US1747978A - Picture-transmission system - Google Patents

Description

Feb. 18, 1930. M. KAGELMANN ETAL PICTURE TRANSMISSION SYSTEM 1929 2 Sheets-Sheet Q m w.

IHVENTOF? Nam Keefe Jinan/z Halo/f Eula/360%? 1 I Filed May 20 I .QTTORHEY Feb. 18, 1930. M. KAGELMANN ETAL 1,747,978

PICTURE TRANSMISSION SYSTEM Filed May 20, 1929 2 Sheets-Sheet 2 9nd bias 1 2 5. 4 (6L)- (b) (C) 4? i w u A :3 :s

)NVEHTORS Ma, Kayellnau/z 5 Halo/f Eu/azzo/el ATTORNEY.

Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE MAX KAGELMANN, OF BERLIN-NIEDERSCHONHAUSEN, AND ADOIiF EULENHfiFER, OF KONIGSWUS'I'ERHAUSEN, NEAR BERLIN, GERMANY, ASSIGNORS T0 0. LORENZ AKTIENGESELLSCHAFT, OF

BERLIN-TEMPELHOF, GERMANY PICTURE-TRANSMISSION SYSTEM Application filed May 20, 1929, Serial No. 364,573, and in Germany February 21, 1928.

This invention relates to the transmission of pictures, documents, designs and the like from one point to another by electrical means through conductors as well as through space.

A well known method in the art of picture t'ansmission for securing a synchronous operation of the transmitting and receiving apparatus. consists in that the transmission of the picture is interrupted periodically and that the interrupting periods are used for correcting the synchronous movement. These interruptions will impress disturbing influence upon the received picture. In order to overcome this disadvantage, it was proposed to use the carrier frequency which serves for the transmission of the picture signals as a means for controlling the synchronism. This method. however, involves complications and in accordance with the further development, it was proposed to transmit simultaneously picture signals and synchronizing signals and to choose the length of the synchronizing signals properly in respect to the length of the picture signals, so as to prevent a disturbing influence upon the received picture.

This invention refers to a system for combining picture and synchronizing signals and transmitting them substantially independently from each other.

In accordance with our invention. a, synchronizing frequency is transmitted simultaneously after having been superimposed upon the picture signals without taking into account whether a picture signal is being transmitted or not. At the receiving station, a receiving apparatus is provided in which, by prope adjustment. no influence of the synchronizing signals is exerted upon the received picture. The primary advantage of this method. in accordance with our invention, consists in that the frequency of the synchronizing signals may be chosen substantially independent from the frequency of the picture signals.

in the art of transmission of pictures by electrical means. it is usual to transmit to the receiving station. a series of electrical signals or impulses which are in some way characteristic of elemcnary portions of the picture to be transmitted. At the receiving station these signals are employed in various ways for forming a facsimile image or reproduction of the picture. For this purpose, a synchronous operation of the mechanical scanning and the receiving reproduction apparatus is necessary in order to secure a reproduction of the picture without distortion. It is usual to transmit both the picture signal and synchronizing signal through electric carriers. such as a wire or a radio channel.

According to one method of reproducing the picture, a light valve having the form of the well known string galvanometer is operated by the received signals to vary the exposure of elementary portions of a light sensitive receiving film thus forming light and dark areas, similar to the elemenary areas of the original picture at the transmitter. It is customary to mount the light sensitive film upon a rotating cylinder in the same manner as the picture which is being transmitted, so that the entire area is exposed in a succession of helical traces.

The object of the present invention is to improve the method and the means employed for transmitting and for reproducing pictures in picture transmission systems, particularly in systems of the type referred to above.

A further object of our invention is to provide a picture transmission system which is simple in design and operation as compared to the existing systems and which at the same time is suitable for high transmission speed such as is necessary for commercial purposes A more specific object of our invention is to provide a picture transmission system for simultaneously transmitting pictures and synchronizing signals on a common transmission carrier, such as a pair of wires or a single radio frequency band, whereby a minimum of mechanical and electrical apparatus is used, and at the same time interference between both kinds of signals necessary for the transmission is avoided.

