US2450649A - Facsimile synchronizing system - Google Patents

Description

Oct. 5, 1948. w. G. H. FINCH 2,450,649

FACSIMILE SYNCHRONIZING SYSTEM 4 Sheets-Sheet 1 Filed Feb. 16, 1944.

32d PICTURE 8 SYNCH.

AMPLIFIER AMPLIFIER CHANNEL -33 OSCILLATOR TRANSLATOR CARRIER -37 OSCILLATOR Mom/TOR FIG. 36

POWER AMPLIFIER INVENTOR.

WILLIAM G. H. F/NCH T0 TELEPHONE BY LINES 0R R.f-'. W

TRANSMITTER u/v/ ATTORNEY Oct. 5, 1948. w. G. H. FINCH FACSIMILE SYNCHRONIZING SYSTEM Filed Feb. 16, 1944 4 Sheets-Sheet 2 /0 7--05CILLATOR /02 I03 /0/) 7 7 g- AUDIO R J PICTURE 051400-- .AMPL/F/ER FILTER ULA TOR VERTICAL HOR/Z. 105- SYNCH. N Z E2 FILTER FILTER I337 BLANK/N6 CIRCUIT STEPP/NG TUNED CATfifi/DE RAY RELAY c/Rcu/T E 5/7) CONTROL VERTICAL DEFLECT/ON RcT/F/R 3 CONTROL I FIG. 2

VERTICAL DEFLEC TION SMOOTH/"G PLATES FILTER HORIZ. DEl-ZECT/ON lZZ AMPLIFIER INVENTOR.

1 1 WILLIAM H. FINCH HORIZONTAL BY DEFLECTION w PL A755 ATTORNEY Oct. 5, 1 948. w, cH 2,450,649

FACSIMILE SYNCHRONIZING SYSTEM Filed Feb. 16, 1944 4 Sheets-Sh eet 3 INVEN TOR. WILL/AM G. H. F/NCH E ATTORNEY Oct. 5, 1948. w. G. H. FINCH 2,450,649

FACSIMILE SYNCHRONIZING SYSTEM Filed Feb. 16, 1944 4 SheetsSheet 4 Patented Oct. 5, 1948 UNITED STATES PATENT OFFICE FACSIMILE SYNCHRONIZING SYSTEM William G. H. Finch, Newtown, Conn. Application February 16, 1944, Serial No. 522,601

My invention relates in general to the field of picture transmission and reception and more specifically concerns the utilization of cathode ray apparatus for picture recording.

In a facsimile system, an electro-optical scanning mechanism at the transmitter is used to generate electrical signals corresponding to the lights and shades of lines of a picture. These signals are transmitted by radio frequency currents or by telephone lines to a remote recorder Whereat the signals are impressed upon a suitable recorder.

In order to make a photographic recording of the facsimile signals received from the transmitter, it has been the practice to modulate the intensity of a light beam and impress these si nals upon an electro-optical film scanning mechanism somewhat similar to that utilized at the transmitter. Scanning, in general, was accomplished by suitably supporting the film upon a rotatable drum and producing a motion between the drum and the optical system such that the modulated light beam traced a helical path about the surface of the film.

As is well-known in the art, the primary probfor a suitable synchronizing system so that scanning systems at the transmitter and recorder would operate at identical speeds and in the same phase.

The solution of the synchronizing problem has been accomplished by various complex electromechanical mechanisms Which generally required that the recorder be driven in a start-stop manner or be driven by bulky synchronous motors.

My invention contemplates the elimination of electro-mechanical optical systems and the need for large driving motors and other complex synchronizing apparatus at the recorder, through the agency of a cathode-ray tube and its associated circuit elements.

In accordance with my novel invention, a cathode-ray tube fluorescent screen is utilized as the source of recording light. Photographic means are arranged so that the moving spot of light upon the cathode-ray screen will be continuously impressed upon a photographic plate, so that its position upon the plate is dependent at all times upon the position of the spot upon the cathode-ray screen.

The intensityof the cathode-ray spot is made at all times proportional to the intensity of the incoming picture signals so that the scanning of the cathode-ray fluorescent screen will produce upon a photographicplate an image representa- Claims. (Cl. 178-695) lem presented by such mechanism was the need tive of the picture transmitted. In order that the photographic recording be in all respects identical to the picture transmitted, it is, of course, essential that the cathode-ray spot on the fluorescent screen moves at the same speed and in the same phase as the light spot projected upon the image at the transmitter.

