Rap 'n Tap
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From: Garry Nichols
Date: 6/7/00
Time: 9:58:27 PM
Remote Name: 209.4.254.107
Underground antennas for MF and HF do work, but signals are greatly attenuated compared to antennas in the air. The characteristics of the ground the wire is buried in will be one factor in the performance picture. The wires should be as insulated as possible. Centering them in an air filled tube of plastic that is a good dielectric at RF is a good approach. The simplest is just buring insulated wire. Depending on the variables, sigs will be down 15 to 40 dB or thereabouts. My info comes from a few articles on underground wire antennas that I have read. Most were tested as "hardened" antennas for military use. One article is in the ARRL Antenna Anthology, Vol I. I'm not sure where all my books are since we moved last month, or I would give the title and page. I have used plastic insulated wire laid on the lawn for ham radio communication. I can make contacts but I won't win any contests! It's really fun--you throw down some wire and then talk to people. It's a little surreal, and most folks are really surprised when you tell them what you're using! They think that it won't work AT ALL -- but it does. The band has to be in at least OK condition or it will be tough going. I have done some approximate tests on 40 meters (7 mHz). On my particular lawn, a wire around 45 ft long center feeds with a good match using a 50:200 ohm balun. (These antennas show feeble or zero resonance--they are "traveling wave" type antennas, like a Beverage.) Compared to a dipole at about 18 ft, it is around 20 dB down (that's 1% efficient!)for sigs around the continental US from my central NY location. If I put 100 W into it, I radiate about 1 W. If a received signal shows as S5 on my meter, then with a "real" antenna it would be about S9. Sometimes I get into QRP CW contests running "full bore" at 5W, but use a wire lying on the ground. And I make contacts! It's truly amazing. 73, Garry