US2310197A - Television system - Google Patents

Description

Feb. 2, 1943.

WH Vf Ffm/E WAVE C. W. HANS ELL Filed Dec. 21,

SYNC. 070/6 uw r 5/6/VOL 8 Sheets-She-et l Gttorneg Feb. 2, 1943. C, w HANsE| L 2,310,197

TELEVIS ION SYSTEM Filed Dec. 21. 1940 e sheets-sheet z Cttorney TELEVIS ION SYSTEM Filed Dec. 21, 1940 8 Sheets-Sheet 5 574/6 /A/Par d70/"F ,lParEA/TML nventor c. w'. HANsELL 2,310.19'7

. W. HANSELL ATELEVISION SYSTEM Filed Dec. 21,- 19.40` BSh'eeQs-Sheet 4 Feb. 2, 1943.

Snnentot mcg Feb. '2; 1943.

C. w. ,HANSELL- TELES/Ls 10N SYSTEM Filednec. 21, 1940 s s neegasheet s Feb. 2, 1943. c. w.-HANs'-LL 2,310,197 TELEVISION SYSTEM Filed Dec. 21. 1940 8 Sheng-sheet 6 nventor Feb. 2, 1943. c. w. HANSELL.

TELEVISION SYSTEM Filed Dec. 21. '1940 8 Sheets-Sheet 7 f AIAA All Feb 2, 1943!v c. w. HANsELL 2,310.197

TELEVISION SYSTEM F11-ed Dec. 21. 1940 a' sheets-sheet s o'tunuuu Snvntor Patented Feb. 2, 1943 TELEVISION lSYSTEM Clarence W. Hansell, Port Jefferson, N. Y., assignor to` Radio Corporation of America, a corporation of Delaware Kilplication December 21,l 1940,

7 Claims.

This invention relates to television systems and more particularly to methods and means for synchronizing the transmission and .reproduction of an optical image.

Television systems in commercial and experimental operation, both in the United States and abroad, generally transmit synchronizing pulses which share time with the picture modulation and which are separated from the picture modulation signals by means of amplitude discrimination. This requires that the amplitude range of the picture modulation signals be reduced by the amount of range necessary to accommodate the synchronizing'pulses.

For example, if all carrier current amplitudes below 80-percent in the output o'f television ra' dio transmitters are assigned to picture modulation, amplitudes above 80 percent are assigned to synchronizing pulses. Under these conditions,

cent in amplitude or 64 percent in power of what it could be if the synchronizing pulses were separated from the picture modulation and transmitted in some other way.

Furthermore, the frequency band width, and therefore the required amount of power, is something like 50 times greater for the picture transmitter than for the sound transmitter operated in conjunction with it. A logical solution tothis problem is to transfer some of the modulation requirements of the picture transmitter to the sound transmitter. This can be doneby transmitting synchronizing e modulation through the sound transmitter.

The present type' of synchronizing pulses cannot be transmitted over the sound transmitter because these pulses require a large band of frequencies for their transmission. Infact, it requires the use of substantially the entire television modulation band to produce a steep wave front of synchronizing pulse in order to minimize the effects of noise upon exact synchronism.

tion range for pictures is only 80 perenergy Serial No. 371,078

(Cl. P18-5.6)

The transmission of saw-tooth wave forms for providing scanning currents at the receiver, in`

mission of at least up to the tenth harmonic of the scanning frequency, and it. is doubtful whether ven this is sumcient to avoid distortion or large loss of time for picture scanning. Also, the use of subcarrier transmission rather than direct modulation of a high frequency carrier by the scanning energy, for a given allowable percentage modulation of the high frequency carrier, results in a loss of effective modulation power of about 4:1 and an increase in frequency band for admitting noise of approximately 2:1. This represents a total loss in sig.- nal-to-noise power. ratio of about 8:1.

According to this invention, sinusoidal instead of short pulse or saw-tooth synchronizing pulses are transmitted preferably through 'the transvmitter which provides the soundaccompanying television, and at the receiver Ithe sinusoidal modulating currents, after passing through frequency selective filter circuits, produce saw-tooth scanning potentials or control the timing ofseparably produced saw-tooth potentials.

Resonant frequency selective circuits give a sort of flywheel effect to sinusoidal currents so as to cause a large number of successive cycles to contribute to the oscillatory energy existing in. ,the circuits at any one time.

Timing or phase errors in the pulses due to the effect of noise are therefore averaged out to a low value because plus and minus errors tend to cancel one another. is eliminated or reduced by the frequency selectivity of the resonant circuits.

The action of the resonant circuits in the pres-` ent invention is similar in its effect upon synchronizing to the `mechanical inertia in rotating wheels or to the mechanically stored energy in resonant vibrating reeds. Observers in the United States and abroad have expressed surprise at the apparent excellence of definition and detail of television images produced by receivers with mechanical scanners. This excellence of detail probably results from the small effect of noise, voltage variations and other disturbances upon the exact timing of the scanning at the receiver so that little, if any, of the apparent definition is lost due to lack of perfect synchronizing.

lWhen sinusoidal synchronizing energy is used, it is necessary to convert sinusoidal currents into saw-tooth wave currents. Heretofore sinusoidal to saw-tooth wave conversion systems have been proposed, but they were subject to a number of objections. The timing or phase relation of the saw-tooth wave with respect to that of the sinusoidal wave varied with variation in ampli- This is equivalent tovsaying that noise n tude of the sinusoidal wave. In a television system, this would cause the picture to shift position on the screen due to fading and other causes of amplitude variation or due to changing the adjustmentof the receiver from one television station to another.

In the proposed prior systems the exact time of tripping or triggering the saw-tooth wave comes when the sinusoidal wave is not far from a maximum value where its instantaneous value is 4changing rather slowly. 'I'his reduces the positiveness of control of saw-tooth timing,` al- By using sine wave synchronizing energy transmission, the power level required for transmission of synchronizing energy may be brought down to a minimum. Sinusoidal synchronizing energy cannot be satisfactorily transmitted over the picture transmitter because it 'would interfere with the picture transmission. However, it can be transmitted over the associated sound transmitter without much difficulty and without substantial interference to sound transmission. For example, BO-cycle synchronizing modulation may be used for vertical synchronizing and 13,230-cycle ysynchronizing modulation may be used for horizontal synchronizing when it is desired to transmit 441-line pictures with a field frequency of 60 per second interlaced to give a frame frequency of 30 per second. These frequencies arel outside the required audio frequency band. I

Transmission o f sinusoidal synchronizing wave forms requires very small band width. Assuming it to be practical to use selective circuits in the receivers which admit only a 2 percent band around the sinusoidal synchronizing current frequencies, itis possible, due to the selectivity, to reduce the frequency band contributing to noise, as compared with transmission of saw-tooth currents by modulation of 'a subcarrier, by a ratio of about 20 F/0.02F or by 1000:1. Thus, the total improvement in signal to noise ratio, taking into account the improvement due to omission of subcarrier power and reduction in band width for synchronizing currents, in changing from the saw-tooth modulated sub-carrier system to the sinusoidal system, could easily be as much as 16,000z1 in power. Y

Furthermore, the total frequency band occupied by the audio transmitter is very greatly reduced. The transmission of .the sub-carrier and its side frequencies by the audio transmitter requires a relatively great frequency band width. According to this invention, the audio transmitter total band width is only 26460 cycles for 44 line, 30 frames per second television.

