[Elecraft] group delay distortion

[Barry N1EU]

I find that the most noticeable impact of a filter's group delay
characteristics is how they pass impulse noise, ie. lightning strike
QRN.  The poorer filters tend to turn the short impulse into longer
roaring noise.  The difference between filters can easily make the
difference in being able to pull out weak cw signals or rendering them
unreadable.

73,
Barry N1EU