Topband: Effect of current max not at base of vertical.

[Richard (Rick) Karlquist]

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