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Re: 3733-helix



Hi Mark.  Great work!

hammond@surrealnet.net writes:
> At least is shows you how I'm moving forward with this idea.
>  Do you have any pictures of your efforts?  What about "wrapping" the dish 
>  in screen cloth?  I haven't even tried yet.

I also built a helix feed for a similar dish yesterday and just got a minute 
to test it today.  In my case it was one of K5GNA's smaller dishes (22" x 17" 
x 3-1/2" deep).  The helix was 3 turns inside a K&W cup measuring 4" in dia 
and 2" in height.  The helix is 1.6" dia. at 1.125" spacing.  I tested it 
using local MMDS (Discovery Channel and Univ of Houston are both strong 
signals here).  A couple of observations:
- the dish seems to have 2 "sweet spots" at 9-1/2" and 11-1/2" focus, 
measured from the back of the cup
- the MMDS signals are horizontally polarized and without a mesh grid, the 
picture was no better than my 16-turn helix, about P4.5
- with an alum screen mesh added, the picture improved significantly to a 
perfect P5.

I did no illumination calculations or anything else... just put it together 
to see how it would work.  I'll see how it performs in a week or so when I 
can finish it and get a decent pass on AO-40.
You can see a picture of the feed and d/c here:
73,
Jerry, K5OE
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