GB654253A - Improvements in or relating to radio telegraph communication systems - Google Patents

Abstract

654,253. Multiplex radio signaling. WESTERN ELECTRIC CO., Inc. Aug. 7, 1947, No. 21761. Convention date, Dec. 1, 1944. [Class 40 (v)] [Also in Group XL (b)] Multiplexed two - tone telegraph signals are simul. taneously transmitted as two discrete frequency bands; and at the receiver the frequencies of the signals in one band are shifted to a position in the spectrum which is nearer to, but still different from the signals in the other band, from each band the individual channels are selected, and applied to current limiters which select the stronger signal. At the transmitter, Fig. 1, each of the channels 1 ... 6 comprises a pair of oscillators, e.g. O11, 012, supplying mark and space tones respectively to sending circuits, e.g. SS11, SS12 and to band-pass filters, e.g. F11, F12. There is also a calling channel 023 &c. The oscillators each produce a different one of the odd harmonics of the base frequency oscillator Oo. The combined output of all channels is passed by a low-pass filter F31 to the transmitter RT; and is also passed via amplifier Al to a modulator MD where it is mixed with the output of oscillator 030, the lower side-band being selected by filter F32 to provide a transposed band of signals which are transmitted simultaneously from the transmitter RT. At the receiver, Fig. 2, the incoming signals are demodulated and amplified, the lower band of signals is selected by filter F39 and passed to channel-selecting narrow band-pass filters F41 ... F53. The transposed band of signals, selected by filter F40, is mixed at DM with the output of oscillator 041, which is of a higher frequency than the corresponding oscillator 030 at the transmitter so as to produce a band of frequencies which is nearer to but still distinct from the original. This band is passed by amplifier A4 to channelselecting filters F61 ... F73. In each channel, e.g. channel 1, the outputs from both bands are combined, amplified, and passed to a current limiter CL which discriminates in favour of the stronger signal. The output is passed by the appropriate filter of the set F81, F82, F91, F92, to a detector and telegraph printer. In a modified system, Figs. 3 and 4 (not shown), the multiplexed two-tone signals are transmitted and received as a pair of different frequency single side-bands as in Specification 516,088, one band of the received signals being, as before, applied directly to the channel-selecting filters ; the other band being transposed by the same amount as before by first mixing with oscillations of the same frequency as 030, Fig. 1, and then with oscillations of the same frequency as 041, Fig. 2. Specification 654,271 also is referred to.