Rodger, not familar with the AFA, but the ZL special is one of the
easiest antennas to build of all time. I used one for my first beam in
1955. Of course, it was a modified version to help match the impedence
of the antenna.
Basically, you use a tripole for each section, connected at the ends
with the center wire open in the middle. Seperate the ends about 6" as
I recall. Make two sections, and feed them 300 ohm electrical half wave
of open wire line with one wire transposed 180 degrees at the center of
the element. You start off with about 600 ohms impedence, cut to 300
ohms with the phasing line, and a 4:1 balun gives you about 1.5 SWR.
Today, I would just come off the center of the line with a quarter wave
stub and adjust matching.
Unfortunately, that was before the days of SWR meters....but I really
ripped 20 meters with a Central Electronics 10B and 4 6AG7s ( and that's
a metal shell receiving tube for you young squirts ).
Plenty of articles around, but this one hummed.
73
Ed
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