I am working with a usrp2+BasicRx and an external tuner with a 21.4 MHz IF output and a bandwidth of about 20 MHz. The same setup but with usrp1 (instead of usrp2) it's working well.
Now I am injecting a tone at 21.45 MHz (-60 dBm) at the input of the BasicRX and set the usrp2 freq at 21.4MHz (with "set_rx_freq()" UHD API).
The problem is that:
a) with sample rate > of about 3.125M I have 2 strong spuriouses. The first in the middle of the FFT (FFTDIM/2) and the second one at about the middle of the second half of the FFT
b) with a sample rate <=3.125 the second spurious disappear but the first at FFTDIM/2 is still present.
In both case I can also see the tone at 21.45MHz. To compute the spectrum I use matlab [10*log10(|fftshift(fft(signal*window))|^2)].
Am I doing mistakes or someone have the same problem ? Suggestions ?