Patent GB-608887-A (GB)
Title: Multiplex communication system
IPC: H04N1/00
Filed: 1946-02-13
Abstract: 608,887. Multiplex transmission. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 13, 1946, No. 4571. Convention date, Nov. 29, 1943. [Class 40 (iv)] [Also in Groups XXXVIII, XL (b) and XL (c)] In a multiplex communication system, a subcarrier is modulated in frequency by facsimile signals and in amplitude by mark and space signals capable of operating a telegraph printer. Selective calling signals similar to the printing signals may be transmitted for bringing the printer into or putting it out of operation. In the embodiment described, a facsimile transmitter 10, Fig. 1, produces a frequencymodulated audio-frequency signal wave 14 which is fed through resistances 43, 44 to modulate a radio or other carrier transmitter 16. A keyboard or tape sender 26 generating fiveunit code printing telegraph signals operates a line relay 32, the contacts of which bridge a resistor 42 across the output of the facsimile transmitter to produce amplitude modulation 17 of the wave 14. A hand-operated key 36 is also provided to control relay 32 to produce a calling signal, At the receiver, the demodulated signals from carrier receiver 20, Fig. 2, are applied to the facsimile receiver 22 which is unresponsive to amplitude modulation and the amplitude-modulated printer signals are recovered by the full-wave rectifier 54 to operate line relay 62 through valve 58. Control of printer from sending station. The contacts of relay 62 control, over lead 84, Fig. 3, the slow-to-operate relay 82 which is unresponsive to printing impulses or a sequence of printing impulses, and a further relay 66 which passes on the printer impulses to the selector magnet 67 of printer 68 when the contacts of relay 77 are closed. Relay 77 is the motor control relay by which the motor 73 of printer 68 is energized and de-energized. When key 36, Fig. 1, is depressed to produce a long control pulse, the relay 77 being deenergized and motor 73 at rest, relay 82 responds to complete the circuit of relay 96 through rotary switch 111. The contacts 98 of relay 96 complete the circuit of relay 77 to start the motor 73, contacts 86 prepare the circuit of the selector magnet 67 and contacts 102 close the circuit of the holding winding 99 of relay 96. The latter circuit is maintained through the back contacts 108 of relay 82 when it falls off and while relay 82 is still energized the circuit is maintained by contacts 104 of a slow-to-release relay 106 operated by contacts 89 of relay 82. When the long motorstarting pulse ceases, relay 96 therefore remains locked and the motor running. The magnet 116 of the ratchet mechanism 118, 121 of the switch 111 is de-energized, however, and steps the switch round to an open-circuited contact 91, so that the next long received pulse does not result in the energization of relay 96 and breaks its locking circuit first at contact 108 of relay 96 and then at contact 102 of relay 77 when the latter releases to de-energize the motor 73 and shut down the printer 68. Thus, alternate long control pulses respectively start up and shut down the printer 68. Power for the motor 73 is derived from an A.C. source 74 and for the relays and other magnets from a rectifier 79 feeding a bus-bar 81.