US2196867A

US2196867A - Television image producing system

Info

Publication number: US2196867A
Application number: US166728A
Authority: US
Inventors: William A Knoop
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-10-01
Filing date: 1937-10-01
Publication date: 1940-04-09
Anticipated expiration: 1957-04-09

Description

April 9, 1949. w. A, KNOOP .TELEVISION IMGEAPRODUCING SYSTEM Filed oct. 1'. 1957 4 sheets-sheet 2 MOD A1155 9 1940- w. A. KNooP 2,196,867

` TELEVISION IMAGE raouucme ss'rwi Filed Dot. l, 1937 4 Sheets-Sheet 3 RECEIVER APPR.

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,263 /NVENTOR 262 By WAKNOOP A 9, 1940.- w. A. KNooP A TELEVISION IM-GE'RODUCING SYSTEM` Filed Oct. l, 1937 4 Sheets-Sheet 4 TIME /N VE N TOR y W A. /f/vooP @M ATT RNEV l Patented Apr. 9, 1940 TELEVISION IMAGE PRODUCING SYSTEM William A. Knoop. Hempstead, N. Y., assignor to Bell Telephone` laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 1, 1937,- Serial No. 166.728

. 24 Claims.

This invention relates to television image producing systems and particularly to a system for producing television images togethe'i` with the accompanying sound effects from sound motion picture films.

In accordance with an embodiment of the invention shown and described herein for the purpose of illustration, a large rotating disc carrying lenses arranged along a circular path near its periphery directs a light beam from a fixed source to the elemental areas in succession along a linear path of a motion picture film. The motion picture film is moved continuously in a direction perpendicular to the direction of scanning of the elemental areas along a linear path so that successive lenses illuminate or scan the elemental areas along successive parallel lines. The disc is enclosed in a housing to reduce Wind resistance and also to prevent accidental contact with the disc while in motion. Asv the film moves past the scanning position it is spaced only a short distance from the disc housing and moreover the lenses in the disc have a short focal length so as to illuminate a small area of the film at a time. Light from the successively illuminated elemental areas of the i'llm is directed by means of a rectangular cross-sectioned light tunnel of glass or, preferably, of a material known as pontalite to the primary cathode of an electron multiplier.

A short time prior to the time that a certain lens of the scanning disc commences scanning a line of the picture film, two or three line scan-- ning periods, for example', light is directed through the lens and through an adjustable aperture upon a light sensitive cathode ofa second electron multiplier for generating a synchronizing-impulse. Due to imperfections in the scanning disc lenses or to dust on the lenses, the light transmission ability of the lenses may vary somewhat and thus cause the amplitude of the synchronizing impulses generated by. the electron multiplier to vary. Therefore; the synchronizing impulses generated by the electron multiplier are impressed upon an amplifier which limits the amplitude of the impulses to a constant value. This amplifier also reverses the phase of the impulses which are supplied to the grid-cathode, circuit'of a gas-filled triode. To the anode circuit of the gas-filled tube is connected a circuit including a condenser which is charged through la resistive element. The condenser is periodically discharged by the gas-filled tube due to the synchronizing impulses impressed upon its input circuit. There are thus (Cl. Pls-5.6)

produced across the resistive element of the condenser charging-discharglng circuit a voltage' wave having 'a fundamental frequency equal to 4the line scanning frequency and having a con- 4circuits of said tubes being connected to different output transformers respectively. One output transformer is connected to a band-pass lter to produce a sine wave current of constant amplitude and having al frequency equal to the line scanning frequency. A second transformer is connected to an adjustable delay network which delays the impulse for an interval equal to the interval between the time that a synchro- .nizing impulse is generated by light directed.

through a certain lens of the scanning disc upon the synchronizing electron multiplier and the time that the first elemental area of a line of the picture film is scanned by light directed through that lens. The third transformer is connected to a circuit for maintaining the scanning disc driving motor at a constant speed.

For transmission to a distant station, carrier transmission over a coaxial cable is employed, the television image current, the line frequency alternating current and the sound current produced by scanning the sound track of the motion picture lm being transmitted over different carrier channels, respectively. The output of the electron multiplier for generating the television image current is connected directly to the image current modulator without the use of alternating current amplication, so that the direct and very low frequency alternating vcomponents. corresponding to the average picture tone value as well as the higher frequency components of the image current are transmitted. At the receiving station the carrier modulated image current, after demodulation, is applied to the control electrodes of a cathode ray image producing device. The sine wave synchronizing current of line scanning frequency, after demodulation, is employed for producing a sawtooth wave for controlling the high frequency" deflection of the cathode beam. A subharmonic generator controlled by the line frequency current may be employedfor generating a frame frequency current which, iny turn, controls the production of a saw-tooth wave for controlling the low frequency deflection of the cathode beam. The carrier modulated sound current, after demodulation, is impressed upon a loudspeaker.

A cathode ray image producing apparatus is also provided at the transmitter for monitoring purposes. The control electrodes of the cathode ray tube may be connected to the output circuit of a demodulator, the input circuit of which is connected to the source of carrier modulatedl image current. However, it is not essential that the image produced by the monitoring receiver should have the correct average tone value.' Therefore, the control electrodes of themonitoring cathode ray tube may be connected to the output circuit of an alternating current amplifier, the input of which is supplied with current from the image scanning electron multiplier. The high frequency deflection of the cathode beam may be controlled either by the sine wave synchronizing current or by the delayed synchronizing impulse current. The use -of the latter has the advantage that the image current impulse corresponding to the first scanned elemental area of a line and the synchronizing impulse for returning the cathode beam to its initial line scanning position are always accurately in synchronism and do not vary in phase due to inaccuracies in the positioning of the lenses of the scanning disc. When the sine wave is to be used for controlling the highkfrequency deflection of the cathode beam, it is utilized for controlling the generation of a square-topped wave and the latter, in turn, is utilized for controlling the production of a saw-tooth Wave which is impressed upon the high frequency deflecting plates of the cathode ray tube. When the impulse Wave is employed for controlling the high frequency deflection of the cathode ray beam, it directly controls the production of the sawtooth wave which is impressed upon the high frequency deflecting plates.

