Hi Piotr, Because of the problem you described, and other similar limitations for stop-and-go usage of the tx_streamer (I'm referring to the C++ UHD API here), I suggest keeping the tx_streamer always on and just feeding it with IQ zeros when you don't want to transmit anything. This solution is a tradeoff: On the pro side the stop-and-go transients will go away, while on the con side you won't get a perfectly zero RF output when you feed IQ zeros (e.g., because of carrier leakage and other RF effects).
Best, Dario On Sat, Sep 23, 2017 at 4:27 AM, Piotr Krysik via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi all, > > I'm currently trying to find out how much USRPs B210 are capable of > doing in different tasks. > > One of these tasks is transmission of burst with use of UHD's burst api. > To access it I have implemented a GNU Radio app that uses tx_time and > packet_len tags. > Particularly the application was configured to send bursts containing > complex sinusoid (frequency 1kHz) every 2.5ms. Length of the burst is > 2ms, so there should be 0.5us of gap between bursts. > > The result of recording of this signal is shown on the attached picture > and it is not what is expected: the gap is about 800us and the length of > pulse is about 1.7ms. About 300us of signal is not transmitted at all. > > What it means is that it is problematic to send bursts with use of burst > api. I can attach 300us of signal at the beginning of a burst but what > if there are two bursts in a row that are closer than 300us? One of my > aims is to add ability to transmit gsm bursts to gr-gsm. GSM bursts are > spaced by 8.25us of guard periods... Probably I could find some other > workaround with use of hacks that probably will fail in specific > situations and the whole simplicity provided by burst api will go away > anyway. But I would prefer to not do that if it's possible. > > I checked on USRP X310 and everything is fine there - it starts to > transmit almost immediately. > > > Why does it take so long (and loss of 0.3ms of signal at the beginning) > for USRP B210 to start transmit anything? > Do you know how to make it start transmit faster (100x faster definitely > would make burst api in B210 much more usable). > > (UHD used for the test was 3.9.2, carrier frequency of the signal was > 940MHz) > > -- > Best Regards, > Piotr Krysik > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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