FM radio tuning circuit

Shown is the FM radio tuning circuit , which is composed of high-frequency amplifier VT1, mixer VT3 and local oscillator VI2
. The FM radio signal (88~108 MHz) induced by the antenna is added to the gate of the VT1 transistor through the input transformer Li. VT1 is the main component of the high- frequency amplifier. After amplifying the FM high-frequency signal, it is added to the mixing frequency
through the transformer L2. The gate of circuit VT3, VT2 and the LC resonant
circuit constitute a local oscillator, and the oscillation signal is sent to the source of the mixing circuit VT3 from the secondary of the oscillation transformer. The radio frequency signal received by the antenna and
the local oscillator signal are frequency differenced in the mixing circuit, and then the intermediate frequency signal is taken out and output by the drain of the mixing circuit VT3. The 10.7 MHz intermediate frequency signal is selected through the intermediate frequency transformer lFT
(L4), and then sent to the intermediate frequency amplifier circuit.