Making some tests I have found that my system (USRP + RFX900) transmits an important signal (it seems a tone) without any application running, just when I plug the power source it transmits this unwanted signal. I'm working at the GSM900 downlink frequency band (between 935 and 960 MHz) and the signal appears close to the upper side of this band, around 959,6 Mhz.
My system makes an spectrum sensing for that band and it locates the present signals, so it produces an error because it detects this undesired signal generated by itself. Any idea of the problem? Any solution?