AA2IZ wrote:
However narrow the bandwidth, there is still a mixture of noise and signal
left inside the pass band. Furthermore, properly implemented algorithms can
identify much of this noise and eliminate it. This is done by digitizing
the signal, then doing Digital Signal Processing (DSP) such as looking for
correlations for example (there are other methods)...then retaining that
portion of the digital content and actually deleting the noise portion.
Then we go from digital back to analog, and you have the de-noised signal.
This takes a lot of processing. That is why only the military can afford to
do it directly on HF frequency signals. So we do it at audio signals - like
the 14 khz stage of the Orion. They call it IF DSP, because its before the
detector, but 14 kilohertz is an audio frequency no matter what we call it.
Bottom line - this should work very well. If done well, it will outperform
bandwidth reduction alone. Timewave does a great job of this in their add
on boxes. I've used really expensive equipment at work to do it at much
higher frequencies.
All of the above is true (maybe with exception to Timewave).
The problem is that all of the above takes a LOT of processing
which adds a LOT of latency (i.e. delay before the CPU is done
processing). Short of having a Cray computer, there is simply
NO WAY any so-called DSP rig (IC-7800 included) can do real noise
reduction (i.e. not simply BW reduction) without at the same time
dramatically increasing latency (e.g. Linrad adds 6-7 seconds
using much faster CPU's than in any rig CPU).
Bottom line - If you see a QSK rig claim to have DSP
Noise Reduction, it is little more than a fancy name for
noise bandwidth reduction. Anything else simply does not
compute (pun intended).
73, Bill W4ZV
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