Intermediate frequency sound transformer for multichannel TV set - has oscillator-frequency changer with second harmonic transmitted on, input being from non-tuner signals

摘要

The sound IF frequency is fed via a band pass filter (3) and the sound output circuit (10), the circuit comprising a bandpass filter (1) for transmission of IF signals not received by the tuner. An oscillator circuit (8) oscillates corresp. to the frequency passing the bandpass filter. A mixer (9) compounds the oscillation signal of the oscillator and the signal running through the bandpass filter. A band pass filter (2) transmits only the second harmonic of the output signal of the mixer (9) to the sound output circuit (10). The oscillator (8) may comprise capacitors (C1,C2) and a resistor (R3) such that through tuning the IF transformer (L1) by hand, the oscillation frequency is set to the frequency of the difference between the pass frequency of the two bandpass filters.