GB554456A - Improvements in electrical communication systems - Google Patents

Abstract

554,456. Multiplex signalling; directive wireless signalling. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). April 23, 1942, No. 5449. [Class 40 (v)] In a multiplex communication system, a pulsemodulated carrier wave is transmitted over radio links, wave guides, or wires, and the channels are identified by a different characteristic of the pulses, e.g. by different pulse amplitudes or by different pulse duration. Fig. 3 shows three series of pulses a, b, c, the channels being identified by pulse amplitude, and separation effected at the receiver by cutting off the pulses at the respective levels 9, 10, 11. A receiver for two such channels, Fig. 4, has the aerial 12 connected through an amplifier 13 to two valves 14, 15 biased respectively to the levels 9, 10 of Fig. 3. The received waves pass through further amplifiers to detectors 18, 19 whence the pulses pass through amplifier 20, 21 to pulse demodulators 22, 23 and to telephones 24, 25. The a channel pulses are excluded from the b channel by a connection 26 or 27 which blocks the b channel while an a pulse is present. If this blocking connection is made at a radio-frequency stage, a phasing device is included. The pulse demodulator 23 of the b channel may also be rendered inoperative by the a pulse. Different carrier frequencies may be used for the various channels in order to avoid difficulties due to continued phase opposition of the carriers conveying wanted and unwanted signals. When the channels are distinguished by different pulse duration, separation of the pulses at the receiving end is effected by a filter having a suitable pass-band width, the emerging pulses being distinguished by their amplitude, and being separable by biased amplifiers. If transmissions are to be received from different directions, the receiver may make use of a vertical aerial 36, Fig. 6, and a frame aerial 35. The received waves are passed through frequency-doublers 41, 42 to limiters 39, 40 which reduce both received waves to the same level so that in general a balance can be effected in the circuit feeding the pulse demodulator 44. For positions, however, of the frame aerial at or near that of zero reception, the balance is upset and the signals received. A second directive aerial may replace the vertical aerial.