If AB7E's model looks anything like the one in figure 2 of L B Cebik's
article http://www.antentop.org/w4rnl.001/mu3a.html I would also be
concerned about the pattern. A simple dipole will beat it in most
directions.
John KK9A
David Gilbert AB7E wrote:
I used EZNEC+ to model the antenna as you described and got an SWR dip
at 10.7 MHz and 13.55 MHz, although the SWR values were different than
yours. Part of that may be due to a 4:1 balun not necessarily being 4:1
if not being fed with the impedances it was designed for, but the dips
match pretty closely with what you see in practice.
In any case, I lengthened the elements to 66' 10" and got a 50 ohm SWR
less than 1.1:1 at 10.12 KHz without the 4:1 balun ... i.e., directly at
50 ohms. This doesn't mean that exactly 66' 10" will work for you, but
you clearly need to lengthen the elements and I'd try it with and
without the balun ... substituting a common mode choke for the balun
when you don't use the balun.
By the way, EZNEC says that the two opposing main lobes have over 9 dbi
gain, but those two lobes are only 26 degrees wide at the 3db point and
the adjacent notches only 27 degrees either side of them are -20 db.
There are four other lobes (and two other notches), with those four
lobes down about 5 db from the main ones and the two notches down about
10 db. This antenna is going to be fairly picky in terms of orientation
and if you get it wrong it's going to be quite wrong.
Hope this helps a bit.
73,
Dave AB7E
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