Hi, This is a known problem with the B20xmini. Have a look at this thread and then follow it up.
You are right, you are seeing caps charge and discharge, basically. Since I made the changes myself on my units, I am not sure where things were left with Ettus and their policy for fixing the problem. But I can say that once you make the changes, the transients are gone and the minis work really well. regards, steven On Sat, Feb 24, 2018 at 3:25 PM, Thomas Teisberg via USRP-users < usrp-users@lists.ettus.com> wrote: > I'm working on a radar project that requires sending a series of short > pulses. Looking at the pulses on a scope, I'm seeing large voltage spikes > at the beginning and the end of each transmission. > > As shown in the attached screenshot, before the transmission starts, there > is a 90 mV spike lasting about 10 us. After the transmission, there's a -25 > mV spike lasting about 20 us. > > The setup for this is simply a USRP B205mini-i connected to a 50 ohm input > on a scope through a 30 dB attenuator. The signal is at 435 MHz with the > scope sampling at 20 Gsps. > > Our initial thought was that we must be seeing some effects of some of the > RF frontend components turning on and off. I found this previous mailing > list post and tried the suggested fix in b200_impl.cpp but nothing changed: > > http://lists.ettus.com/pipermail/usrp-users_lists. > ettus.com/2015-January/012269.html > > Any ideas why we might be seeing these spikes or what we could do about > it? Does the fix suggested in the above mailing list post still apply to > the current codebase? > > Thanks, > Thomas > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > -- K. Steven Knudsen, Ph.D., P.Eng.
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