Multiplex communications – Wide area network – Packet switching
Patent
1980-09-15
1983-03-29
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 62, 370 77, 179 2E, H04J 302
Patent
active
043785980
ABSTRACT:
A communications system is disclosed including a radio junction box controlling a number of radios and a number of crew boxes all linked by a ring circuit consisting of a single coaxial cable which provides both power supply and information. The various communication channels between the crew boxes and the radios and an intercom channel linking the crew boxes are provided by time division multiplexing. The microphone of each crew box is coupled to the coaxial line by a current generator. Each current therefore generates an appropriate voltage signal across the impedance of the cable which is assumed to be constant. Thus, when more than one crew box feeds current onto the line, the currents add and generate a correspondingly greater voltage signal on the line. Therefore, the attenuating effect which would take place if each crew box output were in the form of a voltage (in such a case each output would be loaded by the relatively low output impedance of the other voltage output or outputs on the line) is avoided. Time multiplexing of the crew boxes is therefore not required. Each signal transmitted on the line is pre-distorted to offset any distortion it will undergo upon transmission along the line. The signal received by each crew box is regularly clamped to effect signal separation and provide a known mean signal reference level.
REFERENCES:
patent: 3806807 (1974-04-01), Nakamura
patent: 3940561 (1976-02-01), Heinze et al.
patent: 3943284 (1976-03-01), Nelson
patent: 4268722 (1981-05-01), Little et al.
patent: 4289932 (1981-09-01), Reed
British Communications Corporation Limited
Olms Douglas W.
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