A further objectof our invention is to make use of the characteristic properties of vacuum tubes for combining picture signals and synchronizing signals on a common transmission carrier and for separating both at the receiving end and applying them to their respective functions without an appreciable mutual iuterferei'ice.

These and further objects and advantages of constrrction'and operation of our invention will become apparent as the description proceeds, reference being taken to the figures of the accompanying drawings which represent by way of example and in a schematic form, a complete transmitting and receiving apparatus in accordance with our invention. It is understood that this specific embodimentof our invention, as shown by the drawings, is subject to many modifications coming within the broader scope of the invention as embraced by the appended;

claims.

Referring to the drawings Fig. 1 shows a complete sending and receiving system, in a diagrammatic form, of a picture communication system, in accordance with our invention for transmission by means of electric waves;

Fig. 2 is a diagram illustratingthe periodically occurring synchronizing signal impulses and the irregularly occurring picture signals as they appear when superimposed on the common transmission carrier as obtained in the circuit arrangement of Fig. 1;

F ig. 3 is intended to explain in more detail the production of the signal frequency and the synchronizing frequency as shown by Fig. 2 by making use of the characteristic propertiesof a vacuum tube.

Figs. 4, 424 and 4 are detailed sketches of a part of the receiving galvanometer device in a magnified manner which illustrates the reproduction of the picture elements and the separation of the synchronizing impulses.

Referring to Fig. 1 of the drawings, the three essential parts of the transmitter consist of the scanning arrangement, the amplifier for amplifying the picture signals to an amount necessary for-modulating a wireless transmitter and the transmitter itself. This latter maybeof anywell known type and serves to produce and send out a carrier wave for the transmission of the picture.

Numeral 1 represents a rotating cylinder upon which the picture or object to be transmitted is applied in a manner well known in the art. Cylinder 1 is rotated continuously by .a driving motor 2 through connecting bevel gears 3. The cylinder is furthermore simultaneously moved lengthwise to its axis by means of a threaded spindle 4: driven from the cylinder shaft through gears 5 and a nut ft attached to the cylinder 1. The electro-optical scanning arrangement comprisesa stationary source of light 6, such as an electric bulb. 'which projects by means of lens 7, a small light point of about firth of a m/m upon the cylinder 1, that is, on the picture which is being transmitted. In this manner, the entire picture'is scanned point by point in a spiral-like manner. In the preferred practical embodiment of our invention, it has Y been found advisable to use a speed of the cylinder of about 3 revolutions per second and a speed lengthwise in the direction of the-cylinder axis of about 0.25 m /m per second. 'To such a scanning speed corresponds a number of picture elements of 2400 per second. The amount of light reflected by the individual picture elements, is collected by lens 8 arranged at the side of the original incident beam of light and is thrown upon a photo-electric cell 9 which may be of any well known type and which comprises a light sensitive cathode 10, capable of emitting electrons under the influence of incident light waves and a perforated anode l1 placed opposite thereto, both cathode and anode being inserted into an electrical circuit of a battery 13.

During rotation of the cylinder 1, the picture moves past the light point projected from the source 6 and a greater or smaller amount of diffused light is being reflected upon the photo-electric cell dependent on the relative brightness and darkness of the individual picture elements. The current established in the circuit of the photo-electric cell is thus varied in accordance with the tone values of the picture elements.

