Hi Dave,
> The main problem with bringing ladder line or any open wire line into the
> shack lies with what I call the "hot shack" syndrome. With more than one
> 160 meter antenna the shack was full of hot RF and plenty of RF feedback.
> This also gets into the telephones radios, and even TVs that are not on
> cable. Even using a tuner with a balun can cause a problem.
The problem is with feedline balance and/or distance to the
feedline. The most effective type of balun is a 1:1 choke-
balun....and it belongs on the OUTPUT side of the tuner...not the
input.
There is some misconception that placing the balun at the input
somehow improves balance, when it actually is the opposite.
If you keep the feedline at least several inches from other parallel
conductors, and use the right balun and make the antenna
reasonably symmetrical..it is no worse than any other type of
feedline.
It certainly is not advisable to use coax for any distance more than
a few feet out to a balun, and a 4:1 balun, in a multiband system
designed to be used with a tuner. If any coax is used it should be
as short as possible, and the balun should be a 1:1 "choke" or
"current" type balun.
You can not get a long enough string of beads to make a good
bead balun outside of a 50 ohm system, so the balun has to be a
multi-turn balun on a suitable core or form. It is probably the lack of
good balun designs for this application that has created most of the
misconceptions and problems.
It takes a 2 or 3 inch tall stack of 2 inch diameter 61 or 65 material
cores and perhaps 15 bifilar turns of HV insulation wire to make a
good ladderline balun for 80-10 meters. I don't think anyone makes
one that is acceptable commercially.
73, Tom W8JI
W8JI@contesting.com
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