[USRP-users] Transmit DC Offset Calibration

Steve Peters stevenpeters at gmail.com
Thu Jun 21 17:55:37 EDT 2012


The tuning offset solution is a life saver.  I really wish I knew about it
sooner!

Regards,
Steve

On Thu, Jun 21, 2012 at 12:23 PM, Josh Blum <josh at ettus.com> wrote:

>
>
> On 06/19/2012 09:34 PM, Steve Peters wrote:
> > Hello,
> >
> > I'm hoping there is a crucial step to the DC calibration that I'm
> > overlooking.  The DC offset calibration is only making my DC offset
> worse.
> >
> > For my setup, I'm using tx_waveforms --freq=301e6 --rate=1e6
> > --wave-type=CONST --ampl=0.0. Without the calibration, the received sine
> > wave has an amplitude of about 0.004, and with the calibration the
> > amplitude is about 0.01 (transmission over a wire with 30dB attenuation
> to
> > attempt fairness between tests).  This is well above the noise floor.
> >
> > I've tried setting --nsamps=1000000 and focusing on the narrow band that
> > I'm operating in, but it never seems to actually reduce the DC offset.
> >
> > When running the calibration, I disconnect the internal SMB cable from
> the
> > GDB.  Am I missing some other crucial step to the calibration?
> >
>
> Thats correct.
>
> > I'm running UHD 3.4.1 on USRP N210s, rev4.
> >
> > When the TX and RX are connected to a common 10 MHz source, the sine wave
> > goes away (as expected).  Unfortunately this isn't a long term solution
> to
> > the problem for me.
> >
>
> I'm not sure as to why this might be happening. I'm looking into it. You
> might consider moving the LO out of the passband with a tuning offset as
> an alternative solution. Some notes here:
>
> http://files.ettus.com/uhd_docs/manual/html/general.html#two-stage-tuning-process
>
> -josh
>
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>
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