Micro Power FM Broadcasting Circuits

The CirKits Solar Charge Controller Kits can be used to run 12 Volt devices (such as FM transmitters) from solar power.

High Quality Stereo Modulator

Here are several high fidelity FM stereo matrix generator circuits: The Rev E (2008) is the current version of the project, the older Rev D (2003) project is there for reference purposes only.

This circuit works with the Free Radio Berkeley mono transmitters and similar units.

FM Broadcast Antennas

A good antenna and feedline is essential for making the most out of your measily microwatts, this design works very well if you tune it up properly, an SWR meter is a must for setting up this antenna.
A J-Pole antenna for the Ramsey FM10a in PostScript format (28kb)
A J-Pole antenna for the Ramsey FM10a in GIF format (11kb)

FM10 Stuff

Here are some utility circuits for use with the Ramsey FM10a, and other small FM stereo transmitter kits. This information may be helpful for setting up a micro powered FM radio station. The FM10a and similar kits tend to put out a low quality, broad band output signal. This is not a big problem with a 5-10 milliwatt signal, but amplifying the output of such kits beyond 50mw is a bad idea, as the amplified signal can cause interference with other radio services, drawing unwanted attention to your hobby station.

If you want to work with a higher power transmitter, find a better quality transmitter such as the Free Radio Berkeley Mono PLL kit, and build my circuit for an FM Stereo generator (above).

Here are some tips on squeezing the most performance out of an FM10a kit:
Five Essential mods for the Ramsey FM10a

Also see my constant temperature circuit, it is highly useful for stabilizing VFO circuits like that in the FM10. Better yet, just get a PLL-based transmitter that does not have the frequency drift problem.

Audio Mixer for the Ramsey FM10a in GIF format (16kb)
Description of the FM10a Audio Mixer

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Useful Links

Free Radio Network For info on micropower and pirate radio
Free Radio Berkeley They make very good mono FM transmitters and amps
Broadcast Warehouse Makes several FM stereo transmitters
MyFmStation.com Sells stereo FM transmitters
fm-transmitter.com FM transmitter information

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