[USRP-users] Waveform Corruption

Ian Buckley ianb at ionconcepts.com
Mon Feb 27 23:13:00 EST 2012

I have a recollection that RX gain beyond about 35 on an RFX2200 get's you into a region of non-linear operation...so maybe you've got yourself some significant mixing products in your spectrum? What happen's if you turn down the gain.

On Feb 27, 2012, at 7:00 PM, Steve Peters wrote:

> On Mon, Feb 6, 2012 at 5:15 PM, Steve Peters <stevenpeters at gmail.com> wrote:
> I've run 
> tx_waveforms --wave-type SINE --wave-freq=40e3 --freq=1750e6 --rate=250e3 --ampl=0.3
> and at the receiver run an FFT (using the GNU Radio companion) and checked out the time-domain samples using my own recording & plotting tools.  I've also recorded the samples using rx_samples_to_file, and the result is similar.
> The results are attached.  As you can see, there are harmonics every 40 kHz, which make the time-domain samples look pretty bad.  I've found that this effect gets better as the sinusoid frequency increases.  For example, at 100e3, the harmonics are present but are about 15 dB below the main sinusoid.  At 1e6, I get a pretty clean sinusoid.
> I've tried this in both directions (i.e., had both USRPs act as TX or RX), and it's the same either way.  I'm really not sure what could be causing this.
> I'm running USRP N210 with RFX1800 daughtercards.  Communication is over an SMA cable with 66 dB attenuation, and RX gain is set to 45 dB.  
> I just wanted to ask again about my problem, quoted above.  I'm still observing this behavior in the RFX daughtercards, though it doesn't appear in the BasicTX/RX cards. 
> Thanks again,
> Steve
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