superheterodyne radio circuit

The tuning loop is composed of a variable capacitor cI. , Cn and antenna coil L]. Adjust the variable capacitor G,. The natural frequency of the LC loop can be changed
to make it equal to the frequency of the radio station and generate resonance to select radio station signals of different frequencies. The antenna Lz is then coupled to the lower-level frequency conversion circuit for frequency conversion.
    The frequency conversion circuit is composed of three parts: frequency mixing, local oscillation circuit and frequency selection circuit. The frequency conversion stage is centered on the transistor VT1, which has
both oscillation and mixing functions. The transformer feedback oscillator
    is composed of transistor VTl (3AG24), variable capacitor Cib. Cr2, oscillation transformer (referred to as medium oscillation or short oscillation) T2 and capacitors G and C3 .
It can produce high-frequency constant amplitude oscillation signals, because Ci. and Clh are components of double-connected variable capacitors. They rotate coaxially
to ensure that the oscillation frequency of the local machine is always 465kHz higher than the frequency of the input radio signal, and convert the input high-frequency signals of different frequencies into a fixed
465kHz intermediate frequency . Signal .
    The intermediate frequency signal that is the difference between the input radio signal and the local oscillator signal is always a fixed value of 465kHz. It can flow unimpeded in the
intermediate frequency and be amplified step by step. A fixedly tuned intermediate frequency amplifier is used to The amplification performance of fixed-frequency intermediate frequency signals
is stable.     The main function of transistor VT3 is to detect waves.
    Transistor VT4 forms a voltage amplification stage (push stage). Its main task is to amplify the audio signal so that the power amplifier stage can obtain a larger
audio signal voltage so that the radio has sufficient volume.
    Transistors VT5 and VT6 form a Class B power amplification stage, which amplifies the audio signal to drive the speaker to produce sound. Superheterodyne
radio circuit such as