Greetings:

I would appreciate advice on features desirable in a DSP audio
processor unit. I have no experience with any modern DSP-equipped
rigs and my older radios only have simple xtal filters and IF
phasing controls. I never had a useful CW filter on anything
(my SB300's 400 Hz filter was broken). At a minimum I suspect
that a variable parameter narrow filter, sliding notch, denoiser,
autonotch and selectable preset filters would be useful, together
with onboard decoding of various digital modes.

My DSP processor adjunct to my homebrew receiver is documented at

http://www.cybertheque.org/homebrew/rcvr/dsp.

It is online for listening according to procedures described on
the site. At the time of this posting, the receiver is tuned to a
nearby non-directional beacon on 335 kHz (ID is COQ) which ordinarily
is un-copyable at this QTH due to extreme noise on the bands
below 500 kHz. Using the very narrow filter described on the site,
the signal is quite clean. Another reliable CW source without
a lot of noise is KA0PSE's beacon on 28218 kHz. Please listen
to the wav file of a snipit of a recent 80m CW QSO between N1DZ
and PK1VH which was heard in the late evening when 80m is
usually closed and very noisy around here (the link is on the
page). Not having been active on CW for a long time and never
having had benefit of filters, I felt this was eminently copyable,
but I would appreciate the advice of others who are active.
People have complained in general about 'ringing' or click artifacts
in narrow filters; I hear the spectral components of the background
noise at this filter's center frequency, but I don't think
there is ringing and certainly there are no clicks.

Incidentally, there is a touching description from N1DZ of his
grandfather's radio activity in Java during the 1930's at:

hamgallery.com/qsl/deleted/Java/pk1vh.htm+n1dz+maarten&hl=en&ct=clnk&cd=14&gl=us

This narrow filter represents a maximal implementation of a FIR
framework within the memory constraints of the platform (4k Data space);
only one-half of the available MIPS are used however, which permits
the addition of adaptive control algorithms or additional tasks such
as demodulation of digital modes while employing this filter's framework.
Note that I've coded for the base level of implementation of this
technology; more well-equipped MWave DSP cards have up to 64 kB of data
space. I've written this filter in the assembly language of the DSP
and all processing is done onboard; the host only handles control
and status with the outside and serves coefficient and control-data
sets to the DSP tasks. The only latency between input and output is
the 726 uS needed to pre-roll the input circular buffer.

ALSO:

I would appreciate hearing experiences with PC-based DSP software,
including the package name, system details (speed, o/s, etc.), and comments
on usefulness, stability, etc. I have yet to find a useful PC-based DSP
program that will run on hardware that I own ( 1Ghz, mostly 400 - 600 Mhz PII/PIII)
except for a German collection of FIR filters, which have a long output latency,
or the DSP Blaster on DOS using a Soundblaster card. I have tried perhaps
a half-dozen programs, some open source, some proprietary, and all have either
crashed the O/S (mostly Win2k, or Win95/98 since the majority of programs
are written for them), run out of resources (CPU), have terrible broken audio,
have huge footprints, use unmanageable installers, require a bunch of
MS installs (MSIE, DirectX, database APIs, COM, .NET, etc., etc.) or are
otherwise unfriendly. I realize that DSP on a general purpose CPU is going to
be resource intensive but with MMX and SIMD it should be doable on PII/PIII.
This is really for edification only since I don't intend to use a standard PC
for DSP except for testing and evaluation.

Please let me know what you find most useful and necessary in a DSP unit for
radio work; I hope to have the remote interface running within a month or so
and will then need to add additional filters and demodulators. The entire
project will be documented on the site and source code and binaries will
be available.

Regards,

Michael