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
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