US2291476A - Communication system - Google Patents

Description

C. F. KERNKAMF COMMUNICATION SYSTEM Filed Oct. 8, 1941 July 28, 1942.

2 Sheets-Sheet l M55 i v July 28, 1942. Q. F. KERNKAMP COMMUNICATION SYSTEM 2 Sheets-Sheet 2 Filed 0G13. 8, 1941 .I INVENTOR. /ir/oc@ Kern/wmp,

Patented `luly 28, 1942 UNITED STATES PATENT GFFICE COMMUNICATION SYSTEM Clarence F. Kernkamp, Riverdale, Md.

Application October 8, 1941, Serial No. 414,214

9 Claims.

'Ihis invention relates to facsimile systems and, more particularly, relates to high speed facsimile recording by electronic scanning and electron current recording which may be directly on paper sensitized to the passage of an electron current.

In the conversion of pictures or messages to electrical facsimile signals mechanical scanning operations have been employed whereby a narrow beam of light is traced over the picture or message elements and corresponding variations in the light beam intensity reflected or directed into a photoelectric cell converting them into variations of current strength. In some systems the picture or message may be mounted upon a drum and scanned in a closely wound, long spiral as the drum revolves; in other systems the picture sheet may be successively advanced past an oscillating scanning means which moves transversely with respect to the sheet whereby successive transverse scanning operations are perfected. Corresponding scanning operations are produced at the receiving station in synchronism with the transmitter scanner for composing the reproduction. In the case of the revolving drum type with photographic recording, a recording light beam of varying intensity may reproduce the original upon a photographic negative revolving in synehronism with the transmitting drum. Another method is to replace the light beam by a single Wire finger moving across sensitized paper which is mounted upon a drum and revolved in synohronism with the transmitting drum, thus using the single finger, or stylus, to record directly upon the sensitized paper due to the passage of the electric current through it.

The speed of operation of prior systems is limited by the mechanical scanning operations and the requirements for maintaining the transmitter and the receiver scanning mechanism in perfect phase synchronization. A further limitation is the attenuation of the picture signals by the line wires` connecting two distant stations. The inertia of the moving mechanical components and the mechanical synchronizing operations have limited the speeds of these systems.

A cording. Direct recording iseiected upon paper sensitized to the passage of an electric current,

by a plurality of fixed wiping kstyli receiving their advancesin the art of equalizing long lines, higher `frequencies may now be applied without excessive attenuation. These may be of the order of 7000 cycles as the carrier frequency whic/h may be modulated by the picture tone signals which will be about 2500 cycles maximum. A reduction in the number of lines per inch of recording may further increase the rate of recording. Accordingly, the present invention permits much higher transmission speed and an increase in recording speed since the recording is not photographic, but direct.

In carrying out the present invention a cathode ray iconoscope tube may be used to generate a picture tone signal. Light reflected from the object to be transmitted may be focussed upon a mosaic of photoelectric elements within the iconoscope. The mosaic area acquires potentials corresponding to the intensity of the light reflected from the object. Progressive scanning is used, thereby generating the picture tone signals in an external circuit. At completion of each periodic horizontal excursion across the mosaic the electron beam is caused to return rapidly to the starting margin by means of a voltage applied to the horizontal deecting coils and to drop down a small distance by means of a voltage applied to the vertical defiecting coils of the iconoscope beam. This may be done automatically. No picture-tone signals are transmitted during the return period. A synchronizing impulse simultaneously generated during the return period may be employed for advancing a corresponding recording paper at a remote or receiving station. The recording paper may be thus automatically advanced by an amount equal to the Width of the scanning line of the iconoscope at the end of each horizontal line of scanning. Each successive line of the recording paper may be exposed to an electronic current through the wiping styli of a cathode ray recording tube energized from the transmitting station.

