Re: [Discuss-gnuradio] sending sine wave, but created another unwanted frequency component

[Yang Liu]

Hi Jeff,

I tried to reduced the gain and the second component became weaker, but it is always there. If this is alias, I am wondering if I choose the wrong tx sampling rate. In this case, the sine wave frequency = 2.4e6, current tx sampling rate = 5e6. I tried to increase sampling rate from 5e6 to 10e6 and the second component disappeared.

Thanks,

Yang

On Sun, Jan 21, 2018 at 1:18 PM, Jeff Long <address@hidden> 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 <address@hidden> 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
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio