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[Discuss-gnuradio] USRP2 and external RF tuner

From: Luca Pascale
Subject: [Discuss-gnuradio] USRP2 and external RF tuner
Date: Wed, 1 Sep 2010 15:10:29 +0200

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


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