US2017883A - Television system - Google Patents

Description

Oct. 22, 1935. V. K. ZWORYKIN. 2,017,383

. TELEVISION SYSTEM- Original Filed March '17, 1924 3 s ts-sh t 1 WIIIIIIH E H INVENTOR Wad/MirK Zworyh'n g L [ll w I w I 0a. 22, 1935. v. K. ZWORYKIN ,0

. mmmwxsmn SYSTEM, Original Filed March 17, 1924 sheatS-shm 2 INVENTQRV d ATTQREY Oct. 22, 1935. v. K. ZWORYKIN TELEVISION SYSTEM Original Filed March 17, 1924 3 s t qs t 3 l lll lll lw Q-D E lv/ Mr ga x I" -1 sag 1 a b hm WITNESSES: INVENTOR Wad/77w fl. Z wary/rm a/ yd/w/ ATTORNEY Patented Oct. 22, 1935 PATENT oF FIca TELEVISION SYSTEM Vladimir K. Zworykin, Haddonfleld, N. J.

Application March 17, 1924, Serial No. 699,630 Renewed June 27, 1931 23 Claims.

My invention relates to television systems. One of the objectsof my invention is to provide a system of television that shall be suitable for, use in conjunction with a telephone system. Another object of my invention is to provide a system of the above indicated character in which the amount of equipment at a subscriber's substation is a minimum, and the other equipment is common to all the subscribers and is located at a central ofllce.

A further object of my invention is to provide a duplex method :for the transmission and reception of images or pictures by television.

There. are other objects of my invention which, together with the foregoing, will be described in the detailed specification which is to follow.

While in the drawingsI have shown my invention applied to a telephone system, it will be understood that it is not limited to this use, but

' it may be arranged to'secure the transmission and reception of television over an ordinary power circuit or in other places, as will be obvious.

In practicing my inventioml provide, in addi-- I -tion to the ordinary telephone equipment at each substation, transmitting and receiving apparatus for transmitting the image of the party calling to the receiving apparatus at the substation of the called telephone subscriber. The television transmitting apparatus associated with the substation of the called subscriber causes the image of this party to be reflected by the television receiving apparatus at the calling subscriber's substation.

Referring now to the drawings, comprising Figures 1 to 3, inclusive, I have shown by means of conventional diagrams, circuits and apparatus for connecting one substation A with another substation A.

The apparatus shown in Fig. 1 is associated with the subscribers substation A and comprises the transmitting and receiving television apparatus. In Fig. 2, a portion of the apparatus at the central office is shown comprising means for connecting the substation A to the'substation A. with the substation A and comprises television and transmitting apparatus. c

The substation A is of the ordinary type of 50 subscriber's telephone station, having the usual talking instrumentalities. At the substation A, the line conductors I and 2 are connected through a'transformer '3, with a detector triode 4. The filament of the detector triode 4 is also c nn d o h fi ame 5 9 a sewage-tr y The apparatus shown in Fig. 3 is associated tube 6. The cathode-ray tube 6 is somewhat similar to an ordinary cathode-ray oscillograph, I being provided with a hot cathode, a diaphragm I, a tubular anode 8 and plates 9 and i0.

I A portion II or the cathode-ray tube 6 is sepa- 5 rated from the other portion by means of a composite plate I 2. -This plate is formed first of a thin layer of aluminum foil M about .0003 inch in thickness, upon which is placed a layer of aluminum oxide l5 about ,0001 inch in thick- 10 ness. Upon the aluminum oxide I5 is placed a layer of photoelectric material which may be an alkali metal [6, such as potassium hydride. In front of the composite plate is placed a grid 40. The cathode-ray tube is filled with an atmos- 15 phere of argon at low pressure.

A lens 18 is held in place before the cathoderay tube by means of a container I9. This lens. isadapted to project light. upon the-surface of the photoelectric material. I a small hole cut therein, is positioned before the cathode-ray tube 6. Through this opening, the lens l3 focuses the image from the other side upon thesurface of the photoelectric globules.

