

Why Everything Wireless Is 2.4 GHz - metellus
http://www.wired.com/gadgetlab/2010/09/wireless-explainer/

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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.

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gcb
> 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...

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notauser
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.

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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.

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martey
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.

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

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blantonl
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

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flatulent1
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>

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

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

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rxever
"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).

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known
[http://electronics.howstuffworks.com/cell-phone-
radiation.ht...](http://electronics.howstuffworks.com/cell-phone-
radiation.htm/printable)

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

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

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TheAmazingIdiot
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

~~~
flatulent1
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

~~~
Hoff
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.

~~~
flatulent1
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.

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mfukar
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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yread
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...](http://www.slideshare.net/1ereposition/long-distance-wifi-trial)

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

