33.25ft vertical with KXAT1 - Why did it work?

Posted by Martin Gillen on Sep 12, 2005; 5:27pm
URL: http://elecraft.85.s1.nabble.com/33-25ft-vertical-with-KXAT1-Why-did-it-work-tp382085.html

Hi.

I was trying to build a field portable quick to
install
antenna and I really liked what I read about an end
fed
halfwave having a very low angle of radiation and only

requiring a very short counterpoise however
I remembered that the KXAT1 manual stated not to use
lengths near a halfwave as they would be outside the
matching range.

So... I decided that I would cut an antenna to 33ft
(20m halfwave), and then I would cut it back a foot at
a time until the KXAT1 found a match.

I started at 33.25ft vertical but I did leave a pair
of
18.5ft counterpoise wires running at about 2 feet
above the ground connected to the ground terminal.

I tuned up and ... 1.2:1 match on 20m!

I then proceeded to work KF6GC with 2W (almost 4000km)
in the middle of a K Index = 8 solar storm!  So I know
the antenna worked well.

I modelled it in EZNEC and the impedance at the base
of that antenna should have been 970 + j 1700 ohms,
so I am surprised that the KXAT1 was able to match it.

Any comments?  Was it because I left the counterpoises
connected that it worked so well?  If I remove the
counterpoises in the NEC model the impedance increases
and becomes inductive to 1456 - j 1819 ohms.

Comments?

PS.  I am only learning in this stuff so forgive any
overly simplistic analysis!!

Thanks,
Martin.
VA3SIE.


               
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