More fun with short linear loaded wires and the KXAT1

[Michael Babineau]

I have been doing some more experimentation with shortened linear loaded
wires in an attempt to find more practical lengths of end-fed wires for
portable
and pedestrian mobile operations with my KX1.

Yesterday I used a 11 ft wire supported on a 10ft  fiberglass fishing
pole and managed
to work KO0K in OH on 40M while trailing a 30 foot wire and running
about 2.5W on
my KX1. As before, the linear loaded wire is made from 4 conductor
computer ribbon
cable with the inner two conductors not connected (ie just used as
spacers). I short
the outer two conductors at the top and install banana plugs on the two
outer conductors
at the bottom end of the wire.  With no addedl loading other than the
wire and the
KXAT1 I was able to get about a 2:1 match on 40M. This is not great but
still within the
range of what the KX1 is ok with according to Wayne, N6KR. I am able to
get better than
a 1.5:1 match on 30M and 20M with this setup as well.

Also, those of you familiar with the KXAT1 probably know that this
tuner was optimized
for a 24 to 28 foot end-fed wire. I have been up until now using a 24
footer with great
success, but when I hang it from the ubiquitous 20 ft SD-20 type
fishing pole, the resulting
sloping configuration doesn't seem to lend itself to a great match on
40M, so I have
been using a somewhat heavier and bulkier and more expensive 24 foot
pole.
I tried using a 20 foot wire but that doesn't seem to make the tuner
happy either.
So, yesterday, I tried a 20 foot linear loaded wire, with construction
as above and
suspended it vertically from a 20 foot pole and  I  am happy to report
that this loads
very nicely on all three bands covered by the KX1 using the internal
KXAT1.

Since I am somewhat skeptical about the how well the insulation on the
ribbon cable
actually functions at RF, I think that my next step will be to build
what amounts to
a length of home-brew mini open wire line, using small gauge teflon
coated wire
and some pieces of stiff plastic drinking straw as spacers. I'll
probably try about
1/2 " spacing and see how that works out and how much more, or less
wind load
and weight that adds as compared to the ribbon cable antenna.

Too much fun ... too little time ...

Michael VE3WMB

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Hello Michael,

I've experimented quite a bit with linear loaded vertical dipoles, and
found that placing capacitance hats at both ends helps a lot. Not only
does it lower the resonant frequency for a given length of wire, but it
also raises the radiation resistance so the antenna will be more efficient.

Maybe you could try something like back-to-back telescoping antennas
tied to the top of the wire, such that they balance out and remain
somewhat horizontal.

Have fun!

73, Dale WA8SRA

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