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

[Bill W4ZV]

PA3A wrote:

> 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).

Measurements don't lie when done properly.  I should have thought about
drift since peaking APF is so critical.

I believe the lesson to be learned is to not blame the APF if it doesn't
work like our memories think it did previously.  Look elsewhere for other
reasons...such as:

1.  The character of the noise (atmospheric vs galactic).
2.  Operator error (gain and/or bandwidth settings, tuning errors, etc).

Human nature is to blame anything but ourselves.  
http://www.igopogo.com/we_have_met.htm

> 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.

Yes it definitely helps.  Conditions on 160 were excellent last night so
hopefully they will hold for the contest.  RV9CX, UA9MA and 4L/UT5EO were
all worked with decent signals.  I also heard UN5J in deep Central Asia
(near the BY border) for the first time since 1997!

73,  Bill


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