In a preferred form of apparatus for carrying out the invention there is provided a cathode ray recording tube which has a comb-like member arranged transversely across the lens of the tube and extending through the lens so that on the interior of the tube it is subjected to the sweep of the recording electron beam generated within the cathode ray tube. The comb-like member may be made up of teeth or styli which project outside the wall of the tube and are in surface contact with a film or band of recording material which is advanced line by line by suitable mechanism and which may be backed by a reel or roll of conducting material. 'I'he recording material preferably is provided with an electro-sensitive chemically prepared suriace so that an impression is recorded whenever the paperisinsurfacecontactwiththeendofatooth which is electrically excited. Thus as the recording electron beam strikes a particular stylus inside the tube an imprint is applied to the recording material where itcontacts that particular stylus outside oi the tube. By reason o! the electronic selection of the coasting styli images which have been progressively scanned at the transmission end oi the system are Prolressively reproduced at the junction of the tips oi the styli and the recording material.

In Figure l is shown diagrammatically the apparatus at one end of the line. The transmitting apparatus is shown above the dotted line and therebelow the apparatus for receiving. Identical apparatus is at the other end of the line. I'his provides 4-wire. two-way transmission. Fig. 2 is a diagrammatic showing of a stair step voltage device for the vertical deilecting generator and ampliiler. Figs. 3 and 4 are current curves. Fig. 5 is a voltage curve. Fig. 6 shows time-phase of curves in Figs. 3, 4 and 5. Fig. 7 shows a typical 2500 cycle signal modulated by picture-tone signals. Fig. 8 is a front view of a recording tube showing its teeth. Fig. 9 is a fragmentary horizontal section through the faceplate and teeth ol the recording tube and record nlm. Fig. 10 isan enlarged perspective view of a tooth and Fig. 11 is a fragmentary side elevation of the tube broken away in part to show the faceplate and teeth.

In Fig. 1 the sending equipment for transmitting to a remote terminal is shown above the dot and dash line and the equipment for receiving or recording from the remote terminal is shown below the dot and dash line.

The sending equipment shown comprises an iconoscope tube with its associated power supply, sweep circuits, picture tone amplier, picture tone amplifier modiiier, 2500 cycle audio oscillator, '1000 cycle carrier oscillator, carrier modulator, carrier amplifier, synchronizing impulse generator and ampliiler, line coupling panel composite. signalling system for the operators, a Morse communication system and switchboard for the testing and regulating attendants.

'Ihe iconoscope may be of the conventional type upon the mosaic of which' is formed the diilerent electrical potentials corresponding to the variations in light intensity redected from the message to be transmitted. The object to be transmitted is placed in iront of the focusing lens of the iconoscope and strongly illuminated.

The iconoscope tube is an image pick-up device of the storage type. In this type. the photoelectric current from an element oi' the picture charges an individual condenser for a period of time equal to the scanning time of one complete picture. This condenser is discharged once during the scanning time oi' a complete picture, the timeofdisch'argebeing only thetimeoi'scanning of one picture element.

The iconompe consists oi a photosensitive mosaic and an electron gun. assembled in a glass bulb which is highly evacuated. The electron gunisofthesamegeneraltypeasthoseusedin television cathode ray tubes and is known to those skilled in the art.

'Ihe picture-signals oi' the iconoscope are ampliiled by the picture-tone amplifier and modulate the amplitude of a 2500 cycle audio frequency sine wave oscillator. The audio oscillator frequency and picture-signals are (ed into the picture-tone ampliiier-modulator the output oiwhichmodulatesa'imcycleearrierimquencyat the carrier modulator for trausmllion to the line.

