On Wed, May 16, 2012 at 11:40 AM, Bob McGraw - K4TAX
<RMcGraw@blomand.net> wrote:
> Putting a narrow filter in a slot and telling the radio it is a wider filter
> is more like trying to force a cherry through a soda straw.
It might seem that way at first glance, but that's an oversimplification.
The reason it can actually be a useful technique in dsp radios is that
dsp filtering has steeper shoulders than crystal/mechanical filtering.
By setting the dsp filtering wider than the physical filtering, you
allow the more rounded shoulders of the physical filtering to dominate
in the transition zone until realizing the steeper slope of the dsp
filtering soon thereafter.
MANY serious contesters/dx'ers are doing this with the K3 (e.g., 200hz
filter set to kick in at 300hz selectivity). They want the ultimate
immunity that the narrow roofing filter provides, but they want to
stretch the passband a bit.
Barry N1EU
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