On 03/03/2025 22:59, Mark Gannet wrote:
For an ADC, I believe the noise power is fairly constant. As sample
rate increases, noise power density should decrease and SNR should
improve. Thus a measured improvement in noise figure.
Source:
https://www.analog.com/en/resources/technical-articles/noise-spectral-density.html
x310 ADC (ADS62P48): http://www.ti.com/lit/ds/slas635b/slas635b.pdf
Mark
Thanks. Trying to get my head around this a bit. The X310 runs the ADC
at a fixed rate, and host-directed sample rates are
based on the actions of a DDC filter/sample-rate converter.
On Mon, Mar 3, 2025, 7:48 PM Marcus D. Leech <patchvonbr...@gmail.com>
wrote:
On 03/03/2025 22:23, Dustin Widmann via USRP-users wrote:
> Hi all,
>
> I see an interesting trend and I'm not sure how to explain it ...
>
> I've done a y-factor measurement, sweeping the frequency, sampling
> rate, and rx-gain with an x310 with the SBX-120 daughterboard. The
> results seem similar to the published performance specs. The
part I'm
> not sure quite how to explain is why the NF would vary with the
> sampling rate. Doesn't the X310 use a static sample rate and
> downsample in the FPGA? Why would this affect the NF? Why does the
> effect seem to be more exaggerated at higher gain settings? Why
is the
> effect on NF very small at higher sampling rates but more pronounced
> at lower ones instead of being a linear change?
>
> Dustin
>
What noise inputs are you using for the two levels in your Y-factor?
The amount of power represented at each sample-rate is different, and
shooting from the hip here, the amount of energy
represented in the transition regions at different sample rates
will
be different. For example, odd/even/factor-of-4
sample-rates have different pass-band shapes.
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