FM Stereo Transmitter

Description

This is a small stereo FM transmitter. Output can be tuned from 88to 108Mhz and the transmitter can be battery powered or be used with the low voltage power supply on this page. 

Notes

This circuit is based on the Rhom BA1404 datasheet. The maximum voltage should not exceed 3V. The IC can be driven from a 7805 Regulator with a couple of 1N4001 diodes to reduce the supply voltage to about 2.8 Volts. The IC can dissipate 500mW (this is not RF power output but power dissipated by the IC). RF output power is typically 500mW but range depends upon antenna coupling and efficiency, environment and size of antenna. A small telescopic whip has an expected range of at leaset 100 metres or more.

Transmitter Parts List

• R1,R2 27k
• R3 5.6k
• R4 150k
• R5, R6 22k
• R7 220R
• C1 10uF
• C2 220p
• C3 1n
• C4,C5 10u
• C6,C7,C8, C9, C10 10p
• C11, C13 1n
• C12 10u
• L1 3.5 turns 18 swg
• XTAL1 38kHz Crystal Oscillator

Simple Low Voltage Power Supply

A simple low voltage power supply is suggested below. The output is from a 7805 1 Amp regulator IC. The output voltage is further reduced by two series connected 1N4001 diodes. Thes drop approximately 1.1V each in forward conduction. For less power output three 1N4001 diodes may be wired in series.

The output is filtered by two RFC chokes RFC1 and RFC2. These should be be 20 turns of 18 or 20SWG wound on Amidon FT82-43 cores.