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. > > [image: ramp 3.11 1.0] > > [image: ramp 3.11 1.05] > > [image: ramp 3.13 1.0] > > [image: ramp 3.13 1.05] > > 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 > >
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