Sunday, January 29, 2017

Ground System Performance for HF Verticals, Post #1027.

Ground System Performance for HF Verticals, Part 4, How Many Radials Does My Vertical Really Need?
(http://www.dxzone.com/qsy32482-radials-on-vertical-antenna).
Accessed on 30 January 2017, 00:10 hrs, UTC.
Author:  Rudy Stevens (N6LF).
Please click link or insert title URL into your browser to read the full article. The article takes you to a downloadable link which displays all five pages of the antenna study.  The original article appeared in "QEX", May/June 2009, pp.38-42.

Commment:

One of the drawbacks to most 1/4 wavelength verticals is the need for an extensive ground radial or counterpoise system.  In this exhaustive study done by Rudy Stevens (N6LF), we get an idea of how important ground radials are for the efficient operation of a 1/4 wavelength vertical antenna. Rudy based his experiments on the pioneering work of the late Jerry Sevick, with results closely matching those of Sevick's original investigations.  Rudy's analysis offers several conclusions, all backed up by cited data, on-site performance, and modeling results both in theory and in practice.  Here are some of the conclusions reached by this study:

Use at least 16, 1/4 wavelength radials for a vertical antenna.  More than 16 ground radials will boost antenna efficiency only a fraction of a dB.  Of course, the more radials you put on the ground, the better the performance.  Up to 120 1/4 wavelength radials have been common practice for AM broadcast stations.

If you will be using a short vertical antenna, add more radial wires, even if these wires aren't a 1/4 wavelength long.

Poor soil equals more radials, especially if your ground conductivity is poor (such as Hawaii Island).

Make your vertical antenna more efficient by using high-Q coils, top loading, and low loss coaxial cable feed line.

Rudy offers an extensive list of reference documents and antenna studies for those wishing to pursue the subject further.

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If your property is not suitable for a large number of ground radial wires, try using an elevated radial system.  Initial research indicates that as few as 6 elevated ground radials may provide enough efficiency to make your vertical antenna an effective radiator.  The late L.B. Cebik wrote several articles on elevated radials--studies that may help you to build an efficient vertical antenna where ground losses are high.
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Aloha es 73 de Russ (KH6JRM)