In high-speed television transmission systems, the receiver is arranged to include two sawtoothed oscillators which generate signals for causing the electron beam in the cathode-ray tube to move horizontally a predetermined number of cycles while moving vertically in a similar manner at a different frequency. When the output of these oscillators are applied to the horizontal and vertical deflecting plates of the oathode-ray tube, a rectangular pattern is produced upon the screen which has a number of horizontal lines corresponding to the number of cycles of the horizontal saw-toothed oscillator which occur within one cycle of the vertical saw-toothed oscillator.

In conventional television systems the picture is composed of 551 horizontal lines flashed on the screen at the rate of 30 complete frames per second. In order to synchronize the television horizontal lines and frames with the signal generator at the transmitter, the signal generated at the transmitter is modulated with a series of synchronizing signals, namely, a horizontal synchronizing pulse at the end of each scanning line and a vertical synchronizing signal at the end of each frame.

These synchronizing impulses which occur at a comparatively high frequency are separated at the receiver and are applied to the horizontal and vertical saw-toothed oscillators in a manner Which results in electronic synchronism between the oscillators at the transmitter and at the receiver.

The salient difference between ordinary facsimile transmission systems and television systems is that in facsimile it is generally necessary to send a single stationary picture and to maintain the picture transmission channel within a band of several thousand cycles per second, while in television, it is essential to transmit many frames per second and utilize a band of several megacycles per second.

Evidently, therefore, in cathode-ray facsimile transmission of a single picture, the vertical scanning frequency is merely one cycle over the period of time required to transmit the entire picture. -Since this frequency may very well be of the order of one cycle per minute it is clear that conventional synchronizing impulse means could not be used to stabilize an oscillator for generating a low frequency signal of this type. Similarly, the horizontal scanning in cathoderay facsimile may be of a frequency as low as five cycles per second or less, and hence impulse synchronization of this oscillator is not possible.

In accordance with my invention, I propose to operate the horizontal and vertical deflection circuits of the receiving cathode-ray tubes by signals generated at the transmitter. These signals are generated directly by the transmitter scanning apparatus and accordingly are at all times in the proper phase relationship and at the proper frequency. These synchronizing signals directly cause the movement of the cathode-ray tube of fluorescent spot, and are free from the effects of static or other disturbances which would ordinarily result in a non-synchronous condition in a television recorder.

More specifically the electro-optical signal generating system at the transmitter produces a multiple signal comprising a picture signal of the usual type and a continuous synchronizing signal. This synchronizing signal is a variable frequency signal so generated that the frequency at any instant is proportional to the angular position of the drum relative to the scanning mechanism. This variable frequency synchronizing signal is transmitted to the receiver whereat a novel circuit translates this continuously varying frequency to a signal of correspondingly varying amplitude. This varying amplitude signal is impressed upon the cathode-ray horizontal deflecting circuit to cause the horizontal movement of the cathode-ray beam in a manner which corresponds identically to that of the light beam moving across the transmitting drum.

At the termination of each horizontal scanning line, the fluorescent spot on the cathode-ray screen is extinguished and returns to a position from which it may begin the scanning of the successive horizontal line. Simultaneously with the return of the fluorescent spot, the synchronizing signal transmitted from the scanning apparatus at the transmitter will cause a small vertical displacement of the spot. It is therefore evident that if the spot starts at one side of the cathode-ray screen, moves horizontally across at a uniform speed and then is rapidly returned to a position somewhat below the starting position, that proper scanning is established.

Since the picture signals received from the transmitter are at all times impressed upon the intensity control of the cathode-ray spot, the scanning of the screen will produce an image upon the photographic plate which will be identical with the picture at the transmitter.

It is important to recognize, of course, that the movement of the spot in a facsimile recording is comparatively slow and that therefore the screen of the cathode-ray tube will at no time show an image but instead will always show a slowly moving spot of variable intensity.

It is therefore an object of my invention to provide a facsimile system utilizing a cathoderay tube at the recorder.

