Why Everything Wireless Is 2.4 GHz

http://www.wired.com/gadgetlab/2010/09/wireless-explainer/

by metellus • 16 years ago

84 35 16 years ago

If the article is tl;dr here's the gist.

ITU states that the ISM (industrial, scientific, medical) bands are nearly-anything-goes free for all in the frequency blocks. 5.8GHz was too expensive at the time wireless caught on, but 2.4GHz was cheap enough.

ITU chose 2.4GHz and 5.8GHz because the microwave emits broad spectrum radiation and harmonics at those frequencies, so they ignored them and made them free to use and abuse.

KC9JEF

flatulent13• 16 years ago

I'm surprised the article didn't mention that a ham band partly overlaps the 2.4 GHz WiFi frequencies. In theory at least, anyone operating WiFi gear isn't allowed to interfere with licensed services, including hams. Also, our unlicensed WiFi gear must accept any interference including that which "may cause undesired operation"... from anything, including the neighbors WiFi. (see FCC notice in U.S. WiFi product manuals)

Another related tidbit: Microwave ovens getting water molecules so excited at 2.4 GHz ties in with WiFi performance. It's a tidbit the head tech at a local wireless ISP didn't even know... 2.4 GHz WiFi is particularly prone to fading in fog/rain because water absorbs energy so efficiently at that frequency.

If they really want to get into strange frequency trivia, they should explain why Channel 37 has never been used by any over-the-air television station in Canada or the United States. Hint: little green men

CamperBob• 16 years ago

Microwave ovens getting water molecules so excited at 2.4 GHz ties in with WiFi performance. It's a tidbit the head tech at a local wireless ISP didn't even know... 2.4 GHz WiFi is particularly prone to fading in fog/rain because water absorbs energy so efficiently at that frequency.

No, no, no, no, no.

http://earth.esa.int/applications/data_util/SARDOCS/_icons/c...

Hoff• 16 years ago

NASA publications indicate a microwave absorption peak due to water vapor occurs at 22.234 GHz and peaks due to oxygen occur lear 60 GHz and 118 GHz (..). Below 10 GHz absorption caused by atmospheric gases is small.

The associated absorption graphs do indicate there is a small peak of 2 dB per kilometer around the 2.4 GHz band due to water. (I'd expect to have a larger drop through a wall.)

From: NASA Reference Publication 1108(02) 1987; "Propagation Effects on Satellite Systems at Frequencies Below 10 GHz; A Handbook for Satellite Systems Design; Second Edition" by Warren L Flock.

TheAmazingIdiot2• 16 years ago

And that would be your Part 97 divide: amateur radio.

Your consumer gear runs under Part 15. You cant generate interference, and you accept all interference. It's cut and dry, as in you have no recourse.

Amateur radio, on the other hand, have legal powers to stay on air, and even kick you off. Legally, a ham can command under Part 97 and your Part 15 to turn off your receivers (a good receiver is also a weak transmitter). Now the common courtesy in the ham community is to troubleshoot their problems so everybody benefits. But prior is the law.

As per H2O attenuation, that's way up there in Spark Gap frequencies... around 100GHz. What you're facing is perhaps at most +12dBi from your antenna and -40dB loss due to the good ol inverse square law.

The Water heating in the microwave and associated to 2.4GHz is false. When you have a polar molecule (liquid water) and expose it to alternating EM fields, they gain kinetic energy and warm up. Any polar molecule will exhibit this behavior when exposed to an alternating EM field.

loewenskind• 16 years ago

>Another related tidbit: Microwave ovens getting water molecules so excited at 2.4 GHz ties in with WiFi performance.

Does this have safety implications? I mean, if I stay too close to my wifi router can I be damaged?

blantonl• 16 years ago

Per the garage door reference. Any garage door opener manufactured between 1984 and the preset operates on frequencies between 300-400 Mhz, Which is smack dab right in the middle of US military allocations. There are well documented cases of military communications systems interfering with garage door openers resulting in many problems for the owners.

Edit: Preset == Present

kjuhghjk• 16 years ago

They use a bunch of other unlicensed bands around 416Mhz

flatulent13• 16 years ago

Prior to that, there was equipment using channels that were between some of the channels on the old 23 channel Citizens' Band. That was far worse. C.B. operators running splatter-prone illegal amplifiers were bad enough, but people discovered these apparently "empty" channels (sometimes called 3A 7A 11A 15A 19A 22A and 22B) and modified their radios to use them. Eventually the F.C.C. gave up on those channels being viable for things like garage doors and R.C. model airplanes, and they became part of 40 channel C.B.

