Re: K3 Filter Ring with Noise?
Posted by
Brett Howard on
Aug 09, 2009; 7:58pm
URL: http://elecraft.85.s1.nabble.com/K3-Filter-Ring-with-Noise-tp3410069p3413930.html
At the moment I need things fairly quiet to be able to copy well so for
now narrow filters are the cats meow for me but maybe someday I'll
graduate to wider filters. I prefer the sound of wider but... for me
narrow aids in copy for me.
~Brett
On Sun, 2009-08-09 at 07:31 -0700, Ron D'Eau Claire wrote:
> 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.
>
> ----------------------------------
>
> 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
>
>
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