Motion Detection System creating Interesting Interference

If you are like me and you love interference stories, this is one of them! I came across this interesting interference while I was performing an assessment for one client.

At first I had no idea what it could be and I didn’t know if the 2 pics were part of the same signal or not. So I didn’t know if I was looking for 1 or 2 sources. After a while walking around with the spectrum analyzer open, trying to figure out where these interferences could come from, I still couldn’t figure out where this was coming from.

I was working with my good friend Cédric Terrier on this one and he told me he had seen similar interferences coming from motion detection sensor. BINGO, after that it took us a few seconds to find them. Indeed, two of them were installed in two adjacent rooms.

Here is what they looked like:

THE TECHNOLOGY BEHIND THESE SENSORS

These sensors use an interesting technology to detect motion. It uses 2 directional antennas to send signals on the 2450MHz frequency (according to the specifications. In reality, we see that different frequencies are in use). Their technology allows a more precise measurement of the motion and is event able to detect the speed of the intruder!

Here is their antenna pattern:
And here are the technical specifications:

All the information related to this product can be found in the following specification sheet document:
https://www.semfionetworks.com/uploads/2/9/8/3/29831147/detecteur_aritech_dd400.pdf

MITIGATION

In this case, the mitigation was easy since we found out that the system was not used anymore. So they simply disconnected them.

INTERFERENCE SUMMARY

The following table summaries the characteristics of this interference:

Thank you for reading!

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