GB1234430A - - Google Patents

Abstract

1,234,430. Multiplex television camera control. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 23 Dec., 1968 [27 Dec., 1967], No. 61176/68. Heading H4R. A television camera is connected to a control unit by a single coaxial cable over which the video signal from the camera, control signals to the camera, and speech signals are transmitted in multiplex. The various control signals are time division multiplexed width modulated pulses which modulate a carrier transmitted in frequency multiplex with the video signal and an intercom. signal, with power supplied over the same cable at D.C. to a D.C. to D.C. converter at the camera. As described video signals from the camera are transmitted in their normal frequency band, e.g. 50 Hz to 6 MHz, while intercom. signals from the camera to control unit are modulated on a carirer of 30 MHz. The camera control signals from the control unit and a voice signal from the control unit to the camera comprise 10 channels of relatively slowly varying signals which are each sampled at 12.5 kHz and transmitted as a 125 kHz t.d.m. pulse signal modulating a carirer of 20 MHz. One channel of the t.d.m. signal is arranged to carry a frame synchronizing signal by a width modulation of channel pulse during a frame synchronizing signal, and another channel carries an over-modulated amplitude as a mutliplexing synchronizing signal. Line frequency pulses are transmitted from the camera, mixed with the video signal therefrom, and a line frequency control signal is transmitted from the control unit, over one t.d.m. channel, after comparison therein of the camera line frequency with the standard line frequency of the system. The system may be applied to colour television where the various colour component signals are transmitted in frequency multiplex, the cable may be double screened or two cables may be used, one to provide an earth reference to eliminate parasitic disturbances on the cable. An L.C. circuit is used to separate the video and D.C. power signals at each end of the cable, the circuit being arranged to correctly terminate the cable, and the video signal is given a low frequency pre-emphasis at the camera to compensate the frequency characteristic of the separating circuit.