[Elecraft] DSP / filtering thoughts.

[Darwin, Keith]

Something bugs me about the implementation of DSP filters.  It seems
we're using DSP to duplicate crystal filters by having them do bandpass
functions.  The other thing we do with DSP is noise reduction which I
hear works best at wide bandwidths so the algorithm has some noise to
work with.

But what about other DSP things?

How about a specific CW filter that takes into account CW speed and CW
elements length along with pitch?  Imagine a filter that selects a 12
wpm signal in the presence of 15 - 20 wpm signals.  Or how about a
filter than can de-flutter a signal traveling over the north pole.  Or
maybe one that blocks strong signals!

How about a filter that corrects bad CW spacing?

Or a filter that uses the CW signal as a trigger to drive a synthesized
CW signal for virtually infinite S/N ratio!  It would be like listening
to a code practice oscillator controlled by the other op.

I guess I'm thinking that there are other filtering techniques and
approaches that could be far more novel than simple band pass or low
pass and would really set DSP apart from the tried and true crystal
filters.

- Keith KD1E - 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Solosko, Robert B
(Bob)
Sent: Tuesday, May 09, 2006 9:30 AM
To: 'elecraft at mailman.qth.net'
Subject: [Elecraft] DSP & XTAL filter settings?


Hello All,

	I just added the DSP processor to my K2 and adjusted both the
DSP and XTAL filters to the same center frequency using Spectrogram. The
DSP and XTAL filters work fine together, except that when using the
default filter settings, the DSP and XTAL filters essentially duplicate
each other and it's not obvious what the best combination of filter
settings should be and how the XTAL and DSP filters should be used in
combination, particularly for SSB.

	I found a posting from Tom Hammond from January in which he
recommends that for CW, because of the signal loss of the XTAL filters
below 200Hz, use the DSP filters below 200 Hz. and the XTAL filters
above 200 Hz. Thus, it seems that I should set the CW DSP filters to
something like 200 Hz, 100 Hz, 50 Hz and LOPASS, and the XTAL CW filters
to something like 1.5 kHz, 1.0 kHz, 700 Hz and 400 Hz.  Then, when I
want the wider bandwidth, I'd use one of the XTAL filters with the DSP
filter set to LOPASS, and when I want the narrower bandwidth, I'd use
one of the DSP filters (and since the XTAL filters all would have wider
bandwidths, it wouldn't make any difference which XTAL filter is
selected).

	That seems like a reasonable approach to the DSP and XTAL filter
settings and combinations on CW. (Comments?)

	However, I have no idea how to set up the DSP and XTAL filters
and what filter combinations to use for SSB. It seems to be a waste of
the K2 capabilities just to have the DSP and XTAL SSB filters
essentially duplicate each other, as their default settings seem to do.
So, is there some optimum way to setup the DSP and XTAL filters and use
them in combination for SSB that makes best use of the K2 capabilities?

	Thanks for any advice and suggestions that you can give me.


Bob Solosko
W1SRB
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