Huge interferences on channel 1-3 2.4 GHz

[Heino1]

Hi there,
we are seeing huge interference on channels 1-3 on the RF Spectrum page from two APs in the same area. We have no equipment running on these channels and the floors below and above us are also controlled by us and do not use channels 1-3. Have you seen this before? Do you have any idea how we can find the source of this interference?

Kind regards,

Heino

[KH]

Hey @Heino1 

You will need to walk around with a spectrum analyzer to pinpoint it exactly. However, checking for common causes of 2.4 interference is probably easier. Look out for microwaves , cordless phones, and Bluetooth devices as a start.

[GIdenJoe]

Thank god for dashboard to point you in the right direction!

There are many kinds of transmitters that transmit smallband signals in the 2.4 GHz including: cameras, baby monitors, RF based security motion detectors.

If the environment is large it will be difficult to pinpoint the issue wihout knowing exactly what kind of devices could be transmitting there.  In that case you could hire someone who has a spectrum analyser type of device for example Ekahau Sidekick or Sidekick 2 that can search for where the signal is received strongest.

There is a chance however that the machine that is transmitting the signal is in fact necessary and that would make a good case for avoiding 2.4 GHz SSID's in that area.

[PhilipDAth]

Best tip - turn off 2.4Ghz on your WiFi.  Often the congestion is not solvable.

If you are in an area with many businesses - it may not even be caused by your company.

[BlakeRichardson]

100% Agree this is the best decision I have made when it comes to Wifi. 

[thomasthomsen]

From my experience, narrow band, constant transmitter, at the start of the 2,4 Ghz spectrum is almost always a combined PIR and Microwave sensor (either for lights or building alarm systems).

But I have seen lots of interesting stuff in 2,4Ghz

Trafos from lightfixtures, leaking displayport cables (that was a new one).

Things it is not: Bluetooth, Microwave oven, and it does not look modulated or wide enough for it to be a analogue video camera or cordless phone (but you never know, the resolution of the build in "spectrum analyzer" is not great).

As other people mentions, if possible, try to get your hands on a WiFi spectrum analyzer (or borrow one from your local friendly WiFi consultant. I mean, clearly everyone of "those guys" have at least one in their inventory 🙂 )

Regarding the picture, it looks like the noise is really close, its above -40dbm.

So either the AP is almost right next to the thing that is making the noise, or the thing that is making the noise has a fairly high transmit power.

Just my thoughts.

[thomasthomsen]

PS: In theory it could also be another AP "stacked" right next to your AP (but who would do such a thing ? 🙂 )

We now require pictures of the immediate area around the AP 🙂

[Heino1]

Hi @thomasthomsen,

thanks for your response.

The building has several floors. The interference is very low above and below the floor with the interference. So I assume that the interference is on the floor of the AP. I will try turning off all power to the floor via the fuses and hopefully the signal will disappear.

There is no other AP right next to this AP 😉

As a workaround, we already switched the clients to 5Ghz.

Here are the RF-Spectrum from the floors 13-S (above) und 11-S (below).

[Heino1]

There is a PIR-Sensor in this area. I will check how I can turn is off.

[thomasthomsen · Accepted solution]

Please be aware that PIR stands for "Passive Infrared" (as far as I remember), and if its just IR, then we dont really worry about that :-).

But some sensors also have a microwave part, especially for burglar alarms, because, again as far as I remember, the IR part does not detect you as well, when moving slowly directly at the sensor, but the microwave "radar" does, or something like that.

[thomasthomsen]

PS. And please dont turn off the power for your network infrastructure 🙂 - That has a direct and immediate negative impact on your wireless coverage and performance 🙂

[Heino1]

The interference was coming from the PIR. As a test, I wrapped aluminum foil around the PIR and the interference went down. Thanks for the PIR suggestion.