The iconoscope uses electromagnetic deilectinn of the scanning electron beam, This requires a saw-tooth linear wave of current thromh the horizontal deiiecting coil. Bince a saw-tooth wave of current through a pure inductance pro. duces a rectangular impulse oi' voltage acre. it. and vice-versa. `the horiaontal sweep generator hsodesignedastoproducearectangularimpulse of voltage periodically at a predetermined rate. This is obtained from an inductor-type generator consisting ci a drive-coil, a particularly shaped rotor. and a pick-up coil. so positioned with respect to each other that the magnetic 2o duxwillbecausedtovaryinthepick-upcoii laccordingtotheshapeoitherotor.astherotor revolves. The rotor altersthe magnetic reluctance o! the path oi the ilux. This generates the desired wave-shape of voltage in the pick-up coil which is ampiiiied by a vacuum tube amplifier and applied to the horizontal deilecting 1 coils of th'e deilecting yoke.

Pig. 3 shows the linear saw-tooth character-lp ticcurveoi'currentappliedtothehoriacntaldeiiecting coils. and illustrates how this current through the coils varies with time. This current through the horizontal deilecting coils causa the electron beam to sweep periodically aero. the mosaic. Ine linearly rising portion of th'e curve corresponds to the constant rate at which the beamistransverselymovedacrossthemosaic. I'he return portion oi' the curve corrponda to the rapid return of the beam to the opposite and of the mosaic after the completion of its periodic traverse. 'I'he time interval represented by intercepts a-b of Fig. 3 curve. corresponds to the time in which the beam is imiiormly swept borlzontally across the mosaic. Th'e shorter time intercept b-e represents the rapid return in- 45 tervaloi'thebeamioritsperiodicexcursion.

The horizontal deiiecting coils are contained inaso-calledyokewhichalsocontalnsthevertical deiieeting coils. These coils are so arranged in the yoke that they cause the existence of two magnetic ilelds at right angles to each other. One field is used for horizontal dedection and the other field is used for vertical deilection. An electromagnetic ileld due to the action of the horizontal deilecting coils deilects the electron beam at right angles to the field lines of force. and at right angles to the axis of the tube. The deilecting yoke is placed external to the inbe. usually slipped over the lona rolmd neck o! the bulb.

lhe vertical deilecting voltage applied tothe vertical deiiecting coils of the above mentimed yokemaybeobtained i'roma stair-stepvoltage device such asillustrated inl'ig. 2. 'misconsistsoiavoltagedroppingcircmtthepotenthls atvariouspointsotwhichareconnectedtnscgmentsso'arrangedastoiormasegmentedring. Asolid contact strip 2l is located adlalt to. butlnsulatedi'romthesegmentedringll. A wipingbrushlliscaluedtorotateacrosthese is transferred tcthe'solid ring as contact madefromtheilrstto'thelastaegmentinthe rlng. 'Iheilrstsegmentisconnectedtotbe the solid ring during the interval vlJ---c, Fig. 3.

nizing impulse b-c Fig. is generated in the synchronizing impulse pick-up coil during the return interval b-c Fig. 3, and during the same interval b-c Fig. 4 when the vertical deilecting current is being increased. The synchronizing impulse amplitude is so controlled by its amplier and applied to the picture-tone ampliermodulator in such a manner that the modulated output signal is greater than any picture-tone signal level. This increase in amplitude actu- -ates`y selective equipment at the receiving end whichcauses the recording electron beam in the recording tube to move horizontally in synchro- The solid ring is connected to a vacuum tube amplifier (not shown in detail) the output of which has for yits load the lvertical deilecting coil. 'I'his effectively applies a stair-step of cur-" ,nisni' with the transmitting electron beam in the iconoscope, as will be explained.