It is a further object of my invention to provide a cathode-ray facsimile transmission system wherein the electrical signals required to displace the cathode-ray fluorescent spot are generated at the transmitter.

Another object of my invention is to provide a facsimile transmitter with electro-optical means for generating a scanning signal of continuously variable frequency.

A still further object of my invention is to provide means for synchronizing cathode-ray horizontal and vertical deflection circuits at an extremely low frequency,

These and other objects of my invention will now become apparent from the following specification taken in connection with the accompanying drawings in which:

Figure l is a schematic representation of a facsimile transmitter.

Figure 2 is a schematic representation of a cathode-ray facsimile recorder.

Figure 3 is a developed view of the novel synchronizing strip used at the transmitter.

Figure 4 is a fragmentary View of the rotatable drum and shows the mounting of the synchronizing strip.

Figure 5 is a circuit diagram of the cathoderay recorder.

Referring now more particularly to Figure 1, there is shown one modification of a transmitter mounted on base plate It] to be used in connection with a cathode-ray facsimile system.

The transmitter comprises a rotatable drum l l supported on shaft I I which during operation, is continuously driven preferably by a constant speed motor I2. The drive of drum H is secured through shaft 8 and gear box 9. The speed of rotation of the drum H is, of course, determined by the type of transmission and the band width permissible for the transmission.

The image to be transmitted is secured to the rotatable drum l l by a mounting bar I5, and its associated handle l5, as is well known in the art. Driven from the motor 12, is a rotatable helical feed screw Hi, the angular speed of which is determined by the gear-ratio box l3.

An electro-optical scanning mechanism 3| is positioned adjacent the rotatable drum II and is removably coupled to the rotatable feed screw 56 so that during a scanning operation the optical system moves parallel to the axis of the drum.

Within the electro-optical system 3| is a conventional projection bulb and an optical system 3i for focusing a sharply defined light spot 30 upon the surface of the image I4 to be transmitted. Light reflected from the image I4 is impinged upon a suitable photo-sensitive device 29 Within the scanning system 3|, and accordingly, the intensity of the photo-electric current will be proportional to the lights and shades of the image.

In a transmitting operation, combined rotation of the drum H and lateral displacement of the electro-optical system 31 causes the light spot 39 to trace a helical path about the surface of the image [4.

The photo-electric currents thereby generated are impressed upon the grid circuit of a picture signal amplifier 32 for amplification to a suitable energy level.

As will be described later, it is necessary to transmit a synchronizing signal along with the picture signals. Since both of these signals may be within the same frequency band and since it is necessary at the receiver to selectively separate these signals, it is preferable to translate the picture signals to a frequency band removed from that of the synchronizing signals. Accordingly, the output of picture amplifier 32 is impressed upon a translating circuit 33 which comprises essentially a modulator utilizing a translating frequency generated in oscillator 34.

In general, commercial facsimile systems utilize picture signals ranging from zero frequency to several thousand cycles. The signal emerging from channel translator 33 will cover a band of frequencies equal in width to the band generated in the electro-optical system 3|, but will have added to each frequency, an additional frequency corresponding to that of the oscillator 34. For example, if the picture signal band ranges from zero frequency to three-thousand cycles, and if the frequency of oscillator 34 is three-thousand cycles, the translated band at the output 35 of channel translator 33 will cover a frequency range of three-thousand cycles to six-thousand cycles.

It is desirable in picture transmission system to transmit the output of channel translator 33 by causing these signals to modulate a low frequency carrier of the order of 8 to thousand cycles per second. Accordingly, the output of channel translator 33 and a carrier frequency generated in oscillator 36 are impressed upon a conventional modulator circuit 31 to produce the desired carrier modulated signal. lated signal is in turn amplified to a suitable transmission level in power amplifier 4|.

Transmission may, of course, take place in any well known manner, as for example, over a telephone line or through the utilization of a radio frequency carrier. Such circuits are conventional and are not shown here.

In accordance with my novel facsimile transmission and recording system, a synchronizing strip 5| is securely mounted upon or engraved upon one end of the transmitting scanning drum II. This synchronizing strip 5| which is not at any time covered by the picture l4 comprises as is best shown in Figures 3 and 4, a picture of a continuously variable frequency wave having a constant amplitude.

