That makes total sense, because when I drop the signal to lower values the behaviour disappear but this again reduce my available dynamic range :( I'm going to check every stage looking where the system saturates. Thanks for the idea!
El vie., 6 sept. 2019 a las 0:43, Ross Martin (<ross.mar...@ieee.org>) escribió: > Sebastian, > > It looks like maybe you're using a channelizer size of around 1000. For a > 1000-point channelizer, if you have one sample that overflows in the > channelizer filter, that will act like a source of impulse noise, which is > a constant function across all spectral bins. Furthermore, the amplitude > of the impulse could be approximately full scale, but in only a single > sample. In that case its average power would be about 1/1000. When this > power is put into the spectral domain it's spread evenly across all 1000 > frequencies, and the power in a single frequency bin is approximately > 1/1000/1000. That's about -60dB, which is close to the error level you're > seeing. > > So I'll bet your problem is overflow. If so, reducing the amplitude of > your sine wave by a factor of 4 should certainly fix it. A factor of 2 will > also probably work. > > Ross > r...@bitbybitsp.com > > > On Wed, Sep 4, 2019, 10:52 AM Dan Werthimer <d...@ssl.berkeley.edu> wrote: > >> >> the snr increases with sqr(number of samples added), >> and that increase can be from decimation or adding spectra together >> (integration), or better yet, both. >> but if you don't have noise, the quantization and interleave spurs will >> not improve with sqr(Nsamples). >> >> best wishes, >> >> dan >> >> >> On Wed, Sep 4, 2019 at 12:47 PM Sebastian Antonio Jorquera Tapia < >> sebastian.jorqu...@ug.uchile.cl> wrote: >> >>> One question, at my understanding if I use a filter to decimate I'm ,in >>> a certain way, adding all the samples using the filter for the decimation, >>> like averaging with the appropriate weights for one frequency range. So >>> the decimation filter should interpret the same role as the accumulation >>> you mention. >>> >>> Aside from that, I have a throughput requirement so I can't add a lot of >>> samples... The dithering you mention only works with a proper accumulation >>> right? because I tried to add noise to my system and didn't see a >>> difference. >>> >>> >>> El mié., 4 sept. 2019 a las 14:14, Dan Werthimer (<d...@ssl.berkeley.edu>) >>> escribió: >>> >>>> >>>> you can get extremely high SNR if you add noise to your sine wave >>>> signal. >>>> and then integrate many spectra together to beat down the noise. >>>> to get rid of ADC quantization noise and other spurs, >>>> you should have noise at least at the one LSB level, better if you have >>>> two LSB's of noise. >>>> then you can get 150 dB SNR if you add enough spectra together. >>>> >>>> dan >>>> >>>> >>>> Dan Werthimer >>>> Marilyn and Watson Alberts Chair >>>> Astronomy Dept and Space Sciences Lab >>>> University of California, Berkeley >>>> >>>> >>>> On Wed, Sep 4, 2019 at 10:39 AM Sebastian Antonio Jorquera Tapia < >>>> sebastian.jorqu...@ug.uchile.cl> wrote: >>>> >>>>> Hi casperites, >>>>> I have been working in project that needs a high SNR In order to >>>>> achieve that I made a model with 3 decimation steps with factors 16, 8 and >>>>> 4, to zooming the frequency range [50.625, 52.730]MHz and then put the >>>>> PFB-FFT combo. >>>>> The system achieve 100dB of SNR for inputs with the same frequencies >>>>> of the FFT twiddle factors, but outside those frequencies the noise floor >>>>> goes up 50dB in the worst cases, which is when the signal is between two >>>>> bins. >>>>> I am using the 8 bit aasia ADC, so the SNR without any further >>>>> processing should de 48 dB approx, so in the bad cases we loose the >>>>> improvement due decimation. >>>>> I attached the pictures of the response in the best and in the worst >>>>> case. >>>>> >>>>> There is a limitation in the amount of decimation that one could make >>>>> tho improve the SNR?? Or I am missing some assumption of the improvement >>>>> due decimation that I am not meeting? >>>>> Has anybody faced a similar problem? >>>>> >>>>> >>>>> Cheers! >>>>> >>>>> [image: worst_response.png] >>>>> >>>>> >>>>> [image: best_response.png] >>>>> >>>>> >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "casper@lists.berkeley.edu" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to casper+unsubscr...@lists.berkeley.edu. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/93a6ec1c-7a2e-46de-9d6d-2ea460c9570a%40lists.berkeley.edu >>>>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/93a6ec1c-7a2e-46de-9d6d-2ea460c9570a%40lists.berkeley.edu?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "casper@lists.berkeley.edu" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to casper+unsubscr...@lists.berkeley.edu. >>>> To view this discussion on the web visit >>>> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFFKY2Xysw-B1A0eA9vhvXDvLkn9FEByUPVaMjb33EMOQ%40mail.gmail.com >>>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFFKY2Xysw-B1A0eA9vhvXDvLkn9FEByUPVaMjb33EMOQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "casper@lists.berkeley.edu" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to casper+unsubscr...@lists.berkeley.edu. >>> To view this discussion on the web visit >>> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAASoV%3DMTXOV11tYDZwRG23c%2BNcBiTYCPPZ9Rzoy8z0t93WupvA%40mail.gmail.com >>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAASoV%3DMTXOV11tYDZwRG23c%2BNcBiTYCPPZ9Rzoy8z0t93WupvA%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "casper@lists.berkeley.edu" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to casper+unsubscr...@lists.berkeley.edu. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFXTXRVqEFGgLL8vLkLhahwS6s59Lk2A5MOxHqzbuAj9Q%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFXTXRVqEFGgLL8vLkLhahwS6s59Lk2A5MOxHqzbuAj9Q%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG4nf70iUdnPfTzNgfjo%2BpKp-7G08xenn_%3DSTYzEOnRNpETLuQ%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG4nf70iUdnPfTzNgfjo%2BpKp-7G08xenn_%3DSTYzEOnRNpETLuQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. 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