Dear all, Mleech, Marcus and Nathan Thanks for all your advices.
I've set the samp_rate to 250k and it works perfectly. Marcus, I've checked your answer on USRP users mailing list a few minutes ago. Some settings were set wrong, so the mail was not delivered to me. Sorry for late. Nathan, LFTX and LFRX can use center frequnecy of 0 Hz (maybe....) which are what I am using now. Regards, Jeon. 2015-06-25 22:58 GMT+09:00 West, Nathan <n...@ostatemail.okstate.edu>: > Hi Jeon, > > I stared at this over my morning coffee. I can't quite explain why you're > getting 7.8kHz output on a scope, but there's some other considerations. > > 1) Your UHD block has a center frequency of 0Hz. When you run your > flowgraph do you get messages from UHD? You should see something about not > being able to set a center frequency of 0Hz and using x Hz instead. > > 2) 32 kHz is not a good sampling rate for USRPs. You should see something > similar to #1 about setting the clock. The signal you are seeing is > probably a result of generating a signal with some expected sampling > frequency and looking at with another. If you compare the actual USRP clock > rate to 32kHz and do some math I wouldn't be surprised if it comes out to > be a factor of 8 different. > > 3) Imagine an even simpler case with just a sine wave. You have a sine > wave of 1kHz at complex baseband going in to an upconverter (imagine this > as multiplying your signal by an oscillator at your center frequency). What > would you expect on the scope? If you don't know, then do the math; it's > fairly simple trig. > > Good luck, > Nathan > > On Thu, Jun 25, 2015 at 9:38 AM, Jeon <sjeon87+gnura...@gmail.com> wrote: > >> I build a flow graph like an image in the following link: >> http://i.imgur.com/PpXck09.jpg >> >> >> >> >> After then, I connect the USRP and an oscilloscope and see output, which >> yields: http://i.imgur.com/JEKhnfx.jpg >> >> >> >> As you see, both are square waves, but the frequency, the above is 1k and >> the below is 7.8 kHz. >> If I set a frequency of signal source to 2k, the below says 16.6 kHz. (Of >> course, there are some deviation) >> >> How could I understand this? >> If the oscilloscope shows a frequency slower than the GNU radio, >> I think that is acceptable since there are latency and processing time >> and something. >> >> But the output is 7.8 times faster than what I inteded. >> The only thing I can guess is... 7.8 is rounded up to 8, and 8 indicates >> '8' bits. >> But it seems a bit unnatural and weird... >> >> Could anyone give me a hint? >> >> If you think it is more appropriate to be posted on USRP-users, I'll post >> it there later. :) >> >> Regards, >> Jeon. >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
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