[USRP-users] Strange behavior when receiving a DC signal

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[USRP-users] Strange behavior when receiving a DC signal

Martin Braun via USRP-users

Hi all,

We've been debugging our application and have run across some strange behavior when receiving a pure DC signal transmitted with carrier frequencies in the 2.45GHz ISM band (image attached). We notice a similar amount of I/Q modulation weirdness when transmitting a variety of other signals as well.

The same thing occurs when we use the 5.8GHz band as carrier. I'm no signal processing expert, but I imagine this should not be happening, especially since we don't observe this when using a different SDR unit as the receiver.

Currently using an X310 running UHD 3.9.5, along with the latest version of GNURadio.

--Frank

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Re: [USRP-users] Strange behavior when receiving a DC signal

Martin Braun via USRP-users
On 10/02/2016 03:00 AM, Frank Liu via USRP-users wrote:

>
> Hi all,
>
> We've been debugging our application and have run across some strange
> behavior when receiving a pure DC signal transmitted with carrier
> frequencies in the 2.45GHz ISM band (image attached). We notice a
> similar amount of I/Q modulation weirdness when transmitting a variety
> of other signals as well.
>
> The same thing occurs when we use the 5.8GHz band as carrier. I'm no
> signal processing expert, but I imagine this should not be happening,
> especially since we don't observe this when using a different SDR unit
> as the receiver.
>
> Currently using an X310 running UHD 3.9.5, along with the latest
> version of GNURadio.
>
> --Frank
>
>
It looks like you have two issues there.   One is, you're clipping.
Back-off on the RX gain -- how are TX and RX connected?  Via antenna
   or directly?  If directly, how much attenuation do you have in-line?

Also, if you're operating very close to DC, the DC-offset-removal will
interfere with your signal.  Use offset tuning on the RX side to
   move the DC anomaly out of your pass-band:

http://files.ettus.com/manual/page_general.html




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