>Jim: Do you have the WARC vertical ground mounted - roof mounted? I see
that
>you have had some very good luck with the antenna. Thinking about
something
>better for the WARC bands. Guess you have had good luck with yours. Any
info
>would be appreciated. Thanks in advance.
Aloha Dave,
My tribanders are both up on the roof, at the corners of an upstairs deck,
actually. They are on Radio Shack push up poles, with the bottoms of the
tribanders up around 30 feet or a bit more above the surrounding ground,
or 20 some feet above the general lay of the roof shingles.
Actually, I have them configured as 1/2 wave verticals, not 1/4 wave
with ground planes. That is why they are so high. I have just a single
"radial" for each band which drops down from the Gladiator radial
mounting bolt. This seems to form a 1/2 wave length vertical dipole;
sure works as one would. I still use the Unun balun as it comes
with the Gladiator's lowest tube section/mounting bracket assembly.
Just eliminated three of the four radials as would be used for ground,
or near ground mounting.
I can compare my 20-15-10 meter Gladiator tribander mounted as
described with my de-reflectored C3 antenna, which means it is
now operating as just a mount for two rotating dipoles for 20 and
15 meters. I essentially can tell no difference on my S meter in
recvd signal strength when switching A/B between the horizontal
Force 12 dipoles at around 25 feet high and the 1/2 wave Gladiator
verticals with the feed point up around 30 feet! Except that the
Gladiators present more noise along with the signal since they
are recv'ing from all 360 degrees of azimuth while the dipoles
have nulls off the ends, cardioid patterns actually.
Of course I will be much happier with the C3 when the reflector
carrying part of the boom is repaired later this morning, hi. A
couple of other Kauai amateurs are coming over this morning
to aid in the repair effort. They are accustomed to working up
on 25 foot ladders; I am not, I seem to have a very bad case
of fear of being very high up, hi! Of course, the C3 on the
bands, with around 4 dB of gain over a dipole gives
noticeably stronger signals on recv than do the verticals on
the same bands.....most of the time. There are occasions,
and I always switch between the beam and the verticals,
when the signal is actually better from the verticals. And
of course, this is nearly always the case when the beam is
not pointed in the general direction of a DX signal. Useful
for keeping track of the DX frequency while the beam is
coming about to the correct azimuth, for example -- but
certainly not a great necessity, hi.
I do not have enough room to mount the Gladiators near the
ground; not enough space for radials. I also feel that one
needs a good many more than four elevated radials to
radiate all the energy from one's transmitter set up. W8JI,
Tom Rausch, has convinced me with his extensive field
strength antenna tests, that four elevated ones actually
can cost you from 3 to 5 dB of loss from your transmitted
signal. He believes at least 36 elevated radials would
recover most of the energy otherwise being lost to
ground resistances between the four radials separated
by 90 degrees. The radials, even if 6 or 8 feet
above the ground are clearly still coupling to the
ground, via the electric fields from the lower sides
of the radials. This induces current flow in the ground
and so loss occurs. Much arguing in the literature about
this, but seems intuitively obvious to me. I used to do the
Shwartz-Christofel mapping of E/M field lines when in grad
school, necessary exercise in E/M theory classes a few
decades ago when I was there. It sure is clear to me that
a wire with rf current flowing on it cannot help but terminate
some E field lines on the earth when anywhere near the
ground!!
L B Cebik, W4RNL, encouraged me to go the 1/2 wave
vertical route approach. In fact, he discusses these
issues a bit at his wonderful antenna web site:
http://funnelweb.utcc.utk.edu/~cebik/vdgp.html
At this site he discusses his modeling results about 1/2 wave
dipoles, that is those antennas NOT requiring the ground to
form the other half of the antenna. I tried them, as described,
and feel I am getting all the signal in and out that one can using
a vertical antenna when space around the QTH is limited.
Good luck and 73,
Jim, KH7M
On the Garden Island of Kauai
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