Mistery signal in my poweline

[mio83]

Hello,

today with my new oscilloscope, I wanted to check the noise of my power supply (a TTi EL301R, which should be quite nice).

I noticed that, while generally very low noise, from time to time there was a burst of activity.
It turned out that this bursts occurred even with the power supply OFF!

In figure 1 you can see one of these bursts (with power supply OFF, and scope leads connected to the + and - of the power supply):
 


As you can see, the burst lasts about 0.5ms and has is of about 250/300mv peak-to-peak.

In figure 2 you can see a zoom on the burst:




The signal is composed of two parts:
1) the first part (delimited by the cursors) lasts about 80us. This part is always fixed because at each trigger event it looks the same.
2) the second part, where it seems there is some kind of message.

In figure 3 you can see a zoom on the 2nd part, i.e., the "message":



It looks as some kind of fm/phase modulation. With the cursors I have delimited one cycle having frequency 20Mhz.


QUESTION: Do you have any idea what this could be? It seems like some kind of messaging going on? I tried to turn off all the power supplies around my bench but the signal still persists.


Thanks!

[mio83]

Mistery solved!!! 

After turning off basically everything in my apartment, I remembered that to connect my smart TV to my internet router I use a mains-adapter, that sends data through the electric line instead of using a proper Ethernet cable!

I am very happy with my new digital oscilloscope! I never saw this before with my old analogue oscilloscope!