In addition to the broader channel space required for the sub-carrier arrangement, multipath phenomena would cause distortions in the saw-tooth wave form with resulting distortion crease the effective power of a television transmission system.

Another object of this invention is to improve the reproduction of television images.

Another object of this invention is to provide a television system with -an improved electron ray scanning synchronizing means.

Still another object of this invention is to pro- .vide a means for the transmission of .the Synchronizing signal in the associated sound channel.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawings in which v Figure 1 is a block diagram of a television signal transmision system in accordance with one form of this invention;

Figure 2 is a block diagram showing a television signal receiving system in accordance with one form of this invention;

Figure 3 is a circuit diagram showing a sawtooth wave generator adapted to produce two saw-tooth waves per cycle of synchronizing current;

Figure 4 is a graphical illustration of the operation of the circuit shown in Fig. 3;

Figure 5 shows another saw-tooth wave generator adapted to produce two saw-tooth waves per cycle of synchronizing current;

Figure 6 is a graphical illustration of .the operation of the circuit shown in Fig. 5;

Figure 7 is a circuit diagram of still another oscillator adapted to produce two saw-tooth waves per cycle of synchronizing current;

Figure 8 is a circuit diagram adapted to produce one saw-tooth wave per cycle of synchronizing current;

Figure 9 is a, graphical illustration of the operation o'f the circuit shown in Fig. 8;

Figure 10 is a circuit diagram of still another form of saw-tooth Wave generator adapted to produce a single saw-tooth wave per cycle o f synray deflection equipment;

of images. On the other hand, multi-path Figure .12 is a circuit diagramshowing one form of a receiving tube electron ray deflection means;

Figure 13 is a circuit diagram showing another form of receiving tube electron ray deiiecting equipment in accordance with this invention;

Figure 14 isa circuit diagram showing still another form of electron ray deflection means;

Figure 15 is a circuit diagram showing one form of filter circuit adapted to segregate vertical synchronizing frequencies from their associated horizontal synchronizing frequencies;

Figure 16 shows a modification of Fig. 15;

q Figure 17 shows a circuit diagram in accordance with another form of this invention for segregating the vertical synchronizing energy from the horizontal synchronizing energy;

Figure 18 is a circuit diagram showing a form of television receiving -tube electron ray deflection system in which a, pulsing oscillator is held in synchronism by means of a sinusoidal synchronizing current; and

Figure 19 is a circuit diagram showing another arrangement for synchronizing a pulsing oscillator by means of a sinusoidal synchronizing current. l

Fig. 1 shows a. transmitter tube l having an electron gun composed of a heater element 2, a

, cathode 3, a control electrode 4, a first anode 5,

and a second anode 6. The electron beam I which is generated by the electron gun is adapted to scan the photosensitive mosaic 8 in response to saw-tooth wave form currents in the horizontal deflecting coils 9 and the vertical deflecting coils I0. Such a transmitter tube is more fully described in an article entitled Television pickup tubes with cathode ray beam scanning, published in the Proceedings of the Institute of Radio Engineers, August, 1937. The vertical deyfleeting coils Ill are supplied with a deflection current from a saw-tooth wave generator II. The saw-tooth wave generator II is supplied with lits synchronizing current by a frame frequency sine wave generator I2 which is driven by a synchronous motor I3. The horizontal deecting coils 9 are supplied with their deflection current by a saw-tooth wave generator I4 which is supplied with its synchronizing current by line frequency sine wave generator I5 which is also driven by the synchronous motor I3.

The video or image signal taken from the photosensitive electrode 8 is amplified inthe video signal amplier I6 and transmitted by the video transmitter II.

The associated sound is picked up by the sound pickup and amplifier I8 and transmitted by the sound transmitter I9.

The synchronizing base frequency currents are preferably obtained by mechanically rotating electromagnetic generators such as shown in blocks I2 and I5 driven by a synchronous motor from the public service alternating current power source in the community where the television transmitter is located. Electrostatic or variable condenser type of generators may, of course, be substituted for the electromagnetic generators shown as I2 and I5. In the United States, the standard frequency of the public service power supply is 60 cycles per second. In many other countries it is 50 cycles per second. Preferably, vthe motor generator should be equipped with a flywheel or sufcient mechanical inertia to eliminate any possible rapid variations in phase or frequency as an aid to the use of the receiving system of the present invention and receiving systems with mechanical or other scanning arrangements which cannot follow rapid changes in speed. Electrical resonance and energy storage between the generator and the saw-tooth wave generator may also be used to assist in reducing rapid fluctuations in phase.

A thermionic generator may, of course, be employed without departing from the spirit of this invention, in which case particular care must be taken to eliminate all but very slow phase, and frequency uctuations.

In addition to transmitting a base frequency current for line synchronizing pulses by line frequency sine wave generator I5, a base frequency current for frame synchronizing pulses from frame frequency sine wave generator I2 is also transmitted from the audio frequency transmitter I9, as previously described. In the United States it is preferable to transmit 30 cycles per second for this purpose, which may be done by simply transmitting a steady 30-cycle modulated signal from the audio transmitter, using for sound only frequencies above the frame frequency of, say 30 cycles per second and below the line frequency of, say, 13,230 cycles per second.

In a few cases, it may not be desirable to eliminate all audio frequencies low enough to approach 30 cycles. In these cases, a 15-cyc1e sine wave current may be produced by the frame frequency sine wave generator I2 and multiplied l to 30 or 60 cycles both in the saw-tooth wave generator II and in the receiving equipment, in order to produce the desirable frame frequency.

Still another method of removing the necessity for cutting off the lower frequencies of the audio band is to apply a 30- (or 15 or 60) cycle modulation to a subcarrier current such as the 13,230-cycle line frequency modulation and then to derive the low frequency by demodulation of the higher frequency at the receiver.

Fig. 2 shows in block diagram a receiving circuit adapted to receive television and sound signals as transmitted by the system shown in Fig. 1. The radio receiver 20 supplies a video signal channel and amplifier 2l with video signals which are impressed upon the control electrode 22 of the picture tube 23 which has an electron gun composed of a heater element 24, a. cathode 25, a first anode 26, and a' second anode 2I. A portion of this signal from the radio receiver 20 is also fed through an audio and synchronizing signal channel 28 to an audio signal selective circuit 29 which passes only that range of frequencies which is utilized for audio signals to the audio signal amplifier 30 and the reproducer 3I.

