Pics of my little FM rig
Posted on September 10, 2006
I had to debate with myself a bit over whether or not to post this, since my station is *very* small and low range compared to the AM rigs most of you here seem to have. But what the heck. Just try not to laugh too hard, okay?
Total outlay was somewhere under 30$ for the xmitter and the antenna.
The transmitter is the galvanized steel box between the tape machine and the meter.
The transmitter is kit built, a Cana-kit CK165. Mono, tank-tuned, 2 transistor, didn’t come with a case. With shipping it was a little over 20$, took a little over an hour to build. The kit went together easy, had all the part and etc. Powered up fine, current draw was very close to the 20ma the instruction sheet said it’d draw.
But circuit boards don’t live as long without a case, and it had some AC hum issues even on batteries, so I decided a metal box with something resembling a ground would be good. Could have blown for an aluminum box at Rat Shack, but the circuit board isn’t real big, so I decided to just buy a house wiring outlet box at Home Depot instead.
The range didn’t quite reliably reach to the other end of the house (maybe 45 ft, but with house wiring and plumbing in walls, etc) with a strong signal. Figuring that the antenna wire being partially in the metal box wasn’t the best (instructions had said to cut it to 1/4 wavelength), I opted for connector, cable and antenna.
Elements are 6 guage copper, it’s cobbled together from wooden doweling to hold the copper and make a sort of boom, and using a spare VCR cable as the transmittion line. Yeah, 50 ohms is usually onsidered more optimal than 59, but with only about a 6 ft “run”, I figured I’d lose more signal off the connecter than the cable type I used.
I’d heard a balun was a good idea and I’d seen them in other people’s designs, so I just tried trial and error. I had my trusty old “multi band” reciever (which has a sort of s-meter) with the antenna all the way down and got aproximately an s9 at several feet from the antenna, and tried different numbers of turns and distances from the antenna to find the ones that gave the best signal stength.. After I’d noted all of those, I compared them and picked the one that sounded best on the stereo at the other end of the house. My logic being that a good match (or balun placement, anyway) would be what gave good signal and sound. When I got to the one you see here, the last vestiges of hum also vanished, so I figured it was the right one. Or close enough, anyway.
For compression and other processing, I use Sound Solution and a tweaked “Powerliner FM” setting.
To set my levels, I use the test tone on Sound Solution, and tune my FM stereo (the one on the other end of the house) to my frequency, then run the line out from that into he line-in on the soundcard on the computer near the stereo and kick up a freeware “windows oscilloscope” that does audio frequency through the soundcard.. take down the level going into the transmitter until the test tone has no “flat tops” on the waveform on the reciever.
It delivers a good strong clean signal through the whole house, and though it’s mono, it sounds as good or better then the local FM stations. It doesn’t go far outdors, next door or directly across the street is the farthest I’ve heard of anyone tuning it in. Going out with a headset player and walking up and down the sidewalk, I can pick up a couple houses up and down the street.
Which suits me well, since mostly I just wanted something so I didn’t need to sit at the computer to listen when I’m shoutcasting or spinning mp3s.
But a couple neighbors getting interested in the shows got me to thinking, and after figuring out that was abut the best I can do with FM legally, I started checking into part15 AM, and wound up here. LOL
But if you’re looking to do a reasonable sounding little FM for house/yardcasting, that’s how I did mine and kept it down to around 30$ cash outlay.
And I’ll close with a pic of my setup I do my shows from: