Tunable HF input circuit for TV receiver - has resonance curve of first IF filter coincident with that of tunable second oscillator

摘要

The input circuit has the output of its tunable second oscillator (02) also passed to the input of its first IF bandpass filter (F1) in order to make the resonance curve of the first IF filter coincide with that of the tunable second oscillator. Either the tunable components of the first IF band-pass filter or those of the second oscillator are connected via a first switch (S1) to a voltage supply (UB) that displaces frequency to allow tuning to the second IF frequency to take place in a relatively short time.