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WX-proofing a Helix Feed



Thanks to all of you who answered my questions about flexible coax; now
I have another.

In my continuing saga to Elmer another ham getting a satellite station
up, I was looking for suggestions on how to weather-proof a homebrew
helix feed for an offset dish going on a tower installation in New
England climate and weather conditions.

We've talked before about white PVC, but I wanted to get practical
experience, especially since I have read that the PVC might detune the
helix slightly. The DEM helix and some of the commercially available
helix feeds are in PVC...  how much should I scale the dimensions to
account for the detuning? I have no SWR, return loss, or analysis
equipment that goes over 500MHz.

I asked about Tupperware before, and most commented that it will not be
UV resistance and crumble in a year or so.

I know many of you have also gone without any additional coverage over
the feed, and I'm wondering what "hardened" hardware you have used in
the construction (materials, paints, coatings, sealers -- diameter of
the tubing, matching plate materials). I assume the same question would
pertain to patch feeds, but everything I have read says I should be
using a helix for an offset dish and a f/d greater than .5

I'm still running portable, so my copper-coil-over-electrical-box-cover
feed works fine...

http://webpages.charter.net/acito/dishandboom.jpg

what are you guys with dishes on towers in northern latitudes doing so I
can steer this ham right (especially, since I have to build the feed)?

Bill
w1pa

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