As these variations of electric current in the circuit of the photo-electric cell 9 are very small, they have to be amplified to a sufficient amount, for controllingor modulating the wireless transmitter 27. For this purpose, a vacuum tube amplifier comprising 3 threeelectrode vacuum tubes16. 17 and 18 in cascade connection is provided in the specific example shownby Fig. 1. 'The last tube 18 is used at the same time for the production of the synchronizing signals in accordance with the novel scheme of our invention. Synchronizing signals are produced by a generator of alternating or pulsating current in synchronism with the speed of n1otor.2,'such as, for instance, by, an interrupter 12 arranged on the axis ofmotor 2- which closes and opens the circuit of a battery 24. In 'thepreferred practical embodimentof our invention. a synchronizing impulse frequency of about 1,000 cycles per second is used. This synchronizing frequency. as will be described more particularly later on. is transmitted to the receiver simultaneously with the amplified picture signals on a common carrier. Of the total amount of energy radiated. about 75% is used for the 16. 15 is a biasing battery to secure a negative grid bias necessary for the proper operation of the tube. The magnitude of coupling resistance 14 should not be greater than a certain limitin value. By experiments, it was found that this value should be within 0.5 to 1 megohm. Thus, at the terminals of the resistance 14, a voltage drop will occur which varies in accordance with the tone values of the picture elements being transmitted, and which produces a corresponding voltage at the output resistance 17. This voltage is further amplified by the following tube 17 coupled with tube 16 by coupling resistance 17. Tube 17 has a grid biasing battery 18'. This system is particularly suitable to a. type of picture known as blackand white, that is. where there is no intermediate shading of the individual picture elements. However, picturesof the so-called half-tone type may be also transmitted as explained in a later paragraph. Battery 18' is chosen in such a manner that with a black element on the picture. that is, with no light falling upon the photoelectric cell, the anode circuit of tube 17 carries no current. On the other hand, while a bright spot is being scanned and :1 corresponding current is being established in the circuit of the photo-electric cell, there will be an additional voltage at the resistance 17' in the anode circuit of tube 16 which will cause a current to flow in the anode circuit of tube 17 by partly or entirely neutralizing the negative grid bias of battery 18. The amplified v'oltagc thus obtained at the ends of the anode resistance 26 of tube 17 is furthermore amplified in the same'manncr by the last tube 18 which is provided with a grid bias battery 24-.- The latter servesat the same time, to produce the synchronizing impulses through the medium of the interrupter 12. The operation of producing the synchronizing signals superimposed upon the picture signals by tube 18 is as follows A part of the grid biasing battery 21 of tube 18 in series with a further ohmic resistance 25 is included in the circuit and shortcircuited at intermittent intervals bv the contacts of the interrupter 12. In this manner. additional voltage variations are produced whose magnitude is determined by the value of resistance 25 and'of the size of the biasing battery 24. This may more particularly be explained by reference to Fig. 3 which rep resents a normal vacuum tube characteristic, that is, a curve showing anode current Iodm pendent on a negative grid biasing "oltage. In the case, for instance, when there is no current flowing in the anode circuit of tube 17, there is applied the maximum negative biasing voltage of battery 21 to the grid of tube 18. This corresponds to point G, on the characteristic curve of Fig. 4. When the interrupter 12 of the transmitter is closed, the bias" ng voltage of tube 18 becomes less negative and an anode current is established in the anode circuit of the tube corresponding, for instance, to a valve G The duration of flow of this current is determined by the closing periods of the. contacts of the interrupter 12. In this manner, a synchronizing current impulse is sent out, as designated by a in Fig. 4.

It now, for instance, a picture signal is started.

during an interval between these synchronizing current signals, then the anode current of tube 18 increases to a value of G This picture signal is represented by 7) which has for a so-called black-white signal, a rectangular shape. So long as the interrupter 12 has its contacts open, this value Gr is maintained. If. however, the interrupter 12 is closed, the grid voltage will become less negative again and the anode current Will assume a value of In other words, the synchronizing signals will be added to the picture signals as is illustrated in Fig. 3. In case that a synchronizing signal does not coincide entirely with a picture signal, it is simply divided and is transmitted partly during an interval between picture signals and partly superimposed over the picture signals (see a and s in Fig. 4)

