Forgive the typo, 117 = 10 * 48000/4096 Hz. On Wed, Jun 29, 2011 at 6:48 AM, Robert McGwier <rwmcgw...@gmail.com> wrote:
> Or put another way, if the filter is 10 bins wide (117 Hz = 10*4096/48000) > the noise power in that 117 Hz is the sum of the noise lower in those ten > bins and thus should be ten times or 10 dB bigger than the noise floor. > This is what the meter reads: all the power, noise + signal, in the ten bins > of the main part of the filter. This does not account for the filter edges > perfectly but the difference is minuscule because of the tremendous shape > factor on the filter. > > Great discussion! > Bob > N4HY > On Jun 28, 2011 7:55 PM, "Graham Haddock" <gra...@flexradio.com> wrote: > > 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 > >> > >> ______________________________**_________________ > >> FlexRadio Systems Mailing List > >> FlexRadio@flex-radio.biz > >> > http://mail.flex-radio.biz/**mailman/listinfo/flexradio_**flex-radio.biz< > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz> > >> Archives: http://www.mail-archive.com/**flexradio%40flex-radio.biz/< > http://www.mail-archive.com/flexradio%40flex-radio.biz/> > >> Knowledge Base: http://kc.flexradio.com/ Homepage: > >> http://www.flexradio.com/ > >> > > _______________________________________________ > > FlexRadio Systems Mailing List > > FlexRadio@flex-radio.biz > > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > > Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > > Knowledge Base: http://kc.flexradio.com/ Homepage: > http://www.flexradio.com/ > -- Bob McGwier ARS: N4HY _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