A portion of the signal from the audio and synchronizing signal channel 28 is fed to the vertical synchronizing frequency selective circuit 32 which comprises a selective circuit passing only the vertical synchronizing frequency to the sawtooth wave generator 33 and thence to the vertical synchronizing coils 35 of the picture'tube 23. Still another portion of the signal from the audio and synchronizing signal channel 28 is supplied to the horizontal synchronizing frequency selective circuit 40 which passes only that frequency adapted to drive-the horizontal saw-tooth wave generator 4I which is adapted to supply a saw-tooth wave currentto the horizontal deiiecting coils 42 of the picture tube 23.A

Fig. 3 shows a saw-tooth wave generator designed to operate as the saw-tooth wave generator shown as block II in Fig. 1 and as the sawtooth wave generator block 33 of Fig. 2.

Assuming that we have a 30 cycle and substantially sinusoidal frame synchronizing current, and it is desired to produce and control with it 4a saw-tooth wave form current which repeats at a rate of 60 times per second, We may use a pulse generator of the type described in Hansell and Dow (RCV D-5832), Serial No. 196,125, led March 16, 1938, entitled Pulse generator, and assigned to the Radio Corporation of America,

combined with` a rectifier and suitable circuits asy shown in Fig. 3.

The synchronizing signal current is impressed upon the primary winding 41 of the transformer 48. The secondary of the transformer 48 is divided into two equal sections 49 and 50. 'I'he control electrode 5I of the electron discharge device 52 is connected to one side of the secondary 50 through limiting resistor 53- and the control electrode 54 of the discharge device 55 is connected to one side. of the other of the secondary winding 49 through limiting resistor 56. The other ends of the secondary windings 49 and 50 of the transformer 48 are connected to the biasing and interlacing y,adjustment potentiometer 51 and to the cathodes of both of the electron discharge devices 52 and 55. The potentiometer is preferably bypassed for A.C. currents by condensers as shown.

The anodes of the discharge devices 52 and 55 are connected together and through an im- `pedance to the positive terminal oi.' a source of potential. The negative terminal of the source of potential is connected to the cathodes of the discharge devices 52 and 55 through the potentiometer 51. All three electron tubes 52, 55 and 60 are provided with cathode heating power not shown.

'I'he junctions of the impedance 58 and anodes of the discharge devices 52 and 55 are connected to the anode 59 of the rectier 60 through a coupling condenser 6|.

It is possible to alter the relative timing and l amplitude' of alternate saw-tooth pulses to provide for adjustable line interlacing lby providing a small controllable steady state of unbalance in the circuits associated with tubes 52 and 55. A potentiometer 51 is one means for providing a small direct current voltage unbalance, which is adjustable, in the .bias potential of control electrodes and 54 to adjust the interlacing of lines in images of television transmitting and receiving equipment in which the arrangement of Fig. 3 is used to produce saw-tooth wave form scanning currents.

'I'he operation of the pulse generator will be described by reference to Figs. 3 and 4.

Fig. 4 shows approximately the wave form of the current -applied to the picture tube deilecting circuits resulting from the sinusoidal inputs to tubes 52 and 55. transformer 41 is represented by curve a. The control electrode potential curve of tubem52 is shown by curve b, and the control electrode potential curve of tube 55 is shown by curve c. The resulting current in thel output circuit is represented by curve d.

The sine waves representing the frame frequency currents are applied to the primary -41 of the transformer 48 and subject the control electrode or input circuit ofthe discharge devices 52 and 55 to a push-pull voltage. The control electrodes 5| and 54 are biased with a cutoi voltage so that no current will ilow in the anode circuits when the synchronizing frequency potential applied to the control electrodes 5| and 54 is passing through its zero value, which occurs twice per cycle. The control electrodes are biased positively alternately by the .potential from the synchronizing frequency. voltage source. Thus currents will now in the anode circuit of the discharge device while they are biased positively. Because of the push-pull input circuit, anode current will flow alternately in the pulse generator tubes 52 and 55 except during the instants when the synchronizing voltage passes through zero. During these instants, at which time both discharge devices are cut oi, the energy stored in the reactance 58 in series with the anode supply to the discharge tubes 52 and 55 or a portion of it is transferred in the form of a pulse through the condenser 6| and the rectier 60 giving iirst momentary positive .and then a negative potential to the anode 59 of the rectier 60 and the condenser 6| to which it is connected.

The momentary positive charge on the anode 59 of the diode 50 causesthe diode 80 to-pass a The input voltage to the pulse of current which stores a negative charge in the capacities between anode and cathode of diode 60. Then at the end of the pulse, the potential of anode 59 changes quickly to a negative value with respect to the cathode 'or diode 60. 75

The negative charge leaks of! gradually through the resistance potentiometer 52 in parallel with the rectier 60 causing a gradual reduction in the electrode potential which is applied to the deflecting plates of the cathode ray tubes to cause the desired deflection. This process, repeated at twice the frequency of the sinusoidal synchronizing current provides the vertical orveld frequency saw-tooth scanning currents.

The arrangement shown in Fig. 3 may be modiiied by interchanging the positions of condenser 6| and diode rectier 60, in which case pulses of current ow through the .diode to charge the condenser twice for each cycle of alternating current input to transformer 48. Between charging pulses the condenser then discharges through the circuits connected in parallel with it. When suitably adjusted, the circuits will then provide a substantially saw-tooth wave form of output potential.

When the arrangement of Fig. 3 is modied by exchangingl the positions of condenser 6| and diode 60, unidirectional pulses of current from tubes 52 and 55 andreactance 58 are delivered to the condenser to charge it to peak positive potential but between pulses portions of the charge leak off through potentiometer resistance 62. As a consequence, a saw-.tooth potential wave form variation appears across the condenser.

Fig. 5 shows another form of this invention for deriving two saw-tooth potential pulses per cycle of synchronizing input current and voltage. Like numerals refer to similar parts.

The synchronizing input current and voltage is impressed upon the primary 41 of the transformer 48 whose secondary winding 63 is connected to the electrodes 5I and 54 of the discharge devices 52 and 55. According to this form of the invention, the two discharge devices 52 and 55 have electrode bias derived through the cathode bias resistor 54 such that they are biased to their cut-o voltage during those time intervals when the A.C. potential in the secondary of transformer 48 is passing through zero. 'Ihe potentiometer 55 is connected between the cathodes of the discharge devices 52 and 55 in order that a small direct current bias voltage unbalance may be yobtained in the bias potential of control electrodes 5| and 52 with respect to their respective cathodes for altering the relative timing and amplitude of alternate sawtooth pulses to provide for adjustable line interlacing. In thisv form of the invention, also, the cathode potentials of the discharge devices 52 and 455 are controllably unbalanced. When a synchronizing voltage is impressed upon 'transformer 48, the two discharge devices 52 and 55 provide two momentary output pulses per cycle to tripl argas or vapor discharge tube 66 for discharging condenser 6| almost instantaneously, after which the charge in the condenser 6| builds up gradually through a resistor 61 which is connected to a positive potential source. A gas discharge tube, when .used, provides for higher peak discharge currents and for a lower potential at the end of the discharge than can be obtained readily with high vacuum discharge devices.y i

Any of the synchronizing arrangements of this invention may be adapted to provide an output saw-tooth wave voltage suitable for applying to electrostaticl deflecting plates of a kinescope as well as to the control electrode of a current control tube for applying current to the deecting coils of a kinescope, depending upon which deflecting means is used. It will be noted that there isr provided a means whereby the electrostatic deflecting plates in the kinescope are kept 'at an average positive potential with respect to the cathodes of the discharge devices 52 and 55, which may be convenient in some cases.

