Ian, Thanks for the insight! The changes for the RFNoC blocks are correct, but the DSP cores (rx_dsp_core_3000 and tx_dsp_core_3000) that use the CORDIC should not have been changed. It looks like the fix might be as simple as backing out the changes to rx_dsp_core_3000.cpp and tx_dsp_core_3000.cpp that were made on that commit. We do have this as a high priority to fix and we hope to resolve it very soon.
Regards, Michael On Wed, Sep 12, 2018 at 12:50 PM, Ian Buckley <i...@ionconcepts.com> wrote: > I think look to commit d588005fd87dd2594adb29dbbdcf948bbb0ab0c1 and files > uhd/host/lib/usrp/cores/tx_dsp_core_3000.cpp and > uhd/host/lib/usrp/cores/rx_dsp_core_3000.cpp > > CORDIC compensation gain was mistakenly eliminated in UHD for all 3rd > generation USRP’s rather than just the ones that switched to using an > alternate DDS design. > > Probably should be fixed urgently, I can think of several companies in > production with B2x0 H/W with ugly legal and electrical ramifications on > the TX side > > -Ian > > On Sep 11, 2018, at 11:25 AM, Michael West via USRP-users < > usrp-users@lists.ettus.com> wrote: > > Hi Ron, > > Thank you for bringing this to our attention and for all the detailed > reports on the issue. We will need to look into it. Is it possible for > you to continue using UHD 3.11.1.0 while we look into the issue? > > Regards, > Michael > > On Mon, Sep 10, 2018 at 11:49 PM, Ron Economos via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> I've done more testing. Here are some plots with the spectrum analyzer in >> zero span and a real sawtooth wave being transmitted. >> >> The first plot is with 3.11.1.0 and sawtooth amplitude = 1.0. *Perfectly >> linear.* This also shows that it's entirely possible to have baseband >> amplitudes approaching -1.0 to 1.0 without distortion (at least on the >> B2X0). BTW, the TX gain was set to 74 to limit the output to just under 10 >> dBm. >> >> The second plot is with 3.11.1.0 and sawtooth amplitude = 1.05. You can >> see the AD9361 clamp the output level. >> >> The third plot is with 3.13.0.1 and sawtooth amplitude = 1.0. Something >> is horribly wrong. >> >> The fourth plot is with 3.13.0.1 and sawtooth amplitude = 1.05. Again, >> you can see the AD9361 clamp the output level. >> This is clearly a bug/regression. >> >> <ramp1.png> >> >> <ramp2.png> >> >> <ramp4.png> >> >> <ramp5.png> >> >> >> Ron >> >> >> On 09/10/2018 07:59 PM, Marcus D. Leech via USRP-users wrote: >> >> On 09/10/2018 10:48 PM, Ron Economos via USRP-users wrote: >> >> It seems like it was correct before and wrong now. It's always been said >> that baseband levels must be restricted to -1.0 to 1.0. Now it's something >> different? >> >> I consider this issue to be the same as a patch to the Linux kernel that >> breaks user space. And you know how Linus feels about that. >> >> Ron >> >> Yes, I can see where you're coming from here, and I'll leave it to >> Michael West to comment further on the "fix". >> >> But there has *NEVER* been a guarantee that in any randomly-chosen >> situation a baseband level near MAX can always be guaranteed not >> to drive analog components into non-linear operating states. It's just >> a convenient scaling ceiling. Now, I'll allow as how moving from >> "close to 1.0" to 0.67 as the highest achievable baseband level is a >> significant jump, and perhaps more attention needs to be paid >> to whatever scaling fix was implemented. >> >> Consider for example that mixers and RF amps are being asked to operate >> over a couple of decades of bandwidth. So a mixer baseband level >> that is "nicely maxed without unpleasant artifacts" at one frequency >> might be "ouch" at another. And these edge conditions are notoriously >> manufacturing-batch sensitive, and to a certain extent usage-sensitive >> as well. Theoretically, one could iterate over the entire parameter space >> in an exhaustive calibration exercise, and have calibration tables that >> "hide" all of that. But it would be an expensive exercise, I'm willing to >> bet. >> >> >> >> On 09/10/2018 07:26 PM, Marcus D. Leech via USRP-users wrote: >> >> On 09/10/2018 10:21 PM, Ron Economos via USRP-users wrote: >> >> I have to reduce the baseband amplitude from 0.96 to 0.67 to achieve the >> same IMD. >> >> This is a very annoying issue for me, especially since I've set levels in >> the Gnu Radio gr-dtv example flow graphs based on previous behavior. >> >> Ron >> >> I think it was Michael West who worked on the scaling issues in B2xx. >> The internal implementation had been wrong for a long time, >> from what I understood. This has the unfortunate side-effect that >> previous carefully-set baseband levels may no longer work properly. >> >> Unfortunately, there's no "set the baseband magnitude and RF gain as loud >> as you can without producing excessive IMD" operator in UHD. >> >> >> >> On 09/10/2018 05:37 PM, Marcus D. Leech via USRP-users wrote: >> >> On 09/10/2018 08:34 PM, Ron Economos via USRP-users wrote: >> >> I'll try that. It's going to take a while though since I have to rebuild. >> >> Ron >> >> Understood. Sorry for the PITA.... >> >> >> >> On 09/10/2018 05:30 PM, Marcus D. Leech via USRP-users wrote: >> >> On 09/10/2018 08:27 PM, Ron Economos via USRP-users wrote: >> >> No change with 3.13.0. Haven't tried 3.14, since it's not released yet. >> >> Ron >> >> Is this effect independent of baseband magnitude? >> >> >> >> On 09/10/2018 05:21 PM, Marcus D. Leech via USRP-users wrote: >> >> On 09/10/2018 08:17 PM, Ron Economos via USRP-users wrote: >> >> I had previously noted that the B210 TX power had increased by about 5 dB >> going from UHD 3.11.1.0 to UHD 3.12.0. Today, I was doing some two tone IMD >> testing and noticed that the IMD performance has degraded *severely* >> from UHD 3.11.1.0 to UHD 3.12.0. >> >> Here are the spectrum analyzer plots at roughly the same power level. The >> 3rd order two tone IMD level changes from almost -50 dB in 3.11.0.1 to a >> hideous -20 dB with 3.12.0. Something is terribly wrong. >> >> >> I know that there had been some "futzing" with scaling in the B2xx at >> around that time. What about 3.13 or 3.14? >> >> >> >> >> >> _______________________________________________ >> 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 > > >
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