Hello Jean-Marc:
Not a silly question at all. In fact, a great question.
The panadaptor is fixed at 4096 bins. Each bin is essentially a receiver
with bandwidth
equal to the sample rate divided by 4096.
Example: for a FLEX-1500, which has sample rate of 48,000 samples per
second,
the bin bandwidth is 48000/4096 = 11.7 Hz
The noise level is lower on the panadaptor, because of the lower (bin)
bandwidth.
The difference in dB relative to the "S-Meter" window can be calculated as
the log of the difference in bandwidths.
Example: The difference in noise level seen on the S-Meter, receiving
through
a CW filter of 500 Hz, and the panadaptor on a FLEX-1500 would be:
dB = 10*LOG(Bandwidth-of-Receiver / Bandwidth-of-Panadaptor-Bin)
= 10 * LOG (500/11.7) = 16.3 dB
So the panadaptor noise floor will appear to be 16 dB lower than the S Meter
value with a 500 Hz filter selected.
This only applies to noise. The level of a narrow signal (one that will fit
entirely inside
of your filter) is independent of the filter bandwidth, so the level shown
is the true level
and no correction difference applies.
--- Graham / KE9H
FlexRadio Systems
==
On Tue, Jun 28, 2011 at 11:14 AM, F1HDI <f1...@orange.fr> wrote:
> Hello,
>
> In Powersdr, how is computed the values of the noise floor across the
> spectrum in spectrum, panafall modes ?.
> To be more specific, those values relate to which bandwitdh ?.
>
>
> Kind regards
> Jean-marc F1HDI
>
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