I think some of that remote control equipment shared 72 to 76 Mhz for a while. That's a gap, 2/3 the size of a t.v. channel between channels 4 and 5.

I'm wondering if the F.C.C. will take away t.v. channels 2 through 6. Almost everywhere, the stations formerly on those went to U.H.F. with the digital transition. I guess they figure that few people want to buy really big antennas for the lowest frequencies. (UHF and 7-13 use much shorter antenna elements). Anyway, those channels have the best coverage potential of all of them, but they're hardly used now. (see tvfool.com or the FCC database)

http://www.fcc.gov/mb/video/tvq.html

IChrisI• 16 years ago

Am I the only one amused that wired.com is writing about wireless?

mcav• 16 years ago

Better that than talk about Ethernet all day.

code_duck• 16 years ago

The wire has to come in somewhere, right? Unless we implement Tesla's ideas of wireless power transmission!

mathias_10gen• 16 years ago

They didn't really cover the important question of why modern wifi still uses 2.4GHz rather than the much wider 5GHz spectrum. Anyone living in a crowded apartment building owes it to themselves to get 5GHz routers so avoid interference with their neighbors' wifi. For some reason its getting harder to find 5GHz access points and most online stores don't let you search by frequency band.

jauer• 16 years ago

Look for 802.11a support, otherwise Apple AirPort.

martey• 16 years ago

A lot of higher end N routers are dual-band; they work on both the 2.4 GHz and 5 Ghz bands. It would be silly to have a router that only worked with 5 Ghz, since many laptops and almost all cell phones only work with 2.4 Ghz. Routers that work with 5 GHz should be relatively easy to find - just make sure that you search for "dual band" instead of 5 Ghz.

mike-cardwell• 16 years ago

I use the 5Ghz band. Both my Time Capsule and Macbook support 11n over 5Ghz.

muon• 16 years ago

5GHz opened up pretty recently. This along with high of cost of making a 5GHz radio and wider acceptance of 802.11ng is reason for Wifi still sticking to 2.4 ISM band.

teilo• 16 years ago

Except that the current generation of cordless phones are now in the 1.9Ghz band, the DECT 6.0 standard.

yread2• 16 years ago

Yes, but DECT is not free-for-all, you have to pay licensing fees. And those were fairly high until 2005.

moultano• 16 years ago

Imagine what crazy technology we'd have if more spectrum was available for free-for-all access. Generally I think the FCC does a reasonable job, but I really doubt FM radio is really the best use of that huge swath of beautiful spectrum.

They should think about pulling out little regions of spectra normally used for other things and let the market try to do things with them without restriction. They might end up too saturated to be useful, but we might develop smarter receivers and a cornucopia of new products. It's worth a 1% A/B test I think.

ryanpetrich• 16 years ago

But can you imagine the talk radio chatter if the FCC proposed reallocating the AM bands?

oiuygtfrtghyju• 16 years ago

But if nobody hears them - do they make a sound?

gcb2• 16 years ago

> Imagine what crazy technology we'd have if more spectrum was available for free-for-all access.

Well, FCC only regulates the U.S., right?

what happens in countries where there's more bands available? i remember a router that allowed me to select twice more wifi channels if i mention i was in japan...

gcb2• 16 years ago

btw, one thing that wouldn't happen is me having to move the Wii away from the home theater with wireless back speakers >:

notauser2• 16 years ago

3 extra. 1-11 (US) 1-13 (Europe) 1-14 (Japan).

American MacBook Pros (used to?) come locked to 1-11 with no way to change that, which really sucked if you ever traveled anywhere.

notauser2• 16 years ago

The nice thing about 2.4ghz is that it's pretty well attenuated by walls.

That sounds like a disadvantage... but it does let you cram a lot of transmitters into a city. If everyone had a 102Mhz transmitter the resulting network would be like a class room full of five year old boys who each had their own megaphone.

known• 16 years ago

http://electronics.howstuffworks.com/cell-phone-radiation.ht...

rxever• 16 years ago

"A 900-MHz system will be more easily able to broadcast through a multifloor house, but a 2.4-GHz system will have a longer range (if unobstructed)" - isn't it so that lower frequencies can penetrate longer distances without obstructions? And higher frequencies are better in short distances? If they get interupted they can easily replace the "damaged" data with new ones since it's high frequence(ability to transver more information in the same time).

Why Everything Wireless Is 2.4 GHz

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