Topband: Radials

steve.root at steve.root at
Thu Nov 17 11:03:52 PST 2011

Moxon, G6XN once proposed using elevated radials that wereless than ¼ wavelength long, tied together and fed through a commoninductor.His idea was it would beeasier to achieve current and phase balance between the radials if they weren’tphysically resonant.I believe this waswritten up in one of the ARRL’s Antenna Compendiums.At the time I had my Butternut HF2V mounted about 20 feet aboveground with one radial for 80 meters that was approximately ¼ wavelengthlong.I replaced that one radial withtwo 1/8 wavelength radials and tied them to the base of the vertical through acommon inductor.I don’t remember muchabout that inductor other than that it was an old piece of B&W made from#14 or #16 wire.As you would expectany change to the values of inductance between the radials and the vertical affectedthe tuning of the whole antenna.Sincethis vertical is heavily loaded anyway, it wasn’t obvioushow I could tune it.I decided to construct a current probe froman old toroid core, some magnet wire, 1N34A diode, a capacitor, apotentiometer, and a milliameter.Thethought was to try a value of “radial inductor”, then tune the antenna toresonance using the vertical’s loading coils, and observe how much current wasflowing on the outside of the feedline below the antenna.I might be all wet but it seemed to me thatproperly balanced elevated radials would effectively “screen” anything underthem. After many iterations and carefully monitoring power into the antenna Iwas able to minimize the current measured on the outside of the feedlinedirectly below the antenna.After usingthis antenna over the course of the winter, I was able to conclude that 1) Icould affect the current on the outside of the feedline, and 2) I couldn’t seeany evidence at all that this antenna configuration was better or worse than anythingelse I had tried at this location. That was probably die to my poor QTH, down in a river valley and surrounded by suburban clyutter and noise. All antennas work poorly in a bad location.

73 Steve K0SR

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