\ The amplified picture-tone signals at the outputoftliepicture-tone amplifier are conducted rent through the vertical deflecting coil. Fig. `4 d shows the characteristic stair-step curve offcurrent through the vertical deilecting coil. This current causes the electron beam to be dropped down by a predetermined amount at the mosaic during the interval b-c Fig. 3 when the horizontal deilecting coils are returning the beam to the starting end of the mosaic. The portion of the curve represented by the intercepts a-b Fig. 4 is of a constant value and corresponds to the constant vertical position of the electron beam as it is periodically swept across the mosaic. The portion oi' the curve represented by interceptsb-c corresponds to that interval during which the wiping contact 22 is being transferred from one segment 2| to an adjacent segment 2l The voltages are preferably so selected at the voltage dropping circuit connections that the current which will flow through the vertical deflecting coils Will cause the electron beam to drop down one ftieth of an inch at the completion of each horizontal excursion across the mosaic. Thus the mosaic is scanned progressively. The intercepts a-b in Fig. 4, 5, 6 and 7 represent equal time intervals during which progressive scanning is accomplished. Intercepts b-c Fig. 4, 5, 6 and 7 represent equal time intervals for the return of the scanning electron beam and the generation of the synchronizing impulse to be described. The current values as shown in th'ese graphs are not drawn to scale.

In order to reproduce the message as transmitted over wires by the electrical impulses generated by the iconoscope, it is necessary that the recording tube electron beam be controlled in intensity according to the intensity of the transmitted picture-tone signal and also be maintained in horizontal synchronism with the iconoscope scanning beam.

Horizontal synchronism is accomplished by means of a synchronizing impulse generated and amplied at the sending equipment during the interval b-c Fig, 5. This synchronizing impulse extinguishes the iconoscope scanning beam and at the same time is applied to the picture-tone amplifier-modulator for transmission to the recording equipment at the receiving end. Fig. 5 shows the characteristic curve of the synchronizing impulse of voltage. Fig. 6 shows the Jtimephase relationship of the horizontal sweep current H; the vertical deflecting current V; and the synchronizing impulse voltage S.

The phase relationship of the synchronizing impulse is obtained by a second inductor-type generator mounted on the same shaft as the horizontal sweep generator. 1 By arranging the two rotors with the proper position with respect to each other, it will be seen that the synchro- *toanampliller arid modulator stage (Fig. l) by leadsf- An-gaudio frequency oscillator generating 2500 cycles per 4second is impressed upon the pic- `Ature-tone1amplifiermodulator. The type of modulator whichl'fprefer to use is commonly termed grid-circitfmoduiation.

v Ina.stralcii.asV negative transmission is used, lt-willme understood by one skilled in the art that white tones in the image being transmitted will be representedv by low amplitudes in the picture signal. relative amplitude is indicated in Fig. 7. Suc' v s`siyelydeeper grays are represented by higheramplitudes, until at the level shown in the diagram (d-d Fig, 7) the amplitude represents a total absence of light reflected from the message being transmitted. This signal value is that which would be transmitted from the black print on the message. The minimum or zero values (e-e Fig. 7) correspond to the background of the printed message.

Since this method of transmission is designed primarily for the transmission of printed or typed messages of uniform density the signal output of the picture-tone amplifier-modulator would have the envelope as shown in Fig. 7, which is a graphical representation of a typical signal. In effect, the 2500 cycle audio frequency is suppressed or permitted to ilow with a predetermined amplitude as the background or picture-tone, respectively, is being transmitted.

The time interval a-b Fig. '7 represents one scanned line of the message the reilected light from which is focused upon the inconoscope mosaic. The time interval b-c represents that time during which the synchronizing impulse of greater amplitude, or infra-black is transmitted. The ordinate E is the relative voltage intensity of the picture-tone signal and the synchronizing impulse signal. Fig. 7 is a schematic illustration and is accordingly not drawn to scale. In operation it may be that '75 to 80 percent of the maximum amplitude of the signal will be devoted to the picture-tone modulation while the remaining 20 or 25 percent of the signal amplitude is devoted to synchronization.

. The envelope of the 2500 cycle audio frequency represents the picture-tone signal modulations superimposed upon the audio frequency. The envelope is symmetrical with respect to the horizontal axis as will be evident to those skilled in the art. (Fig. '7.) The signal level represented by d-d corresponds to the black picture element; the zero level e-e corresponds to a white picture element; the maximum level f-f corresponds to the synchronizing impulse signal.

