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Remote Feed: 72-Mile 802.11b Link
An anonymous reader writes "A 72-mile link was installed last month from San Diego to San Clemente Island, using standard 802.11b WLAN gear and high-gain, 2-foot parabolic antennas. More in this Computerworld article."
War surfing!!!
Lovely. Now there is a path 72 miles long for people to exploit. Insecure networks, always fun...
Does this mean I have to wear a 2 foot antenna on my shoulder when I which to connect my laptop to the internet? This all sounds so incredible.
so how did they overcome the earth horizon limitations?
Watson: Did you get it?
Bell: Yes, send more porn.
"Smokey, this isn't Nam, there are rules." -Walter
That would be good for my parents' house which is more than 5 miles from the nearest excahnge, but is in an ideal location for that antenna - at the top of a hill. I hope this becomes available to the masses at a reasonable price soon.
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"The test was declared a resounding success when the message '@#FGGgWEe#GR... +++ATZ +++ATH0 NO CARRIER' was successfully received by the San Celemente station. Congratulations to all involved!"
how would you warchalk this link? I mean, besides the technical difficulties of writing on water. Do you put a really REALLY large ear on the ground near the antenna? In all seriousness, this is quite an impressive feat, especially using a highly crowded spectrum. I am curious though how it handles atmospheric interference. Over 72 miles the beam width on this thing must be miniscule and I would think any atmospheric disturbance would send the link crashing. Then again, I've never passed 802.11b traffic more than 2 or 3 miles.
Great read, but somehow I picture something like this mounted on a 40' mast.
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The link to San Clemente Island -- used to carry data from a seismograph, data logger and Global Positioning System receiver....
During an earthquake, will that data registered by the seismograph still make it to the mainland?
More importantly; if it's a REALLY big one, will the GPS record San Clemente's new position?
Seriously, however, broadcast medium networks like 802.11b are best used for distribution, not long distance point-to-point links (fiber is ultimately cheaper on a bit-for-bit basis), but this demonstrates that you can build a really cheap 802.11b distribtuion network to solve the Last Mile Problem. Another nail in the coffin of Ma Bell...
...-.-
can bring it down! Imagine, if you will, that there's a Quickie Mart in the middle of this stretch. Every time the microwave oven heats a "Pocket", the link is down.
before a Corona commercial shows the guy on the beach adjusting the dish and using it as a shade umbrella?
I have always been under the impression that for part 15 devices that the power is given in mv/m.
According to http://www.radioinnovation.com/Howto/how_pass.htm the maxiumum power for a part 15 device in the 2.4ghz range is allowed an average power density of 50 mV/m at a range of 3 meters, and is a transmitter power of -3.4 dBm when used with a perfect 1/2 wave dipole. -3.4dBm is, http://www.qsl.net/vk6zse/wattsdbm.htm, between 500-800 microwatts.
Now I realize that they are using parabolic antennas, but are they still meeting that average power density, I suspect that ERP is likely greater than 1 watt when using directional antennas.
Then the LA afternoon smog rolled in cause 98% packet loss. Reports of low flying sea gulls being singed as they passed through the deadly rays have also been reported.
Amateur radio operators have been doing stuff like this for years on frequencies above and below 2 Ghz. Here's a listing of distance records .
Tired of being "punished" by the Slashdot $rtbl since 2002. I'm now over at http://soylentnews.org/ .
Which is probably why they shot over water. No trees, shorter towers. It's great to see this stuff getting tested, especially by educators who tend to publish their results. Hams have been enjoying this sort of fun for a long time now, and the basic problems are still in front of you. You have to have line of site (plus some extra height for the Fresnel effect), and you still have to buy and point dishes and since 1 watt WAPs aren't sitting on the shelf, you still have to get a pair of expensive little amplifiers. These things can at least be purchased now, and if you want to set up such a link, attend your local Amateur Radio shindig and you'll find piles of retired microwave enthusiasts, eager for the chance to lend a hand....