The form of current variations tl us obtained in the anode circuit of tube 18 and employed lateron to modulate the transmitter 27 is as shown in Fig. 2 in which 8 represents s -'nchronizing signals and Z) the picture signals. In Fig. 3, picture signals following each other at irregular intervals and lengths are the so-called black-white signals as referrcd to above. The synchronizing signals succeeding each other at regular intervals are supcrim posed upon these picture signals. It has been found in practice that a ratio of 1 to 4 of the amplitude or" synchronizing signals to the amplitude of picture signals insures good results in practice. Itis understood that our invention is not confined to the use of black-white signals only, but that also shaded reproductions of the picture may be transmitted by the use of a screen such as is used in the well known halt-tone printing process. This will be more particularly pointed out later on in connection with the description of the receiving mechanism.

The combined low frequency picture signals and synchronizing signals. as shown by Fig, 3, are applied to the transmitter 27 to modulate a carrier wave oi high frequency in any manner well known in the art. The high frequency cnergv is radiated by an antenna earth system] 2S29 associated with the wireless transmitter 27. For the modulation, any-of the well known schemes. such as the Heising modulation may be employed, but it has been found that he use of a socalled iron core choke modulator arranged in an intermediate circuit between a master oscillator and the power amplifier oscillator insures particularly good results in connection I invention.

structure is out of the scope of this inven-- tion.

Referring to the picture receiving system of this invention, shown on the right side of Fig. 1, there is an antenna earth system 31 associated with a receiver 32 of any well known type. Item 33 represents a rectifying tube arranged at the output of the receiver 32 and having a grid biasing battery 34. As is well known, the operation of the reception and demodulation will establish low frequency currents of the same shape as are produced at the transmitter and are shown by Fig. 3. These currents will flow in the anode circuit of the amplifying tube The current variations of tube 33 are applied .to the string or shutter 34 of a galvanometer type light valve as described below. In series with this galvanometer is placed a pure ohmic resistance 35 which serves as a coupling means to a filter 36, which serves to segregate the synchronizing frequency from the received combined energy w of picture and synchronizing currents. The

Y voltage drop on resistance 35 includes the picture signals and the synchronizing signals, which are applied together to the filter 36. This filter is arranged in a well known manner to pass only the synchronizing frequency, while the picture signals do not pass through it. The output terminals of filter 36 are connected to an amplifier 46 which serves to amplify the synchronizing impulses to an amount suflicient for acting on the driving motor of the receiving mechanism. Amplifier 46 is shown by a dotted line only and may be of any well'known type. The synchronization by means of the synchronizing impulses may be carried out 1n any well known manner and is out of the scope of this invention. In the embodiment shown in Fig;

2, the periodic synchronizing currents are shown, for the sake of simplicity, to-operate directly a synchronous motor- 45 and to deto control only an auxiliary synchronizing.

winding of the motor, or even a separate synchronizing motor while the main driving 3 power is delivered by an independent local these currents is not necessary owing to thesource of power of a separate motor. The picture currents obta ned 1n the anode circuit of tube 33 act directly upon the reeeiv ing galvanometer and anamplification of extremely high sensitivity of this galvanometer type of receiver.

