On 9/16/2011 9:03 AM, Guy Olinger K2AV wrote:
> This is an answer to an off reflector conversation, relating to a "too long"
> electrical length over radials reducing performance. I am writing to the
> list since the subject and it's objection occur in so many posted
> conversations. Reduction of gain by too high current max has been touted by
> some and called myth by others.
A 1/2 wave vertical over perfect ground has a theoretical gain of
something like 2 or 3 dB over a 1/4 wave vertical. If we accept that
the 1/2 wave vertical will have more losses, it is still that
case that the 1/2 wave vertical only has to achieve 50% or 60%
efficiency to equal a gold standard 1/4 wave vertical. I did some
experiments on 20 meters and found that a 1/2 wave vertical with no
radials was indistinguishable from a 1/4 wave vertical with 32 radials
1/4 wave long. A 1/2 wave vertical with a big radial field was about
2 or 3 dB better as predicted.
WWVH with a 1/2 wave vertical plus a radial field is often cited
as some sort of proof of concept. It obviously "gets out" but
I haven't seen any citations of actual field strength measurements,
and in any event, we don't know how it would compare to a
1/2 wave over no radials or a 1/4 wave over radials, and even
if we did, it would be a function of local ground, etc. We
don't know why the NBS engineers built it that way. Maybe
it was a "belt and suspenders" design. If anyone knows anything
published by NBS/NIST about this antenna, please post it.
I'm still waiting to see an actual measurement showing that a 1/2
wave vertical with minimal radials is worse than a 1/4 wave
vertical with radials. My measurements were over high conductivity
ground. Maybe they would be different in the desert.
Rick N6RK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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