RadioBanter - View Single Post

April 25th 06, 10:44 AM posted to rec.radio.amateur.antenna

wrote:
The MFJ-962C "1.5kW" Versa Tuner III description claims to contain a
4:1 current balun. I'm using that "balanced" output on my HF
almost-doublet (slightly unequal leg lengths) with fairly decent
results.

The balun only has a single core. From what I understand, these "4:1
current baluns" aren't.

Dan,

That is correct. It is impossible to make a single core (single hole)
transmission line balun of any ratio other than 1:1. The MFJ balun, if
you actually test it, adds terrible imbalance to the system. I know
because I actually bought and measured one.

The idea for that balun came from Jerry Sevik's book about baluns and
un-uns....but unfortunately the suggestion is wrong.

Trask claims to have a transmission line balun on a single core, but he
actually has a simple isolation transformer. Isolation transformer
designs are old as dirt. You'll see in my articles on my web page and
things I wrote for ON4UN's low band DXing book that I used isolation
transformers for many years on low frequency receiving antennas, as
have many other people. The problem using them for transmitting is
loss, possible core saturation, and core heating. The flux density in
the core is very high under any load condition. They also go out of
balance badly at higher frequencies.

Bottom line is the single core 4:1 current balun used by MFJ is very
poor for balance, and subjects the core to unnecessary flux density.
I'd get rid of it for those reasons.

73 Tom