For controlling the low frequency deection of the cathode ray image producing tube, a voltage impulse is generated once per revolution of the scanning disc by a circuit closed through an insulated conducting segment of the scanning disc drive shaft. These impulses control a vacuum tube circuit for quickly charging a condenser which has been previously discharged at a constantlrate. The voltage across this condenser is amplified by a vacuum tube circuit connected to the low frequency deecting plates for causing the potential on one plate to increase while that on the other plate decreases and vice versa. These impulses are also utilized for causing the multiplying power of the image electron multiplier to be periodically greatly reduced,

thus causing the transmission of current corresponding to black tone value at the end of each picture frame. This results in blanking out the low frequency return sweep of the cathode beam of the receiver in going from the last line to the rst line of the image.

The invention may be better understood from the following description with reference to the accompanying drawings, in which Figs. 1, 2 and 3, if placed side by side in order with Fig. 1 to the left, constitute a schematic showing of a complete television system, Fig. 1 showing a portion of the apparatus in perspective Fig. l-A is a schematic view of a portion of the apparatus shown on Fig. 1;

Fig. 4 is an enlarged plan view, partly in section, of a portion of the apparatus shown in Fig. 1; and

Figs. to 8, inclusive, are curves which will be referred to in explaining the operation of the system,

Referring to thedrawings, the metallic scanning disc I0, about six feet in diameter and carrying 240 equally spaced compound scanning lenses I I arranged along a circular path near the periphery of the disc, is driven at a rate of 24 revolutions per second by a horsepower direct current motor I2 through a shaft I3. Since the lenses in succession scan the eld along successive substantially straight linear paths, 5760 lines are scanned per second. 'I'he disc is enclosed in a casing I4 to avoid accidental contact with the disc and also to reduce air resistance. The sound motion picture film I5 which is to be scanned to produce a television image current and a current corresponding to the accompanying sound effects is fed from the storage reel I6 over roller II past a light transmitting aperture in housing I4 through which the picture portions of the film are scanned, past rollers I8 and I9 to the sprocket wheel which continually unwinds the nlm from the storage reel I 6 at the rate of one frame for each rotation of the scanning disc. 'I'he sprocket wheel is mechanically connected to the shaft 51 through gears 2|, 22 and the universal connection 23. The shaft 51 may be connected to the shaft I3 at a desired time, preferably after the disc I0 has been brought to speed, by means of the electromagnetic clutch 58 the winding of which may be energized by the closure of switch 59. The iilm then moves through the sound pick-up apparatus, the film being driven by sprocket 24 which is connected to the shaft 51 by the gears 28 and 29 and the universal coupling 30. The lm is then wound up upon a storage reel 2'I which is driven through friction clutch 3| and belt drive from shaft 26 which connects the sprocket wheel 24 with the gears 29. The roller I9 is mounted upon an arm 32 at one end thereof, which arm is movable about a fulcrum 33. The other end of arm 32 may be secured to support 34 by a thumb screw 35. By adjusting the arm 32, the position of the film I5 may be adjusted so that a certain lens of the scanning disc will scan the rst line of the frame of a motion picture film. This adjustment is necessary so that theL "frame" or low frequency synchronizing impulses, which are generated once per revolution of the scanning disc when the disc is in a certain position, may occur between the scanning of successive picture frames.

For scannnig the motion picture film light from source 36 after passing through lenses 31 is directed in a convergent beam upon an aperture .03 inch square in aperture plate 38. The divergent beam transmitted through the aperture in plate 38 reaching the collimating lens 39 is transmitted thence in a beam of parallel rays through which the lenses I I of the scanning disc pass in succession. Each compound lens II of the scanning'disc comprising two plano-convex lenses mounted as shown in Fig. 4, has a short focal length and produces an image .003 inch square of the aperture in plate 38 upon the film I5 which moves in close proximity to the housing I4. As the disc rotates, the light beam projected by one lens will trace a path .003 inch wide across the lm, the light beam projected by the next lens will trace a contiguous .003 inch a light conducting tube or light tunnel 40, this end of the light tunnel being positioned close to the portion of the lm which is being illuminated. The light conducting tube may be made of a material such as glass or quartz, but is preferably made of a material known as "pontalite", which is not brittle and which is a better light conductor than glass. The width of the light conductor in the direction of the scanning lines is "/8 inch and its thickness is inch. An electron multiplier 44 of the type disclosed in U. S. Patent No. 2,160,796, granted to G. K. Teal, May 30, 1939, for example, is positioned adjacent to the opposite end of the light tunnel, so that the light emerging from the' light tunnel will reach the primary cathode 300 thereof. The electron multiplier plates 300 to 309, inclusive, are connected to a suitable source of electromotive force such as the rectifier 3|0 and battery 3H, such 'that each secondary cathode is operated at a positive potential with respect to that of the primary cathode and such that the potential applied to each secondary cathode is greater than that applied to the next preceding secondary cathode, as shown and described in said Teal patent, supra. The rectifier is shunted by the voltage dividing resistive elements 3|2 in series each shunted by a small condenser 8|3. The

positive terminal of the rectier 3|0 is connected to the negative terminal of battery 3| the positive terminal of the battery being grounded. Diierent points of battery 3|| are connected to

secondary electrodes

308 and 309, grid 3M, and anode 3|5 through different resistive .elements 3|6, 3|1, 3|8 and 3|9, respectively. A condenser 320 connects

electrodes

308 and 309. The image current in the anode circuit of the electron multiplier 44 flows through the resistive element 3|9 which is connected directly to the input circuit of modulator 46, the latter being supplied with a carrier current from source 41. The modulated carrier current from modulator 46 is transmitted The opening in casing I4 through which the scanning light beam from source 36 passes is so dimensioned that the light beam is cut o for a short period at the end of each scanning line. As a result the cathode ray beam of the receiver will be extinguished or reduced in intensity during the return sweep of the cathode beam occurring between` scanning lines.

