High-quality 500M FM transmitter circuit diagram sharing

This good FM transmitter for stereo or any other amplifier will give you good signal strength up to 500 meters range with power output of about 200mW. The circuit can be powered by 9V battery .

The audio modulation stage is built close to transistor BF494 (T1), which is connected as a VHF oscillator and modulates the audio signal at the base. Using preset VR 1 you will be able to vary the audio signal level.

The VHF frequency is determined by coil L1 and variable capacitor VC1. Reduce the value of VR2 to obtain higher power output.

The next stage is designed close to transistor BC548 (T2) and acts as a class A power amplifier . This stage is inductively coupled with the audio modulation stage . The antenna matching network contains variable capacitor VC2 and capacitor C9. Fine tune VC2 to optimize the power or signal strength transmission to the receiver .

To ensure frequency stability, use a regulated DC power supply and install the transmitter inside a metal cabinet. To obtain better antenna gain, use a telescopic antenna instead of a simple wire. Coils L1 and L2 will be wound on the same air core so that the winding of coil L2 starts from the end point of coil L1.

Here are the coil winding specifications :

L1: 5 turns of 24SWG wire tightly wound around a 5mm diameter hollow core

L2: 2 turns of 24SWG wire tightly wound around a 5mm diameter hollow core

L3: 7 turns of 24SWG wire tightly wound on a 4mm diameter hollow core

L4: 5 turns of 28SWG wire on an Intermediate Frequency Transmitter (IFT) ferrite core