That’s strange, by default the analog filters should be being configured from the master_clock_rate to have optimal bandwidth for the master_clock_rate on the assumption your signal uses the bulk of that bandwidth. UHD version?
> On May 19, 2018, at 2:37 AM, Sylvain Munaut via USRP-users > <usrp-users@lists.ettus.com> wrote: > > Hi, > > > I'm comparing two cases that, in theory (at least in my understanding > of things), should yield the same result but don't :) > > 1) I'm sending data to the USRP at sample_rate N with > master_clock_rate N and the ADI has FIR 4x, HB 2x,2x,2x > 2) I'm sending data to the USRP at sample_rate N with > master_clock_rate 2*N and the ADI has FIR 2x, HB 2x,2x,2x > In this second case I'm also using a patched FPGA image that > essentially disables the half band filters of the FPGA so that it > inserts 0 between each sample instead of doing the half band. > > In both case, the FIR from the ADI is programmed with my own taps (the > same in both case). > > Now I would expect the result to be the same ... since essentially the > only thing that changes is that either the ADI is doing the 4x > interpolation or the FPGA is doing 2x and then the ADI is doing 2x, > but in both case the signal ends up at the same rate and filtered by > the same taps and the final DAC rate is also the same. > > (i.e. in both case the samples before the FIR filtering are "a 0 0 0 > b 0 0 0 c 0 0 0 d 0 0 0 ...". Yes I know that's probably not how it's > internally done in the ADI but that should be mathematically > equivalent to this). > > But turns out the results are not the same. Not a catastrophic > difference but 0.5% ~ 1% EVM change. > > What I'm wondering is if changing the master_clock_rate has an > influence on other parts of the system that I'm not seeing and that > could explain this. At first I thought maybe the analog filters are > configured based on the master_clock_rate, but calling > get_tx_bandwidth shows 56 MHz full bandwidth in both cases. > > Any theory ? > > > Cheers, > > Sylvain Munaut > > _______________________________________________ > 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
