In a message dated 98-02-02 23:45:16 EST, grimm@lynchburg.net writes:
> > So, can anybody recommend a good current balun to use with the 402CD,
> > or is one even needed? Why can't I just follow the directions in the
> > manual and make a coil of coax?
> >
> > 73 - Dave N3RD
> I've burned up BN-86s and had problems with the W2DU type baluns. Come to
> think of it,
> over the years, baluns have been a dependable source of problems! I've
> finally given up
> and gone back to what I used to use and what you are wondering about: a
> choke made of
> several turns of coax. I've never had any problems with that simple and
> effective
> device. Why do we keep buying baluns?
>
The main purpose for a balun as I understand it is to keep the feedline
from radiating. It helps to get all of the RF out the antenna as well as
helping to prevent RFI.
I've had problems with the Hy-Gain, Bencher, W2DU, etc. so I can relate
to the problems and frustrations. The main problem with a questionable balun
is that you can't do anything real simple to determine if it's working or not.
About the only thing you can do is to replace it with another one and see if
that made any difference.
Older balun designs were of the 'voltage type' while newer ones are
'current type'. (I'm skipping lots of theory here that's available in a myriad
of sources.)
A stack of toroids on a feedline does a pretty good job of keeping the
outside of the shield from radiating, thus "choking" the RF off the line.
The aforementioned problems with water in the balun are real common.
The best approach I've seen are the Force 12 version that are vaccuum
assembled. That is, the evacuated air in the balun is replaced with epoxy so
you'll never get any moisture in that baby. For $39.95, it's about the best
and is pretty darned reliable.
I haven't seen one of the Aztec RF ones but since it's a K6NA product,
it's well-built. They're also pretty expensive (I think they're $60-70).
What about coax RF chokes? While I use them myself in the past and they
are reliable, the newest stuff I've read (here on TowerTalk as I recall) was
that they are not as broadbanded as I've been lead to believe. They have to be
a certain size and a certain configuration to work. Would I use them again?
Probably not - I'll use a stacked toroid balun version and probably the Force
12 B-1.
73, Steve K7LXC
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