Hi Martin,
This topic passed through the group a couple of weeks ago.
Don has some very good comments on it.
I can make a few *un-official** comments based on my own limited
experience.
I am a K2 owner rather than a K3 owner, however, I have a hunch the SWR
circuits are close approximations.
The K2's SWR circuit has the typical line passing through the center of
a toroid with a couple of trim-caps and diode FWD/REF rectification.
What is tapped off this are FWD & REF voltages.
The typical SWR circuit in an external tuner is almost identical, except
that the FWD & REF energy is tapped off as a current which is then
series_R limited (trim-pot) for driving an analog meter.
The (trim-pot), in all probability was tweaked to adjust the analog
meter reading with 100 watts applied.
Long story short...
I use an outdoors mounted auto-tuner, and I wanted to watch it adjust
SWR when I switch frequencies.
So I built myself a tiny analog SWR meter using one of the MFJ meters
and a modified rectifier circuit.
I wanted to test its readings up the scale to 100 watts.
Don reminded me of the voltage reading that can be taken on a dummy load
(non-reactive resistance) with an HF probe and a scope.
IF you have a scope, give it a try.
Just tap across the dummy.
Set the probe to 10X so there is no circuit loading.
wattage = (mV reading * mV reading)/400
This assumes an R of 50 ohms.
HAVE FUN!! :)
Duane
N1BBR
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