Electronically tuned FM radio circuit

Shown is an electronically tuned FM radio circuit. A varactor diode (1SV75) (as a variable capacitor) is used in both the high-frequency resonant circuit
and the local resonant circuit . When tuning and selecting a station, 3 to 9 values ​​are sent from the tuning circuit. V DC voltage is added to the load of each varactor diode
to provide reverse bias for the varactor diode. The varactor diode and its parallel coil form a resonant circuit. The
    high-frequency FM signal induced by the antenna is added to the commercial frequency resonant circuit Li. On the first gate of the high-frequency amplification field effect transistor VT1,
the output of VT1 is sent to the base of the mixing transistor VT2 through the transformer and the high-frequency resonant circuit b. It is composed of VT3, coil L3 and capacitor (including
the capacitance of the varactor diode) It forms a local oscillation circuit . The oscillation signal is sent from the emitter of VT3 to the base of mixer VT2 through the 8'pF capacitor.
After the radio frequency signal and the local oscillator signal are mixed in rr2, they are output by the collector of VT2. Then the intermediate frequency signal is selected through the medium-rated transformer and then output.