US1738673A

US1738673A - Synchronizing arrangement for picture transmission

Info

Publication number: US1738673A
Application number: US230423A
Authority: US
Inventors: Schroter Fritz
Original assignee: Telefunken Gesellschaft fuer Drahtlose Telegraphie mbH
Current assignee: Telefunken AG
Priority date: 1926-11-24
Filing date: 1927-11-02
Publication date: 1929-12-10
Anticipated expiration: 1946-12-10

Description

Dec. 10, 1929. F. scHRbTER SYNCHRONIZING ARRANGEMENT FOR PICTURE TRANSMISSION Filed NOV. 1927 2 Sheets-Sheet 2 84070 4100014 mum/rim IMfl/F/f/P INVENTQR Ffifll SCHROTER NEY Patented Dec. 10, 1.929

UNITED STATES PATENT orricr.

rmrz scnnornn, or BERLIN, GERMANY, assrenoa ro en snnnscnu'r' rfln, murm- LOSE TELEGRAPHIE m. 3. 1a., or BERLIN, GERMANY, A CORPORATION or GER- MANY SYNGHRONIZING ARRANGEMENT FOR PICTURE TRANSMISSION I Application filed November 2, 1927, Serial No.

The present invention discloses a circuitarrangement adapted to insure synchronization of apparatus for picture transmission or similar apparatus for communication work in a simple manner. The basic idea of the invention consists in that, with the use of one and the same carrier. wave, and apart from the picture impulses or other signals, a rhythm, cadence or synchronizing frequency for the drive of a synchronous motor at the receiving end is simultaneously transmitted by modulating the carrier wave with two audio frequencies, one of which in turn is modulated by the picture-element or picture-point frequency or signal frequency, while the second audio frequency is transmitted non-modulated. The said two audio frequency waves modulating the carrier frequency in this scheme must be spaced so far apart that no disturbing interference will result between' the said two audio frequencies when rectified. Another essential point is that the audio frequency used for synchronization modue lates the radio frequency only to a slight degree, and, if possible, only to an extent so that its intensity suflices for further amplifi cation in the receiver apparatus.

One embodiment of theidea underlying the invention is illustrated in the accompanying drawing in connection with its application to picture transmission, in which Fig. 1 illustrates a transmitting system, Fig. 2

v a receiving system adapted for cooperation I therewith, Fig. 3 represents a modified form of the transmitter shown by Fig. 1, and Fig. 4 represents a modification of the form of receiver shown by Fig. 2. d I r Now making referenceto the accompanying drawings the picture or documentto be transmitted is placed on av drum 1 which is subject in well known manner to a rotary and a shifting movement- A'photo-electric cell 2 ofannular form isadaptedto explore p I 1 of the transmission of the picture-point frethe picture by the aid of lightjfdiifusely reflected from the picture surface. .';'For .=thi s,

, purpose, the light issuing from, luminous source 3 is passed in the shape of'a'shar-p pencil of li ht formed by the aid of a lens 4 through t e central portion'of the annular photo cell 2 adjacent the picture surface. For

thetransmitter end, two low g'enerators' are provided, one of which furnishesa carrier wave for the icture-point' frequencies, while the other one] rnishes the synchronizing frequency. The former may 230,423, and in Germany "November 24, 1858.;

driving the drum 1 a motor 5 is provided and the rotation thereof is transmitted through a toothed gear wheel 6 tothe drum 1. At the receiving end there is a drum 7 which corresponds to drum 1 at the sending end. The

drum 7 is arranged to revolve in\syncho-- nism with drum 1 and is subject to a similar displacement or shifting motion along its axis. As the means to control thelight striking a light sensitive film suitable for record-- ing the received picture, a' Karolus cell 8 has here been assumed. The cone of light which-passes between the condenser plates of the cell 8 is supplied from a light-source 9.

13. A'motor 15 and a convenient toothedgear wheel, similar to that of the'transmitter, is provided for driving-the drum 7.

