Foreign WiFi Muffler Bag: Take 1

Can I silence the foreign WiFi with an unused faraday bag I have from a previous need? Let’s find out!

A Faraday cage is a enclosure used to block electromagnetic fields. You use it for shielding, for safety, etc. In a nutshell you make sure that there is conductivity all the way around the thing you are protecting at the frequencies in question. The higher the frequency, the smaller the holes you can have.

Recently I wrote about the plight of the foreign WiFi in my home. I have 2 devices that enable their WiFi transmitters as access points, but are not connected to my network. 1 relates to my home security system, and 1 relates to my wife’s work from home setup.

The latter is a bit of a pain, it has a strong transmitter on both 2.4GHz and 5GHz. They are unused other than to cause noise. On the 2.4GHz band, there is only 3 channels, and each of these devices is chirping away on one of them lowering the noise floor.

On the 5GHz band, although there is a lot more spectrum and channels, only a few of them are actually great because of DFS (radar avoidance), see the list here. And of course, this device is eating one of the good channels at -40dBm.

So, can I use a Farraday bag I have left over from a previous need to muffle it? Let’s try.

Bag removed from storage, I assess the problem. The Aruba device will fit, but it has 3 Ethernet cables and 1 power cord to it. Frustratingly the industrial design is the device has no flat side, one Ethernet cable exits the middle of the back, 2 from one end, and the power cord from a side. The remaining sides are slipper and rounded. It fits ok into the bag, but, as you probably guessed from the foreshadowing of “the higher the frequency the smaller the hole size” above, its hard to create a great seal with the four cables exiting differently.

After some scrunching it around and playing w/ the WiFi power meter, yes, it was somewhat successful. On the 2.4GHz band we managed to get it to -53dBm from -35dBm measured at 6m. On the 5GHz band we managed to get it to -61dBm from -45dBm at the same distance. Is this enough to matter? Well, not really. It still renders those channels less than usable. The combination of the lack of seal plus the cables acting as unintentional antenna are blocking the approach.

Somewhere in my collection of stuff I have some ferrite coils, I might have a few that are cat-5 sized and be able to reduce the antenna affect. Hmm… its a big collection.

I guess I can hold off and try another approach, maybe get some copper foil and tape and make a box of some sort.

Anyone have any expierence with this? I mean, the easy solution involves a screwdriver, open the lid, solder the antenna to ground 🙂 But its not my device. The antenna are internal to it so I can’t just do the same on the SMA connectors.

PS I highly recommend these Faraday bags for your laptop sleeve. They are no bigger or heavier, they are tough, and they give you added protection. Give it a go.






2 Responses to “Foreign WiFi Muffler Bag: Take 1”

  1. X

    For 2.4GHz Bluetooth blocking at Aterica, we eventually settled on Faraday cage evidence bags, but our initial hacked thing that worked was a tall biscuit tin with sanded off lid-to-tin paint for good contact (this was key). Worked great even ungrounded. Similar to this:

    Not sure about 5GHz band, didn’t test, but I do suspect it would work.

    So how about a large cookie tin and packed tinfoil around cable entry? Don’t forget to sand off the paint/lacquer between lid and box and around cable hole(s) for the tinfoil electrical contact.

    Wifi leakage over wires is an interesting problem, if it is a problem … unlikely to be compliant with radiated emissions if it is. Sick FCC on them :-).

    1. db

      w/ 5W of power in there should be able to make biscuits at the same time!

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