Re: [Discuss-gnuradio] USRP2 and external RF tuner

[Matt Ettus]

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
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio