Hello Colm, Yes, you're correct. That's how some of our narrowband designs work - you use each PFB channel as a very narrow bandpass filter, and treat its output as a complex time-series. So you can pass it through another PFB to get a higher-resolution spectrum, at the expense of very much lower time resolution of course.
Regards, James On Fri, Aug 28, 2020 at 11:04 AM Colm Bracken <[email protected]> wrote: > Hi Cedric, > > Great, thanks for confirming that. > One more question, if you don't mind? > > If a narrow band signal is off-centre relative to one of my frequency > bins, will the measured amplitude change each time I run the FFT? > For example, if my FFT frequency bins are exactly 1 MHz wide (1024 pt FFT > applied to 1 GSPS ADC data), and I am trying to measure a sinusoid with a > frequency of 5.1 MHz, will the measured amplitude oscillate at a frequency > of 0.1 MHz (5.1 MHz - 5 MHz)? Basically, my sampling (in terms of how often > I sample the full time stream for the FFT) is out of phase with the signal > to be measured? > > I probably didn't explain that very well, apologies. > > Best wishes, > Colm > > On Fri, 28 Aug 2020 at 11:17, 'Cedric Viou' via [email protected] > <[email protected]> wrote: > >> Hi Colm, >> >> You are right. >> >> PFB is a great way to reduce frequency smearing but the down-side is time >> smearing. >> >> A brief event will be convolved with at least one of your PFB 8-tap >> filters that end up feeding several FFT computations in a row. >> So, you get time smearing for that short event... >> >> Regards, >> >> Cedric >> >> >> Le 28/08/2020 à 11:56, Colm Bracken a écrit : >> > Hi All, >> > >> > I have a question, which is probably DSP 101 basics, but I just wasn't >> 100% sure. >> > >> > If I am applying a 1024 point FFT to a continuous time-stream from an >> ADC with sampling ~ 1 GSPS, I will have a time resolution ~ 1 microsecond >> (and frequency res. of ~ 1 MHz). >> > >> > But, if I instead apply an 8 tap PFB, am I essentially smearing out my >> time resolution by a factor of 8, since I am now summing 8 rows of my 1024 >> point time streams? >> > I can't see how the number of PFB taps wouldn't affect my time >> resolution. Or am I missing something? >> > >> > Thanks in advance, >> > Colm >> > >> > -- >> > >> > *Dr Colm Bracken* >> > Lecturer >> > Maynooth University Experimental Physics >> > >> > >> > Maynooth University, Maynooth, Co. Kildare, Ireland. >> > >> > T: +353 1 708 3641 >> > E: [email protected] <mailto:[email protected]> W: >> www.maynoothuniversity.ie <http://www.maynoothuniversity.ie> >> > >> > Follow my work on https://nuim.academia.edu/ColmBracken >> > >> > >> > >> > And >> > >> > >> > Research Associate >> > >> > Astronomy & Astrophysics Section >> > School of Cosmic Physics >> > Dublin Institute for Advanced Studies >> > 31 Fitzwilliam Place >> > Dublin 2, D02 XF86 >> > >> > >> > >> > T: +353 1 440 6656 ext 352 >> > E: [email protected] <mailto:[email protected]> W: >> www.dias.ie/2017/06/22/dr-colm-bracken < >> https://www.dias.ie/2017/06/22/dr-colm-bracken> >> > >> > Follow my work on https://nuim.academia.edu/ColmBracken >> > >> > -- >> > 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] <mailto: >> [email protected]>. >> > To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh9GmrYZ7_uLkXwSKqOp3GYm1Ei_0Bq-TPg9pt8LgQdprw%40mail.gmail.com >> < >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh9GmrYZ7_uLkXwSKqOp3GYm1Ei_0Bq-TPg9pt8LgQdprw%40mail.gmail.com?utm_medium=email&utm_source=footer >> >. >> >> -- >> Cedric Viou <[email protected]> >> >> Ingénieur de recherche >> >> Station de Radioastronomie de Nançay, >> Observatoire de Paris, PSL Research University, CNRS, Univ. Orléans, >> OSUC, >> 18330 Nançay, France >> http://www.obs-nancay.fr/ >> >> phone : +33 (0) 248 51 8609 >> fax : +33 (0) 248 51 8318 >> >> www.openstreetmap.org/?mlat=47.381848&mlon=2.194415&zoom=18 >> >> -- >> 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/68a23cbf-5320-8b50-7a4f-52379c4a2ad7%40obs-nancay.fr >> . >> > > > -- > > *Dr Colm Bracken* > Lecturer > Maynooth University Experimental Physics > > > Maynooth University, Maynooth, Co. 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