A cathode-ray tube 23 is positionedon the othengg side of the mirror,20, in the manner shown. The cathode-ray tube- 23 is similar to an ordinary cathode-ray oscillograph, being provided with a."

hot cathode 24 a grid 25, a tubular anode 23, plates 21 and 28 and a fluorescent screen 23. 30" The plate circuit of the detector triode 4 is connected with the grid 25 of the cathode-ray tube 23. a

An oscillatory circuit 3|, including the primary windings ofthe transformers 32 and 33, is connected to the line conductors I and 2 through the transformer 30.? The secondary winding of the transformer 32 is connected to a detector triode 34, while the secondary .winding of the transformer 33 is connected to another'detector triode 34 The transformer 32 is resonant to the carrier current that is modulated at a pre-"v determined operating frequency, while the transformer 33 is resonant to the carrier current that is modulated at another predetermined operat- 4 ing frequency.

The output circuit of the detector v34 is connected to the coils and and 31 and 38. These coils 35 and 33 are associated with the cathode-ray tube 23 and are so disposed with respect thereto that the magnetic field that they may set up is parallel to the electrostatic field that may be set up by the plates-21 and 23. The coils 31 and 38 are disposed in a like relation to the cathode-ray tube 6. 1 u

A mirror 20, having 20 I of the modulator triodesj43 and 44.

The output circuit of the detector triode 34' is connected to the plates 21 and 28 and 8 and I inthe cathode-ray tubes 23 and 8, respectively. These plates are adapted to set up an alternating electrostatic field to deflect a cathode beam in one direction, while the magnetic field set up by coils as and as and s1 and as deflects the cathode beam at right angles to that set up by the electrostatic fields.

The grid 40 in the portion II of the cathoderay tube 8 is connected to an amplifier triode 4|. The output circuit of the amplifier triode 4| is connected through a transformer 42 to the modulator triodes 48 and. 44. A circuit including an The normal operation of the oscillating cur rent in circuit, including the oscillator triode 48, does not apply a high carrier current to the line conductors I and 2, by reason of the fact that this carrier current is neutralized by the action The only manner in which the carrier current can be broadcasted is by a change in the primary winding of the transformer 42 which causes a pure modulated high frequency current to traverse the conductors I and 2 in accordance with the current in the primary winding of the transformer. The high-voltage current applied to the anodes 28 and 8 of the cathode-ray tubes 23 and 8, respectively, is obtained from a rectifier 52 that is connected to the source of alternating current 58.

The line conductors I and 2 of the substation A terminate at the exchange in an answering jack J, as shown in' Fig. 2. Ordinary line and cut-off relays 60 and BI are associated with the Jack J at the exchange. A line relay 80 is adapted to control aline lamp, 82. The line of the substation A may be extended by means of a .cord circuit 0.

The cord circuit 0 is of the usual type, having an answering plug P and a calling' plug P-I.

The, cord circuit 0 is also provided with an answering key K and a ringing key K-I The plug P-I of the cord circuit 0 may be inserted into any one of the multiple jacks, such as J-I, leading to the desired subscribers telephone. By means of a transformer 88, the cord circuit 0 is associated with an amplifying circuit/that ineludes an amplifying triode 86.

Modulator triodes 81 and 88 are associated with the amplifying circuit through a transformer 88.

. A circuit, including an oscillator triode I0 that is adapted to generate an oscillating current, is

associated with the modulation circuit through a transformerll. By means of a transformer I2,

an alternating-current generator I8 is associated .with the modulating circuit including the modulator' triodes 81 and 88. An alternating-current generator I4 isalso associated with the modulating circuit through a transformer I8.

The oscillating current generated by the os- .cillator triode I0 isnot normally applied to the cord circuit, by reason of the fact that, by the action of the modulator triodes 81 and 88 and the primary winding of thetransformer 88, the output of the oscillator triodes is neutralized. The generator" is adapted to generate an alternating fied by the amplifier. triode 88 and applied to all u the cord circuits in the system through transformers, such as 85. The equipment including the triodes 68, 81, 88 and I0 and the alternators I3 and I4 is common to the exchange.

The called substation A, shown in Figs. 2 and 3, is similar to the substation A previously described, and its line, comprising conductors 80 and 8]. terminates at the exchange in an answering jack (not shown) and in multiple jacks, such as JI The line conductors 80 and 8| are also connected by means of a transformer 82 (Fig. 3) with a detector triode 88. The filament of the detector triode 88 is connected to the filament'84 of a cathode-ray tube 88.. The cathode-ray tube 88 is similar to the cathode-ray tube 8 at the substation A, previously described, having a hot cathlayer of aluminum foil 82, a layer of aluminum oxide 88 and a layer of photoelectric material 84. Disposed in front of the composite plate is a grid H8. The cathode-ray tube contains an argon vapor at low pressure.