Fig. 6 shows the wave form of the output potential supplied to the deflecting plates of the picture tube to provide the vertical or horizontal deflection of the electron scanning beam.

In Fig. '1, there is shown still another means,

of deriving two saw-tooth pulses per cycle of a sinusoidal alternating current voltage input signal which may be applied to the primary 41 of the transformer 48. According to this form of the invention, the potentialy of the secondary 63 of the transformer d8 is divided'by a potentiometer 12,r and its terminals are connected to control electrodes 13 and 1li-of a single multielement discharge device 15 which is adapted to perform all the functions of the three discharge devices shown in Figs. 3 and 5.

It is well known that, by placing a negative or cut-off potential on any one of the series control electrodes in a multi-element tube, it is possible to stop anode current flow. The bias on the control electrodes 13 and 1liA under yconditions of zero instantaneous signal input is adjusted such that there is a current flow through the Vdischarge device 15. Consequently, when the synchronizing voltage is applied differentially between the control electrodes 13 and 14, one or the other of the control electrodes is maintained negative for a greaterporti'on of the time and holds off the current flow through the discharge device 15 with the exception of a very brief interval of time when the synchronizing input voltage is passing through its zero value. At that interval of time, the potentials on both control electrodes are momentarily cutoff value of the discharge tube 15, thus permitting current to iiow. During this interval of time, when anode current is `allowed to flow in the discharge device 15, condenser 8| is at least partially discharged. Condenser 6|, which is connected to anode 95, then charges slowly through resistance 61 until the next discharging pulse of the anode current through the discharge device 15 and thus the saw-tooth wave `form of potential is obtained across the condenser 6| and may be applied either to deflecting plates of a scanning device or to the control electrode of a saw-tooth scanning current control tube. The electrode 16 of the discharge device 15 is provided with a bias potential through resistors 11 and 18. By arranging the proper bias potential on the electrode 16, any of a large range of desired characteristic response of the discharge device 15 may be obtained.

A potentiometer 94 is provided to supply the centering voltage for the range of scansion of the electron beam.

The arrangements of Figs, 3, 5` and 7, which -fe n @anws a means for deriving line synchro nizing pulses in which there is required a pulse .generator which provides'only` one saw-tooth pulse per cycle of alternating current input, since it is usually necessary that the line synchronizing modulation frequency be maintained above the audio or sound frequency range. According to this form of the invention, discharge devices 52and 5 5 contain control electrodes 5| and 54 which are biased such that the discharge devices pass' current at all times except when the synchronizing voltage input wave is passing through its zero axis. It, therefore, follows that the discharge devices 52 and 55 cut-olf two times per cycle. However, during one of these two-time periods, an auxiliary discharge device 19 is supplied with phase displaced current so that it passes current in such a manner that the current iiowing through discharge device 19 surpresses one Aof the output pulses from the discharge devices 52 and 55 but permits the other to charge the condenser 6|, as'previously described. This action of the discharge device 19 is accomplished by connecting the control electrode 80 by way of a phase shifting condenser and resistor to a terminal of the secondary 82 of the synchronizing signal input transformer 85. The

center-tap of the transformer secondary-82 is connected to thecontrol electrode 54 of the discharge device l55, while the terminal opposite to the terminal connected to the control electrode 80 of the discharge device 19 is connected to the control electrode 5| of the discharge device 52. The section of the secondary of transformer 82 which is connected between the control electrodes 5| and 54 is also center-tapped and, in turn, connected to the cathodes of discharge devices 52 and 55 through a biasing resistance and capacity circuit including resistance 83 and condenser 84.

The resulting single pulse per cycle is passed through the condenser 6| to the rectifier 6l), which results in, firsty a momentary positive and .then a negative potential on the anode 59 of the rectifier 6l) andthe terminal of the condenser 6| to which the anode 59 is connected. The

negative charge on the condenser 6| leaks olf gradually through the resistance potentiometer 62 in parallel with the rectifier 6U, causing a f gradual reduction in the negative chargeon the trolling the control electrode potential of a current controlling tube.

-Fig, 9 shows va graphical illustration of the input potential wave form and relative timing which result in one pulse per cycle of alternat- 4ing current voltage input in the arrangement of Fig. 8. Curve e represents the potential yon the control elect-rode 5| of the discharge device 52 shown in Fig. 8. Curve g represents a control yelectrode potential of tube 55. Curve f represents the phase displaced potential on the control electrode su of the tube 1s in Fig-8. It win be t noticed that during one of the time periods per cycle when tubes 52 and 55 are passing through `thel zero A.C. `potential condition,.the tube 19 will have a positive control electrode potential and therefore pass current to suppress the output pulse. During the other period of zero A.C. potential to control electrodes of tubes 52 and 55 the tube 19 will have negative control electrode potential and will therefore allowthe output pulse to take place, Therefore,`only alternate pulses from tubes 52 and 55 appear in the output to rectifier 50 so that, instead of two, we have only one pulse per cycle of sinusoidal synchronizing current.

The arrangement of Fig. 8 may readily lbe modified by taking away the phase shifting condenser between grid and cathode of tube 19 and connecting a suitable grid leak and condenser in place of the resistance 8|. Then the potential between grid and cathode of tube 19 will have a form corresponding to a combination of sinusoidal and saw-tooth wave currents. quence, tube 19 may be' made to pass current to suppress one output pulse, but not the other, for each cycle of synchronizing current.

Fig. l s'hows a form ofpulse generator employing a single multielement tube for providing a single output pulse, or saw-tooth wave, per cycle of sinusoidal synchronizing current. The form of the invention shown in Fig. 10 again depends upon the principle that negative potential on any of the control electrodes of a tube will block the anode current. The electrodes 86 and 88 of discharge device 81 are excited in phase opposition by the synchronizing input voltage, while the electrode 86A is supplied with phase shifted A.C. potential such that it will be excited preferably; but not necesarily, at a 90-degrec phase relation with respect to the A.C. potential on the other electrodesI 86 and 80. This is accomplished by providing in one leg of the secondary 82 of the transformer 85 a series resistance 89 and condenser 90. Theny once per cycle, fo/in a very brief time period, the anode current 'is allowed to flow, thereby charging condenser 9| which is discharged between pulses through the voltage dropping resistance 92.. This provides the saw-tooth wave form voltage in the output circuit. Potentiometer 94 is employed to maintain a proper bias. on the electrodes 86, 86a and 88.

In this case, as in the case of the arrangement of Fig. 8, instead of employing phase shifting, we may employ wave form distortion in the input to electrode 86a by omitting condenser 90 A and by replacing resistance 89 with a suitable condenser and grid leak resistance.

