Stuart Longland (VK4MSL) Inscribed thus:

The full-wave loop looks almost ideal... nice and simple,
apparently good gain over a dipole for an omnidirectional antenna.
I have some 300ohm ribbon I can feed it with (RG58 makes the pole
bend over... and of course anything low-loss will be unworkable).

The catch is, I'm not sure how to go about impedance matching, with
the loop having a theoretical impedance (so I hear) of 100ohms, the
ribbon being 300ohms, and a radio that expects 50ohms. Â*I'm not
sure how the feedline characteristic impedance will impact on
things, being 300ohm... there's no such thing as 50ohm ribbon in
the shops AFAIK. I'm not sure this has to match though. Â*The
antenna itself though, does need some sort of transformation back
to 50ohms.

Regards,
Stuart Longland VK4MSL

Try this url.
http://www.xs4all.nl/~pa0fri/Ant/Quad/quadeng.htm

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Best Regards:
Baron.