There is also provided an image producing receiving apparatus comprising a cathode ray tube 50 of the type disclosed in U. S. Patent No. 2,169,179, granted to F, Gray, August 8, 1939, which may be used for monitoring purposes. The tube 50 is provided with a cathode 5|, a grid 52, an anode 53, high frequency deflecting plates 54 and low frequency deecting plates 55,` While the carrier modulated image current from source 46 may be demodulated and the demodulated current supplied to the grid-cathode circuit of tube 50, for monitoring purposes it is satisfactory to amplify the image current 4by an alternating current amplifier 56, thereby suppressing the direct component of the image current. The output of amplifier I6 is impressed upon the grid-cathode circuit of cathode ray tube 60. f v

The electron multiplier 60 is `provided for generating synchronizing impulses, one for each scanning line, under control of iight transmitted through the scanning disc lenses. y Light from source 6| is focussed by lenses 63 upon the screen 4having a narrow light transmitting aperture therein. The eollimating lens 64 directs the beam in parallel rays upon the scanning disc and each scanning disc lens |l directs the .beam through a narrow slot in the adjustable screen 65-upcn one end oi' a light conducting tube 66, similar tothe tube 40. The other end of the light tunnel is adjacent to the primary cathode 10 of the electron multiplier 60. A rectifier 61, energized from a 60cycle power source, supplies current at 1350 volts to the series connected resistive elements 68 across which condenser 69 of small ca-` pacity vare connected. The negative terminal of the rectifier is connected to the primary cathode of the' electron multiplier. The secondary cathodes 1| of the electron multiplier are all supplied with voltage from the rectifier 61. This is con' trary to the usual television practice when using electron multipliers for generating television signals. 'I'he arrangement shown gives good regulation because the electron current is being delivered over extremely short periods of time compared with the line scanning period and the condensers 69 do not have time to discharge appreciably, Battery 12 supplies potential to the screen grid |51 and to the anode |58 of tube 60, the

, anode current flowing through resistive element 13. The output circuit of the electron multiplier is connected to an amplifier comprising thermionic tube 15 through a condenser 16 by a lead from the resistive element 13 one of the input terminals of the amplifier and the positive terminal of rectifier 61 being grounded. If desired,

. the screen grid |51 and the anode |58 of the electron multiplier may also be supplied with potential from the rectifier 61. 'I'he amplifier includes a resistive element 11 of .5 megohm connected in its input circuit and anode current is supplied by battery 18 of 200 volts flowing through resistive element 19 of .01 megohm. Anode current owing through resistive element of 2500 ohmswbiases the grid of the tube with respect to the cathode so as to cut off the peaks of the impulses produced by the electron multiplier 60 and thus limit the impulses to a constant amplitude, the resistive element 80 being shunted by a 50 microfarad condenser 8|.

The output circuit of amplifier tube 15 is connected to the input circuit of the three-electrode gas-filled tube 82, through condenser element 83 of .02 microfarad. Across the input circuit is connected the grid biasing battery 84 and resistive element 85 of .25 megohm in series Anode potential is supplied to tube 82 by battery 86 of volts, which is connected to the anode through variable resistive element 81 having a maximum value of .1 megohm. Also connected across the output circuit of tube 82 are a condenser 88 of .0005 microfarad and a resistive element 89of 50,000 ohms. The condenser 88 is charged by current from battery 86 and quickly discharged through the anode circuit of gas-lled tube 82 when a synchronizing` impulse is impressed upon its g'rid.

Across the resistive element 89 of the condenser charging-discharging circuit are connected the input circuits of three power amplier tubes 9|.

synchronizing current from and |03, respectively,

' 92 and 93 connected inparalll.

is supplied tothe tubes by battery or rectifier 94 of 450 volts, the positive fterminal of. which is connected to theanodes of tubes 9| 92 and 93 through choke coils k95, 96 and 9 1,` respectively.

The resistive element 396 shunted by.condenser-f` age reaches a certainamplitude,v the tube's are 391 connected in the, anode-cathode Icircuits of the tubes, supplies biasing potential to thegrids thereof. The output circuits of tubes 9|, 92 and 93 are connected through condensers |0|, |02 to the primary windings of transformers |04, |05 and |06, respectively. The secondary winding of transformer |04 is connectedto the input circuit of band-pass filter V| |0 for transmitting the fundamental frequency of 5760 cycles of the synchronizing wave and the output circuit of the filter ||0l is connected through a transformer to the input. circuit of modulator ||2, which is supplied withcarrier current from source ||3, The carrier modulated modulator |2 is transmitted over the coaxial conductor cable 48 to the distant receiver 49.