This figure is constructed upon the strip 5| by dividing the axis 52 of the rectangular strip 5| into points such as 53 and 54; the distance between which increases linearly as these points move away from the beginning of the strip 5|. Approximately 78 of the circumference of the drum preferably is divided in this manner.

Between each pair of adjacent points such as 53 and 54, a half cycle of a sine wave is drawn, and the area beneath one side of these sine waves such as BI and the axis isblackened as shown.

Between the points 55 and the edge 62 of the synchronizing strip representing a distance of approximately /8 of the circumference of the drum II, a constant frequency, constant amplitude sine wave is drawn as shown. This constant frequency sine wave 63 is of a higher frequency than the highest frequency of the variable sine wave 6| covering the V of the drum As is shown in Figures 1 and 4, this strip is positioned along the edge of the drum such that the continuously variable frequency on the synchronizing strip begins at exactly the same point on the drum as the leading edge M of the picture M.

The constant frequency range 63 along the synchronizing strip 5| is positioned approximately at the trailing edge of the picture I4, and continues across that portion of the surface of the drum [I covered by the mounting bar |5.

As is illustrated in Figures 1 and 4, an additional electro-optical scanning system 1| is utilized in connection with my novel transmitter. This optical system is permanently fixed by screws 10 to the frame of the transmitter and is not in any way connected to the rotatable feed screw I6 as is the electro-optical system 3|. A

This modufurther difference between the two electro' optical systems is that optical system 1| projects a horizontal slit of light 69 upon the synchronizing strip 5|.

Light reflected from the entire horizontal strip T2 is selected by the photo-cell 68 of the electrooptical system H, and it will be evident that the currents generated by the photo-electric cell 68 will at all times be proportional to the white area covered by the light strip 69 on the synchronizing strip 5|. This in turn will be proportional to first the continuously variable sine waves BI, and second, the constant frequency sine waves 63 on the synchronizing strip 5|. For best results it is preferable that motor l2 be governed at a constant speed.

As is evident from Figure 4, as the scanning operation of a single line of sheet l4 begins, the scanning by optical system 1| will begin at edge 55 of the synchronizing strip.

The length of the synchronizing strip between 55 and 62 may be made to correspond to the width of mounting bar l5.

Referring now to Figure l, the signal generated in the electro-optical system 1| is amplified by a synchronizing signal amplifier 8| and impressed upon the modulator 3'| simultaneously with the picture signal. The frequency of these signals generated by the scanning of the synchronizing strip are preferably in a range below that of the picture translated signals as it comes out of the translator 33. Hence, the signal out put of the modulator 3'! will be a multiple modu lated wave comprising a sub-carrier modulation including a picture signal and a synchronizing signal modulation.

This multiple signal, in accordance with my invention, is the signal transmitted at all times to a recorder of the type schematically illustrated in Figure 2.

The received signals at recorder terminals lel, Figure 2, is essentially that signal which appears at the output of power amplifier 4| of the transmitter. If the transmission occurred over a .wired line, then the input at terminals llll rnight be the junction to the transmission line; and if the transmission was accomplished by means of a radio frequency carrier, the input terminal Icl represents the output of a radio frequency amplifier and demodulator.

The signals reaching terminals |0| are first amplified in an audio-frequency amplifier M2, the output of which is connected to three parallel channels comprising a picture filter E03, a horizontal synchronizing filter I04, and a vertical synchronizing filter |05the operation of which will now be described.

The picture filter I03 comprises essentially, a high pass filter )3 having a pass band tuned to the frequency band of the translated picture signal. This filter I03 is critically adjusted to discriminate against any signal of the type generated by .electro-opti-cal system 1|, Figure 1. The output of the picture filter is coupled into a demodulator |06 as is the output of an audio-frequency oscillator I01.

The signals impressed upon the demodulator I06 act in the reverse manner of the channel translator 33 of the transmitting circuit of Fig. l, and accordingly, the oscillator I 07 is operative to produce an output consisting of the picture Signals only.

Thus, the output circuit of the demodulator I06 is arranged so that the constant frequency of the oscillator I01 is subtracted from all (the input signals from the picture filter I03, and therefore, it is evident that the input to the picture amplifier H I is essentially that signal which appears in the picture amplifier 32 of the transmitter of Figure 1.

