It actually doesn't matter beyond about 30 dB down
ina roofing
filter...the DSP filters handle things beyond that.
Two points are entirely
sufficient to **center** the filter's 6 dB bandwidth,
which was the
question
asked.
I don't think -6dB bandwidth was the question, but rather
how to measure the
filter. Whatever -- a single number description is quite
limited.
If I wanted to center and match a typical SSB or CW filter
for passband centering, I'd use something like 5 or 10 dB.
I wouldn't match them at a higher attenuation because it
really doesn't mean anything and can be very misleading and
cause the actual useful centers to be misaligned.
It really should just be at some attenuation that is much
greater than the ripple amount, but not so far down on the
skirt it is meaningless for the actual passband.
73 Tom
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