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Ok all noted on the many ideas.
Here is one for you boffins:
After having a look at the circular turnstile type antenna with a
groundplane ,I sent a request to the main manufactureers regarding
using this in an inverted state for what I wanted to do on the
repeater.Still yet to get a reply and after a few months I guess they
are still thinking about it.
If they advertised it so great for horizontal to near vertical
satellite work then the same principle should apply if inverted.
Style of eggbeater looking at .
http://pagesperso-orange.fr/on6wg/Do...Part1-Full.pdf
What do the Boffins suggest.
1. How are you thinking of mounting it whilst upside down? Even if you
were to use a dielectric swan neck of some kind, you'd still have the feed
line passing through the volume into which the antenna is intentionally
radiating, so the radiation pattern would be upset to some extent. Of
course, if you were willing to modify the antenna you could probably pass a
co-axial feed line through an axial tube - but if you were going to that
much trouble you might as well build the thing yourself.
2. Their statement that: 'Each of the two loops forming the antenna has an
impedance of 100 ohms, and when coupled in parallel, they offer an ideal 50
ohms impedance. We will use the properties of a quarter wavelength coax line
to achieve a 90 degree phase difference between the two loops in order to
obtain circular polarisation.' is a bit suspect. This would be true for a
half wavelength of line, indeed that is the basis of a very common form of
balun, but a quarter wavelength of transmission line will cause an impedance
transformation. If they use 50 ohm cable then a quarter wavelength will
transform 100 ohms down to 25 ohms, and when this is connected in parallel
with another 100 ohms the result will be 20 ohms which is presented to the
feed line. Not a particularly good match!
My suggestion is: if you intend to purchase, proceed with caution and keep
asking the proprietor the questions you want answered.
Chris