[amsat-bb] Re: Helix structural integrity

[G0MRF@xxxxxxx]

In a message dated 7/12/02 9:24:07 PM GMT Daylight Time, 
owner-AMSAT-BB-digest@AMSAT.Org writes:



What about a scalar ring/cup to narrow the illumination of the patch against 
these 0.6  and 0.7 f/d offset dishes? Or am I wasting  signal? Can I case my 
helix in 
gray PVC without a noticeable loss of gain to get the  structuralintegrity 
back?



Hi Bill.

The PVC will affect the impedance and the pattern from a helix. I have found 
that a metal support in the center of the feed is invisible to the helix 
providing it's quite small diameter.

My solution to storms (and supporting a plastic rain cover) was a length of 
threaded rod with a small piece of blank (no copper) PCB material at the end. 
The fibreglass from the PCB material is held in place with a couple of nuts 
and a spring washer. 

There's a picture on      www.g0mrf.freeserve.co.uk/ao-40.htm

73

David
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