RF interference at central frequency (NOT LO leak)

[lf_fr]

When receivig signals with our NI USRP 2920 (LV 2013, NI USRP driver 1.3), we are always observing unwanted signal peaks on the 

central frequency, whatever the central frequency. 

I doubt there is much power in these interferences but since we are trying to capture weak and narrowband signals, that

may be an issue. 

Any idea of what these could be ? Certainly not LO leakage since the LO is shifed away. I included some snapshots 

for f_c of 300 and 1500 MHz and a picture of the setup (not that for our experiments, the RF stage of the generator

is off unlike what is shown on the picture but even without any signal source, the noise peaks are there). 

Thanks

Laurent

[ErikL]

Your signals look great. That's great SFDR. Those extra harmonic peaks are very low, below -90dB. You will often see a small peak at the Center due to digital quantization noise but with no signal attached the -70dB number looks realistic.

[lf_fr]

Hi Erik,

OK. Thanks for the clarification !

Best wishes

Laurent