning effects, re-

spectively. It will be clear from a comparison of curves N and P that the control signal so controls the line-scanninggenerator during field-trace intervals that the line-trace and the line-retrace scanning effects produced in image-reproducing device 5'!- have the same'occurence and duration as those positive and negative'amplitude vari ations of the control signal, respectively, obtained in thesame-intervals. In particular, the linetrace scanning effects occur during every other line-trace interval of the received signal and the retrace scanning effects occur during equal intervals that separate succeeding line-trace scanning effects.

For th particular arrangement illustrated, the line-scanning effect endures not only during a given line-trace interval of the received signal but also during the preceding line-retrace interval thereof. This causes a dark'band to border one side of the reproduced image which may be obviated through theuse of a suitable picturecentering device (notshown).

During, field-retrace intervals of the received signal, the control of'the line-scanning generator 80 by the controlsignal of curve N continues to maintain line synchronization. However, the line-scanning signals obtained, having trace portions aand retrace portions b, produce'no scanning effects within tube 51 since the tube is biased to cutoff during such intervals.

Since the line-retrace time of tubeiil occupies at least a full line-trace interval of the received signal, it is necessary to render the image-repro ducing device unresponsive to video-signal components occurring during such line-retrace scanning intervals. To this end, the control signal of curve N- is combined in the input circuit of tube 51 with the received video-frequency signal components, establishing a resultant signalin the input circuit of tube 51 having, a wave formrepresented by curve Q. This signal is stabilized by diode 6T on its ne ative peaks andthe value of bias potential EC is adjusted to set the cutoff level of tube 51 at a value indicated; by broken-line curve S. The resultantstabilized signal includes video-signal components having an amplitude exceeding the cutoff amplitude level of tube 51-, but occurring only during the above-mentioned separated time intervals inwhich line-trace scanning effects are produced. by: scanning elements 10, II. Thus, the circuit arrangement including condenser 91 comprises means for utilizing the control signal of curve N. effectively to apply received video-frequency signals to reproducing duvice 51 only during, the aforedescri'bed: separated time intervals. Therefore, in reconstructing: the transmitted image, reproducing device 51 utilizes only the video-frequency signal components included in alternate line-trace intervals of the received signal.

By way of summary, it may be pointed out that a television receiver including the generator of Fig. 3 or the modified unit 6| of Fig. 4 is adapted to utilize a television signal transmitted by a high definition television transmitter. In order to realize an economy in construction", the receiver includes a simplified'linescanning generator arrangement'synchronized by line-scanning synchronizing-signal components of the received signal, but effective tocontrol the line -scanning elements of the image reproducing device to produce line-trace scanning effects only during separated time intervals corresponding in total time to a preselected fractional portion of the line-trace intervals included in the received signal. The line-trace scanning effects individually have a duration'and a time coincidence corresponding to at least one of the'line-trace'intervals of the received signal and the image-reproducing device is controlled'to'respond only to such of the videofrequency signal components as occur during its line-trace scanning intervals.

While for the assumed received signal of curve K, the receiver is'arr'anged effectively to respond to alternate line-traceinterval's of the received signal, it will be apparent that other division ratiosmay be utilized; if desired. For example, if the received signal has an unusually large number of line scansions in each field-trace interval, a division ratio of one third Drone-fourth may be utilized;

While curve Kindicates' a received signal including line-scanning synchronizing-signal components, it will be "appreciated that such linescanning signals need notbe received as modulation of a single carrier-wave signal along with thevide'o-frequency signal components.

The receiver of the invention is equally useful for receiving interlaced television signals. As is well understood in'the' art, in interlaced systems the received signal incl'udes'a plurality of fieldtrace intervals for each frame of the translated image. In a progressivedine-scanning system, however;'thefield intervals are identical with the frame intervals and, therefore, the term field interva 7 beenJused throughout the description. It will be apparent that in 'an interlaced system. embodying the invention, the receiver is controlled during each field period of the received signal in the manner described above.

