[Elecraft] APF measurements: FW 4.17 vs FW4.25 revisited

[Arie Kleingeld PA3A]

All,

Measured the two FW's 4.17 and 4.25 with APF on S+N/N ratio at MDS 
again, and again.
Question was: if the filter plots are exactly the same, where does the 
measured (marginal) difference of 2 dB come from?

Found no difference this time. Seems that the XG2 drifted a bit in 
yesterdays measurements which, I think,  caused the 2dB difference 
(despite tuning the K3 on the right freq before measurement started).

Positive thing is that I could measure the improvement of S+N/N ratio 
with the APF switched on. Even with the 200Hz roofer and 50Hz DSP BW it 
adds a few dB. So for me it is a good tool for digging holes in the 
noise looking for weak signals.

73,
Arie PA3A