This is the simplest FM transmitter using two BC547 transistors.
Components may be added to the PCB in any order. Note that the electret microphone should be inserted with the pin connected to the metal case connected to the negative rail (that is, to the ground or zero voltage side of the circuit).
The coil should be about 3mm in diameter and 5 turns. The wire is tinned copper wire, 0.61 mm in diameter. After the coil soldered into place spread the coils apart about 0.5 to 1mm so that they are not touching. (The spacing in not critical since tuning of the TX will be done by the trim capacitor.
It is quite possible, but not as convenient, to use a fixed value capacitor in place of the trim capacitor - say 47pF - and to vary the TX frequency by simply adjusting the spacing of the coils. That is by varying L of the LC circuit rather than C.) Adding and removing the batteries acts as a switch.Connect a half or quarter wavelength antenna (length of wire) to the aerial point. At an FM frequency of 100 MHz these lengths are 150 cm and 75 cm respectively.
Good luck!!
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