GB336096A - Improvements in multiplex high frequency signalling systems - Google Patents

Abstract

336,096. Marconi's Wireless Telegraph Co., Ltd., (Hansell, C. W.). Oct. 7, 1929. [A Specification was laid open to inspection under Sect. 91 of the Acis, Oct. 8, 1929]. Multiplex signalling systems employing a single carrier wave are characterized by one or more of the channels utilizing frequency submodulation as a preliminary to single side-band modulation of the carrier, and one or more other channels utilizing ordinary amplitude modulation. In the transmitting system shown in Fig. 3, two keying channels and one telephony channel are afforded by the keys 66, 68, alternators 62, 64, and microphone 70, the joint output being applied to a pair of oscillating valves 82, 84 arranged to produce a frequency-modulated wave. This wave is used to modulate a crystal-controlled oscillator 100, and from the output one side-band is selected by a filter 110, is amplified at 120 and 130 and transmitted to an aerial 140 or to a line. The amplitude-modulation channels comprise a microphone 170 and alternators 162, 164, the joint output being amplified at 178 and utilized to modulate the amplitude of the output from the valves 120. At the receiving-station, Fig. 4, the received signals are amplified (with or without a heterodyne change of frequency) and directed to two separate channels, one of which may comprise a local oscillator 188, first detector 190, intermediate-frequency amplifier 192 and second detector 194. The mixed signals sent by amplitude modulation are thus received and sorted out by filters 184 &c, The second channel includes a limiter 154 which wipes out the amplitude modulation. The frequencymodulated waves may be heterodyned by a source 156 and detector 158 to lower the frequency band, and are amplified at 160 and passed to an analyzer and detector 182 which in known manner converts the frequency-modulation into amplitude modulation. The multiple frequency-modulated signals are then separated by filter circuits 184. Either the frequency channel or the amplitude channel or both may be used as a simplex channel. The frequency-modulated signals may be produced by arranging a key to vary the inductance or capacity of the tuned circuit of a valve oscillator (Fig. 1, not shown).