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

Pirate radio

[Epsillon]

The VHF broadcast band is a regulated resource. What you have created is, in effect, a pirate radio station with all the regulatory and copyright issues that that entails. If the FCC/Ofcom or whatever regulatory authority covers your area doesn't take an interest in your "personal radio station" in fairly short order, I'll be very surprised. The performing rights organisations may take an interest, too.

In short, you will be very lucky if you get away with this for long.

This seems to be asking for trouble

[gabebear]

If you just want a radio station in your home it would seem to make more sense to use a Carrier Current transmitter. What this guy is doing is pretty damn illegal and if you do what he did you can be looking at tens of thousands of dollars in fines!

From what I can tell anyone can setup a Carrier Current station(check for yourself), you can find some pretty cheap kits.

This guy doesn't seem to be all there, he says he has a HAM licence, but is stupidly violating FCC laws. He also says the thing has a BNC type connector but the picture looks like a type RG6 connector.

Cool

[hey!]

I bought one of those little consumer FM transmitters (this was a Belkin model) that you're supposed to plug into the audio jack of your MP3 player, but it really sucked. The main issue is that reception was so bad it was unacceptble even if I put it on top of my car dashboard.

So, since the thing was so useless I was out thirty five bucks anyway, I took it apart. The antenna turned out to be a length of wire about two inches long stuffed into the same cable used for the audio jack. Obviously, this was nearly worthless. I drilled a small hole in the case and soldered in a piece of wire the right length for a half wavelength antenna -- a little less than 63 inches for the low end of the FM band. As a result, I can now broadcast all over my house.

Now, since I was using it in a car, a five foot piece of wire was a bit unweildy, so I wound it around a pencil to make a loopstick antenna. I don't know anything about designing loopsticks, but it still worked OK for broadcasting around the house. Basically, I'd guess just about any length of wire a few feet long would work way better than the tiny length of wire they were using.

The only remaining issue is that the volume is very low; you have to jack up the volume on your receiver nearly all the way to get acceptable listening levels. If you're planning on driving around town with your windows down so your car's subwoofers won't blow them out, this is not for you. Also, the sound is a bit muddy. I suspect that in order to avoid any FCC issues, they took a number of steps: using a low transmit power, using a worthless antenna, filtering out the high end audio frequencies, and undermodulating the signal. I could probably desolder and replace some resistors and capactitors or something if I were motivated enough to analyze the circuit. Plus, as an old fogie I'd have to learn to deal with surface mounting (I learned to solder on bakelite terminal strips for chrissakes). Altogether this is too much trouble.

I'd recommend that if you bought one of these consumer MP3 transmitters and found it totally worthless, then you should replace the antenna with any old piece of wire and it will gain enough range to be some use to you. If you haven't bought one yet, don't. Getting a device like this guy is using would be a bit more expensive but probably a lot more satisfactory.