Vin,
What you are observing at the low end is differences in the diode
characteristics. The WM-2 has a diode compensation circuit which attempt to
correct the readings at low power levels while the KAT1 does not - so the
WM-2 is likely more correct at the low end
The difference at the high end does not have such a straightforward and easy
answer. You might look into your dummy load, the length of coax between the
KAT1 and the WM-2 and various other factors for the answer. Try another
band, you could find the difference is frequency dependent too.
If you have a good 50 ohm non-reactive dummy load (check it with an antenna
analyzer to be certain), you can read the RF voltage across the dummy load
with a calibrated 'scope or an RF probe and calculate the power. This
method is quite accurate (better than most wattmeters), but is highly
dependent on the accuracy of the dummy load.
BTW - I do not perceive anything really bad here - just inaccuracies.
Equate that to the man with two watches - he never knew what time it was
G.
73,
Don W3FPR
-Original Message-
I have been enjoying my K1-4 immensely for many months now, and
am getting ready to build the KAT-1. But I decided to build my
OHR WM-2 first, so as to get a good idea of how the antenna tuner
is actually performing. Well, the meter went together on a
Sunday afternoon/evening very nicely, but there is one thing I noticed.
My K1 goes from 100 mW to about 7.1 W according to the front
panel display (of the K1). Now, when I look at the power out on
the meter, I see good agreement with that from around say 2 watts
to about 5 watts. But at the low and high end, the meter reads
high. Approximately 300 mW when the radio says 100 mW, and about
6 watts when the radio says 5 watts. At the top end, the
difference is even a little worse, approx 8.5 watts on the WM-2
when the K1 says 7 watts.
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