US1626731A

US1626731A - Method of and apparatus for synchronization in picture transmission

Info

Publication number: US1626731A
Application number: US677839A
Authority: US
Inventors: Herman Joseph
Original assignee: American Telephone and Telegraph Co Inc
Current assignee: AT&T Corp
Priority date: 1923-11-30
Filing date: 1923-11-30
Publication date: 1927-05-03
Anticipated expiration: 1944-05-03

Description

METHOD OF AND APPARATUS FOR SYNCHRONIZATION IN PICTURE TRANSMISSION Filed NOV. 50, 19 23 y INVENTOR J. 1% rma44/ Patented May 3, 1927.

PATENT OFFICE.

UNITED STATES JOSEPH HERMAN. OF NEW YORK. N. Y., ASSIGNOR T AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK. I

METHOD OF AND APPARATUS FOR SYNCHRONIZATION IN PICTURE TRANSMISSION.

Application filed November 30, 1923. Serial No. 677,839.

The principal object of my inycntion is to provide for synchronous operation of apparatus at the transmitting and receiv ng stations of a carrier current comnuuncation system. Another object of 1ny invent1on is to provide a carrier current picture trans mitting system in whichsynchronizatlon is effected by means of the carrier current. These and other objects of my invention Wlll it) become apparent on consideration of a specific example which 1 have chosen for disclosure in this specification. It will be understood that the invention is defined in the appended claims and that the drawings and the following specific-a1 ion relate to the particular embodiment of the invention chosen by way oi example.

The drawing is a diagram showing apparatus by which my invention may be practised.

At the sending station the alternating current generator 10 on the shaft 13 1s driven by the honic motor 11, whose rate is determine by the tuning fork 12. Thus, the

generator 10 applies an alternating electromotive force of definite frequency through the transformer 21 on the grid of the threeelectrode vacuum tube modulator 20.

The picture to be transmitted in the form of a semi-transparent film 15 is wrapped on the glass shaft 13. The drum 14 is also provided with screw means to traverse it slowly in an axial direction while it rotates so that the spot of the film 15 adjacent to the opening in the screen 18 travels over a helical path of the film 15.

Light from the source 16 is directed by the lens 17 through the opening in the screen 18 and through the adjacent portion of the film 15 to the photoelectric cell 19. Accordingly, the current through the photoelectric cell 19 varies in proportion to the transparency of the film 15 and a corresponding electromotive force is superposed on the grid of the three-electrode vacuum tube modulator 20.

The output from the modulator 20 goes through the transformer 22 and through the band-pass filter 23 to the line 24. This output will be a carrier current of frequency F determined by the generator 10 and modulated in accordance with the lights and shades of the picture film 15.

drum 14, which is rotated from the Let D be a member such that essential side bands of current frequency will be comprised between the frequency limits FD and -F+D; these are the cut-off frequencies of the band-pass filter 23.

At the receiving end the modulated carrier current from the line 24 goes through .asimilar filter 25 and through a transformer 26 to the grid of a three-electrode vacuum,

tube demodulator 27. The output from the tube 27 goes through the resistance 28 in shunt to which are two multiple branch circuits with

respective filters

29 and 30.

passes Frequencies below where D is a number which represents the maximum essential frequency produced by the revolving drum and photoelectric cell at the transmitting station. In other words the band width of the low-pass filter 29 must be large enough to pass all frequencies which are essential to an accurate reproduction of the trans mitted picture. d

On the other hand, the filter 30 is a bandpass filter with a very small band Width so that the filter 30 passes only the narrow band comprising the carrier frequency F. The band width of this filter may be represented by the limits F-l-(Z and F0Z, where d is a small number.

The frequency band transmitted by the filter 29 goes to the electromagnetic light valve 31, which controls a shutter at 34. The light from the source 32 is directed by the lens 33 through the opening permitted by the shutter 34 and then through another lens 35. through an opening in the screen 36 to the sensitive film 37 on the rotating drum 38.

It will be seen that the variation of current through the photoelectric cell 19 at the transmitting station corresponds to the transparency of the film 15 at the spot under the opening in the screen 18. This same current is again obtained at the receiving station by demodulation of the carrier current from the line 24 in the vacuum tube 27. The current thus obtained passes through filter 29 to the light valve 31 where it determines the opening of the shutter 34 so that a correspondingiintensity of light falls on the spot of the film 37 adjacent to the opening in the screen 36.

The drum 38 carrying the receiving film 37 is rotated and traversed in synchronism The filter 29 is a lowass filter which with the transmitting drum tus now to be described.

The carrier current passed by the filter 30 and amplified by the amplifier 3.) drives the synchronous motor 40, ,which drives an interrupter 41 in the circuit of the control magnet 42 for the tuning fork 43. The tuning fork 43 is tuned to very nearly the frequency of the tuning fork 12 at the sending station, that is it is very nearly a copy of the tuning fork 12. Acco ly, it IS readily forced to vibrate at the non determined by the fork 43 is forced to vibrate at the same rate as the fork 12. The fork 43 determines the speed of the phonic motor 11' on the shaft 13' geared to the receiving drum 38. Thus, the receiving drum is rotated and traversed in synchronism with the sending drum 14.

The shaft 13' also carries an alternating current generator 10' of the carrier frequency F. The current from the alternating current generator 10' goes to a threeelectrode vacuum tube modulator similar to 20 for sending from east to west. At the ending station shown at the west a receiving drum like 37' may be driven from the shaft 13.

It will beseen that for transmission both ways the carrier current frequency F is determined by the tuning fork 12 at the station on the west.

