Phase noise is *not* the problem/solution being discussed.
It is the phase *shift* through the filter. That is signals (within the
passband) of one frequency are not delayed by exactly the same amount of
time as signals of another frequency. That is a different 'animal' than
phase noise.
All filters will have some phase shift. but the better filters will have
minimal phase shift within the flat portion of the passband. As you get
closer to the slope (edges) of the passband, the phase will shift
rapidly as the frequency changes.
The point is - to avoid large phase shift distortion, keep the filter
width as wide as possible given consideration for reducing large signals
by shifting the filter or otherwise moving the offending signal outside
the passband.
Yes, there is often a compromise that must be made in the real world of
operating.
73,
Don W3FPR
On 4/21/2014 3:25 PM, N7RJN wrote:
Phase noise is an issue, however, adjacent signals in the filter passband
seem to have more of an impact on the ability to decode weak signals than
the phase noise associated with narrower filters. I have been able to
decode weak DX stations with 400Hz and even 250Hz filters that I could not
decode at all with wider filters.
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