AM low power broadcast transmitter circuit

The circuit consists of three circuits: audio oscillation (low-frequency amplification), high-frequency oscillation and modulation emission. The transistor VT1 and its peripheral
components constitute an RC phase-shifted oscillator. When the plug is inserted into socket CK, the RC oscillator becomes a low-frequency amplifier, and audio signals can be input from the outside and
amplified as low-frequency modulation signals.
    RP and cs constitute an AC negative feedback network. Adjusting RP can continuously change the intensity of AC negative feedback, thereby changing the gain of the amplifier, thus
changing the amplitude of the output low-frequency oscillation signal or audio signal, so RP is called an amplitude adjustment potentiometer.
    Transformer Tl can be the input transformer of the low amplifier circuit in the radio. Transistor VT2 and its peripheral components constitute a capacitor three-point oscillator
. The high-frequency constant-amplitude sinusoidal signal output by this circuit is used as a high-frequency carrier fc.
    Transistor VT3 and its peripheral components constitute a modulation transmitter circuit . Since the threshold voltage of the emitter junction of the silicon tube is high, in order to improve the modulation sensitivity and reduce
the modulation distortion, an appropriate forward bias (o. 4 ~ 0.5V) is added to the emitter junction of VT3. Make it work in a Class C state close to Class B.
    The AM low-power broadcast transmitter can be combined with the superheterodyne radio to form a simplex wireless intercom system.