[Elecraft] K3S DSP filter plots

[Guy Olinger K2AV]

Hi Charles,

You mention "interaction" as if it were some phenomenon to be avoided. In
the K3 the roofing filter is in the analog 8 MHz IF and the DSP filter is
program code working on the number soup somewhere after the RX analog to
digital signal conversion.

The only "interaction" possible is the sum of the two pass band losses at a
given frequency for the two filter bandwidths chosen.

Speaking particularly of CW contest operation there is a good deal useful
to be said for aligning the -15 dB points on both slopes to create the
narrowest -30 dB points when the actual roofing and DSP bandwidths are set
the same. One might term this a *desired maximum* "interaction" (sum) of
the two filters.

This results in operating bandwidths of 450 and 350 Hz using the "400" and
"250" filters respectively for the most abrupt combined skirts.

When running (calling CQ and listening for answers) in a contest one needs
to listen up and down a little because we get answers to our CQ's not zero
beat. We need to hear that bandwidth well and then have the combined filter
skirts drop off as steeply as possible beyond. This is because as
routinely experienced the next running station up or down frequency can be
obscenely loud.

The combination of roofing and DSP filter skirts is the only defense
against loud adjacent signals which are routinely up and down 500 Hz and as
close as 300 Hz.

When there are nearby clicky signals, the sharp combined skirt drop results
in a reduced amplitude sharper click which the K3 noise blanker handles
well set to DSP 2-7 and IF off.

These very positive K3 behaviors are very well known among serious CW
contest operators and one of the reasons for its high popularity in this
group.

73, Guy K2AV

On Monday, November 16, 2015, <charles at k5ua.com> wrote:

>
>
> Although Elecraft has documented the response curves of their 5 and 8
> pole roofing filters, I can't find any plots of their narrow DSP CW
> filters, like the 50, 100, 150 or 200 hz filters. Does anyone have
> Elecraft published plots of the narrow CW DSP filters, or has anyone use
> a signal generator to plot out their own response curves. It would be
> nice to know the DSP filter shape factors of the various narrow CW DSP
> filters to superimpose on top of the plots of the roofing filters. It
> would help me decide on which roofing filters to get since the roofing
> filters will determine how much IF shift can be achieved before the
> filter skirts of the DSP filters interact with the filter skirts of the
> fixed roofing filters.
>
> Charles K5UA
>
>
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