"Jimmie D" wrote in message
...
Been cleaning out the garage this weekend and came across an old attempt
at build a 432Mhz helix antenna. As I remember I gave up on it because I
was having trouble building the matching section which was a 11/4wl long
fin that attches to the helix as it apprached the feed point. It was
proving difficult for me to fabricate. I was wondering if the fin could
not be attached to the counterpoise instead of the helix, adjusting the
space beteen the fin and the helix to get a match.

Jimmie.

One way is to run a single wire next to the reflector from the feedpoint to
the transmission line. If the Z0 of the helix is 120 Ohms, space the wire
from the refleector so that at that end it forms an impedance of 120 Ohms.
Space it at the coax end so the impedance is 50 Ohms. I think that
theoretically the impedance is supposed to change is some logarithmic
fashion, but linear reduction of distance works. If the reflectopr is not
solid, fasten a metal strip to it to get a smooth impedance. I can't
remember the minimum length for the conversion line; something like a
wavelength. Google helix antenna matching.

Tam/WB2TT