From: "James Apple" <wb1dog@hotmail.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Feeding a multi band loop (cloud burner)
with balanced line
Date sent: Mon, 17 May 1999 17:00:51 PDT
>
> I'm suspicious of the balun, I went with a 1:1 because I figured at some
> freq's the impedance would already be very low. But now I'm wondering if
> anyone else have tried this configuration or is a 4:1 balun the answer.
A 4:1 balun is probably not the answer Jim, unless you add so
much loss the SWR is reduced. Unlike 1:1 choke baluns, 4:1
baluns provide reduced performance when operated at high VSWR.
You have added two random mismatched line transformers to your
system. Each mismatched line section acts like a "transformer"
that changes impedance (both resistance and reactance).
When you feed an antenna through two random length and
impedance tandem connected lines with greatly different
impedances things can get real goofy in a hurry. Now you could go
back and PLAN the lengths and impedances of those lines to give
a reasonable SWR on some bands, but the result would probably
still be less bandwidth and maybe even more loss on most or all
bands.
What were you trying to accomplish with the new feed system?
> Or maybe the balun is bad, if while the RF-1 is connected I ground one
> side of the balun, the swr drops ? I don't know why I even tried this
> test, but I've tried about everything.
I assume you checked and have no bad connections. It's normal for
SWR to change when one side or the other of the balanced line to
be grounded.
Did you try removing the balanced arrestor? Arrestors are OK
(although the protection improvement they offer in most cases is
minimal) on matched lines, but they are bad news on mismatched
lines.
73, Tom W8JI
w8ji@contesting.com
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