Fig. 11 shows an application for one form of this invention to the television transmitter circuit. A synchronous motor I3 drives the 30cycle line frequency generator I5 and a 13230 cycle frame frequency sine wave generator I2 for proxviding constant frequency sinusoidal voltages suitable for 30 frame per second, 441 line television. A motor generator set is used for this purpose, and there is also provided thereon a flywheel or other means having considerable inertia to prevent any rapid freqnency fluctuations above and below average value. A synchronous motor generator has heretofore been used to correctl for deficiencies' in vacuum tube generators in order to prevent any irregularities in the freequency of the synchronizing voltage. A vacuum tube synchronizing frequency generator can, if properly designed and operated, be-very satisfactorily used in the carryingout .of this invention. Each of the two generators I2 and I5 supplies an input voltage having substantially a eine wave form to a saw-tooth vacuum tube pulse genera- As a consetor, as previously described in more detail. to provide potentials for vertical and horizontal deiiection of the electron scanning beam in the transmitter tube to convert an optical scene into a train of picture signals.

There is illustrated a transmitter tube of the electron beam scanning type, one provided with horizontal deecting plates |02 and |03 and vertical deflecting plates |00 and |0I. The signals from the frame frequency sine waveA generator I2 are applied to the primary 41 of the transformer I8 to which is connected a saw-tooth wave generator adapted to generate two complete sawtooth waves per cycle of frame synchronizing frequencies, and such as described in more detail unde;` Figs. 3, 5 and '7 and more particularly, Fig.

The push-pull voltage applied to the electrodes 13 and 14 causes the discharge device 15 to become conducting for very sm'all intervals of time at a rate of twice the frame frequency. Thus the current through the discharge device 15 discharges the condenser 6| by reason of the fact that as the current fiows through the discharge device 15 there occurs a voltage drop across the condenser and in the resistance 61. During the time when no current nows through the discharge device 15 the condenser 8| is charged slowly through resistance 61.

The deflecting plate |00 is connected to the anode resistor 81 and it will readily be seen that the potential on the deflecting plate |00 varies in accordance with the saw-tooth wave generated by discharge device 15, which frequency is twice that of the frequency generated by the frame frequency generator I2. The associated vertical deflecting plate |0| is connected to thevariable tap of a potentiometer 94 in order that its direct current potential may be adiusted to the mean value of the saw-tooth wave whereby the range of scansion of the electron beam may be controlled.

Signals from the line frequency sine wave Benerator I5 are applied to a saw-tooth wave generator adapted to generate one complete saw-tooth wave per cycle of line synchronizing currents as explained in connection with Figs. 8 and 10. and more particularly, Fig. 10.

Electrodes 85 and 88 of the discharge device 81 are excited in phase opposition by the line frequency synchronizing input voltage and the electrode 86a is excited with an A.C. potential from the source 90 out of phase with the potential of the other electrodes 86 and 88.

Once per cycle for a very brief time period, anode 98 draws current which causes a discharge of condenser 9| which is connected in parallel with discharge device 81.' During the interval of time that there is no anode current flowing through discharge device 81, the charge on the condenser 9| is allowed to charge more or less steadily through resistor 92 which is connected to a source of positive potential.

Horizontal denecting plate |02 is connected to resistance 92, and it will be readily seen that a saw-tooth wave voltage having a frequency equal to the frequency of the line frequency sine wave generator I5 will be applied to the horizontal deecting plate |02. The associated horizontal deecting plate |03 is returned to a variable tap on potentiometer 93 in order to control the direct current voltage on the fixed potential horizontal deflecting plate |03-and thus the range of scansion of the electron beam in the horizontal plane may be controlled.

ages.

A portion of the output voltage from the synchronizing frequency generators I2 and. I5 is fed to the associated audio frequency transmitter to be amplified and to modulate the transmitter to produce a synchronizing frequency current for the receiving station.

The transmitter tube employing electrostatic deiiection has been illustrated. If electromagnetic' deflection is used, a linear amplifier would be employed between each saw-tooth wave generator and its associated deflecting coils. Furthermore, vthis amplier might employ negative feedback to assist in providing the saw-,tooth wave form of the current through the deflecting coils.

The synchronizing current generators I2 and I5 are provided with means for adjusting the This may be very readily accomplished by relative timing or phase of. their two output voltmechanically rotating the frame of one generator with respect to the other or by rotating the coupling between the synchronous driving motor and one of the generators. There may also be provided a phase adjustment as well as a volume control adjustment in the channel of each of the two generators connected to the audio frequency transmitter. Exact timing of the phase adjustment of the line frequency input to the audio transmitter is particularly desirable since the timing of the transmitted line frequency synchronizing signal should bear a definite time or phase relation to the line scanning in the transmitting tube.

Fig. 12 illustrates the synchronizing signal channels in a receiving system in which sinusoidal synchronizing current modulations of t'ne audio transmitter are utilized to produce sawtooth wave forms of potential for operating the scanning system in the receiver picture tube. There is shown a picture tube having electrostatic deection but, as previously described, a picture tube having magnetic deflection may be used with a slight modification of the circuit shown. In this form of the invention there are indicated selective circuits for separating out the sinusoidal synchronizing current from the audio receiver and applying these synchronizing signals to saw-tooth pulse generators for producing saw-tooth wave voltages for the deflection of the electron beam in the picture tube.

A portion of the output signal from the audio frequency receiver is applied to transformer 48 through a vertical synchronizing frequency selectiv'e circuit including inductances |08 and |09 in series with condensers I| and II I, respectively, and the primary winding of transformer 48.

A phase adjustment of the synchronizing voltages is provided for obtaining an exact relative timing adjustment of the saw-tooth deection voltages. A variable condenser ||2 is inserted in the selective circuits for making this phase adjustment.

The resulting sine wave voltage having a frequency equal to the transmitted vertical synchronizing frequency is supplied to the input transformer 48 of a saw-tooth wave generator of the type previously described and vshown in Figs. 3,l

5 and '7. It will be noticed that a different form of coupling is utilized between the transformer 48 of the invention to this particular type of coupling shown. The two resultingpulses per `cycle of vertical synchronizing current cause the condenser 6| to apply a saw-tooth voltage to the vertube 23. V The associated vertical deiiecting plate II4 is connected to a variable tap on potentiometer 92 for centering the resulting image in a vertical direction. A portion of the output signal from the audio frequency receiver is also applied to the horizontal frequency selective circuit including inductances |I5 and ||6 which are connected in series with condensers ||1 and H8, respectively, and the primary winding of the transformer. included in the horizontal frequencyselective circuit in order to facilitate phasing adjustment.

The resultant sine wave of the horizontal synchronizing frequency is applied to a saw-tooth wave generator adapted to produce one saw-tooth wave per cycle of horizontal synchronizing frequency voltage. A saw-tooth'wave generator of the type shown in Figs. 8 and l0 may be employed for this purpose.

