GB707513A - Improvements in or relating to keyed frequency modulation carrier wave systems - Google Patents

Abstract

707,513. Multiplex pulse signalling ; frequency modulation. STANDARD TELEPHONES & CABLES, Ltd. July 18, 1952, No. 18211/52. Addition to 679,901. Class 40 (5) Relates to receivers for communication systems, as described in the parent Specification, in which each time-modulated pulse of a multichannel pulse train produces a unidirectional shift in the frequency of a transmitted carrier wave, the odd-numbered pulses producing a frequency shift in one sense and the evennumbered pulses in the opposite sense. The demodulated output from radio receiver 10 is thus a series of rectangular pulses of which the time positions of the leading edges represent the modulation of the oddnumbered channels and those of the trailing edges the even-numbered channels. The synchronizing signal is transmitted as in the parent Specification and separated by circuits 14, 15. After shaping in circuit 16, it is fed to the delay line channel distributer 17 controlling the channel demodulators 21 ... 26. The latter is fed with duration modulated pulses derived in circuits 11, 12 respectively for the odd and even channels. These circuits are fed over conductors 19, 20 with pulses occupying the full width of the odd and even channels respectively and derived from the synchronizing signal by a frequency-multiplying circuit 18. The multiplying factor is twelve for the twenty-four channel system described. Circuits 11, 12 are also fed with the modulated rectangular pulses from receiver 10 over conductor 13 and comprise coincidence circuits, Fig. 3 (not shown), which produce an output during the period of overlap of the two inputs. The channel demodulators 21 ... 26 comprise gating circuits and low-pass filters, Fig. 4 (not shown).