[Elecraft] K2 filter attenuation

[Vic Rosenthal]

Earl, K6SE wrote:

> 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... 

Ron D'Eau Claire wrote:
> 
> 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. 

As a CW DXer, I've been following the comments of Ron and Earl with great
interest.  I used to be 100 percent in Earl's camp, thinking that it was always
better to use as much selectivity as possible on weak signals.  Lately I've been
coming over to Ron's side.  There are a lot of posssible issues here, such as 

1) The characteristics of the interfering noise -- atmospherics, powerline
noise, RF burbles, computer noise, ad. inf.

2) The shape of the filter.

3) Other receiver characteristics, perhaps in the audio and AGC sections.

4) The operator.

For what it's worth, I've moved into the 'low selectivity' camp pretty much
since I've been using my K2 regularly.  Before that I used a TS850 with cascaded
400 Hz Inrad filters with the passband narrowed to about 200 Hz most of the time
-- and I often switched in an outboard DSP or SCAF filter.  Now the outboard
filters are disconnected, I have my K2 set to 1.4 KHz and reduce it only for
QRM, and I rarely use the K2 audio filter.  I'm not sure what's changed.

Vic K2VCO