The saw-tooth wave voltage generated in the tube 81 and storage condenser 9| is applied to the horizontal deecting plate |20 whose associated horizontal deflecting plate |2| is connected to a variable tap on potentiometer 93 for providing a means of centering the image of the A'portion of the output signal in the audio .y

receiver is applied to the transformer |26 whose associated filter circuit including inductances |21, |28V and condensers |29, |30 and I3I together with the terminal transformers are designed to pass only a sine wave current having a frequency equal to the vertical synchronizing current frequency of the transmission system. This sine wave voltage is appliedvto the transformer |32 whose secondary terminals are connected to electrodes |33 and |34 of the discharge device |35. A bias is applied to the control electrodes of the discharge device |35 through potentiometer |36 such that the discharge device |35 passes current during the short interval of time when neither the electrode |33 or |34 is too negative which occurs at the time when the alternating current input voltage passes through its zero axis. When the discharge device |35 passes current, it discharges condenser |31 very rapidly which is then charged through resistance |38 during the time that the discharge device |35 is not drawing current. This results in a sawtooth wave form of potential across the condenser |31 which is applied to the electrode |39 of discharge' device |40 through coupling condenser l4la. A positive source of voltage is connected to the anode |4| of the discharge de-Y vice |40 through a winding |42 ofthe transformer |43. A tap on the winding |42 is connected to the vertical magnetic deflecting coils |43a of the picture tube |44. The other terminal of the deflecting coils |43a is connected to the variable tap of a potentiometer |45 which is provided to supply constant direct current volta-ge to the opposite terminal of the deflecting coils |43a and to control the centering of the image, or the range of the scansion of the el'ectronbeam in the picture tube |44.

tical deiiecting plate I|3 of the receiving picture 75 The saw-tooth wave current flowing through A variable condenser ||9 is also` in the Winding winding |42 of the transformer |43 produces a voltage in winding |46 of the transformer |43 whose terminals are connected to a series circuit including a resistance |41 and a thyrite element, which element is an opening circuit resistance for relatively low potential while it has a relatively low resistance when the applied voltage is greater. It, therefore, follows that while the anode current is increasing slowly and producing the useful portion of the electron beam scansion, the resistance of the thyrite is almost an open circuit resistance because of the low voltage induced |46 by reason of the slowly changing current in the winding |42 of the transformer |43.

However, in the return time of the scansion of the electron beam there is a rapid change in current in the winding |42 of the transformer |43 which results in a relatively -high voltage in the winding |46 which causes the thyrite element to present a relatively low resistance during this period of time when the anode current is decreasing rapidly during a return time interval. This results in a relatively still larger voltage across the resistance |4'| during the return time interval. This voltage is then applied to an auxiliary control electrode |48 of the picture tube |44 and it has a polarity such that it will extinguish the electron beam during that time interval which is employed for returning the electron beam to the starting position of the next succeeding frame.

It`will be readily understood that the thyrite element could be omitted and also that the pulse of voltage might be applied to other control electrodes in t'he picture tube or to one of the ampliers which delivers the videoinput to the picture tube.

Fig. 14 shows one form of this invention by means of which a horizontal or line frequency sinusoidal synchronizing voltage is selectedfrom the audio modulated sound channel in the audio portion of the television receiver and utilized to control a saw-tooth pulse generator adapted to produce one saw-tooth wave per cycle of synch'ronizing frequency. The saw-tooth wave generator is then followed by an amplifier which controls the current through the horizontal deiiecting coil. Provision is also made to provide an exact interlacing adjustmentand for suppressing the horizontal return line of the electron beam and picture tube for cutting 01T or defocusing the electron beam during the return time interval.

A portion of the signal from the audio receiver is fed through transformer |49 to a narrow bandpass lter adjusted to the horizontal synchronizing frequency. The resulting sine wave is then applied to a saw-tooth wave generator of the type previously described and shown in Fig. 10, which applies a saw-tooth wave voltage whose frequency is equal to the incoming synchronizing frequency to the control electrode |50 of the discharge device whose anode |52 is connected through an impedance |53 to one terminal of the horizontal defiectng coils |54 of the receiver tube.

In this form of the invention the thyrite element is connected in shunt with the inductance |53 to suppress the oscillations which might be generated in the inductance. |53 which result from the distributed capacity in the inductance |53 and` capacity in its associated circuits.

Fig. 15 illustrates diagrammatically a resistance and condenser circuit which, according to one form of this invention, is adapted to precede the saw-tooth wave generators which have been previously described. A portion of the signal from the audio frequency receiver is applied to the amplier tube` |60 whose output is applied to a duplex triode |6|. The output from one section of the duplex triode |6| is applied without filtering to the vertical saw-tooth wave generator, such as, for example, the type shown in Figs. 3, 5 and 7, while the output from the other portion of the duplex triode |6| is. fed through a low pass filter to an amplifier tube |62 to be amplified and applied to a horizontal saw-tooth wave generator, such as the type shown in Figs. 8 and 10.

The circuit shown in Fig. 15 has also been used to separate rectangular horizontal synchronizing pulses from rectangular vertical synchronizing pulses by taking advantage of the fact that the rectangular vertical Vsynchronizing pulses are of much longer duration than the rectangular horizontal synchronizing pulses. It may be said that the circuits add or integrate the energy to accomplish vertical synchronizing but utilize the rate of change or differentiate the energy to accomplish horizontal synchronizing.

It will be observed that phase variations in synchronism due to noise are both positive and negative. In other words, there maybe no variation in the averagerate of repetition of the lines but almost every line may be out of position Vertically or horizontally in either direction and in a random amount.

By averaging out the phase or timing of the lines over a considerable period, the average error in synchronism due to noise would approach zero. If at the receiver the timing of the saw-tooth receiver tube scanning potentials or currents is made dependent upon the timing of a large number of synchronizing pulses or waves, a large reduction in the effects of noise upon exact synchronizing would then become apparent.

Fig. 16 shows one form of this invention in which circuits tuned to the fundamental syn- Ichronizing frequencies are introduced into the circuit shown in Fig. 15. The tuned circuits store up synchronizing pulse or synchronizing Wave energy from a large number of pulses and waves and therefore synchronizing signals are applied to the saw-tooth wave generators which are controlled in accordance with the timing contributions of a large number of pulses or waves instead of according to each single pulse or wave. In this manner, the effect of noise which has both positive and negative momentary effects will average out to a relatively low value, as each individual pulse of the wave of the incoming synchronizing frequency current has comparatively little effect upon the output synchronizing current to the saw-tooth Wave generators.

The portion of the signal in the audio frequency receiver is applied to the amplifying tube |63 which is amplied and in turn applied to the duplex triode |64. The output of the lower triode section of the duplex triode |64 is connected to a tuned circuit tuned to the frequency of the vertical synchronizing pulses or waves including iductance |65 and. condenser |66. The output of this tube circuit is designed to have small loading effect on the tube circuit so that oscillations generated therein do not have a very highly damped characteristic.

For the purpose of illustration, another form of saw-tooth wave generator is illustrated comaardse? prising the discharge device |51 connected to transformer |88 which may also be tuned to the frequency of the vertical synchronizing pulse or waves. This type of saw-tooth wave generator is more fully described in the patent to Toison and Duncan No. 2,101,520, patented December 7, 1937, and my Patent No. 1,898,121,l patented February 21, 1933. The output from this generator is then fed to a vertical saw-tooth wave ampliier not shown, which isv utilized to apply current to the vertical deflecting coil of the picture tube.

