[USRP-users] XCVR2450 measurements

Steven Clark steven.p.clark at gmail.com
Tue Nov 16 17:41:12 EST 2010


On Tue, Nov 16, 2010 at 5:24 PM, Jorge Miguel <jmiggal at gmail.com> wrote:

> Hello all,
>
> I tested both transmitter and receiver path of XCVR2450 on a USRP2 under
> Matlab r2010b. Here some comments about details I found and I don´t
> understand.
>
> TX path: (I transmit a 100KHz single tone modulated at 5.5GHz) to a
> spectrum analyzer. The expected spectrum is two components at 5.4999GHz and
> 5.5001GHz
>
> 1) Besides the expected spectrum, I can see a powerful (20dB less that the
> modulated signal) component at 5.5GHz (Leakage from the MAXIM Local
> oscillator?)
>
>
What is the scale of the samples you are sending to the USRP sink? If you
increase the scale, does the delta in power between your expected stuff and
the LO also increase? It may be you aren't exercising enough of the DAC
bits.


> 2) I see how after 20 or 30 seconds the signal spectrum suddenly (a fast
> change) becomes very degraded (a lot of noise in my whole band of interest
> appears and the signal is very degraded. The only good news is that the
> component at 5.5GHz becomes smaller)
>
>
Does the behavior here have any correlation with your sample rate /
interpolation? What is your sample rate?


> 3) From the setting I specify on my USRP TX software I can see about 8KHz
> frequency offset in the spectrum analyzer received signal. I connected a
> signal generator (a good one) to the same spectrum analyzer and the offset
> was 0.2 KHz at the same frequency (5.5GHz). Furthermore there is an
> instability over time. (The signal is moving over time around 0.2KHz)
>
>
I think this is expected. Oscillator only good to ~20 ppm or so?


> 4) How is configured the bandwidth of the TX filters (Of the MAXIM)? (I
> know that several values are possible) I wonder that because sometimes when
> I change the transmission 5GHz from 5.5 GHz, I get a signal very very weak
> that cannot be the case when running again the USRP2.
>
>
Don't know.


>
> Can anybody explain some of these issues?
>
> Many thanks,
> Jorge.
>
> **
>
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>
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