[Elecraft] K3S CW Optimization

[Jim Brown]

On 2/11/2021 4:04 PM, KE8G wrote:
> In my K3s, I have in both the main and sub receiver, filtering of 2.8, 2.1,
> 1.0, 400, & 250.  Lots of folks will say I wasted money on the filters, as
> some of them are very close in response, but again, my preference.

Those are roofing filters, designed to protect the MAIN IF filters from 
VERY strong stations close to your frequency. Those main IF filters not 
hardware filters, they are implemented in DSP, and are what vary when 
you adjust the Width/Center (for CW, RTTY) or Low-High knobs (for SSB, 
Digital).

The 1kHz filter is the only one I'd call wasted. The 2.8 filter is a 
great TX filter, because it's a lot flatter than the default 2.7 kHz 
filter. The 2.1 filter helps a lot with SSB in a contest; my ear/brain 
thinks 1.8 kHz is too narrow. The 400 Hz filter is good for RTTY and CW, 
and the 250 Hz filter helps with VERY strong CW signals in contests.

But in each case, they ADD to the primary filters in the DSP IF. When 
two filters of approximately the same bandwidth are both in the signal 
chain, they response "cascade," meaning that the two in combination have 
skirts that fall off much faster than only one of them, so their 
rejection of off-frequency signals is much greater.

73, Jim K9YC