Wiring Diagram

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3V FM TRANSMITTERS CIRCUIT DIAGRAM

Place the transmitter about 10 feet from a FM radio. Set the radio to somewhere about 89 - 90 MHz. Walk back tothe FM transmitter and turn it on. Spread the winding of the coil apart by approximately 1mm from each other. No coilwinding should be touching another winding. Use a small screw driver to tune the trim cap. Remove the screwdriverfrom the trim screw after every adjustment so the LC circuit is not affected by stray capicitance. Or use a plasticscrewdriver. If you have difficulty finding the transmitting frequency then have a second person tune up and downthe FM dial after every adjustment. One full turn of the trim cap will cover its full range of capacitance from 6pF to 45pF. The normal FM band tunes in over about one tenth of the full range of the tuning cap.

So it is best to adjust it in steps of 5 to 10 degrees at each turn. So tuning takes a little patience but is not difficult. The reason that there must be at least 10 ft. separation between the radio and the FM transmitter is that the FM transmitter emits harmonics; it does not only emit on one frequency but on several different frequencies close to each other. You should have little difficulty in finding the Tx frequency when you follow this procedure.