The most important thing is where are the skirts halfway down and how much more
do they drop with another 10 Hz, NOT the 3 db or 6 db points. The 8 pole
roofers are part of making those skirts dive more in 10 Hz halfway down.
I set up my filters at the +/- 50 dB points, and eagerly await the day when CW
widths and shifts are in 10 Hz increments.
I have had some extremely vociferous contradictions from some insisting that
the 8 pole roofers are simply a waste, and a wide and narrow 5 pole are all
needed, but my contest experience continues to suggest otherwise.
All of the above are in stark contrast to casual operation. Buy filters for
how you use the radio. If you are into hard contesting, do it with 8 poles.
The DSP filter is the driving factor in making the skirts steep, especially
when you're below the 435 Hz BW of the "400" or the 370 Hz BW of the "250",
since there would be little cascading effect there. See K8ZOA's plot for the
"500 Hz 5-pole CW/Data Filter" section about half way down this page:
http://tinyurl.com/dho6j6
You can see the shape of the XFIL itself when looking at the DSP = 4000 trace
(i.e. when the DSP is >> in width than the XFIL). If DSP is about the same as
the XFIL (i.e. WIDTH = ~430 for the "400" or WIDTH = ~370 for the "250"), then
there is some help. If the DSP is inside the flat area of the XFIL, there is
little contribution from the XFIL skirts.
73, Bill
--
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