Microwave ovens can interfere with your WiFi network. Dr Karl shares his tips for staying connected to the interweb while preparing dinner.

Microwave ovens pump out about 1,000 watts – that’s about 10,000 times more than a WiFi access point (Source: bjenkins/iStockphoto)

We are all migrating to a strange new world one in which we are all getting more connected, both with, and without, wires. And more and more frequently, people are finding that the wireless/WiFi/interweb system stops working whenever the microwave oven is used.

WiFi is just a way to deliver acess to the interweb, without cables. It was ‘invented’ in its earliest version back in 1991 for use with cashier systems. Back then, it was called ‘WaveLAN’. The ‘wave’ part of the name refers to the fact that the information is carried on radio waves, while the ‘LAN’ stands for ‘local area network’.

The professional organisation in charge was the IEEE (Institute of Electrical and Electronics Engineers), so they changed the name to ‘IEEE 802.11b Direct Sequence’. This is not a very catchy name, so IEEE hired a brand-consulting company called Interbrand Corporation, who in August 1999, came up with the name of ‘WiFi’. This was a play on the term ‘HiFi’, which for audiophiles stands for ‘high fidelity’.

I first used WiFi in 2000, and I was amazed (and I still am). The ‘WiFi box’ or ‘access point’ is just a gutless little radio transmitter by “gutless” I mean a maximum power of just one tenth of a watt. It broadcasts a radio signal with a frequency of around 2.45 gigahertz. The radio signal carries the interweb information to your computer, which strips away the 2.45 gigahertz carrier signal and suddenly, without any wires, you are surfing the web.

Of course, it’s a little bit more complicated than this.

First, around that nominal 2.45 gigahertz there are about a dozen different frequencies all next to each other (and surprisingly, overlapping each other). This means that a bunch of computers and WiFi boxes can all surf the web at the same time without interfering with each other (at least, not too much).

Second, just to get this out of the way, some WiFi boxes (and computers) can talk to each other on another set of frequencies up around 5 gigahertz. These frequencies don’t experience interference from microwave ovens. On the other hand, their range is shorter.

Getting back to why microwave ovens can interfere with WiFi to heat up food, microwave ovens pump out about 1,000 watts. That’s about 10,000 times more than a WiFi access point. Most of this power is safely contained within the microwave oven.

But you need only the tiniest amount of leakage to cause interference. This microscope leakage is not dangerous to humans, but can really muck up your web access. What you see is that webpages either load very slowly, or totally freeze.

A technical writer, Jim Geier, tested a WiFi access point at varying distances from a microwave oven while it was working.

At 30 centimetres from a working microwave oven, the data transfer rate dropped down by 90 per cent. It was down by 75 per cent at a distance of 2 to 3 metres, and by 60 per cent even at 6 metres.

It was worse again if there were several users on the network. By the way, many other devices also use the 2.45 gigahertz frequency band, which is what WiFi networks use.

These devices include cordless phones, remote doorbell ringers, Bluetooth devices, internal movement sensors for some car alarm systems, video senders that send a video signal from one place (a room, surveillance camera on roof, computer, etc) to another, and yes, baby monitors.

Your microwave oven, as well as all of these devices can interfere with each other, and your WiFi network and sometimes, your WiFi network can interfere with them.

So what can you do?

First, keep the WiFi unit well clear of your microwave oven. Ten metres would seem to be the minimum.

Second, the problem was a lot worse with the higher-numbered WiFi channels (such as 8 – 11) as these channels are closer to the frequency that most microwave ovens run on. So try changing to the lower numbered channels. (You’ll have to log in to the access point with software to do this good luck). But as part of this, check the label on the back of the microwave oven to find out exactly what frequency it runs on.

Or if these measures don’t work, try to not update your Facebook page while you are preparing dinner as hard as this might sound.

Tags: computers-and-technology, wireless-technology, mathematics, physics

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Published 25 September 2012

2012 Karl S. Kruszelnicki Pty Ltd

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Add your comment

25 Sep 2012 7:01:06pm

Hey Karl, somewhere in all this you should have tagged CSIRO who after all got paid this year for inventing the damned thing. Very interesting though.

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26 Sep 2012 6:48:18pm

read his article from last week…

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26 Sep 2012 8:19:36am

Wi-Fry ?? the diet low fat variety.

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28 Sep 2012 7:12:59pm

Im a network engineer so live and breathe this stuff. Probably also worth noting because of the channel overlap you mention, it normally does more harm than good setting your own channel in one of the 2.4 band channel “gutters”. Channels 1,6,11 should be stuck to – avoid anything inbetween as you will find yourself competing with at least two interfering channels that way. Also of note is that the 5ghz spectrum is normally interference free due to lack of APs on this band and the number of channels (much more than 3!). Interested peeps should check out inSSIDer- a free tool to analyse the wifi airspae spectrum, plot it all lovely….. Hope this helps. Love your work Dr Karl!

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10 Oct 2012 4:24:19pm

Cool! Thanks Keiran

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02 Oct 2012 9:53:24am

I can second this, we stream video over wifi, and every time someone uses the microwave sure enough, the video drops out.

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04 Oct 2012 7:52:54pm

Very interesting article, thanks!

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