Here's an article that may help with your NF calculations.
"Calculating noise figure and third-order intercept in ADCs"
https://www.ti.com/lit/an/slyt090/slyt090.pdf
I wrote a little C program from it.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(int argc, char **argv)
{
double k, t, dBm1Hz, dBm500Hz;
double vpp, p, sinad, rate, VdBm, dBHz, dBmHz;
if (argc != 4) {
fprintf(stderr, "usage: bdr <p-p voltage> <sinad> <sample
rate>\n");
exit(-1);
}
vpp = atof(argv[1]);
sinad = atof(argv[2]);
rate = atof(argv[3]);
k = 1.38064852e-23;
t = 290.0;
p = k * t * 1 * 1000.0;
dBm1Hz = 10.0 * log10(p);
p = k * t * 500 * 1000.0;
dBm500Hz = 10.0 * log10(p);
p = (vpp * vpp) / (50 * 8);
VdBm = (10.0 * log10(p)) + 30;
dBHz = 10.0 * log10(rate / 2);
dBmHz = (VdBm - 1) - sinad - dBHz;
printf("overload = %.2f dBm\n", VdBm);
printf("Noise Figure = %.2f dB, %.2f dBm/Hz\n", dBmHz - dBm1Hz, dBmHz);
printf("MDS in 500 Hz bandwidth = %.2f dBm\n", dBm500Hz + (dBmHz -
dBm1Hz));
printf("500 Hz Dynamic Range = %.2f dB\n", VdBm - (dBm500Hz +
(dBmHz - dBm1Hz)));
return 0;
}
Ron
On 8/28/24 15:36, Steve Hamn wrote:
Hi Marcus,
Thanks. Understood, that all makes sense to me. Part of this is I'm
trying to understand the base Noise Figure as a starting point so I
can design my filtered low noise front end as you suggest.
I guess you're confirming that 36.5dB is expected from the X440 and
there's nothing crazy wrong about my math.
Thanks,
Steve
On Wed, Aug 28, 2024, 3:15 PM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 28/08/2024 18:04, Steve Hamn wrote:
> Hello,
>
> I have been trying to estimate the Noise Figure of the X440. I
looked
> through all the documentation I could find and couldn't find it
> anywhere, so I tried to calculate it myself.
>
> It looks like the ZU2xDR RFSoC has a NSD of -146dBFS/Hz @ 2.4GHz
>
(https://docs.amd.com/r/en-US/ds926-zynq-ultrascale-plus-rfsoc/RF-ADC-Performance-Characteristics)
> and the Full Scale Input is 1Vppd (0.707Vrms) @ 100ohms
>
(https://docs.amd.com/r/en-US/ds926-zynq-ultrascale-plus-rfsoc/RF-ADC-Electrical-Characteristics)
> .
>
> Based on this information I calculate NSD of -139dBm/Hz
[-146dBFS/Hz +
> 10log10(0.707^2/100Ω*1000)], so -139dBm/Hz - -174dBm/Hz gives Noise
> Figure of 35dB? Add the 1.5 insertion loss of the TCM2-63WX+ on the
> Daughterboard (https://files.ettus.com/manual/page_fbx.html),
gives an
> approximate noise figure of the X440 at 36.5dB for 2.4GHz.
>
> Is this correct? Seems high, I don't have much experience
calculating
> noise figure from ADC's so I'm wondering if I'm missing something.
>
> Thanks,
>
> Steve
>
>
"Naked" ADCs are inherently very very noisy devices. Since the
X440 has
no RF pre-processing of any importance, you'd at
least need a low-noise filtered front-end to beat the inherent ADC
noise into insignificance. For other USRP radios, mostly,
that's already taken care of, and the receiver noise-figure is
much
more "respectable" (not, radio astronomy respectable,
but adequate to put onto an over-the-air antenna).
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