Hi James, Perfect, thanks so much. It is good to have clarity on these matters.
Best wishes, Colm On Fri, 28 Aug 2020 at 12:23, James Smith <[email protected]> wrote: > 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. Kildare, Ireland. >> >> T: +353 1 708 3641 >> E: [email protected] W: 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] W: 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]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh_2SWV5ahQ7x4bCegn9WkZ%3DPket18wO0QnLb%2BZx8JD7Lw%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh_2SWV5ahQ7x4bCegn9WkZ%3DPket18wO0QnLb%2BZx8JD7Lw%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/CAG67D37EFydE4i2WtHH43SC8oGS_Cwv4VCAHCXhp4SNMEOqzXg%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG67D37EFydE4i2WtHH43SC8oGS_Cwv4VCAHCXhp4SNMEOqzXg%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- *Dr Colm Bracken* Lecturer Maynooth University Experimental Physics Maynooth University, Maynooth, Co. Kildare, Ireland. T: +353 1 708 3641 E: [email protected] W: 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] W: 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]. To view this discussion on the web visit https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh_tQLMpLNvcCkjSW-M_KNiAC96R-g-oGShBQKzj65F_RQ%40mail.gmail.com.
