300m FM transmitter circuit design project
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 3 volts 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 1 mm so that they are not touching. 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.