Parker et al,
QST did a review and test of a bunch of balanced tuners a year or so back.
I don't remember too much of it now but remember being shocked at how high
the losses typically were. As I recall efficiency ran in the 65 to 75
percent range for many of them. The Johnson matchbox was the most efficient
by far (90% or more??) but did not cover all bands.
I have not really studied this issue but have always been interested. My
gut feel is that often much of the loss in these tuners (when driving a
balanced line) is in the internal balun which is at the output of typical
tuners and is driving a balanced line to the antenna which often has a
horrendous SWR. The high SWR on the balanced line is not itself a problem
because balanced twin line or ladder line feeders can easily handle the high
currents and voltages with low losses but the poor balun can quickly get too
hot to touch because of the high circulating currents within the balun.
Don K7FJ K2 4438
I've been using my QRP K2 for the last 2-3 years with a "full sized"
Palstar
tuner. I use a variety of antennas from 160 to 10 meters, fed with coax,
ladder line, choke baluns, the Elecraft balun, etc. I'm thinking about
going to an auto tuner (Dayton Hamvention coming). Has anyone compared
the
efficiencies of the very small tuner like the T1, the KAT2, and larger
tuners like the Palstar? (I've been the Johnson KW Matchbox route as
well.)
Intuition tells me there is something lost when going to very small
components packed into a tiny space compared to large air variables, big
roller inductors, etc., but I don't have anything to back up that gut
feel.
Anyone make any measurements?
Parker K2 2636
WD8JOL
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