Question regarding AC power line EMI meter experiment

Power Components
1

An audio forum I belong to has been passing around this AC power line EMI meter and I’ve been playing around with it. Can someone help me decipher what’s happening please.
My man cave is a spare bedroom (10 x 19) that has a 3 x 4 alcove in the back where I have my desktop computer and desk. At the other end of the room is my stereo system. All components are plugged into a Furman PFi 15 elite power conditioner.

Per the manual, the meter displays as a peak to peak value in millivolts in frequencies from 10kHz to 10MHz. 50Hz and 60Hz frequencies are ignored. A reading below 50mV would be considered ‘low noise’.
Here are some measurements I took throughout the room.

To get a baseline I started with the desktop computer and the Furman both turned off and I was measuring under 50mV at the stereo outlet. Low noise!
When I turned on the computer and the Furman still turned off the reading was 500mV at the same outlet. Wow…noisy desktop!
When I turned the Furman on, and with the desktop still on, the noise went back down to under 50mV, at the stereo outlet.
All the other outlets in the room were between high-300’s to mid-500mV.

So what is happening when the Furman is turned on? Is it absorbing all the EMI and is it getting into the stereo system?

As an aside, I have an Intel NUC in the stereo cabinet powered by a LPS. With nothing else on in the room and the LPS plugged directly into the wall I got no EMI at all from the NUC which was a pleasant surprise.

EDIT: Thought I’d add the fact that I measured the outlets coming out of the Furman at around 25 mV, so that’s about half the noise that would come directly out of the wall outlet without the desktop computer running.

1 Like
2

There’s nothing magic about the limits specified: “10kHz to 10MHz”
I’d argue that 8KHz is important because most of USB’s noise is there.
I’d argue that 22.5792MHz and 24.576MHz are important because many DACs have crystal’s in that range…
The levels of the frequencies above 10MHz are all important in that any of them could modulate into the audio band if they are near the frequencies of any clock or repetitive signal in your system.

2 Likes
3

Due to impedance of cables, the noise is only reduced locally where the filter is, which is probably at mains inlet of Furman. As distance from filter increases, noise most likely will be higher, in all paths, including Furman itself, depending on consumers that are connected to the same line.

4

Please help conduct EMI measurements of the PS Audio power plants in both the AC input side, as well as the post-regeneration power plant duplex side! :kissing_smiling_eyes:

5

Sorry to interrupt.
what mV Level considering as low Noise ?
Thank you