The output signal of the picture signal amplifier III is impressed, as will be described in greater detail later, upon the intensity control or control grid of a cathode-ray tube in order to cause the cathode beam to vary in intensity with the lights and shades of the picture signal.

The phase of the picture amplifier is arranged as desired so that the intensity of the cathode ray beam will vary in phase with the lights of the picture or 180 out of phase thereof in order that a positive or negative may be reproduced.

The horizontal synchronizing filter IM connected across audio-amplifier IE2 is a tuned circuit having a pass band over the frequencies which are generated by the variable frequency section on the synchronizing strip Accordingly, the highest frequency which may be passed is that frequency corresponding to the sine waves at the leading edge 55 of the strip, and the lowest frequency to be passed by filter It; is that corresponding to the sine waves at the left edge of the variable frequency strip. This frequency range as previously described is selected and determined in part by the speed of the rotatable drum I I at the transmitter.

Furthermore, the horizontal synchronizing fi1- ter I04' is tuned to discriminate against signals of the type impressed upon picture filter I83, namely, the translated picture band, and against signals of the frequency corresponding to the constant frequency portion between points 55 and 62 of the synchronizing strip 5 I Therefore the output of the horizontal synchronizing filter I04 will consist of a signal starting at a high frequency and linearly progressing to a low frequency once for each revolution of the drum H at the transmitter. Furthermore, the highest frequency will begin immediately as the scanning cycle at the transmitter begins, and the lowest frequency of the variable frequency signal will terminate immediately after the completion of the scanning cycle of the picture I4.

Since this frequency therefore represents at all times the linear circumferential distance covered by the scanning spot at the transmitter, the output of the horizontal synchronizing filter I05 may be utilized to directly cause the horizontal defiection of a cathode ray spot. Thus, the output of the filter I04 is impressed upon a tuned cir cult H2 so that the variable frequency is-operative along the linear slope of the circuit response characteristic. This circuit H2 may consist of a condenser and inductance having a resonant peak lower than the highest frequency of the variable frequency strip and may be resistance loaded so that the slope is not too steep and covers the frequency range required as described in Chapter III of Termans Radio Enginering published in 1932 by McGraw-I-Iill Book Co. Inc.

By proper adjustment of condenser, inductance and by proper selection of the loading resistance, the linear rising response of the circuit H2 may be made to cover a frequency band which corresponds to a band somewhat wider but of the same frequency range as thelower and upper frequency limits of the output of horizontal synchronizing filter IE4. It is, therefore, evident thatuponthe application of a signal (such as generated. by the photo-electric cell 68 in the electro-optical scanning unit 1| as. it passes over the variable frequency range of the synchronizingstrlp) the output of tuned circuit H2- will be of variable frequency as before, but of linearly varying amplitude-the amplitude being greater as the frequency decreases. To ensure a proper linear amplitude variation, an amplitude limiter circuit may be inserted between filter I04 and tuned circuit H2.

This signal of varying amplitude and frequency is impressed from the output of tuned circuit H2 upon a rectifier H3 and then upon a smoothing filter I2I designed to remove frequency components approximately fifteen times greater than the desired saw-tooth frequency.

Accordingly, the output ofsmoothing filter I2! will be a substantially saw-toothed wave having an amplitude which varies in accordance with the circumferential distance covered by the light spot 38 of scanning system 3| at the transmitter. This linearly rising wave is impressed upon the pushpull horizontal deflection amplifier I22 in which circuit it is amplified to a level suflicient to cause a linear horizontal deflection of a cathode ray beam. This circuit I22 is described in greater detail in connection with Figure 5.

It is important to note that the linearly rising saw-toothed wave will be generated immediately as the scanning of a single line at the transmitter drum II begins, and will continue over the entire variable frequencyrange of the synchronizing strip 5 I.

As the light slit 69 from electro-optical system ll at the transmitter progresses beyond 55 onto the constant frequency range of the synchronizing strip 5!, the generation of the saw-tooth ceases, and the vertical synchronizing filter I at the recorder, Figure 2, comesinto operation.

As previously mentioned, the constant frequency range of the synchronizing strip 5I represents a comparatively high frequency when compared with the variable frequency produced over the major part of the cycle. Accordingly, the vertical synchronizing filter I05 is a tuned circuit critically adjusted so that the constant frequency generated at the transmitter will pass through the filter without attenuation while any other frequencies will be attenuated sharply. Accordingly, upon the receipt of a vertical synchronizing signal through audio-amplifier I02, the sync'hronizing filter I05 will pass a signal to the steppingrelay ISI.

