Jimmie D wrote:
"gwatts" wrote in message
...

Jimmie D wrote:

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.

I've always had success matching a helix by running the first 1/4 turn
(starting at the feed point) parallel to the reflector and changing the
spacing between the 1/4 turn and the reflector until I get a low SWR. If
the reflector is mesh I put a piece of sheet metal on the mesh under that
1/4 turn. It's worked every time, no fins, no 1/4 wave sections of coax,
etc. For my 432 MHz helix it ended up with about 1/4 inch spacing, using
#10 solid wire for the helix.

-W8LNA


Thats what I did yesterday sort of. I. took the piece of metal I was going
to fasten to the helix and fastened it to the reflector and then adjusted
the spacing for best SWR. The difference is I moved the counterpoise instead
of the antenna to get the match. I do see why others have opted to put the
fin on the wire. The spacing is so close doing it the ways we did that you
may get arcing when using high power. If I ever build another one I will
probably use copper instead of Al tubing for the antenna and solder the fin
on the antenna.

You might be misunderstanding me, I didn't attach the piece of sheet
metal to the mesh as a fin but flat onto the mesh so what I ended up
with is a wire over a smooth, flat surface for a matching section.

- W8LNA