It is to be understood that the image to be transmitted is stationary during the scanning operation, It is placed in front of the iconoscope and an intense light is directed upon it. The light is under the control of an operator. Light reflected from the image is focused through a suitable lens combination upon the iconoscope mosaic upon which the electron beam performs the necessary Progressive scanning. as previously explained.

The received message, however. is preferably recorded upon a sensitized film or strip responsive to the e of an electric current through it. This strip is advanced past the recording tube in steps corresponding to the steps oi' vertical displacement oi' the transmitting scanning electron beam.

The synchronizing impulse signal, produced by the synchronizing impulse generator at the transmitting equipment during the interval when no picture signals are being generated or transmitted, is used at the remote receiving station to operate selective equipment for automatically advancing the receiving recording paper past the recording tube in a manner to be described. 'Ihls function of the synchronizing impulse is in addition to synchronizing the horlzontal motion of the transmitting and recording electron beams as described above. Further, the synchronizing Silml suppresses the recording tube electron beam during the synchronizing period.

The receiving equipment (Fig. i) comprises a composite, direct current operators signal relays, line coupling panel, equalizer, level control, ampliiler and demodulator, picture-tone amplifier, synchronizing impulse amplifier, blocking oscillator, linear-sweep generator, horizontal deflecting amplifier, line feed amplifier, line-feed mechanism, and recording tube, with associated power supplies.

The sending equipment, (Fig. l) illustrates a wire transmission system for the message signals and synchronizing impulse. 'I'he output of the picture-tone amplifier-modulator stage may be transmitted to a remote receiving stage along wirelinesorbyradio Thesisnalsinthismethodofwiretransmissionareimpressed upon a carrier frequency modulator stage. A 7000 cycle carrier frequency oscillator produces a carrier wave which is modulated by the 2500 cycle picture-tone frequencies in the picture-tone amplifier modulator. The type of modulation which is preferably used is that in which a bridge arrangement of unidirectional impedances. for example copper-oxide rectiflers, areconnectedintheform oi'asquare,withone impedanceineachsideofthesquare,connected so asto be conductive in a predetermined direcmmsmpuaer (1113.1) .impunes mengnals from the picture-tone amplifier-modulator Thelinecouplingpanelandcompositeprovideameansofintmducingthedirectcurrent operatingsignalsfromthesignallingcircuitsto thelinealongwithtbemodulatedcarrierfrequency.insuchamannersstopreventinter betweenthetwo.

itisdesignedtoseparatethedirectcurrentoperatingsisnalsfromthemodulatedcarrierfrequency. Itisanetwork of reaistances,induct snces,andcapacitances,sosrrangedthatthedi rect currents are divertedthroughrelays'toa signallying circuit without interferingwiththe modulated carrier i' signalswhichare psssedtothelinecouplingpanelandthenceto therestofthereceivingcireuit,tobedescrihed.

The line coupling panel transfers, throh transformer action, the modulated carrier irequenciespassedbythecompositetotheequaliser.

Themlrpoaesoftheequsliseraretoslowdown the velocity of propagation of the hither frequencies,morethanthelowerfrequencies.inthe band-width transmitted; to attenuate the higher frequencies more than the lower frequencies in the band width. This network of impedances compensates for amplitude and phase distortion of the modulated carrier frequencies introduced bytheimpedancecharacteristic ofthelinesused .astheconnectingmediumbetweenthesending sonal and remote receiving equipment.

The level control provides a means of oontrolling the amplitude of the modulated carrier frequency, before application to the receiving ampliner-demodulator, and the rest of the local equipment. It is necessary to control the level ofthesesignalswinsureagainstinterferencein adjacent local circuits.

