Heterodyne radio frequency conversion circuit

Shown is a frequency conversion circuit for a heterodyne radio . In this circuit, Cla and Li form a resonant circuit to select the frequency of the received signal . Clb and L4 form a resonant circuit to generate a resonant signal (local oscillation signal).     During operation, the radio signal is frequency selected through the Cla and LI resonances of the input circuit, and then coupled through Ll and k, and is sent to the base of the VT. The transistor has two functions of high-frequency amplification and mixing. C!b and L4 resonant circuit and transistor VT form a local oscillator circuit. The local oscillation signal is input to the emitter of VT through c3. The two signals are mixed in VT. The difference frequency signal generated after mixing is output by the collector of VT, and then passes through the 465 kHz intermediate frequency resonant circuit composed of C4 and Ls. The intermediate frequency signal is selected from the amplifier, and then coupled to the base of the next stage intermediate frequency amplifier tube through Ls and L6 for the second stage of amplification. The resonant signal     generated by the C1b and L4 resonant circuits is input to the base-emitter of VT through C2 and C2. The amplified signal is fed back to the L4 and Clb circuits through La, and then undergoes amplification, feedback, and amplification processes to form oscillation. The frequency of the oscillation signal depends on the values ​​of L4 and Clb.