Patent GB-673041-A (GB)
Title: Two-way communication systems between two facsimile transceivers
IPC: H04N1/32
Filed: 1950-05-19
Abstract: 673,041. Copying-telegraphy. STANDARD TELEPHONES & CABLES, Ltd. May 19, 1950 [May 21, 1949], No. 12580/50. Class 40 (iii). In a facsimile system having two machines connected together for intercommunication, each machine being provided with a power switch and being constructed to operate either as a transmitter or as a recorder, the closing of the power switch in the first machine for the purpose of transmitting operates a warning device at the second machine and automatically conditions the second machine to operate as a recorder when its power switch has been closed manually. The operation of the switch 44 closes a circuit for the motor 16 driving the drum 12 and also closes the circuit of a transmitter relay 48. The connection of the wires A, A1 applies voltage to a transformer 22, Fig. 2, which through a rectifier 26 provides voltages for the valves of the transmitting and recording amplifiers TP, RP respectively, and heating voltages for the filaments of the valves. The operation of. relay 48 opens at contact 63, the circuit of the recording amplifier RP and at contact 351 completes the circuit of the transmitting amplifier TP. At contacts 71 of the switch 44 a rectifier 65 is connected to the mains A, B and provides a source of D.C. current which is applied over back contacts 68 of a relay 50 and of relays 46, 47 to a conductor 77 and the line L1. The voltage at the rectifier 65 is also applied through a delay network 78 to relay' 50 which is energized for a short period during each revolution of the drum through a conducting segment 19 on a commutator 18 rotated with the drum 12. The voltage applied to the line 77 is interrupted for a short interval during each rotation of the drum 12. At the receiver station, the voltage from the line L1 at the transmitter is applied over line L2 and conductor 80, and operates a line relay 45 which holds operated during the short interruptions applied by relay 50 of the transmitter by condenser 81 connected to ground over the back contacts of a phasing relay 47 and a receiver relay 49. Contact 86 of relay 45 operates a buzzer 87 over contact 88 of switch 44 and conductors A, B. The operator at the recorder station loads the drum with a receiving sheet and operates switch 44, which, as in the case of the transmitter, applies voltages to the valves of the transmitting and receiving amplifiers and connects the rectifier 65. The operation of the switch 44 also operates the receiving relay 49 which disconnects the stylus from the transmitting amplifier and connects it to the plate circuit of the valve 37 of the recording amplifier. Relay 49 also disconnects ground from the retaining circuit 81 for the relay 45 which is now released for a short period during each revolution of the drum at the transmitter. The driving circuit for the motor 16 of the receiver passes through contact 99 of relay 50 which, as in the transmitter circuit, is energized for a short interval during each revolution of the recorder drum 12 and its commutator 18. At this stage the receiver motor is running at less than synchronous speed, the relay 50 is energized for short periods during each revolution of the receiver drum and the relay 45 is released for a short interval by the periodic energization of the relay 50 at the transmitter. The styli at the transmitter and receiver are under control of a stylus motor 17 whose circuit is not completed until a phasing relay 47 is operated. Control of synchronous operation. The phasing relay 47 is connected via leads 100, 101 to the positive side of the rectifier 65 but its operating circuit is connected in parallel with two shorting circuits extending from common point 105 to a grounded back contact 106 of relay 50 and to a grounded front contact of relay 45. When the drums at the transmitter and receiver are in phase, the operation of relay 50 at the receiver is coincident with the release of relay 45 by the operation of relay 50 at the transmitter, and the grounding short circuits are simultaneously disconnected. Relay 47 operates and opens the short-circuiting circuits. Additionally a contact of relay 47 short-circuits relay 50 so that the motor circuit is not interrupted and a further contact operates the stylus motor 17 to lower the stylus 15 and to traverse its carriage 13 along the drum as described in Specification 668,865. A continuous current is also transmitted from rectifier 65 via contact 68 of relay 50 and operated contact 116 of relay 47 to L1 which at the transmitter energizes relay 45, permanently eliminating the shorting ground circuit of relay 47. The other shorting circuit is removed when relay 50 operates during the rotation of the transmitter drum and relay 47 at the transmitter now energizes and operates its stylus motor 17 to lower the stylus 15 and traverse the carriage 13. Transmitting circuit. The signals from the stylus 15 pass via back contact 34 of relay 49 (not operated) to conductor 33<SP>1</SP> and point c of the bridge 32, the resulting variations applied to the grid of a valve 31 being applied via conductor 35, contacts 35<SP>1</SP> of transmitter relay 48 and lead 41 to transformer 39. Receiving circuit. The received signals are applied to the plate circuit of a valve 36 and modulate the output of a valve 37 connected over lead 98, operated contact 97 of relay 49 and conductor 341 to the stylus 15. Termination of transmission. Normally the carriages 13, at the transmitter and receiver automatically open the switches 44 at the end of their traverse and restore the machines to their normal conditions. If the matter to be transmitted is of less than normal size, the operator at the transmitter opens the switch 44 at the end of the transmission, cutting out the motor and the voltage normally applied from rectifier 65, to the line L1. At the receiver station, relay 45 releases and effects release of relay 51 thereby operating relay 46 which opens the circuit to the relay 45 of the transmitter and operates the buzzer 87. If the attendant opens the switch 44, the receiver circuit is restored to normal, but if no action is taken, the stylus carriage 13 moves to the end of its travel and automatically opens the switch 44.