Re: [Discuss-gnuradio] [USRP2] Some problems by sending sinusoidal signals. :-(

[Martin Braun]

On Tue, Mar 17, 2009 at 12:32:57PM +0100, Costantini, Andrea wrote:
> The fft and the scope of the sending and receiving path in USRP A seem to 
> be correct:
> TX: http://img216.imageshack.us/img216/5880/txfftscopeusrp2.png
> RX: http://img256.imageshack.us/img256/7669/rxsameusrp2.png
>
> This is instead the output of fft and scope in USRP B:
> http://img216.imageshack.us/img216/1213/rxdifferentusrp2.png
>
> I really don't understand why I am seeing such a signal on USRP B.
> It seems that the sinusoid here is centered on a frequency of ~ -115KHz.

What exactly is your problem? Is it the frequency offset? If so, at what
frequency are you transmitting and have you sync'd the clocks? If no,
isn't this what you'd expect?
Btw, how do you get these fantastic SNR values, did you connect the USRPs
directly?

> Also note the amplitude of the sinusoid: in USRP B is larger than in USRP
> A, although A is actually the sender.

You are confusing values behind the ADC with power levels. This was
discussed in another thread not too long ago:
http://lists.gnu.org/archive/html/discuss-gnuradio/2009-03/msg00045.html

Don't forget there's a lot of stuff between GNU Radio and the SMD
connector.

Cheerio
MB

-- 
Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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