The two motors 5 and 15, for instance, may

be of the shunt-wound direct current type,

and. their speedis adjusted by means of the series rheostats 16 and 17, respectively. However, it is a good plan to further provide for the motor 5 a speed governor (not shown) of any convenient kind, for instance, a Giebe' t' pe centrifugal governor adapted to keep 't e" fluctuations ofthe speed of rotation inside acceptably low limits. However, at the receiving end the rotationof motor 15 by means of an additional synchronous motor '36 is kept iH,. tep with that of the shaft 'of motor 5. FThe transmission of the synchronizing audio frequency oscillations from the transmitter to the synchronizing motor 36 (which, as to the rest, maybe of any de-' sired form, for instance, it may-consist of a La Cour-wheel) is effected independently quenciesin the following manner e eq n y be of any suitable kind, for instance, it may consist of a tuned thermionic valve generator, or a tuning-fork generator comprising amplification means, or else, as shown merely by way of example in the drawing, it may.

consist of an induction-type machine 18, the same in this case being drivenby a motor 5. Fundamentally speaking, an alternative scheme would be to produce the picture-point carrier frequency by optical means instead of electrically by that, instead of 18, a revolving perforated disk is placed in the path of the raysissuing from 3, the carrier frequency being thus produced directly in the photoelectric cell 22, provided the speed of rotation and the number of holes are chosen conveniently. Hence, while the carrier frequency for the picture-point impulses may be produced alsoindependently of the motor 5 by a great number of methods, the second audio frequency to be used for synchronization must bear an invariable relationship to the speed of rotation of the motor 5 or of the driving shaft, or in other words, it must vary in direct proportion to the variation of the motor speed. For this purpose, a second inductor 19 positively coupled with 5 and most suitably seated upon the same shaft, 1s provided.

The carrier frequency or wave supplied from the generator 18 for the picture-point frequencies is controlled or modulated in amplitude in the following way by the light brought to act upon the photo-electric cell 2: The photo-electric cell 2 forms the arm of a bridge arrangement which further comprises a variable condenser 21 and resistances 22 and 23. At the terminals of one of the diagonals of the bridge is supplied an alternating current potential furnished from the source 18 and conveniently regulated by a potentiometer 20. At the terminals of the other bridge diagonal thisfrequency subject to control of its amplitude by the light brought to act .2 upon the cell 2, is taken as and fed to the control electrode of the amplifier tube 24. The object of the bridge arrangement as stated is to completely compensate the capacitive current flowing by way of the electrodes of the photo-electric cell 2 by the aid of condenser 21, so that, in the absence of illumination of the photo cell 2, no carrier alternating current potential will act upon the grid of the tube 24:, it being understood, of

i course, that for the same purpose any other suitable compensation scheme could be employed. In series with the photo-electric cell there may be, further, provided a direct current potential upon which the alternating current potential taken off at 20 is superposed. If, then, a state of balance 'is established in the bridge when the cell is dark, the balance will be disturbed as soon as light strikes the said cell 2, with the result that a certain amplitude of the frequency furnished from 18 will arise at the control grid of the tube 24, the value of said amplitude varying at the rhythm of the distribution of light an dark in the explored picture, in other words,

the audio fre u'ency furnished from 18, in turn, is modu ated by the picture-point or picture-element frequency resulting from the changes in light and dark. If in the presence of the minimum illumination corresponding to be more precise, only to such an extent that, compared with the noises due to stray, a sufficiently audible sound is heard at the rece1ver end, the latter being'then further amplified until it represents an energy adequately high for the operation of the synchronous motor 36. In case it is not desired or it is impossible to obtain the full energy required for a synchronous motor 36 by means of amplification, the audio frequency tone received need be amplified only to such an extent as is required to operate a synchronous switch by means of which, by the aid of oscillation or rotating contacts, the opening and closing at the proper rhythm of afeeding circuit of the synchronous motor 36 is caused in the manner shown by Fig. 4. Easy modulation of the radio frequency of the transmitter. by the audio frequency of the generator 19, according to the drawing, is effected by the means of a transformer 26 connected in the grid circuit of the tube 24, the primary current of said transformer being regulated to the desired strength. The

battery 25 serves for providing the biasingpotential on the tube 24. Another method of transmitting the frequency of generator 19 to the corresponding station, for instance, as showp by Fig. 3, consists in that this frequency is used for heating the filament of a tube which may be connected in the input amplifier cascade or the transmitter tube itself in the case shown, the filament of the amplifying tube 24 of Fig. 3 is heated from the generator 19 which is here shown as an alternator. The frequency is then intentionally transmitted to the receiver end in the form of what is known as the filament tone, and the amplitude thereof is governed by the thermal inertia of the filament and by the adjustment of plate and grid biasing potential of the tube that is used, the amplitude being thus adjustable at will.

