On 11/3/2011 12:29 PM, Leif Asbrink wrote:
I think commercial applications need a reasonable S/N to start with -
and as amateurs we would then be able to copy without DSP
assistance... 73 Leif / SM5BSZ
Yes. I have used many rigs, including some high-end ones and several
external DSP units, and have yet to find one that can make a weak signal
more readable. This is mostly in the field of VHF+ dxing, but should be
relevant elsewhere.
The signals I am talking about are at or just below the noise level.
Once the signal is +3dB or better then NR can make it more pleasant to
copy because I find it less fatiguing, but it certainly would be
copyable anyway.
I don't think the FLEX system is any better or worse in this regard, as
it is a fundamental limit to signal processing.
A way of approaching it is to match the detection method with the known
characteristics of the signal. For CW that means selecting the proper
bandwidth, and the PSDR does a really good job with it's narrow filters.
For digital modes, such as PSK31 and JT65, the signal structure is known
and the decoding method can get significant processing gain so that the
raw signal can be well under the noise.
I wonder if some of the confusion may be between the different types of
'noise'. The wideband thermal type is what NR is intended to reduce,
while pulse type QRN would be handled by the NB. The later can be
handled quite well with the right approach. I have read your excellent
papers on that topic.
73 Alf NU8I
Scottsdale AZ DM43an
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