GB320024A - Improvements in or relating to multiplex communication systems - Google Patents

Abstract

320,024. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Whitaker, J. N.). Sept. 29, 1928, [Convention date]. Harmonic telegraphs.-In a single channel multiplex communication system for wireless or line telegraphy, a plurality of separate tone frequencies is supplied to a transmitter, the strength of impulses caused by superimposition of single cycles of the various tone frequencies being limited so as not to exceed that ot a single cycle. A plurality of circuits A, B, C, Fig. 1, are adapted for producing tone frequencies by means of tuning forks 1, the oscillations impressed on valve 4 being rectified and modified by valves 6 and 9 to produce a wave form as in Fig. 4. The tone circuits are connected through keys 11 or other modulating apparatus to a limiter 13, which passes superimposed pulses to the pulse amplifier 15, 16, with the same strength as a single pulse. High frequency currents are generated by a crystal-controlled oscillator 24, associated with one or more amplifiers 19, from which they are transferred to the aerial, the carrier being modulated by the impulses from the amplifier 15, 16, through resistances 21, 22, in the grid circuit of amplifier 19. The arrangement. is such that during the intervals between impulses valve 19 has a prohibitive negative bias from resistance 21, the voltage drop across 22, due to impulses in 15, 16, acting in opposition and reducing the negative grid potential of 19. No energy is thus radiated between tone frequency impulses. The receiver, Fig. 3 has filter circuits Fa, Fb. Fc, each accepting the tone frequency of the corresponding circuit. Specification 320,023 is referred to.