[Discuss-gnuradio] Re: Spurious Spikes Seen with usrp_fft.py

[Thomas]

Hello again,

I have some more screen shots that might explain better what I am asking. These screen shots are from the 825 MHz - 850 MHz band, which should include most of the GSM 850 uplink channels.

http://img293.imageshack.us/img293/7831/screenshotusrpfft3vt5.png

http://img442.imageshack.us/img442/1311/screenshotusrpfft4go9.png

http://img253.imageshack.us/img253/170/screenshotusrpfft6hr1.png

http://img517.imageshack.us/img517/3041/screenshotusrpfft7jm1.png

http://img253.imageshack.us/img253/9977/screenshotusrpfft8bk9.png

I have
 circled in red the tops of the spikes I think might be spurious. I didn't check these against a spectrum analyzer like the ones in my original question, so I don't know for sure they are spurious. They appear similar to the ones I'm my original message. Also, disconnecting the antenna doesn't attenuate them much.

Does any one know what these spikes are and if they are normal? Are they a software or hardware artifact? 

Thanks,

Thomas

Hi everyone,

I am using a USRP with only a DBSRX daughterboard installed. The image at the following link is a screen capture I took.

http://img340.imageshack.us/img340/3570/screenshotusrpfftfy8.jpg

Does anyone know why the spike at 921.6 MHz is there? I have observed many of these spikes in other parts of the spectrum using usrp_fft.py. I looked for them using a real spectrum analyzer connected to an antenna and did not observe them.

I used the same parameters in usrp_fft.py that were used in the first image at the following link.

http://273k.net/gsm/find-a-gsm-base-station-manually-using-a-usrp/

This spike does not exist in their plot.

I appreciate your responses.

Thanks,

Thomas

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