[Johnson] Small Johnson Matchbox has its limits

[Kevin J Ward]

Richard -

There is one very good reason to use a balanced tuner like the Johnson;
harmonic rejection!  This type of tuner can significantly reduce the
harmonic content of your signal, especially when used in conjunction with
a good low-pass filter.  The T-network tuner or "transmatch" offers no
harmonic rejection whatsoever.  Yes, it will match a wider range of
impedances, but even the lowly L-network (low pass configuration) will
outshine the Ultimate Transmatch in harmonic rejection.  

A second fact to consider is that the "transmatch" is basically an
unbalanced device.  It requires a balun at the output to feed an open
wire line.  Those baluns will saturate at some power level.  When that
happens the result is a clipped waveform or flat toping, part of the
signal turned to heat, and lots of harmonics.  This combination has
actually made your signal worse!  The balanced tuner won't saturate.  Any
tuner can spit and smoke when fed too much power, but I'm talking about
similar components fed the same amount of RF.  

The T-network tuner is a useful device, but not an unmixed blessing.

Kevin  N2IE


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