Patent GB-828782-A (GB)
Title: Improvements in multiplex phase-shift telegraphy systems
IPC: H04L5/12
Filed: 1956-01-06
Abstract: 828,782. Multiplex transmission systems. COLLINS RADIO CO. Jan. 6, 1956 [April 18, 1955], No. 577/56. Class 40 (4). [Also in Group XL (c)] In a multiplex phase-shift telegraphy system (particularly for V.H.F. forward-scatter transmission) a carrier is modulated by a number of tones of different frequencies ; each tone carries two channels by being transmitted in pulses and each pulse is phase-shifted with respect to the preceding pulse (not with respect to a fixed reference) by a multiple of 45 degrees according to which of the 8 possible combinations of " mark " and " space " occurs at that moment in the two channels. Transmitter.-Considering first the diplexing of two channels on to a single tone, pulses of 20 kc/s tone are generated by two magnetostrictive resonators 42, 52, Fig. 4, of the kind disclosed in Specification 828,781, and these are controlled alternately by gates 44, 54, under the control of a timing wave generator 48, so that when one resonator, e.g. 42 is connected to the output 46 via gate 44, the second resonator 52 is disconnected by the open gate 54 and is rapidly quenched by negative feed-back through a gate 57 which is also controlled by the timing generator 48 via a trigger 58. Gate 57 opens after a short time interval and the resonator 52 then again builds up oscillations due to energy obtained from resonator 42. The phase of these new oscillations relative to those existing in resonator 42 is determined by a phase modulator 31. The timing wave generator 48 then opens gate 44 and closes gate 54 and the functions of the two resonators are interchanged, and so forth. The phase modulator 31 consists of two parallel paths, each containing a ring modulator 33, 34 which reverse the phase of the signal applied to them on receipt of a " mark " signal from input 11 or 10 respectively. The inputs 10, 11 are assumed to be teleprinter converters. The path controlled by input 11 additionally includes a 90 degree phase shifter 30, and the outputs of both paths are added at 36 so that M1S1, Fig. 1, represent vectorially " mark " and " space " from input 10, M2S2 represent the same for input 11, and the dotted lines represent the resultants arising from the various possible combinations of " mark " and " space " in the two channels. A similar phase modulator 32 controls the phase of oscillations in resonator 52. The phase modulated tone pulses at output 46 either modulate a radiofrequency carrier or are directly transmitted by line. Additional pairs of channels are provided, Fig. 7 (not shown), by similar sets of equipment generating tones 100 c/s apart. Receiver.-The original tones are recovered from the multiplexed incoming signal by a homodyne receiver, the local oscillator of which is synchronized with the transmitter in unspecified manner. Each tone is then applied to an individual phase detector, Fig. 5 (not shown), in which it is switched alternately to each one of a pair of magneto-strictive resonators arranged as in Specification 828,781. The outputs of each resonator are sampled towards the end of each pulse period and the two outputs are compared, with and without 90 degrees phase shift, in two phase detectors the outputs of which are stated to be the " mark " and " space " signals of the two channels.