This Wideband VHF FM transmitter will output approximately 250mW of RF power. It utilises a high gain variable audio pre-amplifier circuit around the BC548. The (I/P) input can be used with any feed, whether it be an electret microphone or a Walkman output. A BC548 also is used in the RF oscillator where it outputs 25mW into the Power Amplifier 2N3866, where the signal is muliplied by 10. L1 has 5turns of 22SWG on a 7mm ferrite former and L2 has 4turns of 22SWG on an air former. All capacitors are ceramic and resistors 0.25Watts. Ranges of over 5KM have been acheived using 58cm wire antenna running off 12Volts. It is Ideal to tune up this circuit using a wave detector meter placed a few inches away from the transmitter. I have a circuit on this site.
This page was updated on 15th February 2000.