"Arfa Daily" wrote in message
2.203...
Hi all

I have an odd situation with a Solarcon Ground Zero antenna operating on
10m. I am short of space, and dont have room to erect a traditional
silver rod type vertical, or anything with a large radial system, so I
cast around for something that would fit the bill and go on my existing
mast. I came up with this Solarcon antenna. It is a continuously loaded -
ie helically wound - monopole, about 4 feet long. It claims to be a
groundplane-less electrical half wave, with voltage feed at the base, via
what they call their patented " sidekicker unit ", which appears to be
some kind of clamp mounted ferrite balun. It is able to be moved up and
down a small section of the antenna to facilitate VSWR adjustment. It
claims to be ok for use on fibreglass truck cabs etc, and does not
require a conducting mount. I only wanted it for fairly short range local
FM chit chat at 29Megs, and access to my local 10m repeater about 6 miles
away. So far, so good.

Initial trials were carried out indoors, with the antenna fixed in a
chemistry clampstand, about a foot above a bench, and fed with about 10
feet of coax. The VSWR set up PERFECTLY at 29.5MHz, and a 2:1 VSWR was
maintained over a couple hundred kHz. The repeater could be accessed with
only a few watts, and a good signal was received from it.

I then mounted the antenna at the end of a 4 foot 1.5 inch diameter
duralumin pole, and clamped this to my main 2.5 inch diameter station
mast, at a height of about 4 feet above ground, and ran the full final
length of coax back to the transmitter. I then carried out some final
VSWR tweaks and repeated the tests with the repeater. Again, results were
good. I also ran some simplex tests with a friend located near the
repeater receive site, and again, results were good.

I then moved the antenna up the mast to what I hoped would be its final
installation position at around 15 feet above ground - and here's where
it all went wrong. A recheck of the VSWR at this point revealed that it
had not changed, so the antenna was not being detuned in any way.
However, the performance was now absolute crap. I needed over 20 watts to
access the repeater, and the returned signal was 5 S points down. My
friend could no longer pull me out of the noise below 5 watts. Several
hours of tests then followed, and the upshot of these was that the lower
I brought the antenna, the better it worked.

I am now at a total loss to explain this. As an electrical half wave, the
antenna should not require a ground system to work against, and this
would seem to be the case, as it tunes up so well. I thought maybe the
radiation angle was rather high, although again, it shouldn't be for a
half wave. If it were, maybe the ground was having an effect on this, and
pulling the radiation angle down. I'm loathe to believe this though, as
the antenna is originally designed as a groundplane-less type for CB use,
and this is primarily a short range band requiring a good ground wave.

Does anyone have any thoughts on what is going on here, and whether
anything can be done to improve the situation? I have also considered
using a Boomerang instead, as this can be centre mounted and is designed
to work stood off from a pole similar to my situation.Again, any thoughts
?

I would appreciate any replies direct to



Thanks Geoff G7RTC


I would try to get the antenna up even higher and see what happens. You
could be in a bad spot for quite a few different reasons.