The 5760 cycle sine wave current from the output circuit of filter ||0 may also be utilized for controlling the high frequency deflection of the cathode beam of tube 50. For this purpose the output of filter 0 is connected to the adjustable phase shifter ||4 having the two parallel branches, one consisting of inductive element |5 and resistive element ||6 and the other consisting of capacitive element ||1 and resistive element' I8. The phase of the current transmitted by the phase shifter may be varied by turning the arm ||9 about its axis, this arm carrying a brush |20 in slidable engagement with resistive element ||8 and brush|2| in slidable engagement with resistive element I6. The brushes |20 and |2| are connected, respectively, to the terminals of the primary winding of transformer |22 having two secondary windings |23 and |24. The impedance looking into the pri- `mary winding of transformer |22 is preferably high compared with the resistance of element |8. The resistance of elements ||6 and ||8 are each made equal to the square root of the ratio of the inductance of element |5 to the capacity of condenser ||1. Under these conditions the impedance looldng into the network from lter |0 will be a constant resistance. The windings |23 and |24 are connected to 'a circuit comprising vacuum tubes |25 and |26 for converting the impressed sine wave into a square-topped wave. A battery |21 and a resistive element |28 are connected in the anode circuit of the vacuum tube |25 and a battery |20 and a resistive element |30 are connected in the anode circuit of tube |26. One terminal of transformer winding |23 is connected to the grid of tube |26 and the other terminal through an adjustable contact to resistive element |28. One terminal of winding |24 is connected to the grid of tube |25 and the other terminal is connected through an adjustable contact to resistive element |30. The cathodes of tubes |25 and |26 are conductively connected. The cir- `cuit arrangement is such that when current flows in the anode circuit of one of the tubes |25, for example, the other tube |26 becomes blocked because of the negative bias applied to its grid due to the drop across the portion of resistive element |28 which is connected to the input circuit of tube 26. The transformer windings |23 and |24 apply potentials to the input circuits of tubes |25 and |26 necessary to unblock one tube and, as a result, to block the other tube. 'I'he transformer windings are connected to the iny put circuits` so that, when av small negative sigcaused to reverse condition, the unblocked tube being blocked and the blocked tube being unblocked. As a result, square-topped voltage impulses, one for each cycle of the 5760 cycle alternating current from the output of filter 0 are produced across the resistive element 28.

The circuit comprising vacuum tubes 3|, |32 and |33 is controlled by the square-topped wave to produce across the .0005 rnicrofarad variable condenser |34 a saw-tooth voltage wave which is utilized to control the high frequency deflection of thecathode beam produced in tube 50 at the line scanning frequency of 5760 cycles. The two grids of tube |3| are biased by batteries |35 and I 36, respectively to potentials such that the anode current remains constant over a wide range of anode potentials. The condenser |34, after having been charged, is thus discharged at a substantially cons-tant rate through the anode-cathode circuit of tube |3|.

'I'he potential across condenser pressed through condenser 210 across the gridcathode circuit of vacuum tube 21| which is biased through resistive element 212 by battery 213. Anode current from the rectifier 214, energized from a 60-cycle power source, is supplied to the anode circuit of tube 21| through resistive clement 215 of 10,000 ohms. A portion of the resistive element 215, having about 1/10 of the total resistance of this element, is connected across the input circuit of vacuum tube 216 through condenser 211, having the same capacity as condenser 210. The grid-cathode circuit of tube 216 is biased by battery 218, the same as battery 213, through resistive element 219 of the same value as resistive element 212` Anode current is supplied to the anode circuit of tube 216 by rectifier 214 through resistive element 280 of 10,000 ohms. The tubes 21| and 216 are of the same type, each |34 is im- Consequently,

having an amplidcation factor of about |0. As the condenser |34 discharges, the potential 'at the anode of tube 21| increases with respect to ground at a certain rate and the potential at the anode of tube 216 decreases with respect to ground at the same rate. The anode of tube 21 is connected through condenser 28| to one of deection plates 54 and the anode of tube 216 is connectedof the other plate 54 is decreasing with respectv 1 to the potential of the anode 53. Loss of focus of the cathode beam is thus avoided. The -cycle and 12o-cycle components of the current from the rectifier 214 are amplified by the tube 216 and impressed upon one of the high frequency deiiector plates 54. This results in a scarcely noticeable irregularity in the edges of the image produced by the cathode ray tube. The advantage of the arrangement shown is that the resistance .of the portion of resistive element 215 connected to the input of tube 216 is small compared to the grid-cathode impedance of the tube 216 even at some of the higher harmonic frequencies of the 5760 cycle saw-tooth Wave. If this were not the case, the saw-tooth `wave would be rounded at one peak and sharpened at the other due to the suppression and phase shifting of high frequency components, and the image would appear ytoo u bright at one edge and too dark at the other edge.

For setting up low frequency synchronizing impulses at the frame scanning rate of 24 per second, there is provided on the scanning disc drive shaft |3, a commutator comprising a conducting segment |60 imbedded in insulating material designated by the numeral I6 For a short period during each revolutionof the scanning disc, the brushes |62 and |63 complete a circuit including 9-volt batteryV |64 and resistive element of 2 megohms. The condenser |80 of .1 microfarad is normally charged due to voltage applied to it from a portion of battery |61 and b at tery |1| through a circuit including potentiometer |12, resistive element |13 of 2 megohms and resistive element |65 of 2 megohms. When the battery |64 is connected across resistive element |65 by the conducting segment |60, condenser |80 is partially discharged and, as a result, a negative impulse is impressed upon the control grid of vacuum tube |14 through resistiveelement |15 of l megohm.' The anode current from source |61 iiowing through resistive element |16 and the anode-'cathode circuit of tube |14`is thus decreased. The resistive element |16 and battery |61 being connected across the control grid-cathodecircuit of vacuum tube |11 through condenser |66, a positive impulse is impressed upon the control grid of tube |11 due to the decrease in anode current in the tube |14. The tube |11 consequently draws anode current and the condenser |66 of .04

microfarad is charged by current from battery |61 through the anode-cathode circuit of tube |11, including resistive element |19 of 2000 ohms. The anode of tube |11 is connected through condenser |18 to the control grid of tube |14 to feed back a negative impulse to the control grid of tube |14 to accelerate the action of the circuit in charging condenser |68. The condensenafter being charged, is discharged at a constant rate through the anode-cathode circuit of the vacuum tube |68 to which the condenser is connected, the grids of the tube |68 being biased by batteries |69 and |10 to give a substantially constant anode current over a Wide range of anode potentials.

