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Re: 3733-helix



Do you have any close up pix's of the 1st turn showing how you worked the
matching section?

K5OE@aol.com wrote:

> 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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