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Re: 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

David, one suggestion I've seen for a 2.4 GHz helix might be applicable if
you can get the right materials.  The helix I saw was enclosed in a PVC
pipe "radome" that was about 3x the diameter of the helix -- this was in
Australia and besides the weather the guy had budgies and cockatoos to deal
with -- and seemed to protect it rather nicely.  This might nor might not
work on 1.2 GHz, haven't tried it yet, but if the absorption is low enough
the radome will be transparent to the RF and should not affect the tuning
significantly ..


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         Bruce Bostwick  mailto:lihan@ccwf.cc.utexas.edu
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