(b) The maximum peak output power of the transmitter shall not exceed 1 Watt. If transmitting antennas of directional gain greater than 6 dBi are used, the power shall be reduced by the amount in dB that the directional gain of the antenna exceeds 6 dBi.
I am just guessing at what they mean in the article by "high-gain". They say they are using a 1 watt bi-directional amp. My personal definition of high gain is a lot higher than 6dBi.
Am I misinterpreting this?
Eve Fairbanks says I drive a hybrid!LOL
1 watt + 2ft dish at 2.4ghz would put a useable signal into a satellite in geosync orbit. 72 miles seems modest as far as range goes... the gain with a good 2ft dish at 2.4ghz is pretty extreme. If it is line-of-sight at 72 miles the signal should be way way above the noise.
I want a house along the signal path so I can enjoy roast $BIRD as they fall onto my picnic table.
Trolling is a art,
here's a link to more information via HPWREN's web page: hpwren San Clemente
Frank Dwyer (dwyer@sdsc.edu)
Assistant Director, IT Services
San Diego Supercomputer Center
Not smog, specifically. A place I used to work at had a microwave connection on the roof, feeding from one of the taller skyscrapers downtown. On days when it snowed, or rained really hard, the net connection would flake out like crazy.
'Snow Days' took on a whole new meaning.
Tangent: a bigger problem was the various punks and squeegee kids 'playing' in the microwave field. They would jump back and forth in front of the dish for the little zap it gave you. We tried to warn them....
ZAP 'Owww! My sperm!' ZAP 'Funny, it didn't hurt the second time... '
If Jesus wants me it knows where to find me.
probably. I am only guessing but when they say "runs with the maximum 1-watt power output allowed by the Federal Communications Commission for 2.4-GHz equipment" I assume they don't mean 1W power out of the bridge, but rather 1W effective. So assuming 24Dbi antenna's (the highest gain parabolics I have seen for 2.4Ghz) the should be ok with 100mW bridge units which is probably what they are using. I did not see them mention amp's anywhere in the article.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
(i) Systems operating in the 2400-2483.5 MHz band that are used exclusively for fixed, point-to-point operations may employ transmitting antennas with directional gain greater than 6 dBi provided the maximum peak output power of the intentional radiator is reduced by 1 dB for every 3 dB that the directional gain of the antenna exceeds 6 dBi.
Fab-corp sells a 24 dBi parabolic. If my math is right, that allows you 18 dBi of gain.
'SBEMAIL!' is better than a goat!!
San Diego sporting goods stores are reporting record sales of 12 ga. shotguns to San Clemente SDSC personnel who were alleged to have made cryptic statements about "frame drops", "bandwidth", and "all these f*cking seagulls".
Had seen a chart elsewhere (was really wanting to link to that) that showed the max somewhere around the 18 dBi you mention. Sorry fro tagging up the wrong language from the reg.
Back to the real point, 1 Watt bi-directional amp + "high-gain" directional does not take much to get into violation territory. Since they left out the gain of the antenna all we can do is guess, but 2' parabolics should get you into max gain without the amp.
Unless... [just dawning on me] the amps are only for receiving, i.e., NOT bi-directional! Now THAT would work without violation, just like some of the fancer wardriving rigs. It increases all the noise but the signal is still there to pick the digital bits out of.
Eve Fairbanks says I drive a hybrid!LOL
and since the Oronico card used in this setup is 15dBi intentional radiation per their spec sheet they have 3dBi to play with. The other thing you have to be carefull is bringing the sideband power down so that you are not tramping on adjacent spectrum (eg outside the 2.4Ghz ISM band, they really don't care how much you trounce on other 11b channels as it is an unliscensed application). I know Cisco's bridge has a 20dBi intentional output for the 350 series and they have a certified bundle using a 21dBi dish antenna for a combined power of 41dBi vs 39dBi for this setup. This is the longest shot we've heard of but in theory you could do even longer ones with our setup =)
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
Is there anyway to use seperate transmitting and recving antennas? You could use a big honking dish for the recving and a much smaller one for transmitting?
