[USRP-users] B100 + WBX Aliasing

Andre Puschmann andre.puschmann at tu-ilmenau.de
Thu Oct 16 03:40:28 EDT 2014


On 10/15/2014 08:36 PM, Matt Ettus via USRP-users wrote:
> 
> Quadrature mixers, as used in most SDRs including WBX are sensitive to
> strong signals around the third harmonic of the local oscillator.  312 *
> 3 is 936 MHz, hence you see the GSM signal there.  Analog filters or
> banks of filters are necessary to get rid of signals like that if they
> are a problem in your application.

Germano,

I'd just like to add that, besides analog hardware that Matt has
mentioned, there is also DSP-based approaches for mitigating
non-linearities. Michael Grimm has developed an algorithm for that
during his Ph.D. This has also been implemented and practically verified
on the FPGA of the N210 with GSM signals [1]. Of course, both approaches
have there pros and cons but you may still find that helpful.

Thanks
Andre


[1] http://www.db-thueringen.de/servlets/DocumentServlet?id=24447&lang=en

> 
> Matt
> 
> 
> On Sun, Oct 12, 2014 at 9:20 AM, Germano Capela via USRP-users
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
> 
>     Hi,
> 
>     When I run a simple spectrum measurement around 312MHz, I observe a
>     powerful replica of the GSM900 downlink (arround 935 MHz) spectra.
>     Is it possible that the anti-aliasing filters are not enough to
>     prevent this effect?
> 
>     Regards,
> 
>     Germano
> 
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