An FM Broadcast Transmitter For Your Home

Bruce Perens writes "I wanted to be able to listen to net audio and my ham station around the house and yard. Those iPod FM transmitters don't have enough range. So, I bought a digital controlled, 100 miliwatt transmitter that covered my whole block the first time I plugged it into what was, until then, a recieving antenna."

Comments

Beware of cheap FM transmitters

[Okian Warrior]

Beware of cheap FM transmitters for this purpose: the majority of them are no good.

Ultra cheap FM transmitters use a tuned tank circuit to control frequency (ie - a variable capacitor). These are very difficult to get to the exact center of the frequency you choose, the result will more than likely be poor audio response.

Furthermore, your receiver is probably digitally controlled to an exact FM frequency and the variable cap system will change frequency slightly with temperature and humidity, so that the transmitter will slowly go in and out of channel. The receiver is phase locked to the correct channel, and the result is that the system will gain and lose quality over time. Digitally controlled frequency is a must for this application.

Kit systems are usually poor at doing audio; making a noise-free circuit is somewhat of a black art and it takes a lot of research and tinkering to get it right. For example, Ramsey Electronics makes an FM transmitter kit with digital frequency control and all that. The problem is that the board layout introduces an unacceptablt amount of hiss into the audio signal. No amount of adjustment will fix this, and the average hobbyist is unprepared to even figure out what the problem is.

Finally, Be very careful of high end ($300) transmitters used for gyms. Some of them are mono only (!) but do not specify this on the advert.

Your best bet is to look on the net for reviews of any transmitter you're thinking of buying. When people have good things to say and don't point out the obvious flaws, then the product might be OK.

I purchased several poor FM transmitters before I got one that worked well, and I use it for transmitting FM throughout the house.

That would be the C.Crane FM transmitter. You can get it for about $80, and Froogle lists several vendors.

Re:Slashvertisement

[Bruce Perens]

The images are served by the sales site, that was the easy way to get them. The text is my personal review. I don't have a relationship with the manufacturer other than that I purchased the device.

Bruce