Current variations of only a few milliam aeres are sufiicient to effect a suflicient deviation of the string or shutter 34. This feature of the galvanometer as a receiver, presents a paramount advantage in picture reception systems as the amount of the necessary amplification is reduced to a minimum. The receiving galvanometer itselfcomprises two poles 37 and 38 of an electro magnet placed 0ppositc each other and being provided with two pole pieces between which the g vanometer string '34 is stretched. T his string is preferably made of silver and arranged for a natural frequency of about 6,000 cycles, that is sufficiently high above the highest picture signal frequency. Sulficient damping may be obtained by means of an ohmic resistance placed in parallel. When a current is flowing through the string 34 it is deviated one way'or another in accordance with the direction of the current flow. The pole pieces 37 and 38 are tunneled at the place of the string 34 so as to-allow the passage of a beam of light produced by a source 39 and collected by a lens 40. At a certain distance behind the string a second lens 41 produces a magnified shadow of the same. This shadow covers a slit 42 of a light baffie placed in the path of the light rays between lens 41 and the picture receiving cylinder '44. Behind the slit 42, the light is concentrated again by means of a further collecting lens 43 to a point of about th of a millimeter square corresponding to the scanning picture element size at the transmitter upon a photographic receiving paper applied upon the rec'eiving'cylinder 44. v The explanation of the operation of the light control by the galvanometer string is as follows, reference being made to Fig. 4. In case. there is no current applied to the galvanometerstrin'g, the slit 42 is entirely covered by the magnified shadow of the string as shown by Fig. 4 When asynchronizing current impulse flows through the galvanometer, the string will be displaced by a small amount, such. however, that its shadow willstill cover the slit 42' and prevent "the passage of light '(Fig. 4 It is only when the current assumes a magnitude of G of Fig. 3 corresponding to a picture signal int-hat the deviation of the spring is sufficiently large to pass by the slit and allow the light to be thrown upon the receiving paper, ,(Fig. 4). In case that a synchro- 'nizm signal is added to the picture signal,

the string is deviated further past the slit; this however, has no influence upon the amount of lightpassed by the slit (Fig. 4

In this manner, namely by choosing an apl propriate r-aito of the width of slit 42 as com pared to the width of the shadow 34 produced by the galvanometer string. all influence of synchronizing-current impulses upon the reproduction of the picture is avoided.

Referrin to the further details of the receiving mec anism, item 44 represents the re-' ceiving cylinder which is rotated and moved len hwise parallel to its axis in synchronism wit 1 the transmitting cylinder 1, by means of the driving motor 45. and gears 47 and 49 as well as the threaded spindle 50 in exactly the same manner as in the case of the transmitting cylinder. A magnetic clutch 48 is arranged between the driving motor 45 and the cylinder 44. This serves to start the receiving cylinder from the transmitting end in the proper phase relation corresponding to the transmitted picture. lay 51 may be connected in the output circuit of the tube 33 by means of a switch 52, thus taking the place of the galvanometer string 34. The relay 51 is provided with two windings acting on its armature and is so adjusted that it is in a sensitive position when in the state of rest. When the transmitting cylinder is started, there are sent at the beginning of picture transmission, a number of short impulses at the end of each revolution. These starting impulses may be produced, for instance, by a dark line '54 on the transmitting cylinder parallel to the cylinder axis and definitely oriented to the upper or lower margin of the picture or the fastening means (55). A sufficient portion of the picture cylinder is left blank as seen to the left of the picture sheet 56 at the beginning in order to secure a sufficient number of starting impulses to be transmitted. The first of these impulses after arriving at the receiving end, acts on the relay circuit to close its contacts and sets the clutch 48 into instant operation. The clutch is operated by the current from the source 52 and is locked in position by contacts 53 operated by the clutch movement. Thus, the receiving cylinder receiver 44 and the recording sheet (56) on it is coupled to the driving motor 45 in identical orientation with regard to its upper and lower margin as the picture to be transmitted or its fastening means (55) The reception is begun by putting switch 52 into its normal position in which the receiver galvanometcr is connected with the circuit. This is done after the clutch is closed, while the relay gives visual indication of the starting of transmission by the starting impulses subsequent to the above first impulses.

The system described is applied, as stated above, to a so-called black and white picture, i. e., one which consists of black and white parts.

A picture produced by the Well known halftone process although giving the visual effect of shading, consists in reality of minute black and white points distributed in such a manner that the density of black points corresponds to the tone of the pictures. Therefore, it an ordinary photograph which consists of diflerent tonal values of light is to To this end, a rebe transmitted, it can be first converted into a half-tone picture and this latter be then transmitted by our system in exactly the same manner as the black and white pictures.

