I’ve got a quick question on a project I’m currently working on which is
scanning a range of frequencies using GNU radio and the USRP-N210 with
the
SBX daughterboard.
Basically when I take the FFT of the wgn receiver noise, at certain
sample
rates (e.g. 5Msps) the spectrum output is roughly flat, while at other
rates
(e.g. ~6 Msps), the spectrum takes on a decidedly Gaussian look, where
the
magnitude of the first and last bins of the FFT are 5-10 dB below the
centre
bins of the FFT. Does anyone know why this is? I’ve confirmed this
behaviour
with the fft_sink2 block.
Also, in an unrelated question, is 25Msps the maximum bandwidth of the
host->USRP interface for the N210 without having to modify the firmware?
Basically when I take the FFT of the wgn receiver noise, at certain sample
rates (e.g. 5Msps) the spectrum output is roughly flat, while at other rates
(e.g. ~6 Msps), the spectrum takes on a decidedly Gaussian look, where the
magnitude of the first and last bins of the FFT are 5-10 dB below the centre
bins of the FFT. Does anyone know why this is? I’ve confirmed this behaviour
with the fft_sink2 block.
You may be seeing the filter profile of the half-band filters in the
down converter (or lack there of). When you have odd decimations, there
are no half-band filters in the down conversion chain. 100e6/decim =
samp_rate
Also, in an unrelated question, is 25Msps the maximum bandwidth of the
host->USRP interface for the N210 without having to modify the firmware?
Matt is adding support for smaller samples, but 25 is near link
saturation at 32 bits a sample.