GB581485A - Synchronising and phasing arrangements for electric facsimile transmission systems - Google Patents

Abstract

581,485. Synchronous movements ; copying telegraphy. FINCH TELECOMMUNICATIONS, Inc. Feb. 18, 1944, No. 3056. Convention date, Feb. 20, 1943. [Class 40 (iii)] In an electrical facsimile signal transmission system which includes rotating drums at the transmitter and receiver and in which the receiver drum is driven by alternating currents derived from synchronizing signals emitted from the transmitter as a train of periodic impulses directly related to the speed of the transmitter drum and which incorporates phasing means by which the drums are rotated synchronously with a specified phase relation, the phasing means comprise a start-stop device operated by the received periodic signals. At the transmitter, Fig. 1, the motor 101 is driven from an A.C. or D.C. source and synchronizing impulses are generated by the action of a black strip 116 on the scanning beam which is traversed axially of the drum 103. The synchronizing impulses are intensified by short-circuiting a potentiometer in an amplifier 113 by means of a switch 117 closed by a cam 121 simultaneously with the passage of the black strip 116 across the scanning beam. At the receiver, Fig. 2, the combined picture and synchronizing signals are rectified and passed to the reproducing device 145 and a switch 152 is opened by cam 151 to prevent the transmission. of the strong synchronizing impulses to the scanning device. The valve circuit 153 is biassed so that it passes only the synchronizing impulses which operate a magnet 183 controlling a pivoted stop member 177 associated with a tooth disc 174 forming part of a clutch between the motor 155 and drum 144. The stop member is effective solely when the receiver is out of phase with the transmitter and holds the drum until phase equality has been established. The synchronizing impulses are also applied to a gasfilled valve 157 normally rendered inoperative by battery 161 and after valve has started passing current from driving battery 154 the condenser 165 and inductance 166 operate to switch off current until the next synchronizing impulse arrives. Where necessary a frequency multiplier 156 may be incorporated between valve 153 and the input of the gas-filled valve 157. The Specification as open to inspection under Sect. 91 includes also a system in which the transmitter Fig. 1 (Cancelled) has a drum 11 driven from an A.C. source whilst the optical scanning members 14, 15, 16 are moved axially. The picture signals, amplified at 23, modulate an audio-frequency carrier and at 26 modulate a high-frequency carrier wave. The carrier wave is also modulated by a continuous alternating current from the driving source A.C. If the transmission is over wires, a harmonic of the driving frequency is transmitted. Synchronizing impulses are sent at the end of each line by contacts operated by a cam on the shaft of the drum. At the receiver, Fig. 3 (Cancelled) the demodulated picture signals are selected by a high-pass filter 43 and passed through an amplifier and rectifier to the reproducer 65 traversed with respect to the drum 55 driven from the motor 56 through a reduction gear 57. The demodulated synchronizing impulses are applied through a lowpass filter 44 and control a circuit comprising a driving battery 73 and gas-filled discharge valves 71, 72 which are alternately made conducting by the synchronizing impulses so that current at the driving frequency is fed through a transformer 75 to the motor 56. A condenser 77 connected in parallel across the primary winding of the transformer 75 acts as a commutator to cut off alternately the current flow from the valve 71 or 72 which is made operative. This subject-matter does not appear in the Specification as accepted.