-the anode current from rectier |82 of 1500 volts,

energized from a 60-cycle power source, flowing through resistive element |83 of 10,000 ohms decreases. Across the resistive element v|83 and rectier |82 are connected in series condenser |86 of 1 microfarad, resistive element |89 of 10 megohms and battery |88 of 61 volts. The grid-cathode circuit of vacuum' tube |81 is connected across a, circuit consisting of a portionnfy resistive element |89 of 0.1 megohm and battery |88. Anode current is supplied to tube |81 from rectier |82 through resistive element |90. The anode of tube |8| is connected through condenser |92 to one of the low frequency deiector plates 55 and the anode of tube |81 is connected through condenser |9| to the other of the deflecting plates 55. Across the plates 55 are connected two 10 megohm resistive elements |84 and |85 in series, the common terminal of the resistive elements being connected to the anode 53 of cathode ray tube 50.

There is thus applied across the deflector plates 55 a saw-toothed voltage wave similar to the wave produced across condenser |66 but amplied. 'I'he shunting effect of the grid-cathode impedance of tube |81 at the higher harmonics of the Zi-cycle saw-tooth wave is 'insuiicient to appreciably distort the wave. It is important that the amplitude of the 60cyc1e and l1Z0-cycle components from rectiiier |82 impressed upon the input circuit of tube |81 be of very low value because the presence of a 60-cycle or 1Z0-cycle voltage component across .low frequency deecting plates 55 would cause the spacing of the scanning i ponents across the portion of resistive element |89 connected across the input of tube |81 is about one-tenth of its amplitude at the anode of tube IBI, and, although tube |81, as well as tube |8l, has an amplication factor of 10, the potential of the Gli-cycle component at the anode of tube |81 is small.

'I'he positive impulse produced at the anode of vacuum tube |14 due to the closure of a circuit through contact |60 is also impressedupon the control grid 336 of tube 330 through blocking condenser 33| and resistive element 332 to cause a large decrease in the sensitivity of electron multiplier 44 at the end of the scanning of each picture frame. As a result the image current owing through resistive y'element 3|9 is greatly reduced for a short period between the scanning periods of succeeding frames and the cathode ray beam of the image producing tube is extinguished or substantially extinguished during this period. The cathode 333 and grid 33d are connected to the negative terminal of battery 3| I, the grid 335 is positively biased by a portion of battery 3|| and the grid 336 is negatively biased by battery 331 through resistive element 338. The tube 330 normally draws no anode current. When a positive impulse is impressed upon grid 336 from tube |14,

current from a portion of battery 3H flows through resistive element 3|1 and the anodecathode circuit of tube 330. As a result, the potential applied to

electrodes

308 and 309 decreases almost to the potential of electrode 301. 'Ihe multiplying power of

electrodes

308 and 309 is thus greatly reduced and the current flowing through resistive element 3 I 9 is greatly decreased. Due to the capacity between the anode 3|5 and the leads from

electrodes

308 and 309, a spurious negative impulse was found to be set up at the anode 3|5 due to decrease in potential of

plates

308 and 309 caused by the impulse from tube |14. This spurious impulse is neutralized by a positive impulse from tube |14 impressed upon the grid 3|4 through neutralizing condenser 340.

The end portion of brush |62 is slotted and secured to the insulating block 360 by means of a thumb screw 36| thus making brush |52 adjustable. Successive frames of the motion picture nlm I5 may overlap somewhat or there may be a blank interval or frame line between the bottom line of one frame and the top line of the next frame which may be designated as underlap. For example, the maximum overlap or underlap, as the case may be, may be the width of ve scanning lines. In this case the brush is preferably adjusted so that a circuit is closed through the brushes |62 and |63 and the conducting segment |60 for a period equal to the time required for scanning five scanning lines. The image current is thus reduced to a low value or zero so that the overlap or underlap portions of the lm will not be produced at the receiver.

The 10 horsepower direct current driving motor I2 has a series field winding 200, which is energized by current from source 20| through a starting resistive element 202, and a shunt .field winding 203. 'I'he speed of the motor may be controlled by manually adjusting the variable resistive element 204 to control the current in the shunt eld winding.

It is desirable to maintain the motor at a substantially constant speed for the following reasons: Phase equalizers, not shown in the drawing, are employed for eliminating phase distortion of the television image current over the required frequency range when the pictures are scanned at the rate of 5760 lines per second. The equalizers are not designed for operating over the increased frequency range which would need to be transmitted if the speed of the disc were increased by a substantial amount. The television vcurrent transmission channel is designed t) transmit a certain frequency band and if the speed of the scanning disc is increased substantially above 24 revolutions per second, the frequency range required for image production may extend beyond the range which the transmission channel is designed to transmit. Moreover, if the speed of the scanning discv varied appreciably, the frequency of, and therefore the propagation velocity of, the transmitted synchronizing current would vary sufficiently to cause the image at the receiver to move out of frame. The motor I 2 is therefore maintained at a substantially constant speed (24301 revolutions per second) under control of current from the tuning forkcontrolled oscillator 205, generating constant frequency current of 5760 cycles, supplied to the primary winding of transformer 206 and current, the frequency of which is controlled in accordance with the speed of scanning disc I4, supplied to the primary winding of transformer |06, the frequency of this current being 5760- 6-23 cycles. The

