KK7P:
>With the IF DSP in the K3, the issues that are
of concern in a fully analog radio are less important.
>As long as the crystal filter, which is being
used as a roofing filter, has reasonably good
skirts and ultimate rejection, the DSP will take
care of the rest. The first 20 dB or so of skirt
selectivity, the passband ripple, and the
ultimate rejection at the DSP IF image frequency are the most critical factors.
Below W2VJN (ex-Inrad) says the first ~30 dB of
skirt selectivity is key for IMD issues. It will be important
for you to specify actual IMD and BDR performance with
each of the various CW filters installed. So far I count 4
that are 500 Hz or less, not counting the variable BW
option. I hope you can post this information soon so
that those planning to order will have information to
properly configure a unit.
73, Bill W4ZV
http://www.qth.com/inrad/roofing-filters.pdf (page 6)
5. If 6 poles work so well, why not 8 poles?
The most important part of the filter
characteristic is from the pass-band on down
to about 30 dB on either side of center. Eight poles would provide much better
stop-band isolation, but its not required in a
roofing filter and would make no
noticeable improvement in IMD performance.
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