This type of relay as is Well understood in the art, comprises essentially, a coil and a movable armature such that upon energization of the coil, the armature is deflected against the normal bias of a spring to cause rotation of a shaft I32. This rotation is accomplished by means of an escapement' mechanism and the amount of rotation obtained for each impressed signal is comparatively small.

When the relay coil is de-energized, the armature swings back to its original position and resets the escapement mechanism so that the following signal will cause another small rotational movement of shaft I32.

As illustrated in Figure 2, each energization of the stepping relay I3I will cause a small movement of shaft I32 which, as will be described in connection with Figure 5, will in turn cause a small displacement of a potentiometer movable arm which controls the vertical position of the cathode-ray beam.

' Since during each small vertical movement of the cathode ray beam, the picture signal ceases, that is, the scanning spot at the transmitter passes over the mounting bar I5, the cathode ray beam retraces its path from one extreme horizontal position to the other. It is essential that during this retrace, the cathode ray fluorescent spot be extinguished in order to avoid spurious light streaks upon the film.

Since the mounting bar I is black, the retrace, if the phase is adjusted such that the picture is negative, will be automatically extinguished. However, in order to ensure complete darkness of the cathode ray screen during the retrace period, the vertical synchronizing signals, may be employed as illustrated in Figure 2, to energize a blanking circuit I33 which injects a sharp biasing voltage into the picture signal channel, such that the fluorescent spot is extinguished.

The actual operation of the cathode ray facsimile recorder is best illustrated in Figure 5, considered in connection with the schematic circuit Figure 2.

As illustrated in Figure 5, a cathode ray tube I5I is conveniently disposed within a facsimile recorder and an optical system I52 is arranged to focus the screen I53 of cathode ray tube I5I upon a photographic plate I54. The optical system I52 and the plate I54 may be mounted in any convenient manner upon the frame of the facsimile recorder. For successful operation, the screen I53 of the cathode ray tube, the optical system I52 and the plate I54 must be enclosed in a suitable light-tight enclosure.

The high voltage circuits of the cathode ray tube I5I are operated in a conventional manner as illustrated. Thus the high tension transformer I55 has its primary I56 connected to a suitable source of alternating current.

A filament winding I51 is employed to energize the heater I58 of the cathode ray tube. A second filament winding I50 is utilized to energize the heater I6I of the high voltage rectifier I62.

The high tension winding I63 of the transformer I55 is grounded at one end and connected to the plate of the high voltage rectifier I62 at the other end. Thus, in the well known manner, the lead I64 is raised to a high potential of the order of several thousand volts as determined by the secondary I63.

A conventional resistance capacitance filter I65 is utilized for the high voltage direct current, and a bleeder resistance I66 is connected across the output thereof.

The focusing electrode I61 is connected to a tap I68 upon the bleeder resistance I66, and the high voltage accelerating anode I1I is connected to the high voltage terminal I12.

The picture amplifier schematically illustrated as III in Figure 2 is shown in Figure 5 as the amplifier tube I15. Thus the picture signals are coupled to the grid I16 of the amplifier I15 through condenser I11. The plate of amplifier tube I15 is connected to a suitable B+ source of low voltage direct current I8I through a load resistor I82.

The control grid I83 of the cathode ray tube I5I is directly coupled to the plate of amplifier tube I15 and accordingly the picture signals are impressed thereupon to modulate the intensity of the cathode ray beam coming from the cathode I 14. The cathode of the tube I5I is biased to a positive potential by a tap on a potentiometer I84 connected between the low voltage 13+ source I8I and ground. Accordingly, by an initial setting of this potentiometer, the cathode ray beam may be adjusted to the proper recording intensity so that picture signals impressed upon grid I83 10 will cause the spot focused upon screen I53 to properly vary in intensity over the complete range from black to white.