The Upper triode section of the tube |66 is passed through a low pass :filter and applied to an amplifying tube |69 in whose anode circuit there is an inductanceand capacity circuit including inductance and capacity |1| which is tuned to the line frequency of the synchronizing input signal. This oscillatory circuit is also adapted to feed a circuit which will place thereon a relative small load whereby the oscillations occurring in the inductance capacity circuit are not highly damped. The resultant signal is then applied to 'a saw-tooth wave generator of the type for purposes of illustration, as more fully described in the patent to Tolson and Duncan No. 2,101,520, patented December '1, 1937.

The output signal voltage from the saw-tooth wave generator is applied to amplifier and tubes |12 and |13 whose output circuit is connected to the horizontal deilecting coils |14 of a picture tube.-

In Fig. 11, there is shown still another form of this invention which may be used for integrating the energies of a considerable number of synchronizing pulses or waves lto produce circuit oscillations having the frequency of the horizontal and vertical synchronizing waves. A portion of the signal from the audio receiver of the discharge device |15 whose anode'circuit is connected to the primary of transformers |16 and |11 through a resistance and capacity circuit which tunes each of the transformers |16 and |11 to the vertical and horizontal synchronizing frequency, respectively. The secondary of transtions are produced continuously by means of a` pulsing oscillator and amplifier tube, whether or y not there is any synchronizing current input signal.

The synchronizing signal is applied to the pri-v mary of the transformer |84 whose two-section secondary |85 supplies the synchronizing voltage to the control electrodes of .a duplex triode |86 in a manner similar to that previously described in more detail. v 'Ihe anodes of the tube |86 are connected together and supplied with a positive potential through resistor |81. The anodes are coupled to the primary, of transformer |88 throughV `coupling condenser |89. The duplex triode |80 is employed as a saw-tooth waveA generator. Such an oscillator is Afully described in Toison and Duncan Patent 2,101,520, referred to above.

The resulting saw-tooth wave current generated is applied to the amplifier 'tube |9| through the coupling condenser |92. The output of the amplifier tube |8| is applied to the transformer |93 whose secondary is coupled to the deecting coils of the cathode ray tube.

The use of an' oscillator which is capable of sustained oscillations has the advantage that the cathode ray beam continues to move over the screen of the tube even when the receiver is not tuned to the frequency of a transmitter and no synchronizing current is being received. If the electron beam should stop its scanning movement for an appreciable length of time, the constant bombardment of the electron beam with the screen for any length of time will cause the electron beam to burn a hole in the screen, thu'sseriously damaging the screen.

The sinusoidal synchronizing current signal, when applied to theV duplex triode tube |86, causes pulses of more positivepotential to appear on the anodes of the tube |86 each time the sinusoidal input potential to the control electrodes of the'tube |88 is passing through its zero value. These pulses or a portion of their amplitude are delivered to the control electrode circuit of the pulsing oscillator including the transformer |88 and the tube |90. The oscillator is adjusted to operate by itself at a frequency which is slightly below the required frequency. The synchronizing pulses delivered to it through -transformer |84 cause the oscillator to act a little sooner Ato discharge the storage condenser |94 and, consequently, the pulses synchronize the operation of the oscillator at the proper synchronizing frequency.V The output signal in the form of saw-tooth waves from;the tube. is

fed through an amplier tube` |8l, whereby a current is supplied to the transformer |93. This provides the necessary current for deflecting coils of the cathode ray tube.

It is not necessary that the pulsing oscillator operate at the same frequency as those pulses received from the synchronizing tube |86. It may work also at any multiple or sub-multiple of the synchronizing pule frequency over a very llarge range if the circuits are suitably designed and Iadjusted.

In Fig. 19, there is shown a synchronizing signal input to transformer |95 which supplies synchronizing pulses to the control electrodes of a multi-grid tube |88 two times per cycle of the sinusoidal. input signal. The input circuit to the tube |98 may be o f the type shown or of the type previously described under Figs. 7 or 10.

direction. Consequently, the coupling to the pulse generator tube |90 and its associated trans- A former |88 is made to the cathode circuit of the tube |90 through resistance |91 rather than to its controlv electrode circuits through `the transformer |88, as previously described. The signal from the oscillator tube |80 is then applied to the amplier tube I9 I, which causes a saw-tooth wave current to now through the primary of the transformer |88 which is, in turn, coupled to the deilecting coils of the cathode ray tube.

It should be noted that reduction of the effects of noise upon exact synchronizing. inthe previously adapted synchronizing pulse system. seems to require using-.the minimum possible control of the receiver saw-tooth oscillator by the synchronizing pulses. In other words, the more We can make the oscillator determine its own frequency and the more we reduce the synchronizing pulse, control, the more we also reduce the effects of noise. This method of reducing the effects of noise cannot be carried very far before there is too much difficulty with complete loss of control due to power supply voltage changes, temperature changes, etc.

In the sinusoidal synchronizing system, on the other hand, we have a means of reducing the eiects of noise by selectivity without at the same time requiring a corresponding reduction of the power of the synchronizing current' to control the, saw-tooth oscillator. 'Ihis phenomenon should permit much greater tolerance in design and adjustment of the saw-tooth oscillator with respect to its ability to generate a correct frequency by itself when the sinusoidal system is used.

Phase or frequency modulation of the sinusoidal synchronizing currents at the transmitter would cause diiculty at the receiver if the circuits for passing the synchronizing currents are very selective. This diiculty is of the same nature as was encountered with mechanical scanners when there was phase or frequency v wobble of the synchronizing pulses. The diflculty was overcome by deriving the synchronizing pulses from a mechanically rotating generator in which mechanical inertia overcame the modulation which had been caused by power voltage and phase variations in electrical pulse generators.

It may be noted that prior receivers adapted to receive steep front synchronizing pulses, if they provided an equivalent frequency selectivity by virtue of designing and adjusting the sawtooth .oscillators to more and more determine their own exact operating frequency to obtain an equivalent frequency selectivity, also would suffer from the eiectsl of phase or frequency wobble in the transmitter pulse generators.

This effect may be minimized if at the trans. mitter camera and the receiver the synchronizing circuits are so designed that the synchronizing currents meet the same amount of frequency selectivity or delay in response to phase and frequency change at both places. In the sinusoidal synchronizing system, if We .wish to use 1 percent vband width circuits in the receivers we should preferably employ 1 percent band width circuits between the generator and the camera circuits at the transmitter in-order that phase wobble may be suppressed equally at both ends of the circuit. In any case, difficulties due to phase or frequency .wobble of synchronizing currents are caused by equipment defects which are under control of the equipment designer and can be corrected.

