Channel selector for cable TV redistribution system - has two local intermediate frequency oscillators controlled by PLL operated by single quartz clock

摘要

The selector is used for retransmitting t.v. signals to a public display station and has a preamplifier coupled to a first mixer providing an intermediate frequency signal through a pass band filter to a second mixer. The latter applies its output to the display station through a second pass band filter. The two mixers are served by respective phase locked loop local oscillator circuitry driven by a common quartz oscillator (30) providing a reference signal. Each local oscillator comprises a transistor whose collector is coupled to an inductance oscillator, tuned by a capacitance diode (41,42) whose controlling voltage is supplied by its phase locked loop circuit (11,21). The transistor emitter is connected to its associated mixer and phase locked loop circuit. The intermediate frequency lies in the range 110.75-117.75 MHz.