To make a short story long - A few years back I rigged a long wire antenna out to a tree at the south edge of my palatial estate. I used wire from Radio Shack, and it fell down after a while. I recently found some AWG 16 stainless steel wire on eBay and have rigged a new long wire. But now I’ve made some measurements that leave me a bit confused.
My house is about 15 feet above my back yard, a swale leading to a pond, with a treeline about 200 feet away. My antenna reaches another 75 feet higher at the far end, and the total run works out to about 214 feet if it were a straight line. It should receive best from stations to the northwest and southeast. There are egg insulators at each end, with a 25-foot lead wire to my radio room. I got my first surprise when I looked at the business end of the antenna with my oscilloscope. I expected a big 60 Hz signal to my local ground, a copper water line that leads eventually to power line ground and to a ground rod next to the house at the back. With no load at all, the scope showed a noisy sine wave of 56.2 volts peak-to-peak with a DC offset of 25.6 volts. A DC offset? Where does that come from? Connecting a decade resistor to ground shows the signal source impedance is about 200K ohms. With a 30K load resistance, average antenna output is about 1.6 volts. Does this mean I could charge a Ni-Cad cell with the antenna?
What is it? Does stainless steel wire exhibit unusual characteristics? Are there little dissimilar-metal areas every few feet in SS wire? Is there unnoticed dirt on the egg insulators that are allowing DC from the tree to get on the far end of the run? Can there be DC generated by a tree?
Well, never mind the DC part of the antenna signal; how does it work as a receiving antenna? Plenty fine – I have an old military “morale” SLR receiver in a rack, and there’s a radio shack 4-band radio for everyday use. To protect the radio gear from any storm-related overload, I added an old lightning arrester near the lead-in entry plus a 600-volt, .01 uf paper capacitor to remove the mysterious DC. This antenna brings in plenty of stations to satisfy an occasional SWL guy like me.