At 3/22/2006 20:31, you wrote:
>At 02:58 PM 03/22/06, you wrote:
> >I have a shiny new Antennex FG1440 2 meter repeater antenna, and I
> >thought that before we install it on the tower, maybe I should put an
> >additional protective coating on over the fiberglass. Looking for
> >something that would not get brittle and crack off any time soon. Any
> >ideas? Urethane maybe? I once used some urethane designed as a
> >marine finish with great results, but I'm open to suggestions..
> >
> >Thanks,
> >dave na6df
>
>One local guy is using a double layer of white heat shrink. Went up
>about 3-4 months ago. Dunno how it's going to stand up to to summer
>sunlight / UV.
>
>The outside gelcoat is what gives fiberglass its watertight properties.
>Too many antennas have "died" after the fiberglass allowed rain water
>ingress.
>
>Be very careful that whatever you use is either clear or has a NON-
>METALLIC pigment, for example, many white paints get the color
>from titanium dioxide, a metal.
>Black is OK as the color comes from lampblack(carbon) and won't
>detune the antenna.
FYI, carbon is a nice absorber. You may actually notice an improvement in
VSWR, but the antenna performance may degrade dramatically. The hideous
thing about that is unless you compare the antenna side-by-side with
another antenna of known gain, measure it's gain on an antenna range or do
a calorimetric measurement of the radome (heating under power), you may
never know if you're installing a good antenna or a very leaky dummy load
on your tower.
I recently retuned/refurbished a 460 StationMaster by adding aluminum tape
rings, coating with clear marine resin, & painting with a couple of coats
of white Krylon. At each step I rechecked the VSWR to make sure what I was
doing wasn't detuning the antenna, as I'd spent quite a bit of time
optimizing the aluminum tape width & position. Neither the marine resin
nor the white paint had any effect on VSWR or received signal strength.
& yes I've been asked to write an article about the antenna mod. Been very
busy with the LA Marathon & moving one of my repeaters that lost it's tower
(tree) last year. Maybe I'll get to it next month if things calm down a bit...
Bob NO6B
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