In order to bring the synchronous motor 40 to the proper speed foroperation from the received carrier frequency current, a clutch 45 is provided to engage the shaft of the nchronous motor 40 with that of the phonic motor 11. The phonic motor Ina then be operated from its own tuning for by throwing the switch 44 to make the fork 43 self-operative. \Vhen the motor 40 has become synchronized the clutch 45 is disengaged and the switch 44 is thrown to the 14 by apparaposition shown in the drawing. The tuning fork 43 will then be operated from the interrupter 41 on the synchronous motor 40.

It Will be seen that by my invention no auxiliary currents or impulses are necessary for synchronization but the fundamental carrier current itself is not only modulated to transmit the picture but is filtered out and employed to drive the receiving apparatus at the rate of the carrier current itself, which is determined at the sending station.

I claim:

1. The method of synchronizing apparatus at two places between which transmission is effected by modulated carrier current which consists in determining the speed of the apparatus at both places in accordance with the carrier frequency.

2. The method of synchronizing the transmitting and receiving apparatus in a. modulated carrier current communication systhe interrupter 41, that is, d

mag-r01 tem, which consists in determining the speed of both the transmitting and receiving apparatus in accordance with the frequency ofv the carrier current.

'3. In a modulated carrier current transmitting system, the method of synchronizmg the transmitting and receiving apparatus, which consists in generating the currier current at the transmitting end with a frequency proportional to the speed of the transmitting apparatus and filtering out the carrier cifirrent at the receiving end and rivin t e receivin ap aratus at a s d determined thereby. P pee 4. In the transmission of pictures by means of a modulated carrier current, the method of synchronizing the transmitting and receiving apparatus which consists in drivmg the transmitting apparatus at a speed determined by the speed of the carrier current enerator and at the receiving end contro ling the speed of the receiving apparatus by the carrier component of the modulated received current.

5. Means for synchronizing apparatus at two places between which a carrier current transmission is effected com rising respective motors at the places, an means at each place to correlate the motor speed with the carrier frequency.

6. In a picture transmitting system a carrier current generator at the transmitting end, means to modulate its output in accordance with the elements of the icture to be sent, a line to carry the mo ulated current, means to expose a spot of a sensitive receiving film in accordance with the modulated current received from the line and means to move the receiving film in synchronism with the transmitting film, said last mentioned means having its speed determined by the carrier component of the received current.

7. Means for receiving a picture represented by a modulated carrier current coinprising a filter to separate out the carrier component, a motor with speed controlled by said carrier current and a picture receiving drum driven by said motor.

8. Means to receive a picture transmitted by a modulated carrier current comprising a movable picture receiving film, a source of light, means to direct a beam from said source on a spot of said film, a shutter acros said beam of light, means to control said shutter by the demodulated received current and means to filter out the carrier component of the received current and thereby to determine the speed of the picture receiving drum.

9. In a signaling system means for generating a sustained alternating current, means for continuously modulating said alternating current according to message signals, means for receiving said modulated current,

modulated cur-- means for generating a carrier current, means for modulating said current according to the characteristics oi the picture to be reproduced, means for demodulating said current, means for selecting a portion of the demodulated current to control the movement of said film, and means for selecting another portion of said den'iodulated current to control said tilm ex iosing means.

exposing said film,

11 testimony whereof, I have signed my name to this specification this 23rd day of November, 1923.

JOSEPH HERMAN.

DISCLAIMER 1,626,731.-J0seph Herman, NEW YORK, N. Y.

SYNGHRONIZATION graph Company. Hereby enters this the following words, to wit:

9. In a signaling system METHOD or AND APPARATUS FOR IN PICTURE TRANSMISSION. Patent dated May 3, 1927. Disclaimer filed March 12, 1930, by the assignee,

American Telephone and Teledisclaimer to the said claim of said Letters Patent, which is in means for generating a sustained alternating current,

means for continuously modulating said alternating current according to message signals, means for receiving said modulated current, and

means for dividing said received current into message signal currents and into synchronizing signal currents.

[Oflicial Gazette April 1, 1930.].

DISCLAIMER 1,626,731.J0seph Herman, New York, N.Y.

Picrunn TRANSMISSION. Patent dated 2, 1938, by the assignee, American are in the following words, to wit:

1. The method of synchronizing apparatus at two places current, which consists in determining the accordance with mission is effected by modulated carrier speed of the apparatus at both places in 2. The method of synchronizing the speed of both frequency of the carrier current.

the transmittin a modulated carrier current communication system, w

the transmitting and receiving apparatus the transmission of pictures by means of a modulated METHOD or AND .APPARATUS son May 3, 1927. Telephone and disclaimer to the said claims of said Letters Patent which between which transthe carrier frequency. a and receiving apparatus in ich consists in determining in accordance with thecarrier current,

the method of synchronizing the transmitting and receiving apparatus which consists in driving the transmitting apparatus at a speed determined by the speed of the carrier current generator and at the receiving end controlling the speed of the receiving apparatus by the carrier component 5. Means for synchronizing apparatus at two places current transmission is effected comprising respective motors at the places,

of the modulated received current.

at each place to correlate the motor speed with the carrier frequency.

6. In a picture mittmg end, means picture to be sent,

sensitive receiving film in accordance with the modulated film in synchronism with the transmitting film, having its speed determined by the carrier component receiving 10. The combination of signal recording means, means, means for generating a sustained alternating current, means for modulat and means for utilizing said modulated a carrier current generator at the transto modulate its output in accordance with the elements of the means to expose a spot of a current received from the means for driving said recordcurrents to centre the operation of said driving means and to control the operation of said signal reproducing means.

[Qflioial Gazette November 28, 1938.]