Video Signal Carrier Circuit
Posted on Oct 4, 2012 10608
In the video system of Figs. A and R, a single coaxial cable carries power to the remote location, selects one of eight video channels, and returns the selected signal. The system can choose one of several remote surveillance-camera signals, for example, and display the picture on a monitor near the interface box. The heart of the multiplexer box (A) is a combination 8-channel multiplexer and amplifier (IC1). Cll couples the multiplexer`s baseband video output to the coax, and LI decouples the video from dc power arriving on the same line, This powerapproximately 30 mA at 10 Vsupplies all circuitry in the multiplexer box.
In interface box (B), a desired channel is encoded by three bits, set either by switches as shown or by an applied digital input. Momentary depression of the send button triggers downconverter IC1 and gated oscillator IC2A to initiate a channel-selection burst,