In general, I agree that the big variable at low heights (less than 1/2 WL)
is the ground. Always thought low HF horizontal dipoles are DX problematic,
particularly on the low bands.
Its not clear to me if you are restricting your points to traditional 1/4 WL
verticals with radials, or if you intended the comments to apply to all
verticals including 'vertical dipoles'.
I have been real interested in the FORCE12 move into 'vertical dipoles' of
one flavor or another.
(See http://force12inc.com/sigmainfo-005.htm)
They managed to get a positive QST review (OCT 2002) on their 'stealth'
Sigma 5 (9 ft or so high radiator on 20-10M). But they have several 'fuller
size' models that they claim are 'DX-pedition proven'. And, although it may
be marketing hype (aimed at GAP?), they claim very high efficiency for their
vertical dipoles even when mounted just above the ground! Their use of
'capacity hats' to shorten their vertical dipoles seems quite practical to
me as it avoids the issue of traps.
A consideration in favor of vertical vs horizontal dipoles for DX (e.g, on
80M where a 1/2 WL 80M dipole is 140 ft) is that dipoles must be rotatable
to achieve omni directional coverage. Or you may need two or three to cover
all directions. Even with efficient shortening, they can be geographically
problematic as well as difficult to get high enough. But, for those able to
use 'brute force', these are not issues.
To me, each has pros and cons and circumstances will tend to result in
choosing one over the other. I try to know the strengths and weaknesses of
each so I can use the best for the situation.
73 de Jim WA6PX
JGShaw@Alumni.HAAS.org
-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com]On Behalf Of n4kg@juno.com
Sent: Monday, October 07, 2002 6:23 AM
To: TOWERTALK@contesting.com
Subject: Re: [Towertalk] GAO Challenger DX
Ground Reflections from Horizontally Polarized antennas are
very efficient, suffering only 1 to 2 dB loss regardless of how
poor the conductivity of the ground.
Ground Reflections from Vertically Polarized antennas are
HIGHLY dependent on the ground conductivity and are typically
much higher than for horizontally polarized antennas unless the
reflections are over Salt Water.
On the Low Bands, verticals are often better than (low) dipoles
for DX where a 1/2 WL high 80M dipole needs to be 140 ft up!
Tom N4KG
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