It is, of course, possible to introduce the frequency of generator 19 also at some other point in the amplifier cascade between tube 24 and the modulator 28 of the'radio frequency transmitter 29. In the drawing here shown, the frequency of the generator 18 modulated by the picture-element frequency f and the non-modulated wave of the generator 19 operate at the proper amplitude re-- lations, as hereinbefore pointed out, upon the grid of the .tube 24, and they are further.

amplified by the photo-electric amplifier 27 until they have been raised to the amplitude required for the control of the modulator tube. As regards the diflerence infrequency of 18 and 19, it may be stated that, when 18 furnishes a carrier frequency of 5000 cycles, the one of19fmay be chosen at from 200 to 500 cycles. Assuming that at the transmission rate chosen, there is no need for recording picture-point frequencies above 2000' 'the same kind could anyway be rendered harmless by the filter circuits'employed at g the receiver end.

At the receiving end, as shown by Fig. 2, there is first provided the wireless receiver 30 which may be worked in any suitable manner with radio frequency amplification or with intermediate-frequency amplification, and which comprises further means for demodulation of the radio frequency oscillations. In the demodulation there is obtained a mixture of the two audio frequency oscillations furnished from sources 18 and 1 9 at the transmitter station, theformer one representing the band formed by the picturepoint frequencies. After suflicient preliminary amplification in the audio frequency amplifier 31, the band containing the picturepoint frequencies 'is separated from the synchronizing wave by means of

filters

32 and 33. In a simple case, it would also be sufiicient to replace one of said filters,that is, 33 adapted to pass the higher frequencies by a condenser chain, while the other one, 32,

adapted to pass the lower synchronizing frequency by a coil chain, or a high-pass and a a to the requisite amplitude by amplifiers 34.

low-pass, respectively. The two frequencies thus separated are thereupon raised finally and 35, respectively. The Karolus light valve is united with amplifier "35 in wellknown manner, while the synchronous motor 36 is connected with the output circuit of amplifier 34. An alternative scheme, as

alternating current power ated for the motor '36.

I claim:

"1. Ina facsimile. system, a light sensitive relay, means for introducing-a carrier frequency potential in the output circuit of said relay, means for translating varying intensities of light and shade in a facsimile to be is locally gener-' transmitted into varying intensities of cur-- rent through said relay "and modulating said carrier frequencythereby, a vacuum tube amplifier for amplifying said modulated carrier frequency, means for producing a separate synchronizing frequency, means for applying said synchronizing frequen'c to the filament member of said vacuum tu e amplifier for heating the same and transmitting the said synchronizing pulse as a filament tone, means for transmitting said facsimile modulated carrier and said synchronizing energy, means for receiving said transmitted signals, and.

means at the receiving point for separating the facsimile modulated signals and the synchronizing-signals and controlling a receiving system therefrom.

2. In a facsimile system, a support surface .for a facsimile to be transmitted,"a photo cell and means for influencing the photo cell by light varied in accordance with the intensity of light and shade in the facsimile to be transmitted, a bridge structure having the said photo cell forming one of the legs thereof, an adjustable capacity member in an adjacent leg thereto for balancing the capacity of the said photo cell during periods of zero illumination thereon, means for producing a carrier frequency, means for introducing said carrier frequency in said bridge structure across the diagonal between said cell and said variable capacity, means provided by said photocell for modulating said carrier frequency, means for producing a separate synchronizing frequency, an amplifier, means for amplifying both said modulated carrier and said synchronizing frequency by said amplifier, means for transmitting each of said energies, means for receiving the said transmitted energies, means at the receiving point for distinguishing between the synchronizing energy and the picture frequency energy, and means for utilizing the picture frequency energy to produce at the receiver areproduction of the transmitted facsimile, and means for utilizing the synchronizing energy for producing synchronous operation of the receiver and the transmitter.

3. In a facsimile system,'a sup ort surface for a facsimile to be transmitted, a photo cell and means for influencing the photo cell by light Varied in accordance with the intensity of light and shade in the facsimile to be transmitted, means for generating electrical oscillations of a carrier frequency,

means provided by said photo cell for modulating the output of said generating means, means for generating a separate synchronizing frequency differing from the modulating frequency, an amplifier and means for applying oscillations of said carrier frequency, said modulation frequency and said synchronizing frequency to the input thereof, and means associated with the output circuit of said amplifier for transmitting the resultant output energy.

FRITZ SCI-IROTER.