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 > >
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