Posted by
Ron D'Eau Claire-2 on
Jul 24, 2006; 12:30am
URL: http://elecraft.85.s1.nabble.com/Funny-power-measurements-tp392406p392415.html
Fran, it's almost impossible to get a decent power reading by measuring the
RF voltage at the load unless the load has a very, very low SWR. No common
SWR meter is capable of showing when your load is well enough matched to
give you any significant accuracy. That is, a small mismatch that won't
hardly cause your SWR meter to wiggle is enough to cause very serious errors
in your power measurement.
The sensitivity of most SWR meters drops with frequency too, so 80 meters is
usually the least-accurate band!
The simple fact is that it does not make one whit of difference whether the
load shows an SWR of 1:1 or 1.2:1 to a decently-designed transmitter, so SWR
meters are not designed to show you that difference accurately, but it can
make a big difference in the RF voltage across the load.
You really, really need a good non-reactive 50 ohm dummy load for these
tests.
Ron AC7AC
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