Huanghe 741 radio circuit

The Huanghe 741 radio circuit antenna tuning loop receives the high-frequency signal transmitted by the broadcast station and sends it to the frequency conversion stage. The frequency conversion
stage includes two parts: a local oscillator and a mixer. The frequency of the oscillation signal generated by the local oscillator is 465kHz higher than the input high-frequency signal. These two signals are sent to the mixer for mixing at the same time, producing a series of new frequency signals. After these signals are selected by the tuning loop
at the output end of the mixer : only the difference frequency signal 465kHz is allowed to pass. In this way, the signal of any radio station will always be at a fixed frequency of 465kHz after passing through the frequency conversion stage. After this fixed intermediate frequency signal is amplified to a certain extent by the intermediate frequency amplifier, it is sent to the detection stage to detect the audio signal . It is amplified by the low-frequency preamplifier and the low-frequency power amplifier to push the speaker to emit sound.