-Although the features of the invention have been described and illustrated as. embodied in a specific picture transmission system, it is to be understood that they are not to be restricted thereto. Certain features of the invention may be changed or replaced, and the inventors do not wish to be limited, except as specifically stated in the appended claims.

IV hat is claimed is 1. In a system for transmission of facsimile images by electrical means, scanning means to produce electric picture impulses characteristic of the tone values of elementary portions of the image to be transmitted,

means to produce further periodic electrical synchronizing impulses characteristic of the speed of said scanning means, means to superimpose said second impulses upon said picture impulses, means to impress said superimposed impulses upon a common transmitting carrier current, a receiving apparatus comprising a source of light, means adapted to control said source of light in accordance with said picture impulses and arranged to be operable only by a current larger than said synchronizing impulses.

2. In a picture transmitting system in accordance with claim 1, in which said picture current impulses and said synchronizing current impulses are simultaneously applied to the grid of a 3-electrode vacuum tube, an output circuit for said vacuum tube -to furnish a current varying in accordance with said picture impulses and said synchronizing impulses superimposedupon each other, means to produce a transmitting carrier current and further means to modulate said carrier current in accordance with the output current of said vacuum tube.

3. In a picture transmission system in accordance withvclaim 1, a 3-electrode vacuum tube, a negative grid bias of said tube, means to decrease said grid bias in accordance with said picture impulses, further means similar to said last means to decrease said grid bias in accordance with said synchronizing impulses, an output circuit for saidtube, to furnish a current varying simultaneously 1n accordance with said picture impulses and said synchronizing impulses, means to generate a transmitting high-frequency carrier current and an arrangement tomodul'ate that carrier current in accordance with the output current of said tube.

4. A picture transmission system, in combination, scanning means for producing successive electrical picture impulses characteristic of elementary portions of the image to be transmitted, further means to produce periodic electric synchronizing lmpulses characteristic of the scanning speed of said picture elements, means to superimpose said picture and said synchronizing impulses, said last means comprising at least one vacuum tube, means to vary the control grid voltage of said tube simultaneously in accordance with said picture impulses and said synchronizing impulses, a negative grid bias for said tube of such value that substantially no output current is established in the two resistances and a negative grid biasing battery, one of such resistances serving as a means for furnishing a potential difference in accordance with said picture signal impulses and having a direction opposite said biasing voltage, and the other one of said resistances serving as a means for furnishing a potential difference in accordance with said synchronizing impulses, and being also opposite to said biasing voltage and Whereby said biasing voltage is of such value that with no picture and no synchronizmg 1mpulses occuring, the flow of current in the anode circuit of said vacuum tube is suppressed and that with bothpicture impulses and synchronizing impulses occuringsimultaneously, the current estabhshed 1n the anode circuit remains below the saturation current of said tube.

6. A picture transmission system in accordance with claim at in which the grid circuit of said vacuum tube includes in series, two resistances and a negative grid biasing battery, one of said resistances serving as a means ,for furnishing a potential difference in accordance with said picture current impulses and being opposite to said biasing voltage, means for producing periodic synchronlzing 1mpulses comprising an interrupter operated in synchronism with the seaming speed ofsard picture elements and short circulting periodlcally said second resistance in series with part of said grid biasing voltage, said grid biasing voltage being of such value that with no picture impulses and no synchronizlng impulses occur-ing, the flow of current in the anode circuit of said vacuum tube is zero and that with both picture impulses and synchronizing impulses occuring simultaneously, the current established in the anode circuit remains below the saturation current of said tube.

7. In a picture transmission system in accordance with claim 1 in-which said last means consists of a string light valve having a string is reaching this uncovered state with a current not larger than said picture impulses.

8. In a picture transmitting system, means to produce picture signals, means to produce synchronizing signals, means to superimpose said signals in a magnitude relation such that all of the synchronizing signals are smaller than'the weakest picture signal, a receiver operative only in response to currents having at least the magnitude of said picture cur rents and a filterging circuit for filtering said synchronizing from said picture currents.

