Hi D J, Thanks for the link, this is alias. If I fix the waveform frequency, say 2.4e6, and increase tx sampling rate from 5e6 to 10e6, this problem should be solved right? I just did experiment, and found the second component disappeared.
Thanks, Yang On Mon, Jan 22, 2018 at 9:39 AM, D J <dustin.jones1...@gmail.com> wrote: > What he said^^ > > https://en.wikipedia.org/wiki/Nyquist_frequency > > > On Sun, Jan 21, 2018 at 12:18 PM, Jeff Long <willco...@gmail.com> wrote: > >> Try reducing the RX filter bandwidth, the gain of the receiver and/or >> transmitter, or moving the TX and RX apart, and see what happens. This is >> aliasing, and probably has nothing to do with software. >> >> On Sun, Jan 21, 2018 at 12:56 PM, Yang Liu <lyangbigt...@gmail.com> >> wrote: >> >>> Dear all, >>> >>> In this application, I am trying to send a sine wave at a specific >>> frequency to usrp x310: >>> sine wave generator ---> usrpx310 >>> >>> For the sine wave generator, I use blocks.sig_source_c from gnuradio. >>> The parameters at the transmitter are in the following: >>> center frequency: 1e9 (usrp tuning frequency) >>> sampling_rate: 5e6 >>> waveform frequency: -2.4193125e6 (at the boundary of this frequency >>> band). >>> >>> At the receiver side, I tuned the usrp to 1e9, and used 10e6 to sample >>> the received data. According to the spectrum I observed, there are two >>> frequency components, one is at -2.4193125e6, another one is around at >>> -2.4193125e6 + 5e6 (not very sure if they are exactly symmetric). Actually, >>> this happens when the sine wave is very close to the boundary (near -2.5e6 >>> or 2.5e6). As I moved the waveform frequency to the center (1e9), the >>> second frequency disappeared. Firstly, I thought that it is the power >>> issue, however, after I decreased power level, the second component is >>> still there. >>> >>> According to the function (blocks.sig_source_c), what it generates is a >>> exp(j*2*pi*f_waveform/f_s). Therefore, there should not exist any second >>> frequency component. I feel very confused about why this can happen. >>> >>> Any thoughts about this will be greatly appreciated! >>> >>> Best, >>> Yang >>> >>> _______________________________________________ >>> 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 >> >> > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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