This FM transmitter circuit is very simple and it has a acceptable
transmission . The signal transited from this FM transmitter circuit can
be received at almost 300 meters in open air .The circuit require a
3volts operating voltage and can be tuned anywhere in the FM band.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 in soldered into place
spread the coils apart about 0.5 to 1mm so that they are not touching.
Simple 300m FM Transmitter Circuit Diagram
If you don’t have a trim cap you can use a fixed value capacitor and you
can vary the TX frequency by adjusting the spacing of the coils or
placing a small piece of ferrite inside the coil , but the better way to
change the transmission frequency is to use a variable capacitor
.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.
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