A container 88 holding a lens 81 is placed over the end of the cathode-ray tube. A mirror 88 is placed at anangle of about in front of the lens 81. The mirror 88 has a hole 88 cut therein 0 through which the lens 81 reflects the image on the screen 84.

The plate circuit of the detector triode 88 is connected with a grid I00 in a cathode-ray tube IOI. The cathode-ray tube |0| is similar in all as respects to the cathode-ray tube 28, having a hot .cathode I02, a tubular anode I 08, plates I04 and I05 and a fluorescent screen I08, the whole being enclosed in an evacuated container I01.

An oscillatory circuit III is .cormected to the line conductors 80 and 8|, through a transformer 0., The detector triodes H2 and 8 are associated with the oscillatory circuit I by the transformers H4 and H8, respectively. The transformers, II 4 and H8, are resonant to current of certain frequencies, as before described in connection with the equipment at the substation A.

The grid 8 of the cathode-ray tube 88 is connected to the gridcircuit of an amplifier triode Ill. .The output circuit of the triode I I1 is connected through the transformer II8 with modu-' lator triodes H8 and I20. The circuit including the oscillator triode I2 that is adapted to gen-'- erate' a current of' a. definite frequency, is connected to the modulator circuit through a transformer I22. The output circuits of the-modulator triodes unconnected through a transformer. I23 with the grid circuit of an amplifier triode I24. In turn, the output'circuit of the triode I24 is connected tome line conductors through a transformer I28. Ordinarily, unless there is a change in the flow in the primary winding of the transformer III, the alternating current generated by the circuit including the triode I2| is not applied to the line conductors and 8I. 7s,

station A what number he desires.

aor'ases In the drawings, the various triodes and cathode-ray tubes at the substations A and A, respectively, are in an energized condition. However, this has only been done in order to simplify the drawings, it being obvious that it is quite possible to render the various circuits at each substation inoperative until the receiver thereat is removed from the switch hook.

Having briefly described the apparatus shown in the drawings, I will now explain its detailed operation. For this purpose, it will be assumed that the subscriber at substation A desires to call the subscriber at substation A. In order to accomplish this result, the subscriber at substation A will remove his receiver from the switch hook, shown in Fig. 2. As a result of this operation, a circuit is closed for the line relay 50 on the line circuit at the exchange.

The line relay 50, upon being energized, at armature I50 closes a circuit for the line lamp 62. By the lighting of this lamp, the operator's attention is drawn to the fact' that the subscriber at substation A desires a connection. Therefore,

she will insert the plug of an idle cord circuit,

which, it will be assumed, is the plug P, of the cord circuit into the jack J. As a result of the insertion of plug P in the jack J, a circuit is completed extending from battery. hrough resistor I I, lamp I 52, sleeve of the plug P, sleeve of the Jack J and the winding of the cut-off relay 5| to ground. The cut-off relay Si is energized over this circuit and operates to attract its armatures I53 and I54. By the latter operation, the circuit of the line relay 50 isopened, and this relay is deenergized to extinguish the calling signal 62. The supervisory lamp I52 would also be energized over the above circuit were it not for the fact'that there is a circuit completed over the two-line conarmature I 55, shunts out the answering supervisory lamp I52. The operator'will now operate key K, in order toassociate her head set with the cord circuit, and will ask the subscriber at sub- Upon hearing the number, the operator will test the line of the called substation by touching the tip of the plug P-I to the sleeve of the Jack associated withv the particular'line desired. If the line is idle, the operator will insert the plug into the line jack and will then operate a ringing key K-I.

When the plug P-I is inserted in the jack J-I a circuit is completed for the cut-off relay I51 over a path extending from battery through resistor I 55. supervisory lamp I59, sleeve of plug P-I, sleeve of jack J-I and the winding of cutofl relay I51 to ground.

The cut-oil relay, upon being energized, at armatures I55 and I BI, disconnects the line relay I82 from the line circuit. The supervisory lamp I58 is also energized over the above circuit.

When the ringing key K-I is operated, ringing current from the generator I53 is applied to the line conductors 80 and 8| of the calling line. As

a result of this operation, the bell at the substation A-I is operated.

