Why does my microwave kill the Wi-Fi?

Question

Every time I start the microwave in the kitchen, our home Wi-Fi stops working and all devices lose connection with our router! The kitchen and the Wi-Fi router are in opposite ends of the apartment but devices are being used a little here and there. We've been annoyed by the instability of the Wi-Fi for some time and it wasn't until recently we realized it was correlated to microwave usage.

After some testing with having the microwave on and off we could narrow down the problem to only occurring when the router is in b/g/n mode and uses a set channel. If I change to b/g mode or set channel to auto then there is no problem any more...but still!

The router is a Zyxel P-661HNU ("802.11n Wireless ADSL2+ 4-port Security Gateway" with latest firmware) and the microwave is made by Neff with an effect of 1000W (if this information might be useful to anyone). There is an "internet connection" light on the router and it doesn't go out when the interruption occurs so I think this is only an internal Wi-Fi issue.

Now to my questions:

• What parts of the Wi-Fi can possibly be affected by the microwave usage? Frequency? Disturbances in the electrical system?
• How can setting Auto on channels make a difference? I thought the different channels were just some kind of separation system within the same frequency spectrum?
• Could this be a sign that the microwave is malfunctioning and slowly roasting us all at home? Is there any need to be worried?

Since we were able to find router settings that cooperate well with our microwave's demand for attention, this question is mainly out of curiosity. But as most people out there...I just can't help the fact that I need to know how it's possible :-)

Answer 1

802.11 (b/g/n) operates on the 2.4 GHz ISM band. This is conveniently the same band that your microwave oven operates on. This isn't a coincidence, both operate in the 2.4 Ghz ISM band, because it can be freely used at low power without licence nearly anywhere in the world. Many other RF technologies including Bluetooth, walkie talkies, baby monitors, etc. also use the same band.

Most microwave ovens tend to be very well shielded and will not emit enough radiation¹ to interfere with wireless communications. It is possible that your unit has a damaged shield. You could look into replacing it. That said, the amount of radiation a microwave has to "leak" for it to interfere with your wireless is tiny - 0.01% of it's output, roughly the same amount as your router or laptop, and far less than a typical mobile phone.

A better thing to do would be to upgrade your wireless networking equipment and devices to be 5 GHz compatible (used with 802.11 a/n/ac). This is the other major band WiFi networks can operate in, is capable of providing increased performance, and should not suffer interference from microwave ovens. You can tell if a device supports 5Ghz by checking if it lists "dual-band" capability, or supports 802.11a (e.g. "a/b/g/n") or 802.11ac. 5Ghz capable wireless equipment is becoming more widespread, but 2.4Ghz remains common in older and lower-end devices.

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Addressing your different channels, microwave ovens (which should label the output frequency somewhere) should use ~2.450 GHz.

WiFi (b/g/n) channels typically range from 2.412 GHz to 2.472 GHz, with a bandwidth of 20 MHz and a 2 MHz band gap. If you pick a channel from the upper or lower end, and assuming your microwave oven is precise enough with its frequency, you could sidestep it entirely. This is, however, just a guess.

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sourced from Wikipedia

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¹ I must point out that 2.4 GHz is far from ionising radiation, which is at least 2400000 GHz (the type that can harm human tissue and/or cause cancer). Even if the shield is faulty, it will not cause any harm. Any (very slight) damage would be caused by heating (and not directly by 'radiation'), which you most definitely will feel before any real damage. Also, just don't stand in front of it for hours a day. That always helps. Some countries also have regulations on the maximum energy allowed to be transmitted, ostensibly for human safety (there are other limits designed to reduce interference). Do note that such regulations tend to play far on the safe side, well below any level with concretely proven ill effects.

Answer 2

Both microwaves and Wifi operate on the same frequency, 2.4 GHz. In theory, a "properly shielded" microwave shouldn't leak any radiation. However, in practice, they leak quite a bit.

Here is a blog post from one of the guys over at serverfault. They took a frequency analyzer, and looked at how various other 2.4 GHz devices (like microwaves and baby monitors) affect the Wifi spectrum.

This is what they found the Wifi spectrum to look like normally:

Those diagonal lines are the Wifi broadcast. There is almost no interference, so they are clear and easy to see.

This is what that same connection looks like with a typical microwave on:

As you can see, the microwave causes some serious interference.

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To work around this, I'd recommend switching to wifi equipment which can operate in the 5 GHz band, like the latest 802.11n or 802.11ac routers.

Answer 3

The other answers have mentioned microwave leaks. For anyone concerned (even if you aren't having WiFi problems) an easy way to test this for sure is to put a working cell phone in the microwave and close the door. If possible, unplug the microwave first if you are worried about accidentally hitting any buttons and turning on the microwave with your phone in it, as that would definitely not be good for the phone!! Then see if it can keep any kind of signal either by looking at the screen through the holes in the door if you can safely prop it up, or by calling it, or by trying to interact with it over 3G or WiFi. I did this when I was testing an app that exhibited problems only when it lost a data signal, something that does not happen naturally very often in testing, leading to a hard to reproduce problem. I found that when the microwave door was completely shut my app could not longer talk over the data connection, but if I even pulled slightly on the door so that there was barely a noticable crack it could. In your case WiFi might be better than 3G, although I found my microwave shielded both of them.

Answer 4

What parts of the wifi can possible be affected by the microwave usage? Frequency?

Yes. A microwave operates around 2.4 GHz.
Wireless B, G and some parts of N operate around 2.4 GHz.