It might be said that wave form distortion of sinusoidal synchronizing currents can affect the interlacing. However, the frequency selective circuits may substantially eliminate all Wave form distortion by suppressing the harmonic frequency components which would be required to give wave form distortion. Also, the wave form distortion produced in the receiver tends to be constant so that a slight adjustment for interlacing can compensate for it more or less permanently. d, Thesynchronizing may be effected by multipath in several detail ways. With reference to prior systems using synchronizing pulses, a rectangular wave of modulation at the transmitter will not arrive with the same shape at the receiver. The distortion will not be of the simple stairstep variety because the steps may be both up and down. If we have t/wo paths of different lengths such that their currents add at the receiver then we may expect lche simple stairstep distortion. If their currents oppose at the receiver, then the distortion will be of an entirely different kind causing first a rise to a. peakabove the steady state level followed by a drop to a lower level. Intermediate phase relations cause an infinite Variety of other types of' distortion. In practice, surveys in a metropolitan area have shown a great variety of paths of different lengths adding up with all sorts oi' phase relations at the receiver. On the average this wave form distortion of synchronizing pulses makes necessary a higher initial signal to noise ratio. Forgross synchronizing to hold the multipath distortion makes it necessary to deliver greater synchronizing pulse power to the sawtooth oscillator. This results in an equivalent loss in selectivity in the synchronizing system which permits noise to have more eiect in many receivers. Where distortion in wave form reduces the effectiveness of the synchronizing pulse to perform its function, noise will cause greater probability of loss of gross synchronizing and greater variation in timing in a manner to reduce the apparent picture definition.

It may be noted that fixed multiple paths cannot distort the wave form of substantially zero band width sinusoidal modulations at the receiver in a manner to reduce the positiveness of synchronizing. They can only cause some small steady state phase or time displacement which may shift the position of the received images slightly but which cannot detract from their quality through the synchronizing channel.

Observations made on receivers employed in the rectangular synchronizing pulse system seem to indicate that the most serious effect of the noise is to cause phase or timing variations from exact synchronism in a manner to reduce the apparent picture definition. Usually, in the presence of noise, there appears to be enough contrast between light and dark areas to provide a much better picture if the objects in the picture did not become fuzzy in detail and outline due to variations in timing. Therefore it is reasonable to assume that loss of definition rather than complete loss of synchronizing control is the most serious effect of noise to be overcome.

Because of the narrow band Widths required for sinusoidal synchronizing, and the possibility of amplifying the synchronizing currents in the audio amplifiers along with the sound wave currents, the sinusoidal system offers possibilities for simplifying the design of television receivers. Fewer tubes, with their associated circuits are required.

Furthermore, the blanking time, required for v transmission of rectangular synchronizing pulses.

may be considerably reduced when sinusoidal y synchronizing currents, transmitted through the sound' transmitter, are used. The gain from this reduction in blanking time is greatest with respect to the vertical or 60 cycle blanking. The total gain from this source mayl range up to about 10 percent of image area, or 10 percent ,improvement in image definition. In the .proposed system, the synchronizing current amplitudes may be varied to perform new functionssuch as-control of size 0i' the picture, switching from facsimile to television recording, etc.

sinusoidal synchronizing may be Very advantageously used in the cameras of mobile transmitters for sending programs to the main broadcasting station. The scanning currents may be derived from a receiver tuned to the'main sound broadcasting transmitter. This would eliminate the need for accurate synchronizing frequency control equipment in portable form and would eliminate the problem of synchronizing portable equipment with the public service power system. Phase control of the received sinusoidal synchronizing currents would permit easy control of exact framing. l

- One important function of receiver saw-tooth oscillators is to prevent burning of a spot on the screen of the picture tube if the transmitter should fail. Although the oscillators may to the particular organizations shown and' de` scribed, but that many modifications may be made Without departing from the scope of thisinvention as set forth in the appended claims.

I claim as my invention: l. In a television system including electron ray scanning devices,the combination of means for transmitting a sinusoidal electron ray scanning synchronizing signal having a lfrequency equal vto the scanning rate of said electron ray in one direction of relatively rapid scanning rate, a saw-tooth wave generator` controlled by said synchronizing signal periodically only 'at alternate intervals when said sinusoidal signal passes through its axis and adapted'to generate sawtooth waves having a frequency equal to said synchronizing signals, means for transmitting a second sinusoidal synchronizing signal having a frequency equal to a submultiple of the scanning rate of said electron ray in another direction of relatively slow scanning rate, and a second sawtooth wave generator controlled by said second synchronizing signal and adapted to generate saw-tooth waves having a. frequency equal to a multiple of said second synchronizingsignal.

2. In a television system' including 'electron ray scanning devices, the combination of means for' transmitting'a sinusoidal electron ray scanoidal signal passes through its axis and adapted to'generate saw-tooth waves having a 4frequency double said synchronizing frequency.

said sinusoidal signal passes through its axis and whose frequency is double said synchronizing frequency.

4. The -invention as set forth 4in 'claim 2 and wherein said saw-tooth wave generator includes a pair of discharge devices ,each becoming conducting alternately at a frequency equal to said synchronizing pulses, and means connected in parallelwith said discharge devices and adaptedto presenta low impedance load to said dischargel devices during alternate intervals in which neither of said discharge devices is conducting.

5. The invention as set forth in claim 2 and wherein said saw-tooth wave generator includes a discharge device which is adapted to become conductive periodically at a frequency twice that of said synchronizing frequency, and means connected in parallel with said discharge device and adapted to present a low impedance load to said discharge device during alternate periods during which said discharge device is conduct ing.

6. In a television system including electro ray scanning devices, the combination of means for transmitting a sinusoidal electron ray scan-, .ning synchronizing signal having a frequency ing frequency and connected to a saw-tooth wave generator controlled by said synchronizing signal periodically only at alternate intervals when said signal changes its amplitude most rapidly and adapted to generate saw-tooth. waves having a frequency equal to said synchronizing signal, means for transmitting a `second sinusoidal synchronizing signal and having a frequency equal to a submultiple of thescanning rate of said electron ray in the other direction of relatively slow scanning rate, a second oscillatory circuit tuned to said second synchronizing fre- Vperiodicallyr only at intervalslwhen said slnusl I quency and connected to a second saw-tooth wave generator controlled by said second synchronizing signal periodically only at intervals when said signal changes its amplitude most rapidly and adapted to generate saw-tooth waves having a frequency equal to a multiple of said second synchronizing signal.`

7. In a television system yincluding electron ray scanning devices, the method of maintaining .synchronism of the scanning of said electron rays including the steps of transmitting a sine wave synchronizing signal and having a frequency equal tothe scanning rate of said electron ray in one direction of relatively rapid 'scanning rate, generating a lsaw-tooth wave -whose frequency is equal to said synchronizing frequency, transmitting a second sine Wave #3nchronizing vsignal having a frequency equal to z vsubmultiple of the scanning rate ofl said electro i ray'in another direction of relatively slow scanning rate, generating pulses periodically only when saids'econd signal passes through its axis,

and generating a second saw-'tooth wave from 3.'The invention as setforthin claim 2 and said pulses whose frequency is equal to a multiple of said second synchronizing frequency.

CLARENCE w. nANsmL.

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