Hi Brendan, 80% is an excellent rule of thumb for both the analog and digital filters. If you use "odd" decimations (e.g., you try and capture at 66 Msps), then the digital filter response is worse, but if you capture at say 50 Msps (at a 200 Msps sampling rate) then you have two nice half-band filters doing the resampling. The filter taps for those half-bands are in the code, if you want the raw numbers without running UHD then we can pick them out for you.
Also thanks to everyone here with your suggestions! --M On Wed, Feb 19, 2025 at 1:13 AM Brendan Horsfield < brendan.horsfi...@vectalabs.com> wrote: > Thanks for the suggestion about the noise source -- that's what I would > normally do. Unfortunately I haven't actually purchased the hardware yet > -- I was hoping to clarify this issue before raising a purchase order. > > Perhaps I should follow this up with one of the application engineers at > NI? They might have access to an X310+UBX-160 system that they can use to > answer my question directly. > > Thanks again for your help in this matter. > > Regards, > Brendan. > > > On Wed, 19 Feb 2025 at 09:55, Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 18/02/2025 18:45, Brendan Horsfield wrote: >> >> Yes, I assumed that was the case. However, it is not clear from the X300 >> documentation how sharp those filters are. Can you tell me how wide the >> transition band is at the lower sample rates? >> >> To give you some context, I would like to use an X300 (or X310) with a >> UBX-160 daughterboard to digitise the entire 2.4 GHz Wi-Fi band, which is >> 83.5 MHz wide. Ideally I would like to use a sample rate of 100 Msps to >> minimise the data rate between the USRP and the host PC. However, before I >> do this I need to be certain that the usable bandwidth at this sample rate >> will be greater than 83.5 MHz. Is this information documented somewhere? >> >> >> It somewhat depends on the decimation. If the decimation has a factor of >> two or 4, the edge roll-off is fairly sharp. Otherwise, >> there's a half-band filter in-place that causes a less-desirable >> pass-band. >> >> But I don't know, precisely, what the transition band is in the "nicer" >> filter shapes. >> >> >> If you have an X310+UBX-160, you can always just use a noise source, and >> measure it yourself to see if it's appropriate for >> your application. >> >> >> >> >> On Tue, 18 Feb 2025 at 23:11, Marcus D Leech <patchvonbr...@gmail.com> >> wrote: >> >>> There will always be some edge roll off. Decimation includes filtering >>> and those filters cannot be infinitely steep. >>> Sent from my iPhone >>> >>> > On Feb 18, 2025, at 2:12 AM, Brendan Horsfield < >>> brendan.horsfi...@vectalabs.com> wrote: >>> > >>> > >>> > Hi All, >>> > >>> > I have a question about the usable bandwidth of the X300 USRP / >>> UBX-160 daughterboard combo at sampling rates below 200 Msps: >>> > >>> > As I understand it, the UBX-160 receiver has an analog (hardware) >>> filter before the ADC that limits the usable bandwidth to 160 MHz, while >>> the ADC runs at 200 Msps. Therefore the usable bandwidth is around 80% of >>> the sample rate. >>> > >>> > My question is: What is the usable bandwidth at lower sampling >>> rates? Does the 80% factor always apply? >>> > >>> > For example, if I set the decimation factor to 4, so that my sampling >>> rate is 50 Msps, does this mean that the usable bandwidth will be 40 MHz? >>> > >>> > Thanks & Regards, >>> > Brendan. >>> > >>> > _______________________________________________ >>> > USRP-users mailing list -- usrp-users@lists.ettus.com >>> > To unsubscribe send an email to usrp-users-le...@lists.ettus.com >>> >> >> _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com >
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