Hi Don, the problem is that the second peaks are not at DC in baseband. For example: I generate a sine tone at 2.444 Ghz. Then I tune the usrp to centre frequency of 2.448 GHz. Now I can see the peak at -3 Mhz in base band. Ok, this is correct because what Iam seeing is the original sine. When I tune the USPR to centre frequency 2.450 Ghz I see an attenuated peak at 1 MHz in baseband what correspond to 2.451Ghz. This second peak is 6 Mhz above the original sine.
If I rise the gain in the usrp_fft.py tool there appear more undesired peaks but I am still feeding the USRP with olny one tone. If I decrease the gain to eliminate all secondary peaks my original signal gets too weak and it is less than 10 db over the noise floor. I am trying several setting to find out what is the reason of all this. The last try was: 1 sine tone at 2.488 Ghz feed into USRP The result was: one peak at 2.488 Ghz and one alt 2.432 GHz (20 dB's lower) Now the secondary peak is 56 MHz away from the original tone!!! Please, can anyone help me? I am getting desperate... Luis On Wednesday 18 October 2006 20:12, you wrote: > I have observed a similar phenomenon with the LFRX daughterboard. It seems > there is often (or always?) a peak at DC in the baseband (USRP output) > spectrum, regardless of the tuned frequency of the USRP. I suspect it is > due to rounding down in the CIC decimation filter. Adding a value of > e*complex(1.0,1.0) where 0.5 <= e <= 0.8 to the USRP output will cancel it. > > -- Don W. > > ----- Original Message ----- > From: "Luis Simoes" <[EMAIL PROTECTED]> > [snipped] > > > As I feed the USRP with a single sine tone with a frequency of 2.444 GHz > > and > > an amplitude of -50dbm I saw on my plot a nice peak at 2.444 GHZ but also > > a > > second peak at 2.452 GHZ but attenuated by 15 db's when daughter board is > > tuned to 2.452 Ghz. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio