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.
[IMG]http://i96.photobucket.com/albums/l186/RattanRadio/part15xmitter.jpg[/IMG]
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.
[IMG]http://i96.photobucket.com/albums/l186/RattanRadio/part15antenna.jpg[/IMG]
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:
[IMG]http://i96.photobucket.com/albums/l186/RattanRadio/part15station.jpg[/IMG]
Daniel
Interesting Balun
I have tried a similar approach with FM BCB and experienced similar results – it really does seem to help – I cheated and used an SWR meter 🙂
Experimental broadcasting for a better tomorrow!
Re: Interesting Balun
[quote=scwis]I have tried a similar approach with FM BCB and experienced similar results – it really does seem to help – I cheated and used an SWR meter 🙂
Experimental broadcasting for a better tomorrow![/quote]
Well, I wouldn’t call that cheating. If I’d had one handy I would have used one. LOL I see them at yard sales and second hand stores for CB, but those are for 5 watt devices (not to mention a different frequency band) and since I doubt my xmitter puts out more than maybe 10 mw at best, I doubted it’d be enough to even register.
I did look at some schems for QRP 2m SWR meters online, but I figured they’d cost me more to put together than the whole outfit had cost to build. Since I doubt anything but a dead short would be likely to burn out the xmitter considering the output power is tiny, I figured my crude method would do well enough.
It was educational, though. I’d never used a balun for anything before (my electronic experience is more with audio than RF), and I was surprised with how much difference a few loops in the cable made on the signal. Also it was interesting to notice that the spot and number of turns that gave the hottest signal on the meter was *not* the one that actually sounded best on the recievers.
For me though, the tinkering is a lot of the fun.
about the meter in the pic
One thing I forgot to mention is the multimeter behind the xmitter. That measure the current draw off the batteries. The circuit draws just a teeny bit over 20ma when the tank section is warming up (maybe 20 min or so) and when it settles down to 20ma it’s stable and I hook up the antenna and touch up the tuning. When it drops even a tiny bit below 18ma, it starts drifting too much and instead of just touching up the tuning, it needs new batteries.
I leave it in when I’m on the air so I can see when the batteries are getting low and also if I saw the current draw go way off the mark high or low, there’d be something seriously wrong going on.
If I was doing this and actually intended to have a steady listener base on a day to day basis where I needed it to be reliable with less fussing, I’d go with PLL instead of a tank design. But for what I paid to put it together, I really can’t complain and feel I certainly get my money’s worth out of it.
But it def convinced me that for part15 AM, I’d want to go with a crystal instead of the tuned tank approach.