On 21.10.2014 13:47, Frederik Wing wrote: > Hello Marcus, > > thank you very much for your hints! >>>> - You're using an ancient UHD version. Is there a reason you can't >>>> use a >>>> newer one? >>> I am using Ubuntu 14.04 LTS and just pulled GNU Radio and UHD from the >>> packet sources. There is no newer version available. And I don't >>> like to >>> compile myself unless it is absolutely necessary. >> Consider it outdated. Ubuntu's packet sources are most of the time >> horribly out of pace compared to GNU Radio's development process. >> For UHD it's the same. Note that Ettus ships its own Ubuntu packages >> for UHD *and* GNU Radio, so you can get a non-ancient version of both >> without even compiling it. >> By the way: GNU Radio is a software radio developer's framework. You >> can do great things with it without touching a compiler, but at many >> points it becomes helpful when one can write his own C++ block, so >> you definitely need to lose your fear of compilers if you want to use >> GNU Radio to its fullest potential :) > > After some hours of compiling time I could finally update GNU Radio to > version 3.7.6 and UHD to 003.008. > >>> I don't think it's because of an outdated version of UHD as the >>> "tags_demo" application is working perfectly with my current version. >> ... Well, my old tube radio also still works ;) > > Unfortunately, even with the newest version the USRP is still > transmitting its carrier over the air. I tried both with the Message > Burst Source as well as with the Stream to Tagged Stream Block > combined with setting a Length Tag name in the USRP Sink. With the Tag > Debug Block I see tx_sob+tx_eob and the Length Tag, respectively. They > all seem to be at the right place and have the right value. :( ok, so we see something that looks like significant LO leakage.
You can use offset tuning, by specifying a tune request instead of simply a target frequency f_t. By doing so, you instruct the USRP to tune the oscillator of the daughterboard to some frequency f_LO, and let the FPGA shift the resulting signal to baseband by a second frequency f_FPGA, so that f_LO+f_FPGA = f_t. You thereby would move the LO leakage out of your desired signal. Would that help you? Greetings, Marcus > > The Length Tag should arrive properly at the Sink. I checked by > changing the tag's name at the Stream to Tagged Stream Block to > something stupid and finally got an "tG" printed out. > > Another interesting observation: > I don't get the "U" underrun output if I use a larger number of > samples for my burst (in Vector Source). Even with only Vector Source > and USRP Sink (no blocks in between) I don't get any "U" printed. I > tried that with 500 samples. > > Has anyone ever succeeded in transmitting proper bursts with a GRC > flow graph? Or at least on Python level? I really feel desperate right > now... > >>>> - In current GNU Radio, you can use 'length tags' to mark bursts, if >>>> that's any help. >>> I tried using length tags by inserting an "Stream to tagged Stream" >>> block and adding the length_tag_name property to the USRP Sink. Here is >>> my sample code, now with a burst of 5 samples: >> The GNU Radio doxygen contains documentation for the current GNU >> Radio build, containing the newly available message passing >> functionality. >> Maybe that's of interest to you! > > That's definitely an interesting feature. But first of all I'd like to > make sure that transmitting bursts works as expected before making > other improvements in my transmitter chain. > > Frederik > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
