Lets back up a bit before it gets too deep and I get confused.
The comment about an amp requiring a good input VSWR is valid when
dealing with broadband SS rigs. It matters less with a tube rig. But
that is probably already known by most.
My contention is that altho the SS ricebox xcvr is designed for a 50 Ohm
output, that is purely a nominal number and can vary over the range. This
is due to the use of broadband LP filters with less than perfect
performance.
The VSWR sensing circuitry is at the output of the filters, naturally,
and do not indicate what is happening back at the input side.
A simple test can be run by monitoring the collector current of the
output transistors while tuning from 1.5 to 30 MHz, or even from amateur
band to band if your rig has not been modified for wide band xmit. On a
TS-940, Ic will vary over 2A over the range while maintaining a constant
100W output.
I cant say what happens with other rigs but on the 940 that variation can
not be helping IMD performance. This may also explain the different band
to band IMD specs in various QST reviews; when they bother to do them. Or
not charge extra money for the privilege.
Anyway, 'nuff said for now. Am I somewhat on the right track here?
73....Carl KM1H
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