[hpsdr] HPSDR transverter fonction

[Joe Martin]

Hi Dom, 

The RA  option uses as input for the signal levels the same wdsp routine as the S-meter.  Therefore the RA routine and S-meter should read the same values but may in some cases read differently from the panadapter display levels.  As Warren NR0V has explained numerous times on this reflector because this question seems to frequently arise, the indicated baseline noise level shown in the pan adapter displays may differ from the S-meter readings due to the fact that the S-meter reads the the noise power within the width of the bandpass filter you have happen to have selected within the sampled spectrum whereas the highlighted pixels of the panadapter display show the noise power within each individual frequency bin within the entire sampled spectrum.  Here is the text of the message that Warren posted on June 12, 2017 regarding the S-meter readings and how they are calculated:

> …excerpt from Warren NR0V June 12, 2017 message….
> "Sig Avg" is the correct S-meter setting to read noise.  "Signal" gives you a peak reading (appropriate for signals) while "Sig Avg" gives you an average reading.
> 
> The S-meter reads the noise power within the width of the bandpass filter, 1.5Khz in your example.  The panadapter shows the noise power within each frequency "bin".  The width (bandwidth) of the bin is displayed on the Setup/Display/RXx tabs.  To correctly read noise on the panadapter, you should choose the "Average" detector and either "None" or "Recursive" as your averaging mode.  If the "1Hz BW" box is checked, the result displayed on the panadapter will be normalized to a 1 Hz bandwidth.  The noise readings of the S-meter and the panadapter are therefore related by the equation:
> 
> S_reading = Panadapter_reading + 10*log10 (bandpass_width / panadapter_bin_width)
> 
> I realize all that is a bit complicated.  However, if you master the various settings, your SDR is an excellent spectrum analyzer for accurately measuring both signals and noise.
> 
> 73,
> 
> Warren  NR0V
> 
>> 
I’m not sure if this answers your question adequately or not but in any case I hope reiterating this information helps you understand something about how the RA option signal levels and S-meter readings are derived, as those calculations differ from those used for the panadapter and waterfall display pixel positions. 

73, Joe K5SO

> On Nov 20, 2017, at 12:11 PM, Dominique Dehays <f6dro at wanadoo.fr> wrote:
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> 
> Hello ,
> 
> 
> I have a question :
> When I am in the transverter settings screen , and I vary the RX gain using this setting there , I can see the noise floor moving on the spectrum screen , and I can see the waterfall colour changing. But when I go on the R.A. screen , there is no difference in the noise level , I don't think it is normal , Am I wrong?
> 73
> Dom
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