Folks,
Of course Lee is correct, but the range of the KXAT1 should also match a low
impedance - and short antennas do produce a low impedance even if the
reactance is close to zero.
Whether you need a 'unun' (unbalanced 'balun') at the antenna or not depends
a lot on the length of the coax to the antennas is and the operating
frequency. The coax losses increase with feedline length and also increase
with frequency. With a short coax run, such as that normally encountered in
a portable situation, the losses should be quite low, and the only question
is the matching range of the KXAT1.
An antenna having a low impedance at the feedpoint will translate into a
high impedance with a quarter wavelength of coax attached - so figure
whether you need a balun such as the Elecraf BL1 (1:4 balun) or a 1:1 balun
(alternately unun) depending on the antenna feedpoint impedance AND the
feedline length. In antenna situations, look at your feedline length in
terms of how many quarter wavelengths it is - if it is an even number it
will repeat the antenna impedance, but if it is an odd number of 1/4 waves,
it will transform a low impedance to a high impedance and vice-versa - if
the length is somewhere in between, it will still act as an impedance
transformer, but you will have to do a bit more involved calculation to
determine the impedance presented to the KXAT1 output.
73,
Don W3FPR
----- Original Message -----
Alan's Balun from WB6ZQZ will help low impedance antennas such as
electrically short verticals, and is an easy build. Placed at the antenna
base and hooked to coax with a BNC connector, it will reduce SWR on the
coax feed, and ease the matching job of the KXAT1 at the rig end of the
coax.
Elecraft's balun has a step-up transformer to go to high-impedance
antennas, but Alan's Balun has a tapped step-down transformer to match to
a Pac-12 or MP-1. A plus is that once you find the right tap, you can use
the Tenna Dipper and actually hope for something closer to 50R 0X.
I built one and it was pretty fun.
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