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Re: helix location vs focus



My experience/modelling indicates that just a bit beyond the "mouth" of
the "can" is about right; for my 1-1/2" high can and 2-1/2 turn helix
the focus seems to be about 1.9" down the helix from the ground plane.
The depth of the can (if used) does make a difference; my experimental
set indicates about 0.4" past the can.
YMMV :-)
I have been hoping to publish all my modeling results etc. but lack o'
time.

"Greg D." wrote:
> 
> >   I read somewhere (can't remember) that you should place the
> >   bottom (i.e. feedpoint) of the helix at the focus of the dish.
> 
> I seem to recall someone on this BB experimenting, and finding
> that the hot spot was at the end of the first turn for a simple
> helix.  My own experiments seem to put the hot spot at the mouth
> of the can, for "canned helix" antennas.
> 
> The best thing to do is to create (or locate) a weak signal
> source, and adjust it for best signal.  Then, let the rest of
> us know where it is!
> 
> Greg  KO6TH
> 
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