[TowerTalk] Baluns

[w8ji.tom]

Hi Paul,

I use a G5RV quite often. 

Mine is about 130 feet high, on the side of one of my tall 160 m towers.
Others reported no difference when a regular dipole at about the same
height on the low end of 80 or high end of forty was compared to the G5RV
with its slight mismatch.

Mine has several "resonant" points that fall inside or near amateur bands,
it presents a reasonable SWR on the low end of 80 (2.6:1), high end of
forty (2.0:1), and 20 meters (1.3:1.)

There are a few other bands where SWR is pretty reasonable, because the 450
ohm feedline-antenna combo "just happens" to present a reasonably low
impedance at the feedpoint of the ladder line. It really sucks on 21 MHz,
and parts of ten meters. I don't even try to use it there, because SWR is
very high.

A choke or current balun is a good addition idea at ANY balanced to
unbalanced junction in a system, unless the length of perturbance caused by
the transition is very small.

I use a choke balun, consisting of a long string of 43 Mix beads, over the
50 ohm cable leaving the feedpoint as a choke balun. It is probably a good
idea to use a choke-type (current) balun, unless you plan on feeding the
antenna as a "T" on 160 meters. A coil of coax ( maybe ten or twenty turns
4 inch dia) would also work.

In any event, you probably need to use a tuner with your antenna. If the
coax line feeding the G5RV is fairly low loss, you can put the tuner in the
house. Since I have 7/8 inch heliax running back 400 feet to my tower, I
just use a tuner in the house.

When I had 200 feet of RG-8X, I put the tuner near the antenna. I did that
in Conyers GA. I switched an L network in line (with remote control) so my
antenna system could be used efficiently on 75 meters and other spots where
SWR was high.

73 Tom

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