Hi Tom - this is a question we deal with over and over again, and have
sold hundreds of heavy duty baluns and kits for the purpose. A 10 ft max
run is suggested, and the balun is one Lew McCoy tested and wrote up in
CQ Mag a few years ago after testing it to a 10:1 SWR at 3Kw. (HF)
The rationale is typically explained as follows:
~~~~~~~~~~~
The balun can be wound any way one wants it - a transformer of 1:1 to
16:1 is possible. On the other hand, 4:1 is what you want, if your use is
the typical one, that of allowing coax to finish the last few feet of a
balanced line run from antenna to tuner.
The function here is to extend the tuner's field of operation, so to
speak, from where it sits, to balanced line terminals outside the house.
It does two things: - first, it makes the match from balanced to
unbalanced(coax or unbalanced output from the tuner) to balanced - the
ladderline.
Second, it gives the tuner more latitude. Most tuners do their best work
when handling loads of impedance in a range from less than 25 ohms to 300
to 1000 ohms, depending on the tuner's design
and quality. A typical dipole of any given length fed with ladder line
(300 to 600 ohms) will present a load of, say 20 to 2000 ohms as a system
- the characteristic impedance of the LL is not relevant.
The 4:1 balun, either remote or in the tuner as an option or design.
centers that device at a point 4 times greater, and expands its
capability tremendously. It has been proven over the years that 4:1 is
the most effective effective ratio for the job, in or remote.
Just remember - you are not matching the characteristic impedance of a
piece of ladderline - you are matching a system at its feedpoint to a
signal at any given frequency.
Hope this makes it easier to deal with!
~~~~~~~~~~~~~~~~~~
73,
Press Jones, N8UG, The Wireman, Inc., Landrum, SC, 29356
Sales (800)727-WIRE(9473) or orders@thewireman.com
Tech help (864)895-4195 or n8ug@thewireman.com
http://www.thewireman.com and the WIRELINE bargain page
Our 22nd year!
On Tue, 27 Apr 1999 15:21:17 -0700 Tom Osborne <w7why@harborside.com>
writes:
>
>
>
>Michael Tope wrote:
>>
>> Jim,
>>
>> Unless your a using a Johnson matchbox (no balun), put the balun >at
>the
>window interface
>> and run a piece of 3/4" or 7/8" hardline the rest of the way.
>>
>> Mike, W4EF.............
>
>
>HI All
>
>In regards to the balun, how does it work when the impedance of
>the line keeps changing? If you use a 4/1 balun, some
>frequencies will be 300 ohm impedance and it will work, but at
>some frequencies, the impedance will be as high as 2000 ohms, and
>it seems that would be kind of hard on the balun if you're
>running any power. 73
>Tom W7WHY
>
>
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