Vacuum tubes

201 and 208 with their associated circuits constitute a balanced modulator and vacuum tubes 209 and 2I0 with their associated circuits constitute a second balanced modulator. The variable frequency source is applied to the input circuits of

tubes

201, 208, 209 and 2I0 in phase. 'I'he voltage of constant frequency source 205 is applied to the input circuits of tubes 201 and'208 in phase opposition. The bridge circuit comprising resistive elements 2|| and 2| 2, each of .1 megohm, and the condensers 2|3 and 2I4 each of .0003 microfarad is employed for shifting the phase of the voltage from source 205 applied to the input circuits of tubes 209 and 2I0, so that the voltages from source 205 applied to tubes 209 and 2I0, respectively, will be 180 degrees out of phase with respect to each other but degrees out of phase with respect to the voltages from source 205 applied to

tubes

201 and 208. The four-phase synchronous motor 2|5 having stator windings 2|6, 2|1, 2|8 and 2|9, is driven by the difference frequency output currents from

modulator tubes

201, 208, 209 and 2I0 in one direction or the other, depending upon whether the frequency of the current from transformer |06 is higher or lower than that of the constant frequency source 205. The higher frequency components of the modulated currents are shunted out by the 2-microfarad condensers 220, 22|, 222 and 223. Anode potential for tubes 201. 208, 209 and 2I0 is provided by grounded battery 225 and the potential drop across the G-ohm resistiveV element 226 shunted by the 2-microfarad condenser 221, connected in the anodecathode circuits provides biasing potential for the grids of tubes 201 to 2| 0 inclusive.

The motor 2|5 drives, through suitable speedreducing gears 230, a shaft carrying contact arm 23| for opening or closing contact 232 in accordance with the direction of rotation of the motor 2|5, and a shaft carrying an arm 233 for continuously varying the resistance of variable resistive element 234 in one direction or the other in accordance with the direction of rotation of motor 2|5. When the switch 235 is closed to its upper contact, as shown in the drawing, the manually adjustable resistive element 236 is connected in circuit with the shunt field winding 203 of motor I2 and, when the contact 232 is closed, the resistive element 231 shunts the resistive element 236. Thus when the motor |2 is moving too fast and the frequency of the current supplied to transformer |06 is greater than 5760 cycles, the motor 2|6 -rotates in a direction to close contact 232 and thus cause the speed of motor I2 to decrease and vice versa. With this arrangement the scanning disc motor was found to hunt at a low frequency of about 1.5 cycles per second. This hunting can be eliminated by throwing the switch 235 to its lower position to connect the variable resistive element 234 in series with the shunt field winding 203. Withy this arrangement, when the speed of motor `I2 is too high, the motor 2 I5 will run in a direction to decrease the resista-nce of resistive element 234,- causing motor I2 to slow down, and vice versa.

The sound track of the motion picture film I5 is scanned by the usual sound pick-up apparatus comprising a light source 250 and a photoelectric cell The photoelectric cell is connected through amplifier 252 to a monitoring loudspeaker 255. The output of amplifier. 252 is also connected to a modulator 256 supplied with. carrier current from source 251 and the output of the modulator is transmittedover the coaxial conductor cable 46 to the distant receiver 49. At the distant receiver 49, vthere are provided apparatus 260 for demodulating the image modulated carrier current from modulator 46. apparatus 26| for demodulating the synchronizing modulatedcarrier current frommodulator II2 and the apparatus 262 for demodulating the sound modulated carrier current from modulator 256. The sound current from demodulator 262 is supplied to a loudspeaker 263 and the image current from demodulator 260 is supplied to the appropriate electrodes of cathode ray tube' 264. The beam deiiecting electrodes of the cathode ray tube are controlled by apparatus 265, which in turn is controlled by the synchronizing current from demodulator 26|. The sweep control apparatus 265 may include a subharmonic generator for deriving a 24-cycle low frequency synchronizing current from the 5760 cycle high frequency synchronizing current and saw-tooth wave generators similar to those employed for controlling the potentials impressed upon the

delector plates

54 and 55 of the cathode ray image producing device 50.

The curves of Figs. 5 to 8 inclusive, type of wave produced under control of the light beam from source 6| directed upon the electron multiplier 60.

Fig. 5 shows the type of synchronizing impulses produced across the resistive element 13 and impressed upon the grid of amplifier 15. These impulses are of non-uniform amplitude due to differences in light transmitting ability of different lenses, respectively, and, while not apparent from the drawing, are slightly irregular in occurrence due to slight irregularities in the positioning of lens Il. Y

Fig. 6 shows the constant amplitude impulses measured across the circuit consisting of resistive element 19 and battery 18 in series.

Fig. '7 shows the voltage wave produced across the resistive element 89 due to the alternate charging and discharging of condenser 80.

Fig. 8 shows the sine wave alternating voltage measured across the output of filter IIO.

To obtain a small image of the illuminated aperture 38 upon the film I 5, scanning disc lenses I! having a short focal length are employed and theillm is ypositionedto move in close proximity to the housing I4. It is impossible with this arrangement to direct light from another source 6I through a certain lens, at the time that it is in position to commence the scanning of. a linear deprcthe portion of a picture frame, 'to an electron multiplier 60. to-set up synchronizing impulses for controlling the deection of the cathode beam of cathode ray tube 50 to return the cathode beam to position for commencing the scanning of a' this arrangement, due to slight irregularities in the positioning of the lenses II, there would be expected to occur phase variations between the time of commencement of scanning of a line and the time of production of a synchronizing impulse, thus causing the return sweep of the cathode beam of tube 50 to occur too soon at times and toolate at other times with respect to the occurrence of the image current impulses corresponding to the first scanned elemental areas -of the linear portion of the picture. To avoid such an occurrence, the delay network |5I is provided and the aperture plate 65 is made 'adjustable. In setting up the system for operation, such'a number of delay sections of network I5I are connected in circuit that the time delay introduced by vthe network is approximately equal to the time which elapses between the time of producing a synchronizing impulse by a certain lens II and the time of commencement of scanning of the picture frame by said lens. For example, if this interval is equal to the time required for scanning three lines of the picture frame, the network is adjusted to give a delay of approximately %760 second. It can be determined by observing the image produced by the cathode ray tube 50 (the switch |38 closing the circuit to contact |50) whether the delay introduced is too large or too small. If the delay introduced is too small, Aan accurate adjustment can be made by moving the aperture plate 65 in the direction of movement of the lenses II, and vice versa. When this adjustment has been made, thel time delay introduced by network I 5| will be equal to the interval between the production of a synchronizing impulse by a certain lens and the time of commencement of scanning a linear portion of the picture frame by said lens. When the sine wave synchronizing current from filter ||0 is employed for controlling the high frequency deflection. of the cathode beam of the irnage producing device 50 (switch |38 being in the position shown) the phase shifter II4 is ad- Ijusted to bring the image current and the high frequency 'deiiecting impulses into proper time relationship.

