Why does Wi-Fi use the same frequency as the microwave oven?

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Aina Prat Blasi
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When I start the microwave, do I lose the Wi-Fi signal on a nearby device? Wi-Fi and Microwave both work on a similar frequency, which can cause interference. But why? And if that's what happens at home or in the office, why isn't Wi-Fi cooking you?

Microwave and Wi-Fi use the same unlicensed spectrum

In 1947 the International Telecommunication Union established the ISM bands, short for Industrial, Scientific and Medical. The goal was to define which devices would be allowed to operate on certain radio frequency bands so that they would not cause interference with other radio communication services.

The ITM has designated the 2,4 GHz band as an unlicensed spectrum specific to microwave ovens. This band has three interesting properties: it does not require a lot of power to transmit, it is easy to contain, and at relatively low power it can heat food. All this has reduced the cost by becoming accessible to consumers.

As the name ISM suggests, the original intention was to use this frequency only for devices that were not providing communication. In the years when the prospect of an unlicensed spectrum has been used outside of its original purpose, such as cordless phones, walkie-talkies, and most recently Wi-Fi. The 2,4 GHz band was ideal to implement due to its low cost, lower power requirements, and decent range capabilities.

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Microwave ovens are not a Faraday cage

Whatever runs on the ISM bands should be designed for intolerances and avoid interference, and Wi-Fi devices have algorithms specially designed for this purpose. However, a microwave is powerful enough to overwhelm any nearby Wi-Fi signal.

Microwaves have shielding to prevent this, but they aren't a perfect Faraday cage. The very nature of a mesh window on the door prevents this. It is not uncommon to have leaks from a microwave oven, just look at one that hasn't been cleaned for a while to see it. You will likely see dirt and grease on the outside, which may have been from the food inside it. If it can cause solids to escape, it can also cause radio waves to escape.

Microwaves and Wi-Fi devices use a similar enough frequency that they can interfere with each other. Wi-Fi won't do anything noticeable to the microwave, partly because of its shielding and partly because all it's trying to do is reheat food.

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Wi-Fi cannot cook

Wi-Fi and Microwave use an extremely similar radio frequency, but there are two significant differences: focus and power.

A Wi-Fi modem sends its signal omnidirectionally. That is, it sends it in all directions in an approximate circle as far as possible.

Your microwave, on the other hand, sends its signal in only one direction, approximately towards the center of the oven.

That signal continues until it hits a wall, bounces, and comes back (at a slightly different angle).

It is not a perfect system, due to the nature of radio waves, and therefore every microwave oven has hot and cold spots. That's why microwaves make dishes turn.

Microwaves consume more energy than a Wi-Fi modem; typically they generate 1000 watts of power.

Conversely, a standard Wi-Fi router generates around 100 milliwatts (or 0,1 watts) of power.

You should increase the power of the Wi-Fi modem by about 10.000 times and confine the range to be able to cook anything.

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You probably don't need a new microwave

If interference problems are found, there is no need to replace the microwave; most likely the loss is minimal and not harmful to you.

Wi-Fi is much more sensitive and it doesn't take long to cause a problem. Instead of replacing the microwave, you could move it. Alternatively, buy a new Wi-Fi modem that works on the 5ghz band. Not only will you avoid interference from the microwave, but you will also avoid interference from your neighbors.

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Further Reading:

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  • Phone does not connect to WiFi, 8 solutions

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