[hpsdr] Further Observations on the PowerSDR Noise Blanking Process

[Mike F]

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