[Elecraft] K2 filter attenuation

[Ron D'Eau Claire]

Earl, K6SE wrote:

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.
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No, I typically listen with AGC off and manage the gain using the "RF"
gain control. 

Probably the largest issue in the design of filters for receivers since
they were first explored almost a century ago is the issue of their
effect on many types of noise with sharp rise and fall times. Many of
the names given various filter designs are the names of engineers who
investigated the relative benefits of various shapes of filter response
on signals. In general, the sharper the edge on a filter, the greater
the effect on noise with high-frequency rise and fall times that
produces more overall noise within the filter bandpass, but a meaningful
analysis is the stuff of much research and complex mathematical
modeling. 

In GENERAL, narrower bandwidths means a better signal-to-noise ratio.
But when getting down into the signals that are in the noise, it is
unlikely that anyone has built a filter that can compete with a
well-trained human brain and ears. It is in that "twilight" zone that
narrower is not always better. Often the brain can do better with a less
highly filtered signal, in my experience. That's based on 50 years of
digging signals "out of the mud" as a commercial radiotelegraph operator
and as a radio amateur. 

Something else that experience has taught me is that no two operators
approach a problem in exactly the same way. What seems to work better
for one operator doesn't work as well for another. The technique varies
just like any other expression of personal skills. I didn't bring this
up to argue technique or to say that only one way of doing things is
"right" and others are "wrong". I only made the suggestion because Colin
reported that signals sounded weaker when his filters were narrow, and
it was my experience that can be due to the way the filter reacts in the
presence of certain noise when listening to very weak signals. 

Ron AC7AC
K2 # 1289