Re: RE: How do you measure filter offset
Posted by
W8JI on
Aug 19, 2008; 11:31pm
URL: http://elecraft.85.s1.nabble.com/How-do-you-measure-filter-offset-tp733034p734433.html
> 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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