-'i`.'he ampliiier-demodulator amplifica the carrier-frequency modulated signals impressed upon it and rectifies them. In passing the rectied modulator carrier through a low Dass iilter which is part of the amplitler-demodulator the desired picture-tone signals and synchronizing signals are obtained, as is mual. This output signal wave-form corresponds, for example, to the anvelope of the upper side-band of the, graphical representation in Fig. 7. This signal wave form is applied to the picture-tone ampliiier, and the synchronizing impulse generator, which are selective circuits in parallel.

Sinceadarkelementinthetransmittedmessageresultsinalargeamplitudeofsianthe output of the` picture-tone amplifier will correer'may notr be sumciently free from distortion under actual working conditions to be used as an accurate means oi' triggering the linear sweep generator for horizontal deflection. Accordingly, as is usual. there may be inserted a blocking oscillator which will produce impulses, controlled by the synchronizing ampliiier', of constant amplitude and the correct duration to make the linear sweep generator circuit produce the required wave shape of sweep voltage (Fig. 3). 'I'he blocking oscillator should produce .positive pulses at a rate slightly lower than the correct frequency for the linear-sweep generator, and should be so designed that its frequency will be increased to the correct value automatically when fed with the synchronizing impulse.

The horizontal deiiecting plates 23 oi' the recording tube are actuated by the linear sweep oscillator, through the horizontal deilecting ampliiler (Fig. 1) which is a stage of push-pull ampliilcation. Thus the linear sweep generator is impulse excited by the synchronizing signals so that it will have the exact frequency of the transmitter horizontal scanning frequency. The electron beam of the recording tube will accordingly be oscillated horizontally across the face plate of the recording tube by the deilecting plates.

The balanced field method of deflection is used. The output of the push-pull horizontal detlecting amplifier (Fig. 1) is connected through a transformer to the deflecting plates 29. Each de'ilecting plate is connected to the second anode 28 of the recording tube through a high resistancHne or more megohms-and for deflection purposes one plate is lowered in potential by exactly the same amount as the other is raised.

, The high resistance is in parallel with the transformer secondary, and the deflecting plates, and is center tapped with the connection to the second anode.

'I'he horizontal motion of the recording electron beam will correspond to that of the transmitting electron beam. The phase adjustment of the recording beam is automatically provided by proper design of the impulse excited linear sweep generator in relation to the predetermined occurrence of the periodic synchronizing impulse at the end of each scanning line.

The output of the synchronizing impulse amplier is connected also to the line-feed amplifier which ampliiies the impulse which is applied to the automatic line-feed mechanism for advancing the recording paper past the recording tube (Fig. l).

The line-feed mechanisms may, for example, be Well-known electromagnetic periodic advancing means which is actuated by the electrical impulses produced at the end. of each scanning excursion of the electron beam, namely, the synchronizing impulse. The paper is accordingly advanced the proper amount during this interval so that the adjacent line may be scanned during the next cycle of operation.

The essential elements of the recording tube are a glass bulb 23 with a narrow neck 24, a specially designed face plate 25 at the end of the glass bulb, an electron gun 26, means for shaping and focusing the electron beam, and means for defiecting said beam across the internal part of the face plate in a horizontal motion, and means for controlling beam intensity.

Fig. 1 shows a schematic drawing of the recording tube. The electron gun 26 generates a beam lof electrons of rectangular cross-section,

for this purpose, approximately 0.5 inch high and 0.125 inch wide. -The beam is acceleratedand focused by anodes 21 and 2l so that it impinges upon the face plate with a cross-sectional area approximately 0.5 by 0.015 inch.

The `horizontal deecting plates 23 are oonnected to the horizontal sweep amplifier as above described for moving the electron beam horizontally across the face plate in a predetermined, periodic manner.

The accelerating-focusing anodes 2l and 2l are connected to suitable taps on a high-voltage power supply bleeder circuit 30. This provides bi-potential immersion lens accelerating and focusing action.

