This is a VCO FM Transmitter with range 500m - 4km depending on antenna used

Specifications

 

- Power supply: 12-14 V stab., 100 mA
- RF power: 400 mW
- Impedance: 50-75 ohm
- Frequency range: 87,5-108 MHz
- Modulation: wideband FM

Description

This circuit originally published on www.pira.cz but a new PCB design is introduced here.

Connect the 6 V / 0,1 A bulb to the output and use R1 to tune the right frequency. Maybe you might stretch coils of the L1. Then use C14 and C15 to adjust the highest power (the highest light of the bulb). Then you can connect antenna and audio signal.

Adjust R2 until the audio sounds as loud as the other stations. With good antenna (dipole placed outdoor and high) the transmitter has very good coverage range about 500 meters, the maximal coverage range is up to 4 km.

PCB Design

Eagle CAD PCB layout

 

 

 

 

3D PCB rendering

PCB Dimensions

PCB Photo

 

assembled PCBs

Downloads

Download project files in Eagle format

Download Gerber files