Long Range FM Transmitter

This FM  transmitter circuit described here has an extra rf power amplifier stage,after the oscillator stage,to raise the power output to 200-250 milliwatts.With a good mathcing 50-ohm ground-plane atenna or multi-element Yagi antenna,this transmitter can provide reasonably good signal strength  to a distance of about 2 km.

The circuit build around transistor T1(BF494) is a basic low power variable-frequency VHF pscillator.A varicap didoe curcuit is included to change the frequency of the transmitter  and to provide frequency modulation by audio signals.The output of the oscillator is about 50milliwatts.T2(2N3866) forms a VHF-class A power amplifier.It boost the oscillator signals power four to five times

For best result,assemble the circuit on a good quality glass epoxy board and house the transmitter inside an aluminium case.Shield the oscillator stage using an aluminium sheet coil winding are given below:

L1 - 4 Turns with 20 SWG

L2 - 2 Turns with 20 SWG

L3 - 7 Turns with 24 Swg

L4 - 7 Turns with 24 SWg

Potentiometer VR1 is used to set the center frequency whereas potentiometer VR2 is used for power control.Do not switch on the transmitter without a matching antenna.

In place of mic you can place mp3 player etc

For Fm Receiver use your mobile phones or fm radio tune it for frequency

Frequency used is between : 87Mhz to 107Mhz

This transmitter is used only for educational purpose and hobby purpose.For frequent use its illegal in india.