DescriptionA multi frequency modulated transmitter circuit. The circuit transmits the same input simultaneously across all channels. Although the transmitters are of the FM type, there is enough cross modulation to be heard on AM receivers.
NotesPlease read the disclaimer on this site before building any transmitter. It is illegal to operate a radio transmitter without a license in most countries. This circuit is deliberately limited in output power for this reason. The tank circuit, L1, C1 (first section), L2,C4 (second section) and L3,C7 (third section) determine output frequency. With a fixed 200uH inductor coil and a range of the tuning capacitor from 50 to 500PF the output frequency range is approximately 500kHz to 1600kHz. The tuning capacitor is shown fixed but may be a variable capacitor in each section. The resonant frequency for different coil and tuning capacitors can be found by using the calculator below.
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