[Elecraft] Filter Selection Approach

[Bill W4ZV]

For some strange reason Nabble is not attributing quotes correctly on posts sent to the main list...even though they appear correctly on the Nabble website.  Just to make sure there's no confusion as to who said what...

K2AV wrote:  

********************************************************************
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.
**********************************************************************

I responded:

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


-- 
View this message in context: http://n2.nabble.com/Filter-Selection-Approach-tp2630347p2640706.html
Sent from the Elecraft mailing list archive at Nabble.com.