[USRP-users] B2x0 and automatic DC-offset removal

Mike Jameson mike at scanoo.com
Thu Sep 18 14:36:58 EDT 2014


An alternative is to tune slightly higher or lower than the signal
frequency and multiply the signal with a sine wave.  If the sampling rate
of the B210 is 8e6 the sine wave can be set to amplitude=1 and a frequency
something like +/-2e6.

This mixing technique is shown in the second video of Michael Ossmann's
awesome SDR video series:

http://greatscottgadgets.com/sdr/2/

See attached screenshot showing the GNU Radio flowgraph.

Mike

--
Mike Jameson M0MIK BSc MIET
Email: mike at scanoo.com
Web: http://scanoo.com

On Wed, Sep 17, 2014 at 7:59 PM, Marcus Müller <usrp-users at lists.ettus.com>
wrote:

> Yeah, I forgot about that fact.
> Basically, the AD chipset takes care of a lot of these aspects, and also
> runs a calibration every time you tune; we enable this behavior in the
> firmware for robustbness reason. You can fiddle with the firmware and
> disable these features, if you feel like working a bit with the AD9361
> registers, but I can't promise that'll be trivial.
> What's bad about offset tuning?
>
> Greetings,
> Marcus
>
> On 17.09.2014 19:49, Daniel Malafaia wrote:
> > Any other way instead of the offset tunning? I tested the
> set_rx_dc_offset()
> > but it doesn't work on B200,
> > UHD Warning:
> >     Setting DC offset is not possible on this device.
> >
> > Best Regards.
> >
> >
> > 2014-09-17 14:43 GMT+01:00 Marcus Müller <usrp-users at lists.ettus.com>:
> >
> >>  You can just use offset tuning, by using an instance of tune_request_t
> >> with a RF frequency that is away from your signal and let the B200
> >> digitally tune there.
> >> Also, see the set_rx_dc_offset() method of multi_usrp.
> >>
> >> Greetings,
> >> Marcus
> >>
> >> On 17.09.2014 13:31, Daniel Malafaia via USRP-users wrote:
> >>
> >> Hi,
> >>
> >>  I'm using a B200 to receive a sine wave that is very near DC, but the
> >> signal that I'm receiving is not showing it for low power and for higher
> >> power at the TX the receiver saturates. This looks like it may be a
> problem
> >> caused by an automatic DC-offset removal algorithm. It there any way to
> >> disable it?
> >>
> >> Best Regards.
> >>
> >>
> >>
> >>
> >> _______________________________________________
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> lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
> >>
> >>
> >>
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> >>
> >>
>
>
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