Hi Matt, I have connected the RF tuner that provides (nominal) a gain of 30 dB. So the chain is (SIGGEN)--->(TUNER)--->(USRP2). The tuner itself introduces spurious signal (below -70dBm). The output spectrum is:
a) without tuner (description is above the picture) http://imagebin.ca/view/ZTARvXd.html b) with tuner http://imagebin.ca/view/KOYDSsHI.html Do I need more amplification on the IF signal ? Or does exist another way to obtain a clear spectrum with the injected tone only ? Is it possible that some spurious are due to the downconvertion process ? Regards, Luca 2010/9/2 Matt Ettus <[email protected]> > > > The BasicRX has no amplification. Its full scale amplitude is +10dBm. The > ADC in the USRP2 has a rated SFDR of 88dBFS. That means you may see spurs > at levels high as -78dBm equivalent when using a BasicRX. In the plots you > sent me, your signal is -50 dBm and the spur is more than 40 dB lower, > putting it at better than -90dBm, or more than 12dB better than the spec. > That is what you need to expect from a real-world ADC. > > Normally, if you want to look at a -60dBm signal, you will amplify it a lot > before you put it into the ADC. That will make it much stronger than the > spurs. This is why boards like the RFX, DBSRX, and WBX all have amplifiers. > I suggest amplifying your signal by at least 30dB. > > Matt > > > On 09/01/2010 06:10 AM, Luca Pascale wrote: > >> Hi all, >> >> I am working with a usrp2+BasicRx and an external tuner with a 21.4 MHz >> IF output and a bandwidth of about 20 MHz. >> The same setup but with usrp1 (instead of usrp2) it's working well. >> >> Now I am injecting a tone at 21.45 MHz (-60 dBm) at the input of the >> BasicRX and set the usrp2 freq at 21.4MHz (with "set_rx_freq()" UHD API). >> The problem is that: >> >> a) with sample rate > of about 3.125M I have 2 strong spuriouses. The >> first in the middle of the FFT (FFTDIM/2) and the second one at about >> the middle of the second half of the FFT >> >> b) with a sample rate <=3.125 the second spurious disappear but the >> first at FFTDIM/2 is still present. >> >> In both case I can also see the tone at 21.45MHz. >> To compute the spectrum I use matlab >> [10*log10(|fftshift(fft(signal*window))|^2)]. >> >> >> Am I doing mistakes or someone have the same problem ? >> Suggestions ? >> >> Thanks in advance >> >> Luca >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > >
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