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[Discuss-gnuradio] USRP2 noise floor peculiarities

From: Jordan J Riggs
Subject: [Discuss-gnuradio] USRP2 noise floor peculiarities
Date: Mon, 26 Oct 2009 14:20:21 -0600


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.


Attachment: 3_bw1M_d100.png
Description: PNG image

Attachment: 4_bw781.25k_d128.png
Description: PNG image

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