[Discuss-gnuradio] Artefacts in usrp_fft.py

[Luis Simoes]

Hi all,

We implemented a spectrum senser based on GnuRadio for our cognitive radio 
research. In order to calibrate the senser we check the performance of the 
RFX2400 and DBS RX d'board with the usrp_fft.py script. We use the norma FFT  
and the waterfall plot of the script. Feeding the usrp with generated signals 
by a high performance signal generator we could observe the appearance of 
some strong artefacts in the spectrum. To find out the origin of this 
artefacts we put a calibrated 50 ohm termination on the sma antenna connector 
in order to assure we only measuring the noise floor of the usrp. Now we 
could observe several artefact in almost all frequencies between 800 and 2500 
MHz. Sometimes the artefacts are sharp peaks some times wider peaks and the 
total number of peaks varies also from center frequency to center frequency. 
Normally we use a decimation rate of 8 to sense a chunk of 8 MHz and we try 
several gains of the d'board. If someone know how the origin of these 
artefacts and/or how to avoid getting them in the sensed spectrum please 
answer. Every advice will be appreciated. Thank you all in advance

Luis Simoes