2006 KØS, Kurt N. Sterba Strange Antenna Challenge

Hosted by Erik Weaver nØew and Dwayne Walker wb5plj,

Memorial Weekend, May 27, 2006

    This was the first strange antenna we tried to "fly" this year. It is a dipole made from two exercise machines, sitting up 2x4's (on edge for a height of approx. 3.5 inches). We are using the same 1:1 current balun we used last year, and one of the "breakout boxes" we have used in the past to get the coax hooked up to the exercise machines. In the image at the bottom of the page you can see the large c-clamps used to press the wires against the machines.

    We set the balun / breakout box on the seat of the green plastic chair for support. We used 20-feet of LMR-400 running from our operating station to the balun. The split ends of the balun are then connected to the binding posts on the breakout box. The short blue wires are also connected at this point. The opposite ends of these blue wires are pressed against the exercise machines with the c-clamps.

    While we didn't do so, one could alter the position of the c-clamps. As the position of the c-clamps is altered, the impedance at the feed point will in turn be altered. This is something like finding a useful impedance match when feeding your antenna tower as an antenna, or feeding an off-center long wire antenna. With such strange items being used as antennas, I don't know how to predict the impedance change. By experimenting with different connection points better, and worse, impedance matches to your transceiver may be found.

    We were a little concerned about this antenna. It is very close to the earth, which tends to increase losses unless there is a fair amount of metal to act as a return path along the surface of the earth (such as the ground radial system used with a vertical antenna system). As you can see, this wasn't the case with this antenna. We are also at the bottom of the solar cycle.

    Being able to construct useful strange antennas in the bottom of the solar cycle was a major concern. As the atmosphere becomes less charged by the sun, propagation conditions worsen. One of the effects this has on marginal antennas, as many strange antennas are, is to reduce their effectiveness to the point one can not generate a sufficiently coherent RF waveform to send or receive radio signals. As one increases the amount of metal used this begins to help off-set the "penalty" of using such strange shapes to capture / transmit one's radio signals. We suspect there is a point of diminishing return, and that a balance between the transmitted power output vs. the mass of metal one is attempting to vibrate / excite. A more correct interpretation is likely accounting for the surface area as opposed to the mass of the strange antenna. RF is of sufficiently high frequency that skin effect comes into play, and only the outer surface of the metal is affected by the RF.

    Our concerns were well founded. This was only a marginal antenna. We called CQ for about an hour and only were able to make two contacts. On the other hand, we did in fact make two contacts with a pair of exercise machines standing only a few inches above the earth!

WB5PLJ Holding the Balun & Altiod's Breakout Box