Double-conversion TV tuner arrangement for all-band reception off-air or from CATV input

摘要

Input to the tuner is via a bandpass filter (1) and wideband amplifier (2) which feeds signals from the full range of VHF/UHF TV bands to a first mixer (3). A fixed-frequency local oscillator (4), running at 1000 Mhz, provides injection to the mixer. The resultant first IF, corresponding to signals between e.g. 50 and 860 Mhz, is supplied, via a tuned band-pass filter (5), to a second mixer (6). The second mixing stage receives injection from a tunable local oscillator (7) and produces an output at the standard TV intermediate frequency. The second local oscillator operates with varicap diode tuning controlled by a programme setting unit (8). Manual control with reasonable linearity may be performed with a logarithmic potentiometer.