When I first started with DSP on my IC-765, I *could* copy signals with
the original Timewave DSP-9 that I couldn't copy without it. This was
with or without the ICOM 500 Hz filters cascaded. It would take the
signal from uncopyable to marginally copyable. (I have cards from
several of these, so they weren't phantoms! I've had those QSO's too,
but that's another story.) When I upgraded my DSP to a JPS NIR-12, the
effect was more noticeable, but not a lot more. There is only so much
you can do when you're working on audio at the end of a long multistage
conversion process. IF DSP holds some hope, although none of the current
implementations have proven it to be head and shoulders over the better
audio DSP's. When I purchased my Omni VI+ about 1.5 years ago, I put the
NIR-12 on the shelf and have yet to plug it in to see how it compares to
the VI+ DSP. Better, the TenTec 250 Hz filter does a nice job of noise
reduction as a side benefit. I've been so pleased with the VI+ that I
haven't bothered comparing DSP's.
So, back to your question - I think your old design points are the same -
concentrate on low noise figure preamps and conversion amp stages, preamp
and/or convert at the antenna end of the downlead coax, and use good
design practice. Your improved IF rig will only add to that!
73, Duane AC5AA
Duane A. Calvin, AC5AA
Austin, Texas
ac5aa@juno.com -or- ac5aa@earthlink.net
Day: dacalvin@us.ibm.com
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