While there have been described what are at present considered to bethe preferredembodiments of this invention, it will be obvious'to those skilled in the art'that various changes and modificationsf may be madev therein without departing from the invention, 1 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.

Whatis claimed 1. A television. receiverfor'utilizi'ng a signal includingvideo-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated: by line-retrace intervals comprising, an. image-reproducing device ior utilizing video-frequency signal components and-including:line-scanning elements, a signal generatorfor'controllingrsaid line-scanning elements to produce: line-trace scanning effects only duringv separated time intervals corresponding in total time to a preselected fractional portion of said; plurality of line tra'ce intervals, and

13 to produce line-retrace scanning effects having a duration several times that of said line-retrace intervals, said line-trace scanning effects individually having a duration equal to and a time coincidence with a substantial portion of one of said line-trace intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

2. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components and including line-scanning elements, a signal generator for controlling said line-scanning elements to produce line-trace scanning effects only during separated time intervals correspond: ing in total time to approximately one-half of said plurality of line-trace intervals and to produce line-retrace scanning effects having a duration several times that of said line-retrace intervals, said line-trace scanning effects individually having a duration equal to and a time coincidence With a substantial portion of one of said line-trace intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

3. A television receiver for utilizing a signal indevice for utilizing video-frequency signal components and including line-scanning elements, a

signal generator for controlling said line-scanning elements to produce line-trace scanning effects only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of line-trace intervals and to produce contiguous line-retrace scanning effects, said line-trace scanning effects individual ly having a duration equal to and a time coincidence with a substantia1 portion of one of said line-trace intervals and said line-retrace scanning efiects individually having a duration corresponding substantially to the separation of said separated time intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

4. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components and including line-scanning elements, a signal generator for controlling said line-scanning elements to produce line-trace scanning effects only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of line-trace intervals and to produce line-retrace scanning effects having a duration several times that of said line-retrace intervals, said line-trace scanning effects individually having a duration equal to and a time co incidence with a substantial portion of one of said line-trace intervals, and means responsive to said last-named means for effectively applying said video-frequency signal to said reproducing device only during said separated time intervals.

5. A television receiver for utilizing a signal in cluding video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-scanning synchronizing-signal components occurring during line-retrace intervals comprising, an imagereproducing device for utilizing video-frequency signal components and including line-scanning elements, a signal generator responsive to said synchronizing-signal components for controlling said line-scanning elements to produce line-trace scanning effects only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of linetrace intervals and to produce line-retrace scanning effects having a duration several times that of said line-retrace intervals, said line-trace scanning effects individually having a duration equal to and a time coincidence with a substantial portion of one of said line-trace intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

6. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-scanning synchronizing-signal components occurring during line-retrace intervals comprising, an imagereproducing device for utilizing video-frequency signal components and including line-scanning elements, a signal generator for generating linescanning signals having trace portions for controlling said line-scanning elements to produce line-trace scanning efiects and having retrace portions for controlling said lements to produce line-retrace scanning effects of a duration several times that of said line-retrace intervals, means responsive to said synchronizing-signal components for deriving a control effect, means for utilizing said control effect to control said generator so that said line-trace scanning effects occur only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of line-trace intervals and so that said line-trace scanning effects individually have a duration equal to and a time coincidence with a substantial portion of one of said line-trace intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

'7. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-scanning synchronizing-signal components occurring during line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components and including linescanning elements, a signal generator for generating line-scanning signals having trace portions for controlling said line-scanning elements to produce line-trace scanning efiects and having retrace portions for controlling said elements to produceline-retrace scanning effects'of a dura tion several times that of said line-retrace intervals, means including a pair of cross-coupled electron-discharge devices responsive to said synchronizing-signal components for deriving a control effect, means for utilizing said control effect to control said generator so that said line-trace scanning effects occur only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of line-trace intervals and so that said line-trace scanning effects individually have a duration equal to and a time coincidence with a substanti'al portion of one of said line-trace intervals, and means for applying said video-frequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

8. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-scanning synchronizing-signal components occurring during line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components and including linescanning elements, a signal generator for generating line-scanning signals having trace portions and contiguous retrace portions for controlling said line-scanning elements to produce line-trace and line-retrace scanning eifects, respectively, means responsive to said synchronizing-signal components for deriving a control signal of substantially rectangular wave form having a reference amplitude level, predetermined amplitude variations in a given direction therefrom, and alternate predetermined amplitude variations in an opposite direction therefrom, said amplitude variations of said given direction occurrng only during separated time intervals corresponding in total time to a preselected fractional portion of said plurality of line-trace intervals and individually having a duration equal to and a time coincidence with a substantial portion of one of said line-trace intervals and said amplitude variations of said opposite direction having a duration substantially equal to the separation of said separated time intervals, means for utilizing said control signal to control said generating means so that said line-trace and lineretrace scanning effects have substantially the same occurrence and duration as said amplitude variations of said given and opposite directions, respectively, and means for applying said videofrequency signal to said reproducing device to effect image reproduction during said separated time intervals and for preventing image reproduction throughout the periods between said separated time intervals.

9. A television receiver for utilizing a signal including video-frequency signal components occurring during a plurality of substantially identical line-trace intervals separated by line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components and including line-scanning elements, a

signal generator for controlling said line-scanning elements to produce line-trace scanning efiects only during separated time intervals corresponding in total time with a preselected fractional portion of said plurality of line-trace intervals and to produce line-retrace scanning effects having a duration several times that of said line-retrace intervals, said line-trace scanning effects indi- 16 vidually having a duration equal to and'a time coincidence with a substantial portion of one of said line-trace intervals, means for deriving a control signal of substantially rectangular wave 'form having a reference amplitude level, am-

plitude variations in a given direction therefrom, and alternate amplitude variations in an opposite direction therefrom, at least certan of said amplitude variations of said given direction having substantially the same occurrence and duration as said separated time intervals, means for applying said video-frequency signal components to said reproducing device, and means for utilizing said control signal effectively to render said reproducing device responsive only to those of said video-frequency signal components which occur during said separated time intervals.

10. A television receiver for utilizing a signal including video-frequency signal components occuring during a plurality of substantially identical line-trace intervals separated by line-retrace intervals comprising, an image-reproducing device for utilizing video-frequency signal components having an amplitude level exceeding a predetermined cutoff amplitude level and including line-scanning elements, a signal generator for controlling said line-scanning elements to produce line-trace scanning effects only during separated time intervals corresponding in total time with a preselected fractional portion of said plurality of line-trace intervals and to produce line-retrace scanning efiects having a duration several times that of said line-retrace intervals, said line-trace scanning eifects individually having a duration equal to and a time coincidence with a substantial portion of one of said linetraoe intervals, means for deriving a control signal of substantially rectangular wave form having a reference amplitude level, amplitude vari- .ations in a given direction therefrom, and alternate amplitude variations in an opposite direction therefrom, at least certain of said amplitude variations of said given direction having substantially the same occurrence and duration as said separated time intervals, and means for combining said video-frequency signal components and said control signal to derive a resultant signal including video-frequency signal components having an amplitude exceeding said cutoff amplitude level but occurring substantially only during said separated time intervals and for applying said resultant signal to said reproducing device.

DENNIS C. ESPLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,988,931 Alexanderson Jan. 22, 1935 2,052,184 Lewis Aug. 25, 1936 2,189,843 Soller Feb. 13, 1940 2,208,374 Lewis July 16, 1940 2,226,229 Linsell Dec. 24, 1940 2,226,230 Linsell Dec. 24, 1940 2,402,091 Schade June 11, 1946 FOREIGN PATENTS Number Country Date 102,547 Australia Dec. 2, 1937 OTHER REFERENCES Prin. of Tel. Eng, Fink, McGraw-Hill Book Co., 1940, page 169,

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