I have an older Hy-gain 4-element 20 meter mono band beam. I
downloaded the LJ-204BA manual from the Hy-gain (MFJ) website. I
took the antenna apart and verified that all the element lengths are
the same in the manual. Other than a different style hairpin, my
older antenna is identical to the current version.
Hy-gain makes use of swagged element tips. I have a slight issue
with the amount of overlap with the non-swagged elements closer in to the boom.
I'm aware of the electrical characteristics of tapered elements and
know you just can't shove one the second element in and extra inch
and make up for it by pulling out the third element an inch. The
diameter of the tubing effects the electrical length of that half-element.
Well, understanding, and knowing how to compensate for changes, is
two different things and I could use your help.
I can download a YAG file from the ARRL website
(http://www.arrl.org/antmodels/), but need YO to play with it. I
believe YO compensates for tapers. I don't have a NEC file of this antenna.
So let me get specific...
The second tube out from the boom (for all eight half-elements) is 1
1/8" x 48". The instructions call for 46" exposed. This leaves only
2" inside the 1 1/4" tube! The 1 1/4" tube is NOT swagged. The
third tube out is 7/8" x 55". The instructions calls for 50 1/2"
exposed. This leaves 4 1/2" inside the 1 1/8" swagged tube. Here is
the thing though, the 1 1/8" tube is swagged for the first 2". The
remainder 2 1/2" of the 7/8" tube if just floating inside the 1 1/8" tube!
What I would like to do is move the 1 1/8" tube in one additional
inch (3" overlap instead of 2") and compensate for the shorter
half-element by pulling the 7/8" out...but by how much, I don't
know. I have 2 1/2" to play with since it is only floating in
air. This is where I need your help! I do know that 1" of 1 1/8
requires more than 1" of 7/8" to compensate.
The rest of the elements have enough overlap per diameter. My issue
is that there is a lot of weight on only 2" of the 1 1/8" tube! It's
a good argument to say this is the way it's been done for years, so
why mess with it. My 1 1/8" tubes are bent at the 2" mark and I'd
guess it would be better if there was a bit more overlap.
One of these days I may get a copy of YO and learn to use it, or
build a NEC file for use in Eznec, but for now, I'm useless! :-)
Dino...k6rix@earthlink.net
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