>From: km1h@juno.com (km1h @ juno.com)
To: <topband@contesting.com>
>Date: Fri, 20 Mar 1998 10:26:27 EST
>
>On Fri, 20 Mar 1998 01:56:04 -0500 jbmitch@vt.edu (John Mitchell) writes:
>>
>>But resonance has a lot to do with current flow, right? Revisit
>>the diagram I drew of antennas over salt water, if you would. I
>>had hoped to stimulate some debate over this. After all, if a
>>1/4 wave vertical with only 2 resonant radials suspended 66 feet
>>above the ocean will work as well as one with an infinite number
>>of radials at the same height over the same perfect ground,
>>doesn't this have implications for elevated radials in general.
>>Am I seeing this right or not?
Everything works better over perfect ground. Strategies which
are designed to overcome losses caused by nearfield interactions
with imperfect ground are unnecessary when operating over perfect
ground. In fact, if you really have perfect ground, zero radials
is the optimum number.
>
>
>To resonate or not to resonate elevated radials? There seem to
>be 2 distinct camps represented here. I feel that I am sitting at
>the baseline of a tennis match!
>
I have seen discussions suppoorting both strategies. I tend to
side with the non resonant camp. When only two or four radials
are present, it is FAR easier to make them current share if they
are slightly longer (or shorter) than resonant length. If they
don't current share, then the far field cancellation doesn't take
place and they are more properly thought of as antenna rather
than counterpoise. It gets a bit murky as the number of radials
increases beyond four due to coupling between the radials that is
not present in the two or four radial case. When there are many
radials, the issue isn't really if they are resonant or not but
if they are long enough to screen at least most of the nearfield
interaction zone.
Snip...
>>Don't elevated radials give some near field advantage over
>>standard ground radials when the ground is very lossy?
It depends on how many radials you are talking about. I think a
good case can be made that a system with four elevated radials
could suffer less total loss than a system with four radials
laying on the ground surface. But as the screen density
approaches the diminishing returns region, it doesn't matter much
whether it is elevated or on the surface. There might be some
advantage to elevating a dense screen if dense vegetation was
brought below the plane by doing so.
73, Eric N7CL
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