As illustrated in Figure 5, the horizontal and vertical deflection plates I and I86, respectively, are maintained at a comparatively high potential by joining them to taps on the high voltage bleeder resistor I66. Thus, as illustrated, one of each of the horizontal and vertical deflecting plates are joined to tap I81 of the high voltage bleeder through protective resistors IBI and I92 respectively. The second horizontal deflecting plate as illustrated is connected through protective resistor I93 to the variable point of a potentiometer I94 connected across the high voltage bleeder resistor I66.

Accordingly, by a proper adjustment of tap I95, the cathode ray spot may be adjusted so that its position is in the center of screen I 53 when no deflecting voltage is applied to the horizontal deflecting circuit. The second plate of the vertical deflecting plates I86 is connected through protective resistor I96 to the movable tap I98 of a potentiometer I 91 connected in the manner described for potentiometer I94. However, the movable tap I98 of the potentiometer I91 is controlled by shaft I32 of the stepping relay I3 I.

Prior to a picture transmission, the tap I98 is set manually to one end of the potentiometer I91. During the picture transmission, each vertical synchronizing signal as received through filter I05 of Figure 2, causes a small movement of tap I 98 across the potentiometer I91 sothat at the end of a, transmission the tap will be at the opposite end of the potentiometer I91. It is evident, therefore, that the stepping relay I3I is adjusted to cause a complete cycle of movement of the tap I99 across the potentiometer I91 in as many steps as is determined by the number of horizontal scanning lines in the picture.

The horizontal deflection of the cathode ray spot as described in connection with Figure 2, is accomplished through the generation of a sawtoothed wave of voltage from a variable frequency signal. The output of the smoothing filter IZI as illustrated in Figure 5, is impressed upon a horizontal scanning amplifier I22 of the push-pull" type. Thus, the signal which is sawtoothed in form is coupled through condenser MI and through potentiometer 202 to the grid of the first triode element 203' of a conventional duplex triode tube 203.

The tap 204 on the potentiometer 202 is adjusted initially so that the extent of the horizontal sweep of the cathode ray beam is suificient to cover the complete screen I53.

The plate of the first triode element 203' is energized from the low voltage direct current B+ source I8I through the series resistors 205 and 206, and the cathode of this first section is connected to ground through a resistor 201.

The saw-toothed voltage generated at the output of the first section 203 of the triode 203 is coupled to the second section 203" through condenser 2II connected from the junction of resistors 205 and 206 to the grid of the second section 203". The grid is joined to ground through resistor 2I2 and the cathode is connected to ground through resistor 2I3.

The plate of the second section 203" of double triode 203 is connected to the direct current source I8I through load resistor 2I4. Accordingly, as is well understood in the art, the output between the plates of the triode sections within .l'i tube .253 will comprise anamplifled saw-toothed wave symmetrical in voltage. This saw-toothed output is applied to the horizontal deflecting plates 185 of cathode ray tube I51, directly through couplin condensers H and H6. The capacity of these condensers is chosen to suitably pass the saw-toothed wave of the frequency required for horizontal scanning in facsimile.

Due to the symmetry of the saw-toothed wave, as generated by the push-pull amplifier 263 shown, the cathode raybeam within tube i5l will be symmetrically deflected about the center so that the beam will start at one side of the tube and travel to the otherside of the tube at which point the saw-toothed wave generator, namely, circuit H2 of Figure 2 will discharge and be ready for the following cycle, after the vertical synchronizing signal is received and utilized. Accordingly, it may be seen that in the operation of the novel-cathode ray facsimile recorder, a cathode ray beam is caused to scan thescree I53 of a cathode ray tube l5! at a comparatively slow speed. The scanning signal required for thehorizontal deflections are received directly from the transmitter and hence are in synchronism therewith, and the vertical deflection signals are received at the end of each scanning line to cause a vertical deflection equal in width to approximately one scanning line.

The moving spot on screen I53 is at all times focused sharply upon .plate !54 and hence the spot correspondingly scans plate 254 of any well known light sensitive material suitably housed against external light exposure. The intensity of the fluorescent spot is governed by the incoming picture signal impressed upon control grid L83 of the cathode ray tube so that it is evident that helical scanning of an image at the facsimile transmitter maybe converted into a photographic image upon plate I54 by the system escribed and il1ustrated.

At the completion of the scanning, the last operation of the stepping relay I3l may be employed .to return I98 to its neutral position and at the same time present a new frame [54 for recording.

