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Re: Weatherproofing helix feeds.

Using a radome to suppress water is a good idea. Here are two hints:

(1) To see if the material you have used for the radome has much loss, put
it n your microwave oven. Run the oven for ~15 seconds and feel the
plastic. If it i war, don't use it. If it is still cool, try a 30 second
soak and if it's warm discard it. Then, if it is still cool after a minute
soak, it has low absorptivity at S-band and should be fine to use. This
test makes use of the fact that microwave ovens heat their targets with
2.45 GHzRF.

[ If you want to see a dynamic demo of an unsuitable radome material, put a
piece of aluminzed mylar (used to package potato chips and other junk food,
and used for "Happy Birthday" helium-filled balloons) into the microwave
oven. The fireworks during the first ~5 seconds are spectacular! But don't
tell your significant other what you are doing to the oven. ]

(2) To help keep water from building up on plastic surface of the radome,
go to your nearest auto parts store and buy some RainX -- this is a liquid
polymer intended to be used on car windshields to make the use of
windshield wipers unnecessary. RainX was tested by me at 20-24 GHz and then
later by the Deep Space network as a coating for the radomes covering
microwave feeds and it was found to work well. It has the side benefit that
it contains alcohol that makes a good solvent for the crud that has built
up on the surface, so applying it also cleans the surface. The RainX should
be re-applied every 1-2 months for best protection. [ And it works well on
your car's windshield too, if you can stand squeaking windshield wipers. ]

73, Tom

73, Tom
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