Tuner efficiency question
I've spent many years testing and evaluating tuner designs.
Using the Ten Tec 2KW L tuner, the Nye Viking 5KW MBV, the Johnson
KW Matchbox and home brew T network tuners. As well as my own
designs for a number of different types of dual balanced line tuners.
At the time I used a flat top ant fed with KW open wire 450ohm (72 ft
each side of center.) The main use was for full power 1.5KW RTTY
operation on all freqs 2 to 30mhz Navy Mars and amature freqs. The
Johnson Match box was only good to be used on the narrow bandwidth of
the non warc ham bands. It couldnt be used outside the ham bands so
I sold it without doing any further tests with it. I took note it
was an excellent design for a narrow bandwidth link coupled tuner. I
also noticed it couldnt always be adjusted for a 1 to 1 input swr due
to the narrow bandwidth of the input link coupling. But usually less
than 3 to 1. It was designed for tube rigs that had SWR tolerance in
the tube output tank circuits.
The tuners would work for about five to ten minutes before the 1.5kw
and the high circulating current burnt up the coils. The Nye MB5
5KW tuner ran so hot after 7 minutes that the large tape wound heavy
inductor was totally destroyed. Which is also what happened to the
inductors in the other tuners. The dual inductor balance line
tuners used the 1 to 1 balun on input. And they also failed to
perform without burning up at the 1.5KW power level. I used 10amp RF
amp meters in each side of the balanced line to be sure the output was
indeed balanced.
After all the years of testing, I finally got smart. Now, I dont
own an antenna tuner. All my ant are less than 2 to 1 SWR at the
design freq. So almost all the power is radiated. When SteppIR came
out with the BigIR Vertical a few years ago, I jumped all over it.
It has 1 to 1 swr on all freqs 7mhz to 50mhz. No tuner required :-)
Its true that the typical antenna tuner can tolerate up to a 3 to 1
mismatch without burning up at the 1.5KW continuous power level. But
I would never use one to match anything outside that range unless
there is no other alternative. The main thing is to try to get your
ant to be lower than 3 to 1 swr to begin with. Then you will have a
fighting chance of not burning up your 2KW tuner when using it at
full 1.5kw continuous on RTTY !!! Which is even more important
using QRP. No tuner is a good tuner :-)
Frank W7is
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