Posted on May 7, 2012 7312
Transistor Q1 acts as an amplifier for condenser microphone MIC1. The output of Q1 is applied to the base of transistor Q2 through a 4. 7 -I`F capacitor. C2 and 11 form an LC tank circuit. which is used to set the frequency at which the transmitter operates. Coil 11 is a variable inductor, centered a bit below 1~tH, that is used to adjust the modulating frequency of the circuit. Capacitors C1 and C2 are 4. 7 pF units. A lower value can be used to raise the circuit`s operating frequency. The microphone and Q1 provide a varying voltage at the base of Q2, with the output of Q2 applied to the LCtank circuit.
That causes a modulating action in the tank circuit that, when applied to the antenna, a short piece of wire 6-to 8-inches long, will provide a good, clear FM signal somewhere in the range of 88 to 95 MHz with a range of about 100 feet.