Note that the microwave should be properly shielded and that the effect should be minimal.

How can setting Auto on channels make a difference?
I thought the different channels were just some kind of separation system within the same frequency spectrum?

The 2.4 GHz range for home usage (read: for wireless, bluetooth, baby phones, some cordless phones, .... ) is a small range of frequencies. It could be (guess!) that with auto channels turned on your devices move to either a less jammed 2.4GHz channel, or possible even only to the 5 GHz band (often used by wireless-N, which can use both 2.4 and 5 GHz bands).

Could this be a sign that the micro is malfunctioning and slowly roasting us all at home? Is there any need to be worried?

Are you feeling slightly cooked?

But seriously: Yes and no. The microwave should be shielded. It should not emit any harmful amount of radiation. Unless you removed the door and manually jimmied the safety mechanisme you are probably safe.

Answer 5

Your microwave is emitting at the same frequency that your wifi operates on. I spent a considerable amount of time working for a major internet provider as a field technician, and wifi interference was one of our main issues.

Interference can also be caused by seemingly random electrical objects throughout your home, such as cordless phones (showing my age), treadmills, refrigerators, electrical wiring in your home, electrical lines, and oddly enough, AM radio signals. It should be noted that generally the electrical wiring in your home and the AM radio signals will not directly interfere with your wifi signal, but will interfere with the signal you are receiving from your internet provider, which will make your internet as a whole slower, or the service itself will drop in and out depending on the severity of your ‘line noise’.

Your wifi is a radio signal, just at a much higher frequency than most broadcast radios operate on. The best source of comparison I can draw on is to think about what happens to your AM radio signal, when you drive underneath a power-line. The signal noise you get is comparable to the noise your wifi is competing against near the aforementioned electrical devices.

Auto channel may help alleviate some of your problems, but auto channel is more meant to cope with multiple wifi signals in a small place, such as in an apartment complex, or an office building that is home to many different businesses all operating wifi.

Best advice I can give you, is get into the user interface for your router, and adjust the signal to the low or high end, or start cooking more in your over. Unfortunately, there is not a whole lot you can do about signal noise bleed. It is always present, and at least for the immediate future will not be going away.

Answer 6

As several have noted both the microwave and the WiFi operates at the same frequency band. Also Bluetooth is in the same frequency band. Microwave affects WiFi more than Bluetooth as Blutooth is designed to just send and then resend if it fails while WiFi is designed to wait until it is quiet so starting a microwave will cause the WiFi to stop and wait.

Answer 7

I had to replace my Microwave. The brand new one completely took out the 2.4g WiFi band in my house when the oven was on. I have never had this problem before. I dug out my 30 year old microwave leak detector, and for the first time in 30 years, it registered a high reading around the door. I ordered a new electronic leak detector and I rechecked the Microwave. The federal limit is 5 mW at 2 inches from the Microwave. The leak detector registered a reading of 7 to 9+ (above 9 it shows OL for overload) at 2 places of the Microwave door. Also the door seemed very loose.

I returned the Microwave and replaced it with a different model. I now have no problems with my WiFi and the leak detector registers a very small reading around .03 mW.

This was the solution to my WiFi problem going out when the Microwave was on. Leak detectors are not that expensive. It might be a good investment. They are making Microwaves cheap as heck now and they seem to have a lot of "door problems".

Answer 8

Replace the microwave owen immediatelly. Could be a coincidence of the frequencies, but most probably shields of your microvave owen are disconnected or not implemented at all. Therefore for example for people with heart clock (Artificial cardiac pacemaker) it could be very dangerous to be exposed to your microwave. But replacing your microwave oven could have effect that it will emit different freqencies and will not interrupt your WiFi - as usual. I think your case is exceptional.

Answer 9

I think InSSIDer will show you some channel power levels but what I think you are looking for is a true spectrum analyzer. Using a SE you can see non-wifi interference like monitors, bluetooth, phones, microwaves, etc... I have a leaky microwave at work that when used increases the channel utilization on CH11 to about 30%. So my wifi deployment current runs at about 20% utilization so when the microwave runs it jumps to over 50%. What I was able to do in the interim was to move my devices closest to the break room off of channel 11. I know this is not the best solution but it's only until we can get our facilities folks to install a newer commercial grade microwave in there. BTW the one currently in there and leaking is commercial grade but might be too old or the shielding is just off.

Answer 10

A microwave functions by using a heating element to pulsate off small amounts of radiation which excites water and fat molecules in food that produce friction and heat up. Basically, the radiation that normally heats up food may be in the same hertz range as a wifi router (something I've never heard of before, but certainly is possible). That can interfere with the radio waves used by the wifi router and other types of electromagnetic waves used by other wireless devices. The best way you can avoid it is just to keep your router away from the microwave, or get a type of material off of eBay that can absorb electromagnetic waves (I can't think of any off the top of my head).

Answer 11

I have found microwaves to interfere strongest on channel 9 or so (which you can see in the photo, the microwave blasts the whole band pretty well but is strongest towards the top of the band.) If in N mode the access point tries to use a wider channel, it's almost impossible to avoid noise versus a 20mhz channel. You might be able to run N but restrict it to 20mhz instead of automatic channel width.

Answer 12

Shields are down! Check for cloaked Klingons!

Or just make sure the back of your microwave is against a wall - preferably facing the opposite direction from your router. A wall or wooden partition between the two also helps, as does a fridge. Turning a toaster on at the same time as the microwave has even been known to help. The last thing I did was to place my router - a FritzBox - into a desk drawer. No more interference.