The subscriber may converse over the circuit shown in heavy lines in the drawings.

As soon as the plug P is inserted into the jack J of the calling line, the carrier current modulated by the current from the generators I3 and I4 is 5 transmitted over the line conductors I and 2 and through the transformer 30. By the operation of the transformer 32, the carrier current that is modulated by current from the low-frequency generator I4 is applied to the detector 34. By the operation of the detector 34, the high-frequency carrier current is eliminated and an alternating current of a frequency the same as that generated by the generator I4 is applied to the coils 35 and 36 of the cathode-ray tube 23 and the coils 31 and 38 of the cathode-ray tube 6. By the operation of the transformer 33, thecarrier current modulated by the current from the highfrequency generator I3 is applied to the detector 34a. The output of this circuit is connected to the plates 21 and 28 of the cathode-ray tube 23 and to the plates 9 and III of the cathode ray tube 6.

By reason of the fact that the coils and 36 of the cathode-ray tube 23 are sov disposed with 25 respect to the plates 21 and 28 that the magnetic field generated by these coils lies parallel to the electrostatic field generated by plates 21 and 28, the cathode beam in the tube is caused to be defiected in one plane which is at right angles to the magnetic field set up by the coils. In a. like manner, the operation of the coils 9 and III of the cathode-ray tube 5 is deflected in one plane. By the application of alternating current of operating frequency to the plates 21 and 28, the cathode- 5 ray beam in the tube 25 is deflected in a plane at right angles to the one before mentioned and by its application to the plates 9 and III the cathoderay beam in the tube 5, is similarly deflected.

The resultant action of the magnetic and elec- 40 trostatic fields is such that the cathode beams cover the whole area of the fluorescent screen 29 and the composite plate I 2. 'By reason of the-frequency of the currents used, the whole area of the screen 29 and the plate I2 is covered in 1/20 of a second. e

As the cathode-ray tubes 6 and 28 are so disposed close to the telephone that. when the calling, subscriber removes his receiver, he will be within the objective of the lens I8 and his image will be projected upon the photoelectric material Iii of the composite plate I2. For each particular point of the image on the photoelectric globules, there will be a certain electron emission from the globules in accordance with the intensity of the light. 55 This electron emission ionizes the argon gas'in the container II and gives a connection of varying resistance between the grid 40 and various portions of the photoelectric material in accordance with the light from the party telephoning. 6o

However, the latter is without effect, except at. a certain point at which the cathode beam is located, as will be explained.

At the point that the cathode beam impinges on the composite plate, it will be of 'suflicient velocity to penetrate the aluminum foil and aluminum oxide. thereby making a connection from the grid of the amplifier triode 4| to the filament of said triode, and the amountof current flow in this circuit wili'be directly proportional to the intensity of the light falling upon the photoelectric globule thatis covered by the cathode beam, that is governed by the light intensityof the image of the party calling.

, Thus, as the cathode beam coversthe whole is the carrier current, generated by the circuit including the oscillator 48, will be modulated in accordance with the image of the party point by point in a definite sequence. This takes place in l/20 of a second. That is, when there is current flowing in the grid circuit or the amplifier triode 4I, this current is amplified and transmitted to modulator triodes 43 and 44, whereby the highfrequency current generated by the oscillator 46 is modulated in accordance with this current and transmitted by means of transformer 41 to amplifler triode 48. The output of the amplifier triode 48 flows through the transformer 49 and over the line conductors I and 2.

At the receiving station, by the action of the detector triodes H2 and H3, the cathode beams in the cathode-ray tubes 85 and II" are deflected in synchronism with the cathode-ray beams in the tubes 6. and 23 at the calling substation. That is, these beams are all in the same relative position at the same time.

By the operation of the transformer 82, the high-frequency current which is modulated in accordance with the varying intensity of light is transferred to the detector 83, whereby the carrier frequency is eliminated and the current is applied to the grid I00 of the cathode ray tube Ifll. By the varying potential upon the grid, the intensity of the cathode ray which strikes the fluorescent screen is regulated in accordance with the intensity of light falling upon the particular portion of the composite plate at which the cathode beam in the transmitting tube 6 is striking at that particular instant. Thus, the intensity of the light given oil? by the fluorescent screen IIil at that particular point is relatively, to other spots thereon, the same as the intensity of the light falling upon that particular point from the object at the transmitting station.

