Mike,
STRENGTH vs External power meter (Daiwa) (output to 50ohm load)
Smeter readings are not accurate since these are discrete dots not continuous:
For S1 through S9 the linear (r=0.999) relationship is:
Strength = 5.4 n - 48.2 where n is S meter. From this, difference between S1
and S2, for instance, is 5.4 not 6 as one might expect for Smeter reading power.
Strength between S9 and S9+20 = 18
S9+20 and S9+40 = 18 and not 20.
In both cases delta-Sreading is low.
It appears that S meter is calibrated to 6dB per unit as you thought, which is
what I expect for Smeter power.
Since Strength is evidently on a log scale (dB), plot Strength vs log power:
linear (r=0.96) relationship: Strength = 52.7 log (power) - 76.5
Now, if I change HamlibTransceiver.cpp as:
// strength.i = pow(10,(strength.i-30-107)/10.0);
strength.i = pow(10,(strength.i + 76.5)/52.7);
then I get a sensible answer. There are obvious inaccuracies here, not least
the measurement of power from the Daiwa meter - all I have at the moment. But
basically this works. Power on your meter also changes when I alter RFPOWER
with L RFPOWER 0.25, for instance. How this fits in with the service manual
on the Smeter and the meaning of "Strength" returned from hamlib is something
you will no doubt have a look at.
--- John G4KLA
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