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
A perfectly fed 2ft. diamater dish at 2.4 GHz has a gain of 24db, but even a Pringles can feed will give you a dish with 21db of gain. More importanly, the spatial extent of the signal will be minimized, allowing for cellular reuse.
Personally, at 2.4 GHz I'd go with a loop Yagi-Uda array instead, as they're still cheap, and much more wind resistant, something you care about when pointing matters. Make enough of them and they'll be as cheap or cheaper than the Yagis used for UHF TV reception.
Bottom line: There's nothing inherently expensive about gain antennas, and they're the cheapest way to improve the link equation.
...-.-
Theoretically, yes, but not sure how practical it would be, since the tranciever has only one external antenna input. I suppose you could use a splitter and diode setup of some sort (really guessing here) to have 2 antennas with one only transmitting and the other only receiving.
Does not look like what they did, they are using 40" mesh antennas, there is a link direct to the project site in another thread.
Eve Fairbanks says I drive a hybrid!LOL
in areas that experience significant rainfall and rainy season storms?
the 802.11b link was interesting but I want to know more about there 10mile+ 45mb 802.11a links.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
>They must have used a huge pringles can.
c/pringles/garbage
They probably need to keep the signal above the water a bit to prevent interference with signals skipping off the water. The antenna at San Diego is undoubtedly on a tower. And most of the edge of San Clemente island on the side facing California is a pretty high cliff, much higher than even a large ship. Presumably they picked a high point on the island for placing antenna.
Why does everybody type 'line of site' when it really is 'line of sight'?
Websight.
--- Hindsight is 20/20, but walking backwards is not the answer.
The 1 watt limit only applies to point to multipoint. For point to point, you can do 4 watts. BIG difference.
Theoretically you could get 802.11b over 80 miles with ideal conditions.
The FCC is more lenient when it comes to p2p links because their directional nature spams the airwaves less. The rule is for every 3dB over a 6dBi antenna you must reduce total power output 1dB. 24dB of gain is permissible if your TPO is 1/4 watt. I know the article says their TPO is 1 watt, but it isn't a quote. The link may be illegal, but it's only 4 times the legal limit, not 200.
Education is a better safeguard of liberty than a standing army.
Edward Everett (1794 - 1865)
There's one small problem: this installation is illegal! 47-CFR-15.203
You might want to read 47-CFR-15.23 - The device does not violate section 203 because it is exempted by section 23.
High power, long range links deny service to other users of the spectrum. That's why they require licensing and use a licensed spectrum allocation. If you need a long range microwave link, get licensed! Don't hog a shared resource.
They aren't hogging a shared research. That's why they have parabolic dishes at both ends. They aren't omnidirectional transmitters. The FCC encourages unidirectional point to point links and has relaxed regulations for them.
Education is a better safeguard of liberty than a standing army.
Edward Everett (1794 - 1865)
Depends on the equipment. Some cards have a connector for a second "receive only" antenna, and can (in most cases) be configured to use them for the purpose you're after. These cards aren't cheap though, so expect to pay a bit more for them.
Cards that support this sort of thing are usually noted as being capable of "Diversity", which is used mainly for noise cancellation in reflective environments, but could be used for a send/receive antenna scheme. You would want to separate your antennas by a big margin though, to avoid any sort of interference. Separation by something that reduces 2.4 Ghz signals would be best.
If you are restricted to a given ERP, you would not be able to increase the field strength at the receiver by using a smaller antenna and more power; all you would do is cover more area with your signal (and create more potential for interference). Plus, you have the expense of TWO antennas... it makes much more sense to use a bigger dish and reduce transmit power to remain legal, because you can squeeze a lot more out of the spectrum that way. (Sometimes the rules actually do make some sense.)
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