In a like manner, all the various points of the object are transmitted and recorded in varying intensity of light for a particular point. Thus,

' the image of the party calling is reproduced on the fluorescent screen III! in 1/20 of a second. This image is reflected to the eye of the observer by means of the mirror 98.

The transmitting tube at the receiving station is operated in a like manner and causes the carrier frequency generated by the circuit, including the oscillator triode 9|, to be modulated in accordance with the intensity of the light-falling upon the photoelectric material 54 at a particular point at which the cathode beam is impinging.

As the cathode beam in the receiving tube 23, at the substation A is in the same relative position, by the action of the detector triode. 4, a certain potential is placed upon the gridv 25 ofthe receiving cathode ray tube 28, and the intensity of the cathode beam striking the fluorescent screen 25 is modulated in accordance with the intensity of light at that particular point on the screen at the substation A. As this takes place.-

in'1/20 of a second, the whole image will be reproduced in that time and reflected to the eye 7 of the calling party by means of the mirror".

By reason of the high frequency at which the image istrtted, any movement of the person at either the substation A or substation A will be reproduced at the other substation, and

the party thereat will be able to see such movement.

between the anodes and the cathodes in the area of the composite plate in l/20 of a second,

It will be seen that the high voltage applied from a source of alternating current 53 through the operation of the rectifier 52. This gives a unidirectional pulsating current. As this potential governs the speed of the cathode rays, the

cathode beam is made up of a number of im- 5 pulses in accordance with the alternations in the alternating current supply. This action is intensifled by reason of the fact that thepotential on the grids of the cathode ray receiving tubes is supplied from a rectified alternating current 10 by the action of the detector triodes. The cathode 'beam is thus made up of what corresponds to a number of impulses, and the tendency of the fluorescent spots to spread is minimized. The

same arrangement holds true for the substa- 15 7 serves to apprise the operator of the replacement :5

of-the receiver at substation A. I

The replacement of the receiver at substation A causes the deenergization of. the relay; I64 and' the lighting of the lamp I59, whereby the operator is apprised that the receiver at substation A- has 30 been replaced. The operator will now withdraw the plugs P and P--I from the jacks J and J. The connection is released in the above manner.

In the event-that the called line is busy when the operator attempts to connect thereto, there 35 will be a battery potential upon the sleeve of the jack anda click will be produced in the operator's ear, when she tests it with the tip of the calling plug. She will then inform the calling subscriber that the line is busy. 1 0

From the above, it will be seen that I-have provided a system whereby it is possible to simultaneously transmit and receive vision over a single pair of wires, and that any movement of the obiects under observation at either station will cause 45 a corresponding movement in the reproduced image. 1

It is, of course, obvious, that as many views of I the object mayibe transmitted as desired-by reg-v ulating the frequencies of the synchronizing currents.

My invention is not limited to the specific arrangement of the apparatus illustrated, but may be variously modified without departing from the spirit and'scope of my invention, as set forth in 55 the appended claims.

the central oflice and operating over said lines for operating said devices in synchronism and framing the resulting image reproductions, and means controlled by the.image-'-transmitting device and cooperating with said lines for causing said image- 7 reproducing device-to reproduce the image'of the subscriber at the calling station.

2. In a system of intelligence communication. the combination with telephone lines, substations on said-lines. a, central ofilce and means at (I the central omce for connecting a calling line to a called line, of means at the substation on the calling lineand at the substation on the called line respectively for generating an electron stream, means at both of said stations for deflecting the respective electron streams and means for operating said deflecting means, said operating means comprising a plurality of sources of electrical energy of predetermined frequency at the central station operatively associated with the connecting means between the calling and called substationswhereby the developed electron streams at each substation are synchronized and framed in time and like deflections of the electron stream at both stations are simultaneously produced. 3. In combination with a telephone system havingsubstations, lines to the substation and a central exchange by which the lines may be connected, television sending devices, one at each substation, television receiving devices, one at each substation, point-selecting means constituting part of each television device, a source of energy associated with the central exchangeand impressing energy upon the lines connected by said exchange, means for modulating said energy according to the desired system of point selection, and means at each substation for receivingsaid energy and controlling the point-selecting means of both television devices at said substation in accordance with the modulation of said energy, whereby four television devices, located two at one and two at the other of a pair of connected substations, will be caused to select corresponding points simultaneously and means at the central station for causing the image production and reproduction at each point to be in proper frame and synchronous relationship.

