[Elecraft] K3 Filter Ring with Noise?

[Ron D'Eau Claire]

Brett wrote:
I'd never had a rig capable of going lower than 500Hz till I got the K3
and really found myself quite annoyed at times when the noise was high
and I really necked the filter down.  

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You've discovered exactly why many of us avoid narrow filters whenever
possible. Our brains are much better at recognizing a CW signal in broadband
noise than in narrow-band noise. The same is true for digital noise
reduction. 

At very narrow bandwidths the filter also modifies the CW signal, softening
the keying to make it sound more and more like noise rather than a keyed
signal. Both the tx at the far end and your receiver must allow enough of
the CW sidebands through to hear clean, sharp keying transitions. That takes
some reasonable bandwidth. The faster the CW the more bandwidth is needed.
Some people don't want to hear any keying transitions (what, when excessive,
we call "clicks") at all only a few Hz from the carrier, but that really
compromises readability. Our brains hear those sidebands and help us detect
the signal from the noise, and the sidebands must be passed through your
receive filter. 

The first step to using wider bandwidths is to learn to copy CW when other
signals are present, just like learning to listen to one conversation in a
crowded room even though you can hear others talking all around you.

When another signal within the passband is sufficiently loud to be a serious
distraction, sort of like trying to hear a quiet voice with someone else
shouting in your ear, a notch filter is preferred over narrowing the
bandwidth. All the notch need to is reduce the offendingly-loud signal
enough to make it less troublesome. Poking a narrow 'hole' in the noise
doesn't cause the problems a narrow filter does.

Optionally, you can often tune the rx off frequency just a bit to push a
'loudmouth' off the edge of the filter bandpass while keeping the desired
signal within the bandpass. 

It takes practice, but it's a skill worth having on a crowded band. Probably
90% of my brass pounding is done at a bandwidth of 1 kHz or wider.

Ron AC7AC