Friday, June 02, 2017

Microwave Ovens and WiFi Routers

I never cease to wonder about the electromagnetic spectrum. Much of it is invisible to our senses, and yet, we have reached a stage when it is quite impossible to survive without it.

The microwave oven in out kitchens sends out waves at around 2.45 GHz (2,450,000,000,000 vibrations/second!), heating up food at the molecular level. The ubiquitous WiFi that keeps us connected to the internet - and the rest of the world - are "harmonized" worldwide in the 2.4 and 5GHz bands. Even without getting into the world of electronic waves that send signals across great distances (radio, satellite and space probes), getting a grip on regular household devices seems complicated enough!

Both the equipment's - the microwave oven and the WFi router - produce signals in the Industrial, Scientific and Medical (ISM) bands that have been allotted by ITU for non-communication purposes. There seem to be 12 frequency ranges in the ISM band that ranges all the way from 6.78 MHz to 245 GHz. Out of this, home equipment like ovens and WiFi routers use the frequency range 2.45-2.5 GHz.

Since a licence is not required for equipment produced in this range, the part of the spectrum is also crowded with radio-communication services, including amateur satellite services. Thanks to this dual-use, the WiFi equipment you purchase from one country country is likely to interfere with the microwave oven imported from another country. So, if you are heating a mug of coffee in your microwave oven, your internet connection may get disrupted.

International standards - especially IEEE 802.11 a/b/g/n - tries to deal with this problem:
  • 802.11a supports bandwidth up to 54 Mbps and signals in a regulated frequency spectrum around 5 GHz. More expensive, usually used by businesses. Higher frequency makes it difficult to penetrate walls, so its best for open areas.
  • 802.11b supports bandwidth up to 11 Mbps, comparable to traditional Ethernet. Usually for home networks.
  • 802.11g supports bandwidth up to 54 Mbps; uses the 2.4 GHz frequency for greater range
  • 802.11n is an improvement on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one.

It is still mind boggling to think that we have actually figured out ways to precisely control devices that produce more than a trillion vibrations per second! How do we do it? And why is it that microwave ovens need chunky magnetrons to produce the same kind of signals that are produced by lightweight WiFi routers?

In an emergency, can I rig up my WiFi router to heat up a mug of coffee? :)



Wireless Standards -

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