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Re: 2.4 GHz Helix & static type noise





> Thanks for the info. It has been hard to get any exact
info on the posistioning
> of the feed point. I want to give the 60cm dish idea a try
and see how it
> compares to the Bar-B-Q grill I use now.

Hi all,
Some years ago I built an experimental setup to test the
need for positional accuracy
on these frequencies. I used a full metal 1.6 metre ground
mounted dish which I polished using auto polish. At the
feedpoint I had an arrangement consisting of a round sheet
of tracing paper mounted on a one foot length of wooden
dowel. The tracing paper could be moved towards or away from
the dish about 6" either way from the focal point. When this
'contraption' was pointed at the Sun it became apparent that
the position of "best-focus" wasn't all that critical. In
fact it was hard to get an actual "fix" on it within an
inch.

I settled on a derivative of the G3RUH 2.25 turn helix feed
for the antenna and I put the focus point where James
recommended, at the end of the first turn. On subsequent
tests using signals from Arsene and AO-13 and the GMS series
of weather satellites (1.7GHz), I was not able to better
that arrangement. I've stuck to it ever since.

73, Bill...vk3jt
Milawa
Australia


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