I don't quite understand why it is important if it is "analog" bandwidth. While I understand that the UBX cannot change its analog bandwidth, it seems to me that digital bandwidth that is inherent in downconversion from 200 MS/s to 5MS/s is still going reduce the noise power by the ratio of the original bandwidth (160 MHz) to the new bandwidth (say, 4.5 MHz). Rob
On Tue, Apr 21, 2020 at 12:24 AM Lukas Haase via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi Marcus, > > > Von: "Marcus D. Leech" <patchvonbr...@gmail.com> > > [...] > > > My question is if my approach/understanding is right. > > > > > > In particular I do not understand Question 4 (why does noise not > reduce if I reduce bandwidth). > > If you're varying *analog* bandwidth, rather than sampling rate, be > > aware that UBX doesn't have variable analog bandwidth. It's always > fixed. > > I see. > Great point. > > I just found: > http://ettus.80997.x6.nabble.com/USRP-users-Which-bandwidth-does-uhd-usrp-multi-usrp-set-rx-bandwidth-set-td11897.html > > And it seems set_tx_bandwidth() and set_rx_bandwidth() do nothing then on > the UBX. > > I wrote before my noise level should be -174+NF+10*log10(5e6). > > But based on this, it should be more correctly -174+NF+10*log10(160e6) ... > is that correct? (I just receive the raw samples from the USRP via USRP > Source. There is no other digital filter?) > > > > Furthermore, I'd be interested if Question 5 is conceptually correct. > > Conceptually, I don't see any problem with it, but it very-squarely > > enters "consider a spherical cow" territory. You CANNOT use a purely > > arithmetic analysis, due to uncertainties. I would, in fact, > > encourage you to acquire a decent broad-band, calibrated, noise source > for > > you lab so that you can do Y-factor analysis, if for no other reason > > than to satisfy yourself that the noise equations work. > > The issue with the bandwidth calculation above would be one of them ;-) > > > I've used these on a budget-sensitive project just last year: > > https://g8fek.com/precision-noise-sources.html > > Thanks for the pointer. I think I'll get one of these. > > For a proper use I would need a steep filter though, correct? (in order to > have a well defined total input power Pin=-174+ENR+10*log10(FilterCuroff) > dBm? ) > > Thanks, > Lukas > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
_______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
