CIRCUIT DESCRIPTION
The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up and amplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (L1 coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor T2. The tank circuit is connected in a Hartley oscillator circuit.
Components List
R1=220K
R2=4.7K R3,R4=10K R5=100ohm |
C1,C2=4.7uF Electrolytic
C3,C4=1nF C5=2-15pF C6=3.3pF |
Q1=BC547C
Q2=BD135 P1=25K MIC=Electret Condenser Type |