If desired, the synchronizing impulses from the secondary of transformer |53 may be transmitted to the ,distant receiver 49, instead of the sine wave current from filter I I0 for controlling the high frequency deection of the .cathode beam of the image producing device at that station. In that case, it may be found necessary to introduce an additional delay in the image current channel or the synchronizing channel to compensate for differences of delay in the transmission of the synchronizing and television currents, respectively, by the respective channels. Moreover,l if desired, high amplitude synchronizing impulses of brief duration, such as those produced in the output circuit of ampliertube 15,

compensated for by What is claimed is:

l. Television apparatus comprising means including a rotatable scanning device carrying a plurality of light directing elements for scanning the elemental areas in succession along Successive parallel lines of a neld of view to produce a television image current, means including said scanning device for generating synchronizing impulses in succession under control of light received from successive light directing elements,

each light directing element controlling the promotion picture film, light sensitive electric means for receiving light from the illuminated elemental areas to produce a television image current, a second light sensitive electric means, a second light source from which light is directed through said lenses in succession to said second light sensitive means to produce electric synchronizing impulses, means for delaying the transmission of said impulses, and an adjustable member having an aperture therein positioned in the light path between said second light source and said second light sensitive means, said member being adjusted to a position such that the delay occurring between the time that a synchronizing impulse is generated by light transmitted through a certain lens and the time of commencement of scanning of a linear portion of the motion picture film frame by light directed through said lens is the delay introduced by said delay means.

3. In a television system, a rotatable disc having mounted thereon a plurality of lenses, means comprising said rotatable' disc for scanning a field of view along successive linear paths to produce a television image current, means for generating synchronizing impulses comprising means for directing light through said lenses in succession, light being directed through each lens prior to the time that said lens is utilized for scanning, and means for compensating for irregularities in the positioning of said lenses comprising means for delaying the transmission of each synchronizing impulse to compensate for the time elapsing between the time of generation of an impulse under control of light transmitted through a certain lens and the time of commencement of scanning of a linear portion of the field of view by said lens.

4. In the method of television image transmission in which the line deflection of a cathode ray beam of an image producing device is under control of synchronizing impulses generated at a transmitter and in which the synchronizing impulse for returning the cathode beam to the position for commencement of scanning of a certain line is generated at the transmitter at least a considerable portion of a line scanning period prior to the commencement of scanning of said line at the transmitter, the step of delaying the transmission of the synchronizing impulse to compensate for the time interval occurring be'- tween the generation of the synchronizing impulse and the time of commencement of scanning said line at the transmitter, thereby compensating for variations in the intervals between successively generated synchronizingimpulses.

5. The method of image transmission which comprises the steps of deflecting a cathode ray beam of an image producing device under control of synchronizing impulses, scanning a field of view line by line to produce an image current, generating a synchronizing impulse for returning the vcathode beam to the position for lcommencement of scanning of a certain line prior to the commencement of scanning of said line at the transmitter by a period equal to at least a considerable Aportion of a line scanning period and delaying the transmission of the synchronizing impulses to compensate for variations in the periods between successively generated synchronizing impulses.

6. In a television system, means including a rotatable scanning device having a plurality of light transmitting apertures for scanning a field of view, a moto-r for driving said rotatable scanning device, a light sensitive electric device, means for directing light tlnough said apertures in succession to said light sensitive electric device to produce current impulses in succession, a source of constant frequency alternating current, and means responsive jointly to said current im` pulses and said constant frequency alternating current for controlling the speed of said motor.

7. In a television system, means including a rotatable scanning device having a plurality of light transmitting lenses for scanning a ileld of view, a motor for driving said rotatable scanning device, a source of light, a light sensitive electric device controlled by light from said source directed through said lenses in succession for generating current impulses in succession, said impulses varying in amplitude somewhat due to variations in the light transmission ability of said lenses, means for converting said current impulses into recurrent current impulses of fixed amplitude, an independent source of constant frequency alternating current, and means responsive jointly to said fixed amplitude current impulses and to current from said source of constant frequency current for maintaining the speed of said driving motor substantially constant.

8. In a television system, apparatus for scanning a field of view, means for generating synchronizing impulses in succession at a rate determined by the speed of scanning the field of view, said impulses varying somewhat in amplitude, means for converting said synchronizing impulses into a sine Wave alternating current of substantially constant amplitude, image producing apparatus, and means under control of said alternating current for maintaining said image scanning and said image producing apparatus in synchronism.

9. A television system comprising means including a rotatable lens disc for scanning a field of view to produce 'a television image current, image producing apparatus under control of said image current, an electron multiplier, means for directing light through the lenses in said disc in succession to said electron multiplier to produce recurring synchronizing impulses, the amamasar current for charging said condenser, a gas-iilled electric discharge device controlled by said amplified impulses for periodically discharging said condenser, means lfor amplifying said condenser charging and discharging current, `a filter for transmitting only the fundamental frequency of -the current from said last-mentioned ampliiler,

thereby producing a constant amplitude sine wave alternating current, and means controlled by said alternating current for maintaining the l production 'of the image in synchronism with the scanning of the eld of view.