4. In the art of simultaneous communication by telephone and television between two of a plurality of operating stations connected through a single central station, the method which comprises developing at each of the stations a cathode ray for producing image signals, developing at each of the stations a cathode ray for reproducing image signals, generating in the system at the central station electrical impulses of selected frequency, and utilizing the generated impulses to synchronize and frame the operation of the image signal producing ray at each station with the image reproducing ray at the opposite station.

5. Ina system for communication between any two of a plurality of three or more substations by television, apparatus for transmission by television'including at each substation a cathode ray tube having structure for receiving an image of an object located at a given position and apparatus for reception of an image by television including a second cathode ray tube, means at each substation providing for observation from substantially said position of a received image developed by said receiving apparatus simultaneously with transmission by said transmitting apparatus of an image of said object located at said position, a central station for connecting any two of the plurality of substations for two-way communication and means located at the central station for producing energy to synchronize and frame the image production and reproduction at each substation.

tive from the central station to synchronize and framethe image transmissionand reproduction at each selected two stations.

' 7. In a television system, a-central station, a

plurality of outlying sound and image transmit-'- 5 plurality of outlying stations each including a cathode ray image transmitting tube and a cathode ray image reproducing tube, means to connect any one selected transmitting and receiving station with at least one other station through the central station-to establish two-way :7

image signal communication betweenthe selected stations, and means-positioned at the central station and operative upon the establishment of connection between two stations for synchronizing the image transmission andv reproduction at each selected two stations.

9. In-combination, a plurality of subscribers stations each provided with television transmitting and receiving apparatus, a central star.- tion-having a single communication channel permanently established with each subscriber's station, means at the central station for connecting the communication channel for the transmitting and receiving apparatus of any one subscriber's station'established with the central station with the communication channel connecting the re- 4 ceiving and transmitting apparatus of any other .of the plurality of subscribers stations with the central station to provide two-way image communication between the selected stations, and means located at the central station andoperative upon establishing connection between the selected stations forsynchronizing and framing the transmission and reception of the image signals "at the selected stations.

'10. In a communication system, three or more 60 television transmitting and receiving stations, a central station, a single communication channel connecting each transmitting and receiving station with the central station, meant at the central station to establish connection over the single communication channel between any two transmitting and receiving stations to provide two-way I television communication between the connected stations, and means at the central station for establishing proper framing and synchronous analysis and reproduction of the television images at each station.

11. In combination, a plurality of subscribers stations each provided with image transmitting and receiving apparatus, a central station, means at the central station forconnecting the transmitting and receiving apparatus of .any one station with the receiving and transmitting apparatus of any other of the plurality of subscribers stations through a single con- (0 ducting circuit to provide two-wayimage com- ,munlcation between\-the -selected stations, and

means positlonedat the central station and oper- -ating upon the establishment of the connection betweenthe desired stations for synchronizing 7| image and sound transmitting and receiving station in the network to provide simultaneous twoway television and sound communication between the selected connected stations, and means at the central station for establishing proper framing and synchronous analysis and reproduction of the resulting television images at each station.

13. In'combination, a plurality of subscriber's stations each provided with television and sound transmitting and receiving apparatus. a central station, means at the central station for connectin the transmitting and receiving apparatus of any one station with the receiving and transmitting apparatus of any other of the plurality of subscribersf stations through a single conducting circuit to provide two-way image communication between the selected stations, and means for synchronizing and framing the transmission and reception of the image signals produced at each station. V l

14. In a commtmication system, three or more outlying stations each including television transmitting and receiving apparatus, a central station a single communication channel'connecting each transmitting and receiving station with the central station, means for producing at the central station a signal to indicate a desire for one outlying station to communicate with a second outlying station, means located at the central station to establish connection over the single communication channel between the calling station andany other transmitting and receiving station to provide two-way television communication between the connected stations, and means at the central station for generating electrical frequencies of predetermined value, and means operative upon establishment of connection between the selected outlying stations through the central station for supplying the generated frequencies to each station connected to synchronize and frame properly the analysis and reproduction of the television images at each selected two stations.

