[hpsdr] Further Observations on the PowerSDR Noise Blanking Process

[David McQuate]

Mike,
   Your surmise is correct.  Noise blanking is performed before the 
bandwidth filters are applied.  This is the same order as is usually 
done in analog radios.  In reducing the bandwidth, the filters slow the 
rise & fall times of the signal, "smearing out" noise impulses, making 
them harder to remove.  And yes, noise processing is usually done in the 
time domain.
73,
Dave
wa8ywq


On 4/19/2011 8:04 AM, Mike F wrote:
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>
> I made a posting couple of weeks ago on a noise floor phenomena where 
> the noise floor across the displayed band varied up and down with the 
> presence or absence of strong in-band signals.  Phil Harman explained 
> that it had to do with the NB and NB2 functions in PowerSDR.  At that 
> time I had it in mind that these functions might be making the noise 
> worse.
>
> Recently the noise floor has been quite high at my QTH (S5) and I have 
> determined the following.
>
> As I turn the NB and NB2 functions on, the noise floor drops 
> significantly.  When a strong signal within the band increases 
> amplitude the noise floor noticeably increases, dropping when the 
> signal decreases or goes away.  I don't believe that the noise floor 
> ever gets as high as it is without the NB-NB2 functions turned on, but 
> it does vary.
>
> Based on these observations I would surmise that the noise blanking is 
> applied to the whole 192kHz (in my case) bandwidth (as a time domain 
> function???) and if there is a significantly large signal within the 
> band, the blanking threshold/algorithm becomes less sensitive to the 
> lower amplitudes.
>
> Can anyone out there confirm or deny my suppositions?
>
> Thanks.
>
> Mike Fager, K7SR
>
>
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