[hpsdr] Frequency Calibration in PowerSDR?

[n3evl]

I noticed the other day (when setting up PowerSDR 1.19.3 for the first 
time) that the frequency calibration was a little off (about a couple of 
hundred hertz: enough to make SSB signals sound off-frequency, for 
example when tuning to the nearest 1KHz or 500Hz).

I did some comparisons against my SDR-1000 using on-air signals, 
including WWV and also using my Elecraft XG1 at a nominal 7040 KHz.  In 
all cases the SDR-1000 seemed to be spot-on whereas Mercury seemed to be 
off as described above.

I am using Excalibur and have performed the slight adjustment (using WWV 
or the XG1) to the on-board Osc using the Phase display technique to get 
minimum rotation of the pattern so I think Excalibur is ok.  I don't 
have any external input to Excalibur.

I  was able to correct the apparent error by, for example, tuning to WWV 
at 10 or 15MHz and running the PowerSDR Freq. Calibration.  I did this 
by tuning the signal to coincide with the red line in the center of the 
panadapter display and running the calibration.  The peak of the 
as-tuned signal now appears to line up correctly with the nominal 
frequency red line.

I guess my question is: is this PowerSDR correction normally necessary 
with HPSDR Mercury/Excalibur as described?  If not, is there something 
amiss with my HPSDR hardware to cause this frequency error?

Pete, N3EVL