10. In combination, means for scanning the elemental areas of a fleldof view line by line to produce an image current, a light sensitive electric device, means for directing a light beam upon said device, for a period which is short compared to a line scanning period, prior to the time of commencement of scanning of a predetermined line of the eld of view, a cathode ray image producing device, and means for controlling the deection of the cathode ray beam of said image producing device, said last-mentioned means comprising means for producing under control of.

said light sensitive device electric synchronizing impulses, and means for delaying said impulses for a period to compensate for the interval which occurs between the time that said light beam activates said light sensitive device and the time -of commencement of scanning of said line.

11. In combination, an electron multiplier having a primary cathode, a plurality of secondary cathodes and an anode, an output circuit therefor, means for directing light of varying intensity upon said primary cathode to produce current of varying amplitude in said output circuit, a circuit having a normally high impedance connected between two of said secondary cathodes, and means /for periodically reducing the impedance of said circuit to decrease the sensitivity of said electron multiplier.

12. In combination, an electron multiplier having a plurality of electrodes comprising a primary cathode, a plurality of secondary cathodes and an anode, an output circuit therefor con'- nected between said anode and one of said sec-,.

1means for periodically applying an impulse to said control electrode-cathode circuit to,reduce the anode-cathode impedance of said electric discharge device thereby greatly reducing the sensitivity of said electron multiplier.

13. In combination, an electron multiplier having a plurality of electrodes comprising a primary cathode, an anode and a plurality of sec, ondary cathodes at different positions respectively, between said primary cathode and said anode, means for applying to each of said secondary cathodes and to said anode a positive po tential with respect to the potential of said pri-` mary cathode, the potential applied to each secondary cathode and to said anode being greater than the potential'applied to the next precedingI cathode, means for producing periodically recur? ring voltage impulses, and means .under control of said impulses for reducing the potential differy to reduce the amplitude of said image current.

15. In a television system, means including a light sensitive'electronic device for setting up a unidirectional image current having amplitude variations corresponding .to the tone values of elemental areas in succession of a field of view, an image of which is to be produced, means for producing periodically recurring voltage impulses, and means under control `of said impulses for periodically reducing the sensitivity of said electronic device to reduce the amplitude of said image current.

16. A television system comprising means including a light sensitive electric device for setting up a unidirectional image current having ampli,- tude variations corresponding to the tone-values of elemental areas in succession of a field of view, an image of which is to be produced, means including a cathode ray device under control of said image current for setting up animage, said device including means for producing a cathode ray beam, means for producing periodically recurring voltage impulses, means under control of said impulses for controlling in part at least the deection of said cathode ray beam, and means under control of. saidimpulses for periodically changing the sensitivity of said light sensitive electric device to change correspondingly the amplitude of said image current.

17. A television system comprising means at a transmitting station for scanning the elemental areas in succession along successive linear paths of a eld of view to set up ai television image current, a cathode ray image producing device at a receiving station under control of said image current for setting up an image of said field of view including means for producing a cathode beam and means for deflecting the beam at a substantially uniform rate from a first side of the image field to the second side and more rapidly from the second side back to the rst side, means for producing a continuous substantially sine Wave constant amplitude current at said transmitting station for transmission to said receiving station for controlling said deiiecting means, and means for causing a reduction in the amplitude ofsaid image current for a brief period between the scannings of successive lines to obliterate the cathode ray beam during its return movement from the end of one line to the beginning of the next line.

18'. The combination with television scanning apparatus comprising means for continuously moving a motion picture iilm at a uniform rate and means for scanning all portions of said lm in transverse elemental lines while it is moving to set up image currents representativeA of the vscanned lines, of means for generating electrical synchronizing impulses and means under control of said impulses for substantially suppressing such portions of said current as are not already `substantially zero between the scanning of successive frames for at least several line scanning periods. 1

19.'The combination of claim 18 in which said scanning means comprises an electron multiplier :for setting up the image current and said suppressing means comprises means for applying a periodic voltage to said multiplier under control of said synchronizing impulses.

20. In combination, an electron multiplier having a primary cathode, a plurality of secondary cathodes and an anode, an output circuit therefor, and means for applying a varying potential to at least one of said secondary cathodes with respect to said primary cathode for controlling the current in saidvoutput circuit.

21. In combination, a light sensitive electron multiplier tube, means for causing light to' impinge upon said tube intermittently for generating electrical impulses, a gas-filled electric discharge device having a control circuit and an anode circuit and means for impressing said impulses upon said control circuit for causing current to flow in said anode circuit.

22. A signaling system comprising a light sensitive electron multiplier tube, an output circuit therefor, means for directing a modulated light beam upon said tube to produce a unidirectional signaling current in said output circuit, means for modulating alternating carrier current in accordance with variations of said unidirectional current, and means for directly conductively connecting said output circuit to said modulating means.

23. A television system comprising means including a movable scanning device having light directing apertures through which light is directed for scanning a field of view to produce a television image current, image producing apparatus under control of said image current, a light sensitive electronic device, means for directing light through the apertures in said scanning device in succession to said light sensitive device to produce recurring synchronizing impulses the amplitude of which may vary, means under control of said synchronizing impulses for producing a constant amplitude sine wave alternating current, and means controlled by said alternating current for maintaining the production of the image in synchronism With the scanning of the eld of view. 24. In combination, means including a light source and a light sensitive device for generating recurring electric impulses the amplitude of which may vary, a condenser, means under control of said impulses for causing said condenser to be charged and discharged alternately, and means under control .of said condenser chargingdischarging current for producing a constant amplitude sine wave alternating current.

WILLIAM A. KNOOP.