15. A two-way television system comprising transmitting and receiving apparatus, an optical system for the transmitting apparatus and an optical system for the receiving apparatus, a reflector having an opening therein through which light intensities representative of the subject of which the image is to be transmitted are adapted to pass to the transmitting apparatus and upon the reflecting surface of which the image produced in the receiving apparatus is observable by the subject of which the'image is being trans-- mitted. r

. A 16. A television system comprising a single signalling channel, terminal transmitting and receiving apparatus located at each end 'of the 818- nalling channel, a central station for connecting the apparatus 'at one end of the-signalling channel with the apparatus at the other end of the signalling channel, and means located at the central station for controlling by framing and synchronizing theproductionand-reproduction of s,o17,sss

image signals at each end of the signalling channel, whereby the image of an observer at each end of the signalling channel may be sent to the observer at the other end of the signalling channel simultaneously. 5

' and maintain synchronous production and re-'- production of image signals at each two stations. 18. 'A communication system comprising three or more subscriber's stations, each subscriber's station including cathode ray image transmitting and image receiving tubes, a reflecting device separating the transmitting and receiving tubes at each station-so that a subscriber at each station may simultaneously view, upon predetermined conditions, the image of a subscriber at a remote. station and simultaneously cause the production of imagesignals representative of the to viewing subscriber to be produced and transmitted to the other selected subscriber, a central station to connect the selected subscribers'stations one with the'other, a source of controlling frequencies provided at the central station for synchronizing the cathode rays generated at each station so that upon connection -of one subscrib ers station with another subscriber's station through the central station the cathode ray image producing and image transmitting devices 40 transmitted to the other selected subscriber, ass

central station to connect the selected subscribers stations one with the other, a source of controlling frequencies provided at the central station for synchronizing the cathode rays generated at eachstation so that upon connection of so" "one subscriber's station with another subscribers station the cathode ray image producing and image tr tting tubes at opposite ends of the 1 communication channel may be maintained in a state of synchronous operation. a

20; A visual telephony system including at least three subscribers stations each having a cathode ray image transmitting tube and a cath ode ray image receiving tube, a viewing device for v the receiving tube separating the transmitting 7o andreceiving tubes at each station so that a subscriber at each station may view in the viewing device, upon predetermined conditions, the image of a subscriber at a remote station, a central station, means positioned at the central sta- (6 tion for connecting any two stations with each other over a single communication channel, and means positioned at the central station for generating controlling frequencies for synchronizing the cathode rays generated at each station so that upon connection of one subscriber's station with another subscribers' station the cathode ray image producing and image transmitting devices may be maintained in a state of synchronous operation. i

21. The method of establishing communication between any two of three or more subscriber's stations each provided with image transmitting and receiving apparatus which comprises producing at each selected station an image of a subject located thereat, transmitting signals representative of the electrical image at one station to the other station, traversing a viewing plane at each station with an electron stream to produce light efiects thereupon, controlling the observable intensity of the light efiects' produced by the electron stream on the viewing plane of each station by the signals representative of the electrical image producedat the other station, generating at a central exchange point intermediate the two stations controlling signals, and controlling the coordinate positions of the controlled intensity light effects observable at each station in accordance with the intensity of the electrical image at a related position at the other station.

22, In the art of establishing two-way television over a single signalling channel between any two of three ormore terminal transmitting and receiving devices located at the ends of the channel and an intermediately positioned central sta-- tion for connecting the terminal apparatus at one end of the signalling channel with the apparatus of one other terminal point at the other end of the signalling channel the method which in-, cludes generating at the central station DSC11181? 5 tion frequencies for controlling the production and reproduction of image signals, producing electrical signals representative of a subject at a each end of the signalling channel, connecting the selected terminal points through the central 10 station .to convey the produced electrical signals from each end of, the channel to the opposite and, producing from the electrical signals at each terminal point an electro-optical image of the subject at the other terminal point, and synchronizingand framing the production of the electro-' optical efiects at each terminal point with the electrical image signals originating at the opposite terminal point by the oscillation frequencies generated at the central station. v

23. The method of establishing synchronized two-way television communication between two separated points which includes developing a cathode ray at each-stationfor causing image signal transmission to the .other station, developing a cathode ray at each station for reproducing an-image of a subject at the. other station, controlling the image producing ray at each station from the signal transmission from theother station, generating at a central station electrical impulses of predetermined frequencies, and controlling the operation of each developed ray by H the generated frequencies to synchronize and frame the movement of all rays generated.

- v VLADIMIR K. ZWORYKIN.

Images