[Elecraft] K2 filter attenuation

[k6se@juno.com]

Ron, AC7AC wrote:

"Sometimes I can read a very weak signal better at wider bandwidths, even
with some QRM. That's because of what the filter does to the background
noise.

When the band noise encounters a narrow filter, individual spikes of
noise get stretched out - made broader. That's a normal consequence of
any filter and it shows up dramatically in a narrow filter. It also
happens to the signal itself on the on/off transitions at the end of each
dit and dah. That makes the transitions at the end of every dit and dah
less clear. The combination can make a weak signal much harder to copy at
a narrow bandwidth than it is with a wider bandwidth.

The total effect is to make the signal sound weaker in relation to the
noise and, unless he is sending quite slowly, makes the CW a little
harder to copy even without the extra noise because the code element
spacing has been shortened and less distinct."
==========
I "specialize" in weak signal DXing on 160m CW (the 2nd on the west coast
to achieve 160m DXCC, 55th in the world - now at 182 countires on 160m),
and I have never run into the phenomenon that Ron talks about (and there
is a LOT of "band" noise there!).

Simply because a narrow CW filter provides an appreciable improvement in
the S/N ratio of the receiver, the narrower filter ALWAYS makes copy of
the weak signal better (even with the K2, as long as the temperature is
such that the signal is centered in the narrow filter passband).

NEVER have I been able to copy a weak CW signal better with a wide filter
than with a narrow filter.  The opposite has ALWAYS been true while using
many different receivers over many years.

BTW, "ringing" when using a narrow filter is no problem if you have your
receiver adjusted to listen to a low-pitched tone (400 Hz or less). 
Those who complain of "ringing" invariably are listening to a
significantly higher tone.  The lower pitch also helps to "filter out"
high-pitched band noise and IF noise (as well as the "ringing").

If the DX station sends very slowly, this tends to make copy more
difficult due to QRN and QSB.  Most 160m DXers prefer to use around 20
WPM for DX contacts.

Perhaps Ron runs his receiver with the AGC turned on while listening to
weak CW signals.  In that case, a loud static crash would obliterate
reception until the AGC decayed.  With the AGC turned off, this would not
happen.

73, de Earl, K6SE