Why Everything Wireless Is 2.4 GHz | Hacker News Reader

Why Everything Wireless Is 2.4 GHz

wired.com

84 pointsmetellus35 comments

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.

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

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

> 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...

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

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.

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.

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.

Look for 802.11a support, otherwise Apple AirPort.

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.

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

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.

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

They use a bunch of other unlicensed bands around 416Mhz

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

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

Better that than talk about Ethernet all day.

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

"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).

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

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

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

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

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

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...

Well, that's not very helpful, because he's not talking about the standard atmosphere, but about a particularly humid atmosphere.

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.

I wonder what level of humidity that 2 dB per kilometer figure is for? Is that typical or worst case?

At 20 kilometers (about 12.4 miles), a distance this ISP is trying to serve some customers at, that 2 db becomes 40db. Overcoming an additional 40 db loss would require increasing the power by a factor of 10,000 times. They're using amplifiers and directional antennas but the fade margin is nowhere near 40 db. And they do have fading problems. Of course refraction/reflection from temperature/humidity inversion gradients and other propagation effects come into play too. It isn't just simple absorption.

Are we still talking about WiFi? The one with coverage limited in fractions of a kilometer? Achieving 20 km coverage radius (or even targeted coverage) sounds like a sisyphean task to me.

I dont know how they do it but the longest range wifi link is 382km[1]. And 10 km with good directional antennas is not that special, really.

[1] http://www.slideshare.net/1ereposition/long-distance-wifi-tr...

Wow, that's actually kind of exciting (and disturbing!), even though the link is unstable. Thanks for the info.

Hoff, which graph are you looking at? I'm looking at page 20 of chapter 3 (http://descanso.jpl.nasa.gov/Propagation/1108/1108Chapter3.p...) - it does show a small peak but it looks to me as if it's at ~22 GHz, not 2.4. Note that it lies between "10" and "10²" on the X-axis. Also the magnitude of even that peak is only 2 x 10 to the minus 1 - i.e. 0.2 dB per km, and the nearby freqs are really not much different. The graph on page 21 agrees.

This article: http://www.martin.chaplin.btinternet.co.uk/microwave.html suggests that 2.4 GHz was chosen for microwave ovens as a NON-optimal absorption frequency, as this allows some of the energy to penetrate past the outermost layers of food!

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.

>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?

No. Because it doesn't work that way. See comments above.

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