The beam intensity is controlled by a screen grid 3| and control grid 32. The screen grid 3l has applied to it a constant predetermined potential of negative polarity with respectto the cathode 33 such that it exerts a definite amount of suppression upon the electron beam.

The control grid 32 is connected to the picture-tone amplifier and responds according to the picture-tone signals, overcoming the action of the screen grid during the interval when a black picture element is being transmitted. During this interval the control grid 32 increases in potential in a positive direction permitting electron flow, as will be apparent to one skilled in the art. .The transmission of a white element of the message, however, causes the control grid 32 to decrease in positive potential, thus aiding the screen grid 3l to suppress the electron beam.

The cathode 33 is a thermionic emitting surface heated by a separate heater circuit, the potential of which is not shown.

The face-plate or lens 25 of the recording tube has set in it a series of teeth 34, insulated from each other, acrossthe front of the tube forming a recording stylus comb. They provide a means of conducting the beam current to the outside of the tube, where it is caused to ilow through the sensitized recording paper 35, thus recording the transmitted impulses from the transmitted message.

A preferred form of recording stylus comb consists of german silver teeth 34, preferably 50 teeth to an inch, each tooth 0.015" thick, and 0.5" high and of a length which varies with its distance from the center of the comb. Those teeth toward the ends of the comb should be progressively longer than the teeth in the middle of the comb. 'Ihe center tooth is 0.5" long, and the other teeth vary in length up to about 1.0. The comb is 7" in length across the front of the tube and 0.5 high. Each tooth is approximately arrow-shaped with the external tip 36 blunted to form a square 0.015 on each side. The external tips of the teeth in the comb as shown in Fig. 9 form a straight edge along the length of the comb. The teeth extend into the tube further on the ends of the comb than in the middle in suchv a manner as to form a curved inner surface the radius of curvature of which is approximately the distance from the inner base of the Acomb to the nearest end of first anode plates 21 (Fig. 1) of the electron gun. A perspective of one enlarged tooth is shown in the acompanying drawings, Fig. l0, and the arrangement of the teeth in the combis shown in Fig. 9. These figures illustrate the preferred shape and arrangement of the teeth between which are insulation strips 31 and sealing compound 38, used to form the comb and to render an air-tight joint where they pass through the faceplate 25.

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5. In a communication system, a cathode ray tube, a plurality of insulated contactors passing through the faceplate of the tube the inner ends of the contactors being arranged in an arc about the final aperture of the electron gun as a center, means for directing rays of electrons within the tube successively and selectively on the contactors, and means for holding a chemically prepared film against the ends of the contactors outside the tube so that selected contactors will affect the lm.

6. in a communication systema a cathode ray tube, a plurality of insulated contactors arranged in a row and passing through the faceplate of the tube, means for directing rays of electrons within the tube successively and selectively on the contactors, a film of carbon fibrous substance treated with aluminum on one side and with silver in colloidal state on the other side and means for holding the lm with its silver side against the ends of the contactors outside the tube so that the electronic currentin selected contactors will affect the iilm.

7. In a communication system, a cathode ray tube, a plurality of insulated contactors arranged in a row and passing through the faceplate of the tube, means for directing rays of electrons within the tube successively and selectively on the contactors, means for holding a chemically prepared lm against' the ends of the contactors outside the tube so that selected contactors will affect the nlm, and means for advancing the nlm step by step.

8. In a communication system, a cathode ray tube57 a plurality of insulated contactors arranged in a row and passing through the faceplate of the tube, and means for directing rays of electrons within the tube successively and selectively on the contactors.

9. 'in a communication system, a cathode ray tube, a plurality of insulated contactors arranged in a row and passing through the faceplate oi the tube, means for moving the ray of electron discharge along the row of contactors, and means for modifying the electron ray so that it has a shorter dimension in substantially the direction of movement and a longer dimension at approximately right angles thereto.

CLARENCE F. KERN'KAMP.

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