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RE: Weatherproofing helix feeds.



Hello David

I'm not sure if this is of any use to you as you're at the business side of
the reflector, but for 'weather proofing' my preamp which is directly
connected at the other side of the reflector I've simply used a fairly heavy
duty transparent plastic bag cable-tied to the boom with two tiny scissor
snips above and below at the highest and lowest points to let any water
ingress and condensation out.

Although it's only been two or three months, so far so good, even during
some pretty nasty downpours (for England at any rate).

Don't know what attenuation or dielectric affect this makeshift radome might
have of course though.

It certainly doesn't win any points for aesthetic quality either.

73 Howard G6LVB

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of G0MRF@aol.com
Sent: 27 April 2001 13:50
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] Weatherproofing helix feeds.


After some success with AO-40 reception in the past few days, I mounted my
helix outside with mixed results.

The helical winding rests on insulating PCB mounting pillars pushed into the
half inch square Aluminium boom. This works fine and rain cannot
electrically
connect one turn to the next.

However at the first sign of rain the antenna detuned. This turned out to be
due to water droplets bridging the gap between the ground plane and the
quarter turn matching section.

Any practical suggestions  from the reflector on how to waterproof this
without de-tuning?  I've looked at a few web sites, but you lucky people all
seem to be blessed with sunny climates.
I suspect silicon sealant may change the dielectric constant between the
matching section and the ground plane giving the same detuning effect as the
rain.

Thanks


David G0MRF
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