Experience and also literature suggests less than 100hz for SSB
bandwidth (2.2-2.8khz) and less than 1/10th the bandwidth
or >30hz for CW filters (200hz to 800hz bandwidth).
Practical filters also depend on crystal Q and series resistance
among other factors for sucess.
My experience with many published recipie design filters is if they
are just built with any crystal they will likely work but bandwidth
and passband shape will be unpredictable. Usually the passband shape
is degraded the worst. So simply matching for frequency is only one step.
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