does your microwave screw with your wifi?

[solarbird]

Does your microwave screw with your LAN’s wifi signal? It might well. Depending upon your microwave and wifi, it could be pretty severe. In our case, the microwave would stop wifi in the whole west end of the lair.

This happens because microwave ovens can throw out a lot of radio interferences in the 2.4Ghz range, and that’s where 802.11b, g, and n all operate. Now, sure, you can upgrade your equipment to dual-band 5.0Ghz/2.4Ghz gear, but that’s annoying, and costs money, and a lot of your devices won’t upgrade anyway.

So I started thinking about how this could happen, because I know the requirements for microwave oven shielding. Microwaves ovens are basically grounded metal boxes – I saw someone jokingly suggest putting your microwave into a Faraday cage, but these ovens basically are Faraday cages, so that won’t help. Okay, yes, the glass front isn’t a solid sheet of metal, but that grating that makes it hard to see through the glass is there for a reason, and it’s reasonably effective as shielding.

Then I realised one part of the oven isn’t shielded. Typically, it’s not shielded at all. It’s the power cord. Which makes the power cord a transmission antenna for microwave oven RF noise.

Now, thanks to all the RF issues we were having with the studio wiring last year, I’d stocked up on things called RF chokes. They’re used to filter out radio noise. This is all very high frequency noise, so you need ferrite chokes, specifically.

Clamp-on ferrite RF choke

They cost less than two dollars. Basically, they convert the RF field coming off the cable into self-cancelling magnetic fields, which – pleasantly – don’t interfere with your wifi. You want a tight fit, because physics reasons.

So I clamped two tight-fighting large ferrites onto the power cable, one on each end, because for all I know the RF issues with our building wiring were making things worse. Also, we seemed to be having a lot of RF coming off that power cord. And we gave it a go.

The wifi hasn’t fallen over while using the microwave once since attaching those chokes. Not even once. We’re still seeing interference – and the resulting slowdown in net performance which results from that interference – but it’s dramatically reduced, and we no longer lose connections and even audio and video streaming keeps going. It’s still an impact, we absolutely see it in performance testing. But it’s no longer an impact that matters.

So, yeah. If you’re seeing this, give it a try. It’s a hell of a lot cheaper than replacing all your networking kit.

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Comments

[angelwolfgeek]

daymn. I've heard of microwaves messing with wifi before, and of ferrite beads but... this is new.

My microwave *dosen't* do this, but I'd try this if it did. Unfortunately my wifi suffers from too many neighbours and I ended up using homeplug as a backbone network ;p

[solarbird]

We're using homeplug tech too - the entertainment system is using a wiring-based hardline for linking all that kit (Tivo, AppleTV, XBOX, etc) through a local switch over to our server closet and that switch. This gets us across that plumbing wall without having to run as much ethercable through walls and it's been working quite well for us.

(Our West hub actually is wired through that wall to the server closet - it took six tries to find a place we could make a wire fit, too. It's a fucked up wall, it is.)

I presume you've done the usual WiFi-channel-avoidance dance? If so... hoo, yeah, that's just a mess. Sorry about that. (But if you haven't: set your router on a different channel to your neighbours, and it will actually help.)

[angelwolfgeek]

heh. Yup. We live in a 25 story building with 4 apartments each on all but the ground floor (which is empty) and the top floor (where we are) which has 2. I did a site survey, and we have a mix of a shitload of interference on all the channels, and bad feng shui.

I'm technical enough to have a basic wifi survey app on my phone (and occationally using it when I help people out with their issues). Even with the best possible channels, 2.4ghz wifi still sucks.