The chief advantage of such a cathode ray facsimile recorder is the lack of mechanically moving elements at the recorder and hence the attendant complex synchronizing problems are absent. Of course, other means may be utilized to transmit the horizontal deflecting signals and similarly other electronic means maybe utilized to cause the stepping of the fluorescent spot in the vertical direction. In view therefore of the many modifications of this invention which will be apparent from consideration of this specification and these drawings, I wish that the scope of my invention be bound only by the appended claims.

I claim:

1. In a facsimile system, a transmitter, said transmitter comprising means for scanning a line of an image and generating corresponding picture currents and means operable during the scanning of said image line to generate -a synchronizing signal having a characteristic varying linearly with the proportion of said image line scanned.

2. In a facsimile system, a transmitter, said transmitter comprising'means for scanning a line of an image and generating corresponding .picture currents and means operable during the scanning of said image line to generate a synchronizing signal having an instantaneous frequency '12 proportional to the percentage of the image 'line scanned.

3. In a facsimile system, a transmitter, said transmitter comprising means for scanning a line of an image and generating corresponding picture currents and means operable during the scanning of said image line to generate a synchronizing signal having an instantaneous frequency proportional to the percentage of the image line scanned, and means for generating a second synchronizing signal at the terminationof the scanning of said line.

4. In a facsimile system, a transmitter, said transmitter comprising means for scanning a line of an image and generating corresponding picture currents and means operable during the scanning of said image line to generate a synchronizing signal having an instantaneous frequency proportional to the percentage of the image line scanned, and means for generating a second synchronizing signal at the termination of the scanning of said line, said second mentioned synchronizing signal being a current of constant frequency.

5. In .a facsimile system, a transmitter, said transmitter comprising means for scanning a line of .an image and genera-ting corresponding picture currents and means operable during the scanning of said image line to generate a synchronizing signal having .an instantaneous frequency proportional to the percentage of the image line .scanned, and means for generating a second synchronizing signal at the termination of the scanning of said line, said second mentioned synchronizing signal being a current of constant frequency, .said first and second synchronizing signal generating means comprising an electro-oiptical scanning mechanism.

6. Ina facsimile recorder, a cathode ray tube having an electron beam for generating a fluorescent spot and means for horizontally and vertically-deflecting said electron beam, means for generating a horizontal saw-tooth deflection voltage comprising means for converting a constant amplitude variable frequency signal into a vari able amplitude signal.

.7. In a facsimile recorder, a cathode ray tube having an electron beam for generating a fluorescentspot and means for horizontally and vertically deflecting said electron beam, means for generating a horizontal saw-tooth deflection voltage comprising means for converting a constant amplitude variable frequency signal into a variable amplitude signal and means for-deflecting said electron beam vertically at the end of each horizontal scanning cycle.

8. In a facsimile recorder, a cathode ray tube having an electron beam for generating a fluorescent spot and means for horizontally and vertically deflecting said electron beam, means for generating a horizontal saw-tooth deflection voltage comprising means for converting a constant amplitude variable frequency signal into a variable amplitude signal and means for deflecting said electron beam vertically at the end of each horizontal scanning cycle, said means comprising a relay operable at the end of each horizontal scanning cycle.

9. In a facsimile system, a recorder comprising a cathode ray tube having a fluorescent screen and an electron beam for generating a fluorescent spot on said screen, means for horizontally deflecting said .electron beam comprising means for converting a received synchronizing signal of variable frequency into a saw-tooth deflection voltage, means including a second re ceived synchronizing signal for vertically deflecting said electron beam substantially the width of one scanning line at the end of each horizontal scanning cycle, and means for modulating the intensity of said electron beam with said picture signals.

10. In a facsimile system, a recorder comprising a cathode ray tube having a fluorescent screen and an electron beam for generating a fluorescent spot on said screen, means for horizontally deflecting said electron beam comprising means for converting a received synchronizing signal of variable frequency into a saw-tooth deflection voltage, means including a second received synchronizing signal for vertically deflecting said electron beam substantially the Width of 14 one scanning line at the end of each horizontal scanning cycle, and means for modulating the intensity of said electron beam with said picture signals, and means for photographically recording the movement of said fluorescent spot.

WILLIAM G. H. FINCH.

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

UNITED STATES PATENTS

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