Hi Dean,
At 01:54 PM 3/29/97 +0000, you wrote:
>Way back, before the dinosaurs got smaller, I used (all homebrew)
>transmitters with balanced outputs. I also used 'true' balanced
>tuners when I got rich enough to afford them. They worked fine.
>
>Now, I use unbalanced tuners with either internal or external baluns.
>They also work fine.
>
>I can't see any difference in signal strength between the two.
Well, you probably can't. We're kind of splitting hairs here. I've been
testing tuners for efficiency, and in the process have discovered that
baluns are sometimes the cause of some losses.
For some time I used a St. Louis tuner, and enjoyed it very much. - but I
began to have a feeling that I just wasn't getting out quite as well as I
should. When I started doing comprehensive tests, it was obvious that the
tuner was more lossy than my previous tuner. The difference was as little
as 1dB in some cases, and more in others. It was not normally very
noticable in signal strength, yet there was a difference. -- But, I'm one
of those guys who has to try to squeeze every ounce of juice from a grapefruit.
So, I've been working on tuner efficiency ever since.
>I thought that a balun was simply a transformer, just as a link
>coupling is.
Well, it is, but like most transformers baluns react differently as
impedance changes. (even "wide band" ones)
>In addition, most baluns have one side of the balanced
>output connected to the ground side of the unbalanced input. I had
>thought this was to help reduce static buildup on the antenna,
>but I could be wrong.
>Do you know if a balun is something other than a wideband
>transformer?
I'm far from a Balun expert. The interconnecting of windings usually has to
do with the baluns ratio, however, ie, 4:1 or 1:1. It may also have the
effect of reducing static buildup when there is an earth ground. (maybe
someone can comment on that)
Baluns have a design impedance, and they are most efficient at that
impedance. Unfortunately, when we use them around Antenna tuners, they are
usually seeing something other than their design impedance. A balun
operated at, say, 50 ohms impedance may be fairly efficient over a wide band
of frequencies. But, if the impedance changes, then it may be less
efficient as it faces a wide frequency range.
As someone said, if it works, be happy, and don't sweat the details! I'm
going to continue testing tuners and will report the results, so we all will
know which are the most efficient. -but, in the meantime, lots of
tuner/antenna combinations will enable us to enjoy good contacts.
CUL,
Bob Kellogg, AE4IC, Greensboro, NC
Prolably, but not nececelery. - Benny Hill
WIMPS: Qs=000 30m=0 17m=0 12m=0 States=00/00/00
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