[Discuss-gnuradio] QT Freqency Sink vs. Log Power FFT values

[John Ackermann N8UR]

I'm doing a simple flowgraph to determine the peak value (dBFS) within 
an FFT.  The Log Power FFT sends vectors to a Max block which outputs 
the result -- it seems to be working reasonably well.

I also have a QT Frequency Sink as eye candy, and notice that its 
display is about 6dB different than the Log Power FFT output.  I can 
think of a number of reasons why that could be, but my simple question 
is... is there an appropriate way to adjust one or the other to align 
their readings?  (Later I'll send the log power results into a 
calibration routine to convert to dBm based on measured results.)

Also while I'm at it, there's a "Reference Scale" parameter in the Log 
Power FFT, set by default to "2".  Is there a way to use this parameter 
to align the two readings?  I tried changing it to "1" but that threw an 
error at runtime.

Also, there doesn't appear to be any window applied (or at least 
apparent) in the Log Power FFT block.  Is there a way to window the output?

Thanks,
John