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Why Everything Wireless Is 2.4 GHz

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Re: Why Everything Wireless Is 2.4 GHz

#11

Post by flatulent1 »

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…

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.

Re: Why Everything Wireless Is 2.4 GHz

#13

Post by mathias_10gen »

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.

Re: Why Everything Wireless Is 2.4 GHz

#15

Post by moultano »

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.

Re: Why Everything Wireless Is 2.4 GHz

#16

Post by jauer »

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.

Look for 802.11a support, otherwise Apple AirPort.

Re: Why Everything Wireless Is 2.4 GHz

#17

Post by ryanpetrich »

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?

Re: Why Everything Wireless Is 2.4 GHz

#18

Post by martey »

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.

Re: Why Everything Wireless Is 2.4 GHz

#19

Post by TheAmazingIdiot »

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…

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.

Re: Why Everything Wireless Is 2.4 GHz

#20

Post by mfukar »

flatulent1 wrote: post #11
Hoff wrote: post #10

Earlier quoted context omitted.

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…

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 th…

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.
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