Hi Jack, Yes, I found this notebook very useful alright.
Thanks, Colm On Tue, 1 Sep 2020 at 17:24, Jack Hickish <[email protected]> wrote: > Hi Colm, > > Just to add -- you might find this ipython notebook a useful place to > start poking around if you want to do some software sims -- > https://github.com/telegraphic/pfb_introduction/blob/master/pfb_introduction.ipynb > > On Fri, 28 Aug 2020 at 17:17, Ross Martin <[email protected]> wrote: > >> Hi Colm, >> >> I realized that I forgot to mention that time resolution and response >> duration aren't exactly the same thing. >> >> When you switch from an FFT to a PFB with an equivalent number of >> channels, the PFB filter has a length equal to N FFTs. So your time >> response length becomes longer by a factor of N. However, the PFB output >> still has a definite and distinct peak that hasn't really changed in width >> from the original FFT case. >> >> So for many ways of measuring time resolution, switching from FFT to PFB >> doesn't change time resolution much, even though it does extend the time >> length of the response. >> >> Regards, >> >> Ross >> >> [email protected] >> >> >> On Fri, Aug 28, 2020, 7:58 AM Ross Martin <[email protected]> wrote: >> >>> Hi Colm, >>> >>> Events with narrow time resolution will have larger bandwidth, which >>> means that energy from them will appear in multiple PFB output channels. >>> >>> If you retain only a single PFB output channel, then you have lost time >>> resolution exactly as described by previous answers. >>> >>> However, PFBs, when done correctly, are invertible. If you retain *all* >>> PFB channels, you can reconstruct the entire original time series (with >>> some controllable processing noise). Since you can reconstruct all your >>> original data, you've lost nothing at all regarding time resolution (or >>> anything else). Fine time resolution can be hard to see in this form, but >>> all the data is there to extract it. >>> >>> It's also possible to invert part of a PFB. For example, if an event >>> has energy primarily in three adjacent channels, you can keep just those >>> three channels and invert just the three channels. This effectively gives >>> you a bandpass filter with three times the channel bandwidth, and three >>> times finer time resolution than the time resolution of a single channel. >>> >>> Regarding your second question of whether amplitude of an off-center >>> sine wave varies. It essentially does not. A PFB, when properly >>> constructed, is exactly equivalent to a complex mixer, followed by a >>> lowpass filter, followed by a downsampler. (Presentation on my web >>> site.). For an off-center sine wave these steps will give as a primary >>> output signal a complex sine wave whose amplitude is constant but phase >>> varies. There will also be secondary aliased output components, that do >>> distort the amplitude measurement a little. However, these components will >>> certainly be in the stopband of the filter, and with even weak PFB filters >>> be at least 60dB down. If that's too much amplitude measurement variation, >>> you can get stronger PFB filters -- but these will give you lower time >>> resolution in a single output channel. >>> >>> Regards, >>> >>> Ross >>> >>> [email protected] >>> >>> >>> >>> >>> On Fri, Aug 28, 2020, 3:40 AM Colm Bracken <[email protected]> >>> wrote: >>> >>>> 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 >>>> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAEx9wh_tQLMpLNvcCkjSW-M_KNiAC96R-g-oGShBQKzj65F_RQ%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/CAG4nf73pRTk2xjv7tRXXn6rwDtHbGsYCxzRzz8qtGQR6EG1%3DGw%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG4nf73pRTk2xjv7tRXXn6rwDtHbGsYCxzRzz8qtGQR6EG1%3DGw%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/CAG1GKSnAHpJzpbtt23Su0G7jQX0SPymL%2BjO%2BSCrgoEjp0eXMQA%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAG1GKSnAHpJzpbtt23Su0G7jQX0SPymL%2BjO%2BSCrgoEjp0eXMQA%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/CAEx9wh8Bx7yT%2BVTgMJtxbBeUB-z%3DMdv4c0KA-%3DSbA4%2BKzKGhzQ%40mail.gmail.com.