9. A picture transmission system comprising means for sending on a common carrier superimposed pictureand synchronizing impulses, differentiated by their magnitude only, means for segregating said picture and synchronizing impulses at the receiving device to perform their individual functions independent of each other, said means compris ing a receiver responsive only to impulses of at least the amplitude of the former of said impulses and a filtering circuit for separating the other of said impulses.

10. A picture transmission system as in claim 9 with additional means for orienting the beginning of the picture reception relative to the location of the beginning of picture transmission.

11. A picture transmission system as in claim 9 with means for orienting the beginning of reception comprising means for sending initial orienting impulses, a magnetic clutch on the receiving device, a relay, means for energizing said relay by said orienting impulses, energy supply controlled by said relay and operating said clutch to couple the receiving device in proper orientation relative to the sending device.

12. A picture transmission system as in claim 9 with means for orienting the beginning of reception comprising means for sending initial orienting impulses, a magnetic clutch on the receiving device,a relay, a switch receiving station, means for transmitting said currents of predetermined amplitude limits and varying in frequency in accordance with the speed of operation of the translation means in covering successive portions of the picture, the amplitude of said picture currents and said synchronizing currents being different, means for superimposing said picture and synchronizing currents on each other, means for transmitting said currents to said remote receiving station, picture receiving and synchronizing apparatus at said received currents through one of said apparatus, means whereby said one apparatus is responsive only to currents of the predetermined amplitude of one of said currents whereby said apparatus is operated in accordance with said variable currents, filtering means at said receiving station for filtering the other of said variable currents, said other apparatus at said receiving station being connected to said filtering means and operating in response to said other variable currents.

14. Ina picture transmission system having a picture transmitting station and a picture receiving station remotely disposed from each other, an image at said transmitting station, means for translating elemen-' tary portions of said image into picture currents varying between predetermined amplitude limits inaccordance with variations of the image characteristics, further means simultaneously operative with said translating means for generating synchronizing currents of predetermined amplitude limits and varying in frequency in accordance with the speed of operation of the translation means in covering successive portions of the picture, the amplitude of said picture currents being different from that of said synchronizing currents. means for superimposing said currents on each other, means for transmitting said currents to said remote receiving station, picture receiving and synchronizing apparatus at said receiving station, means for transmitting said superimposed receiving currents on said picture receiving apparatus, said picture receiving apparatus being rcsponsive to currents of the predetermined amplitude of the picture currents whereby it responds only to said picture currents, a filtering circuit,rmeans for impressing said synchronizing currents across said circuit, said filtering circuitsbcing ar 'anged to filter said synchronizing currents from said picture currents and synchronizing means connected to said filtering circuit whereby it is operated b T said synchronizing currents.

15. n a picture transmission system having a picture transmitting station and a picture receiving station remotely disposed from each other, an image atsaid transmitting station, means for translating elementary portions of said image into picture currents varying between predetermined amplitude limits in accordance with variations-0f the image characteristics, further means simultaneously operative with said translating mems for generating periodic synchronizing currents of predetermined amplitude limits of a variable periodicity in accordance with the speed of operation of the translation means in covering successive portions of the l picture, the amplitude of said currents and said periodic synchronizing currents being diil'erent, means for superimposing said currents on each other, means for transmitting said currents to said remote receiving station, picture receiving and periodic synchronizing apparatus at said receiving station, means for impressing said superimposed receiving currents on said picture receiving apparatus, said picture receiving apparatus being responsive to currents of the predetermined amplitude of said picture currents whereby it responds only to said picture currents, a filtering circuit, means for impressing said synchronizing currents across said circuit, said filtering circuits being arranged to filter said periodic synchronizing currents from said picture currents and synchronizing means connected in said filtering circuit and responsive to said periodic synchronizing currents.

