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 [email protected] On Wed, Sep 4, 2019, 10:52 AM Dan Werthimer <[email protected]> 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 < > [email protected]> 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 (<[email protected]>) >> 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 < >>> [email protected]> 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 "[email protected]" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> 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 "[email protected]" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> 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 >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> 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 " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > 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 "[email protected]" group. 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