On Wed, 19 Jul 2006 17:21:17 GMT, Bart Bailey wrote:
I'm thinking of trying a 5BTV on a 30 foot pole with one good
counterpoise about two thirds way up and a good earth stake ground at
the bottom. I don't have room for an array of radials in all directions
but am hoping the solitary long one at the twenty foot level will allow
the thing to tune. Are the multiple fanned out radials really necessary
to get resonance, or aren't they just to create a more uniform pattern?
The one long counterpoise is several hundred feet long.

At least three symmetrical radials are required for a
close to omnidirectional pattern when the radials are
elevated by an appreciable amount. The horizontal radiation
from symmetrical radials tends to cancel due to destructive
interference thus adding constructive interference to the
vertical radiation pattern. So the gain and efficiency are
also affected. Resonance may not be the only consideration.

Thanks Cecil
At this point I'm not afforded the geographical luxury of multiple
radial placement, and am hoping any radiation at all will be better than
none, thus am thinking that the solitary counterpoise will have to
suffice. With my luck I'll likely have a prominent lobe out into the
boonies where there aren't any stations, and a steep null right into
choice DX. g

Hi Bart,

Having noticed your question went unanswered, and that you have a very
curious arrangement that begs discussion:

Yes, the fanned out tuned radials are necessary for resonance (or at
least reduce interaction during the tune process). This is because
these types of antennas are especially designed for these very
requirements. That, or ground mounting that allows the proximity of
earth resistance to wash over the inherent Q that forces attention to
radial lengths. You have chosen to mount up high, and that demands
that attention to those lengths. This much should already be apparent
with a SWR meter reading.

Alternatively, this curious several hundred foot long "counterpoise"
may give some relief to a raging SWR meter, but along with that comes
unintended consequences. Given this "counterpoise" is easily ten
times bigger than the "antenna" you may note that my usage of "quote"
marks is to denote another irony. You have, in fact, a horizontal
dipole with a vertically oriented, tuned, short half. The 5BTV is
more the radial than it is the antenna.

This is not to say that it affects performance poorly. In fact it may
be a boon, but it certainly isn't going to be performing for the
reasons you might ascribe to it. Let's just say this is an example of
Ham Luck which proves radio is fun for not having critical
requirements. Any pretense to gain and efficiencies being obtained
through carefully balancing this "counterpoise" are sheer fantasy. You
could as easily pull down the 5BTV, leave the "counterpoise" connected
to the mast, and drive the mast to the same advantage. (Or leave the
5BTV up there as a sort of top-load.)

If you want to resurrect the 5BTV's dignity that is now in shreds,
follow the manufacturer's recommendations for installing tuned radials
for each band, and attached at the correct point. Unfortunately,
there's no promise of any increase of performance, but others may
offer reports that confound my advice.

73's
Richard Clark, KB7QHC