16. in a picture transmission system having a picture transmitting station and a picture receiving station remotely disposed from each other, an image at said transmitting I station, means for translating elementary portions of said image into variable picture currents in accordance with the variations of the image characteristics, further means simultaneously operative with translating means for generating synchronizing currents of a periodicity varying in accordance with the speed of operation of the translating means in covering successive portions of the picture, said synchronizing currents being of a smaller amplitude than said picture currents, means for superimposing said synchronizing currents and picture currents on,

' therethrough and synchronizing apparatus in synchrcnism with the trims ating means in covering successive portions of the picture.

17. In a picture transmission system having a picture transmitting station and a picture receiving station remotely disposed from each other, an image at said transmitting station, means for translating elementary portions of said image into variable picture currents in accordance with the variations of the image characteristics, further means simultaneously operative with said translating means for generating synchronizing currents,

said synchronizing currents being of a smaller amplitude than said picture currents, means for superimposing said synchronizing currents and picture currents. on each other, means for transmitting said superimposed currents to said receiving station, a receiving circuit at said receiving station, means for impressing said superimposed currents on said receiving circuit, a reproducer receiver at said receiving station connected in said receiving circuit, said receiver being responsive only to currents of at least the picture current amplitude, whereby said receiver responds only to the picture currents, a filtering circuit connected to said receiving circuit for filtering currentsof the frequency of'said synchronizing currents whereby said synchronizing current flows therethrough and, synchronizing apparatus connected to said filtering circuit,

responsive to said synchronizing frequencies for maintaining the reproducing receiver in covering successive portions of the reproduced picture in synchronism with the translating meansin covering successive portions of the picture.

18. In a picture transmission system having a picture transmitting station and a picture receiving station'remotely disposed from each other, an image at said transmitting staton, means for translating elementary portions of said image into picture currents varying between predetermined amplitude limits in accordance with variations of the image characteristics. further means simultaneously operative with said translating means for generating synchronizing currents of predetermined amplitude limits in accordance with the speed of operation of the translation means in covering successive portions of the picture, the amplitude of said picture currents and said synchronizing currents being different. means for superimposing said picture and synchronizing currents on each other, a thermionic tube, means forimpressing said currunts on said tube, an output circuit connected to said tube, means whereby a carrier current modulated in accordance with said superimposed currents flows in said output circuit, means for transmitting said currents to said remote receiving station, picture receiving and synchronizing apparatus at said receivmg station, means for transmitting said received currents through one of said apparatus, means whereby said one apparatus is responsive only to currents ofthe predetermined amplitude of one of said currents whereby said apparatus is operated in accordance with said variable currents, filtering means at said receiving station for filtering the other of said variable currents, said other apparatus at said receiving station being connected to said filtering means and opcrating in response to said other variable currents.

19. In a picture transmission system having apicture transmitting station and a picture receiving station remotely disposed from each other, an image at said transmitting station, means for translating elementary portions of said image into picture currents varying between predetermined amplitude limits in accordance with variations of the image characteristics, further means simultaneously operative with said translating means for generating synchronizing currents of predetermined amplitude limits in accordance with the speed of operation of the translation means in covering succcssive'portions of the picture, the amplitude of said picture currents and said synchronizing currents being different, a thermionic tube having a negative biased grid, means to decrease said bias in accordance with said picture currents, means to further. decrease said negative bias in accordance with the synchronizing currents, an output circuit for said tube, means for generati n g a carrier current in said circuit, means whereby said carrier current is modulated in accordance with said-picture and synchronizing currents, means for transmitting said currents to said remote receiving station, pic ture receiving and synchronizing apparatus at said receiving stat-ion, means for transmitting said received currents through one of said apparatus, means whereby'said one apparatus is responsive only to currents of the predetermined amplitude of one of said currents whereby said apparatus is operated in accordance with said variable currentsffiltering means at said receiving station for 'filtering the other of said variable currents,

said other apparatus at said receivin station being connected to said filtering means and operating in response to said other variable currents. v

In testimony whereof said parties aflix their signatures. Y

ADOLF EULENHUFER. MAX KAGELMANN.

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