Portable/Indoor AM Antenna Ideas
Posted on May 28, 2007
I escaped to the lake house for a few days. Of course, my SSTRAN and computer came along! Nice thing about being out in the country is that there are quite a few more clean frequencies– at least in the daytime. But I didn’t have time to set up an outdoor antenna.
So I tried the floppy 10′ wire tacked to the wall on my wooden screened porch. The signal was reasonably OK inside the house and a little way into the yard, but faded badly at the end of the dock about 100 feet away. That was one of the places I wanted to listen, so I decided I needed something better.
A trip into town to Radio Shack netted a 100′ spool of 22 gauge 2-conductor speaker wire. I had the idea of making a “T” antenna out of this. It’s a lot like an FM dipole, except here we’re going to drive the two conductors together. Thus, I connnected both wires to the antenna plug and tacked them vertically to the wall for a distance of about 6 feet above the transmitter, which sits on a tabletop. At the ceiling, I pulled the conductors apart and ran them in opposite directions along the wall to create the “T”. This is in effect a “large-ish” top hat for a very short vertical monopole. In my case, the two horizontal sections are each 20′ long. The final step was to tie all of the ham radio antenna cables together and use those as a ground.
The results were pretty satisfying. I didn’t have to make any modifications to the transmitter because there was still enough tuning range to accommodate the T antenna, and it tuned easily. Inside the house, the signal is now extremely strong. Outside, it covers my yard very well, and is quite good at the end of the dock. In fact, it goes about another 100′ out into the lake and covers my two adjacent neighbors’ homes as well.
Of course I had to do some drive-around tests to see how far it would go. Under absolutely perfect noise-free conditions, I could hear the signal to a fair degree out to about .2 mile. I could even detect its presence here and there much further– perhaps 1/2 mile. I think that’s pretty good for an indoor antenna. The ground conductivity in this area is probably pretty low. The soil composition is primarily sand.
Setting up an effective indoor AM antenna poses unique challenges. I have another idea that I want to try involving the use of one of those spring-loaded metal poles that are intended to support plants, etc. I think I might try that with the transmitter sitting on the floor right next to it, with a loading coil in series. Finding a good ground is still a challenge. I have used cold water pipes, heating ducts, and electrical conduit with mixed results. Still, some sort of ground is naturally better than no ground!