On 3/5/2020 11:26 AM, Mike Waters wrote:
Many hams --including myself-- have had very good results using only a few
elevated radials.
Yes. One of the key factors is the height of the radials. N6BT, who has
done a LOT of work with elevated radials on topband, told me that 18 ft
is a minimum height. After my first tower (120 ft) was up, I had sloping
wires rigged to points about 60 ft from the tower base, insulated from
the tower and fed from the base against elevated radials. The tower has
about ten on-ground radials to improves its performance as a reflector.
I had started out based on Rudy's early work with much lower elevation
and wasn't satisfied with the result -- I had directivity, but the gain
was poor. When I raised them to 18=20 ft (gull wing from about 3 ft at
the feedpoint), I started seeing the few dB of gain that NEC predicted.
A few other important points. The ends of the radials are a high voltage
point, so must be carefully insulated. Second, Rudy emphasizes that four
elevated radials is a minimum, and twice that number is better. He also
observes that they work better if current distribution between them is
equal, that current distribution can be varied by variations in the soil
underneath them, and that cutting them slightly shorter than a quarter
wave minimizes those variations.
These are slides for a talk I've given about 160M antennas and
counterpoise/radial systems, all based on good work by others.
http://k9yc.com/160MPacificon.pdf
73, Jim K9YC
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