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.