[USRP-users] Noise floor on the N2x0

Marcus Müller marcus at hostalia.de
Thu Sep 26 14:38:33 EDT 2013


Hi Frank, hi Matt,

as Marcus Leech figured out, this is due to the IIR that is doing the rx dc offset correction, to be more exact due to the fact at every reset (e.g. when tuning) the accumulator of that IIR is reset to zero.
The effect lasts about 60ms every retune (for our four N210s and wbxes and sbxes at least).
@Frank: If you can live without dc offset correction, or can do it on your host, disable the dc offset correction (multi_usrp.set_rx_dc_offset(false)). That solved it for me.

Happy hacking,
Marcus

On 09/26/2013 07:21 PM, Matt Ettus wrote:
>
> When you start reception, there is some settling that the radio and filter have.  The best way to handle this is to start receiving 20-30 samples earlier than you need to and drop those extra samples.
>
> Matt
>
>
> On Wed, Sep 25, 2013 at 12:51 PM, Wallace, Frank L CIV NSWCDD, Q41 <frank.l.wallace1 at navy.mil <mailto:frank.l.wallace1 at navy.mil>> wrote:
>
>     When I record noise on both my N210 and my N200, there is the 20-30 sample filter startup stuff and then noise settles at a fairly high level and then starts to drop down.  At about 55 milliseconds, the noise level goes down to the 1-2 bit level and then stays there.  The drop off is exponential and some people here have said it looks like a capacitor discharging.  This happens whenever I restart my application.  Is this normal?
>
>     Thanks,
>     Frank
>
>
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