Hi Dmitry, I did more tests today, found that the these two frequency components are not symmetric, and the distance between these two is 5e6 (sampling rate at the transmitter side). If I set the tx sampling rate to be 10e6, and waveform frequency to be 4.8e6 (close to 10e6/2.0), then the distance between two signals are 10e6.
If this problem is caused by not enough attenuation, why as I moved the sine wave to the center frequency, the second component disappeared? I feel confused about this. I am thinking that maybe it is caused by incorrect sampling rate at the transmitter side, if I want to let the sine wave move from -5e6/2.0 to 5e6/2.0, should I set the sampling rate at tx higher than 5e6? Thanks a lot for your help, Yang On Mon, Jan 22, 2018 at 3:48 AM, Дмитрий Михайличенко via USRP-users < usrp-users@lists.ettus.com> wrote: > > > 2018-01-21 20:55 GMT+03:00 Yang Liu via USRP-users < > usrp-users@lists.ettus.com>: > >> 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 >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> > What you see is perhaps image of original frequency. It should be missed > in an ideal world but in real world there is imbalance of quadrature > channels as well as filters used during downsampling have limited stop band > attenuation. > > thanks, > Dmitry > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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