Super regenerative receiver
In this type of receiver, (as in the synchrodyne radio receiver), a local oscillator is used to increase the reception sensitivity.
Another essential aspect in the operation of this type of receiver is that the received signal influences the amplitude of the oscillations generated by the local oscillator.
In the present case, the essential element of the receiver is the oscillator built with the transistor T1. It is mounted in the "common base" connection, the matching circuit (consisting of L1 and C1) being mounted in the collector of the transistor. Coil L2 is mounted in the emitter of T1, which constitutes the radio frequency shock. Practically, it prevents the radio frequency signal from leaking to the circuit board and towards the audio frequency amplifier. Without the L2 coil, the receiver would be very unstable, it would lose the useful signal when you touch the ground of the circuit, the speaker, the batteries or other elements with your hand.
The adjustable capacitor mounted between the emitter and the collector of transistor T1 has the role of determining its entry into oscillation. A variable capacitor is used, so that it is easier to find the operating point of the oscillator.
The operating point of the oscillator is also established with the help of the semi-adjustable resistor R2. The oscillations of the overreaction place the operating point of the T1 transistor near the threshold, thus increasing the sensitivity of the receiver.
This overreaction stage also performs detection, the detected (demodulated) signal is sent to the audio frequency amplifier, equipped with the T2 transistor.
This overreaction stage is also called a overreaction demodulator. It amplifies a received signal and then demodulates it.