Thanks to Joe W4TV for recently mentioning the effect that cascading
both the DSP and roofing filters can have when the nominal WIDTH setting is
near the roofing filter BW. The following is part of a private message I
recently sent which may be of interest to others:
I chose my CW filters mainly based on bandwidth. I have 5-poles, which do
have the offset issue, but I prefer their BWs. The published specs are:
500 - 565 (mine is 549)
400 - 435
250 - 370
200 - 224 (mine is 203)
Another factor I didn't think about until recently is how the cascading
effect of the DSP filter can significantly narrow the above. With my 500
and DSP set to 600, the cascaded BW is actually 426 Hz. My 200 with DSP set
to 200 is actually 157 Hz. I feel the 500 combination is a little narrow
for contest running and it may explain why I'm sometimes surprised to find
stations calling me off-frequency that I didn't hear the first time (BTW
this was sometimes true with Orion also). I really wish there were a filter
around 700 Hz actual BW that would give me 600 cascaded. The 1k is just a
little too wide for a heavy duty contest when folks are spaced 500 Hz or
closer. Maybe the variable filters will be the answer if they don't have
IMD issues due to using varactors.
My point is to realize that the cascaded BWs may be 20-25% less than what
you think the maximum BWs are from their specs.
73, Bill W4ZV
--
View this message in context:
http://n2.nabble.com/-K3---Filter-Cascade-Effect-tp473531p473531.html
Sent from the Elecraft mailing list archive at Nabble.com.
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