[Discuss-gnuradio] USRP2 noise floor peculiarities

[Jordan J Riggs]

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

3_bw1M_d100.png
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4_bw781.25k_d128.png
Description: PNG image