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Why Everything Wireless Is 2.4 GHz

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Re: Why Everything Wireless Is 2.4 GHz

#31

Post by mfukar »

yread wrote: post #22
mfukar wrote: post #20

Earlier quoted context omitted.

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.

Re: Why Everything Wireless Is 2.4 GHz

#32

Post by [deleted] »

Confusion wrote: post #21
CamperBob wrote: post #9

Earlier quoted context omitted.

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.

[deleted]

Re: Why Everything Wireless Is 2.4 GHz

#33

Post by mike-cardwell »

martey wrote: post #18
mathias_10gen wrote: post #13

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.

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.

Re: Why Everything Wireless Is 2.4 GHz

#34

Post by loewenskind »

flatulent1 wrote: post #5
TheAmazingIdiot wrote: post #2

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 an…

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 manua…

>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?

Re: Why Everything Wireless Is 2.4 GHz

#35

Post by oiuygtfrtghyju »

ryanpetrich wrote: post #17
moultano wrote: post #15

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…

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?

Re: Why Everything Wireless Is 2.4 GHz

#37

Post by blueben »

loewenskind wrote: post #34
flatulent1 wrote: post #5

Earlier quoted context omitted.

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 manua…

>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.

Re: Why Everything Wireless Is 2.4 GHz

#38

Post by jeh »

Hoff wrote: post #10
flatulent1 wrote: post #5

Earlier quoted context omitted.

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 manua…

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 Publ…

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!

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