On 08/23/2010 01:11 PM, jan acosta wrote: > Hello, > > I am currently testing two USRP radios with 3 WBX transcievers. > > When I test the receive path, I would use gnuradio companion and go > from USRP source to FFT plot. > > However, I see that at every center frequency of the FFT window there > is a signal even though I am not inputting anything. > > The signal power is about 0 dBm. > > Also, if I inject a signal, the power of the signal is shown to be > much higher than the true power I am sending through. > > For example, when I send a -50 dBm signal it shows up to be +30 dBm > and I've tried using multiple signal generators. > > So now I'm stuck. > > How do I fix this? > > Thank you. > The FFT plot in Gnu Radio is *uncalibrated*--it's showing you *relative power* and *NOT* dBm
You *could* perform some calibration and apply calibration constants to the output of the FFT to turn it into dBm, but "out of the box", it *is not* dBm. It's rather hard to make it be dBm, as well, since each daughtercard type is different, etc, etc. So, that "signal" at 0dB is actually quite small compared to your -50dBm input signal. it's an artefact of the down-conversion process. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
