RE: [linrad] noise blanking comparisons

["Leif Åsbrink" <SMTP:LEIF.ASBRINK@xxxxxxxxxxxxxxxx>]

Hi Jim and All,

> From what I have seen, one thing that is normally incorporated in an SSB
> noise blanker is AGC. This tends to decrease distortion on strong 
> signals.
Yes, this is included in Linrad if you set the blanker in mode auto.
It will remove the distortion on strong signals but it may degrade
blanker performance slightly for weak signals.

> A more advanced way I have seen and done myself is to sample 
> the linenoise from a passband close in frequency to the SSB 
> signal, but the passband does not include
> the SSB signal. In my implementation of this technic, some 
> distortion still
> resulted on the SSB signal from intense line noise, but overall it was an
> improvement. No doubt, my blanking gates and/or pulse timing was less then
> perfect.
Linrad uses a compromise. It is far better than what you suggest here
for weak signals. SSB or CW does not matter. To do it "properly" I would
need a 3GHz PentiumIV - something for the future:)

To actually explain what the problems are is a long story but it is
related to the use of 16bit MMX instructions for FFTs. I would have 
to do everything in floating point (or 32 bit integers) to get rid
of the problems and get a straighter and easier to understand 
noise suppression routine.

73

Leif



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