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Author Topic: strange signal found in mains line, wtf!  (Read 732 times)

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Offline AdminTopic starter

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strange signal found in mains line, wtf!
« on: September 13, 2012, 01:16:43 PM »
I noticed huge amounts of electrical noise in my sensors at work, of which were powered from a decent power supplies. So I hooked up an oscope to the power supply output and noticed this really odd signal.

Thinking it was the power supplies which was broken, I tried 3 others, each of a different model/brand. They all outputted this strange signal.

Thinking it was the oscope, or EMI, I measured a lead acid battery. No signal/noise measured from the battery, so clearly it was something in the mains.

I also used the ADC from my Axon, without the oscope, and still see the noise.



The signal, after passing through a power supply, looks like this:
- exactly 92 sine waves, about 0.9Hz, of amplitude ~70mV
- a 10 second pause with no noise and no signal
- repeat

Between each sine wave is another very short pulse of what appears to be a very high frequency signal. It is perfectly synchronized with the sine wave.



I've managed to filter out the low-frequency sine wave by adding > 300uF capacitor, but haven't yet figured out which cap to use for the high frequency stuff.

But my real question is . . . What the heck does this?!

Offline Soeren

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Re: strange signal found in mains line, wtf!
« Reply #1 on: September 13, 2012, 02:17:35 PM »
Hi,

The signal, after passing through a power supply, looks like this:
- exactly 92 sine waves, about 0.9Hz, of amplitude ~70mV
- a 10 second pause with no noise and no signal
- repeat

Between each sine wave is another very short pulse of what appears to be a very high frequency signal. It is perfectly synchronized with the sine wave.
[...]
But my real question is . . . What the heck does this?!
It's E.T. phoing home ;D

Not that I have any personal experience with X10, but it sounds a bit like the X10 protocol - Some internet connections piggy back on the mains as well and perhaps someone close by is experimenting with main carried signalling (synch'ing, timing or data), or it may even be a radio transmission being picked up in the mains wiring somewhere (perhaps in the group filter coils).

If you have the option to test outside the junction box you're on, you can determine whether it's local or if you indeed have to call the MiB :P
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline AdminTopic starter

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Re: strange signal found in mains line, wtf!
« Reply #2 on: September 13, 2012, 02:26:41 PM »
That was one of my first theories, that someone was passing data through mains. But I'm really surprised at how huge the signal is, and that it is able to pass through filtering in a power supply.

I don't think it's the X10 . . . the frequency is way too high compared to the 0.9Hz sine wave I'm seeing:
Quote
The starting point of the X10 home automation installation is the emission of signals
through the mains, this will use a carrier signal frequency 120 kHz, a duration of 1 ms and is
issued by passing through zero wave the conventional electricity grid. I.e. we have a signal at a
frequency 2400 times greater than the frequency of the mains.

Tomorrow I'll walk around the building with my oscope and take measurements, and ask around.

Offline Gertlex

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Re: strange signal found in mains line, wtf!
« Reply #3 on: September 13, 2012, 03:02:29 PM »
You could find the building's circuit breakers and test each one...

Nahhhh. :D
I

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Re: strange signal found in mains line, wtf!
« Reply #4 on: September 17, 2012, 01:55:57 PM »
The signal disappeared. I haven't seen anything in the mains since September 14, oh well . . .

Good news is that it is gone.

Bad news is that I have no idea what caused it, and it could come back without me noticing . . .

Offline Billy

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Re: strange signal found in mains line, wtf!
« Reply #5 on: September 17, 2012, 02:23:24 PM »
Look here for industrial version X-10.

http://www.echelon.com/technology/power-line/

 


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