Hi Joe, Thank you for your answer is fully clear for me now. In my side, I am currently working on a new SSTV algorithm (using the recent image compression progress) in order to improve what exists. But it will be long because I do not have much free time to work on this.
My 73, David -----Message d'origine----- De : Joe Taylor [mailto:[email protected]] Envoyé : vendredi 25 août 2017 19:16 À : WSJT software development Objet : Re: [wsjt-devel] A technical question.. Hi David, Welcome to this list! On 8/25/2017 9:20 AM, David Alloza wrote: > I would like to know how you evaluate the noise level used for the SNR > calculation, it seems to me that there are two ways to do it: > > 1> You take the average spectral power present in the spectrum > 1> received (on > 2.4Khz bandwidth) , and you compare to the power of the station received. > > It's simple, but the presence of several powerful stations will change > the result. > > 2> or you are trying to evaluate the background noise level in the > 2> spectrum > of 2.4Khz by hide the influence of the stations received, and in this > case how is this evaluation done? SNR calculations are done in somewhat different ways for each of the WSJT-X modes, but all are intended to be a close approximation to your #2. Briefly stated, we fit a "baseline" to the spectral regions in the Rx passband that do not contain signals. The spectral density of noise close to a signal's frequency is evaluated from this baseline. This value is scaled up to 2500 Hz bandwidth, and becomes the denominator in the S/N calculation. For interest: at present, calculation of SNR in the new FT8 mode comes close to the above ideal only for signals *in the clear*. SNRs for signals with nearby interference are effectively evaluated as Signal/(noise + interference) We'll do a better job in an upcoming release. -- 73, Joe, K1JT. ---------------------------------------------------------------------------- -- Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
