Diagram Diagosis

This is the simple design and sensitivity and selectivity of the receiver are good. This circuit is use a compact three transistor, regenerative receiver with fixed feedback. The circuit is based on transistor as core of the operation. The transistor that is used is BC549. This is the figure of the circuit.


The tuned circuit is designed for medium wave, but the circuit will work up to much higher frequencies if a different tuning coil and capacitor are used. Q1 and Q2 form a compound transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit. Q1 operates in emitter follower, Q2 common emitter, self stabilizing bias is via the 120k resistor and the tuning coil. As Q2 operates in common emitter its base voltage will be a V be drop higher than ground or about 0.71V in my test sample. The 120k resistor provides regenerative feedback, between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit.

The tuning coil can be salvaged from an old AM receiver. However to make your own wind about 50 to 60 turns of 26 swg enamel coated copper wire over a 3/8 inch ferrite rod about 3 inches long. This circuit is powered by 9 VDC.