Re: [Discuss-gnuradio] USRP2 noise floor peculiarities

[Douglas Geiger]

I believe the filtering used does change with the decimation - per an
earlier posting by Matt Ettus: if the decimation is a factor of four
there are two half-band filters + CIC filter, if it is a multiple of
two (i.e. even, but not a factor of four) then there is only one
half-band filter + CIC, and if it is an odd number, just a CIC filter.
 Doug

On Mon, Oct 26, 2009 at 4:20 PM, Jordan J Riggs <address@hidden> wrote:
> Folks,
>
> I have been trying to get a better understanding the noise characteristics
> of the USRP2/RFX2400 platform. To get an idea of the noise floor at various
> bandwidths, I connected the SMA's on the RFX2400 to a 50ohm load and
> averaged out the FFT at various bandwidths. Naturally, I would expect the
> floor to drop at lower bandwidths (higher decimation), but this is not
> always the case. For example, the floor at decim 100 is slightly lower than
> it is at 128. This is counterintuitive. The only explanation I can come up
> with is some filtering quirk in the FPGA. Does anyone have any ideas?
>
> I've attached screenshots at decim 100 and 128.
>
> Thanks,
> Jordan
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>



-- 
Doug Geiger
address@hidden