Can satellites "see" the RF from SMPS?

[24vtingle]

Hi,
Supposing someone wanted to see where there are industrial operations going on within a city.
One good way would be to sense where lots of SMPS's are operating as modern industry uses
loads of these.
So could a satellite or high flying drone, (or even a low flying "loitering" drone for that matter) with an RF sensor, look down on a city and spot where lots of SMPS are operating by "sniffing" the RF from them? -Eg with a directional receiver antenna scanning over the city?
Presumably the RF can get through concrete rooves and ceilings.

 

[dick_freebird]

Sub-MHz fundamental, EMI requirements make this iffy, and other powered electronics abound; does this add insight, or clutter?

 

[24vtingle]

Most offline SMPS's are in cheap plastic enclosures and so will fail radiated emissions testing but are sold noneTheLess. I suspect that the 20-300MHz or so RF will be detectable from aeroplanes etc with a directional antenna, or some kind of phased array RF detector?

 

[andre_luis]

Satellite transmissions are made by antennas with high directivity and at frequencies well above GHz; unless you attach a parabolic dish to your SMPS and manage to do some wizardry to switch at frequencies close to that, I don't see any point in this concern.

 

[volker@muehlhaus]

I suspect that the 20-300MHz or so RF will be detectable from aeroplanes etc with a directional antenna, or some kind of phased array RF detector?

Check out the max. level of radiation per EMI regulations, then use free space path loss calculator

Friis transmission equation - Wikipedia

en.wikipedia.org

Free Space Path Loss Calculator (FSPL) - everything RF

www.everythingrf.com

Let's assume we have a bad 30 dBµV spurious emission at 30 MHz, that is -77dBm @ 50 Ohm.
Let's assume a small distance of 100m and a 0dBi receive antenna, path loss is 42dB at 30 MHz.
Let's assume the SMPS is loacted at the rooftop for best "visibility" of radiated EMI signals.

The EMI level is then -117 dBm.
From my understanding, measurement bandwidth for EMI Tests up to 30 MHz is 9 kHz, that would put thermal noise floor at -134 dBm.

I hope my math is correct.