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
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