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Remote Feed: 72-Mile 802.11b Link

Posted by ryuzaki0 on from the that-should-reach-the-back-40 dept.

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."

39 of 227 comments (clear)

  1. Can you say by Anonymous Coward · · Score: 5, Funny

    War surfing!!!

  2. bahh by Anonymous Coward · · Score: 3, Funny

    Lovely. Now there is a path 72 miles long for people to exploit. Insecure networks, always fun...

    1. Re:bahh by Tenebrious1 · · Score: 3, Informative

      Only if you have a boat...

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  3. physics by Anonymous Coward · · Score: 5, Interesting

    so how did they overcome the earth horizon limitations?

    1. Re:physics by LordHunter317 · · Score: 3, Interesting

      Earth horizon limitation would be more like 300 miles. I know people who've hit that problem talking at 24GHz.

      Beat that!

    2. Re:physics by IvyMike · · Score: 5, Funny

      so how did they overcome the earth horizon limitations?

      Poles.

    3. Re:physics by Anonymous Coward · · Score: 3, Interesting
      Earth horizon limitation would be more like 300 miles.

      I thought at sea level it was more like 20 miles.

    4. Re:physics by afidel · · Score: 5, Informative

      They put it on a high tower, for 72 miles the earth bulge is ~90 feet so with fresnel zone allowance you would need an ~210 foot high tower. As to the other complaint about insecurity, at these distances the antenna's required will make an extremely straight beam, in fact the beam width is probably only in the mid single digits which is part of what makes shots this long hard, they are extremely hard to line up. Basically you would need to be on a tower inbetween the two sites and somehow intercept the information without knocking out the signal, not a trivial task. Besides they are sending seismograph data, not Top Secret documents.

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    5. Re:physics by jhines0042 · · Score: 5, Funny

      seismograph data ... and you are telling me that these dishes will _stay_ lined up?

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    6. Re:physics by rspress · · Score: 5, Informative

      Yes at 802.11b frequencies the radio waves do not bounce, the will pretty much head out into space. At these frequencies it is pretty much line of sight, you may get a little bending in the wave but not much. You will need height at the transmit/receive site to overcome the horizion. Southern California does have one seasonal effect on radio waves however. In the summer when a high pressure area sits in the pacific ocean radio links between the west coast and hawaii are possible. This is called Troposhperic Ducting and people in So-Cal may hear radio stations both AM and FM coming in from Maui. The stronger the duct, the higher the frequency that can be passed between two points. I had a 2 meter repeater (Amatuer Radio) that was meant to be low-level, local area only. When ducting was happen my range went from about 20miles to well over 400miles. It would cover the entire Sacramento/ San Joaqiun valley stoping only when you went out of the duct. People 400 miles away sounded as if the were next door.

    7. Re:physics by iofire · · Score: 5, Informative

      I am a student working on the HPWREN project responsible for this link, and you can find out much more information about this link and the wireless network in general at our website:
      http://hpwren.ucsd.edu
      Also note the November 1st news item that deals specifically this with link, and includes photographs of the setup here:
      http://hpwren.ucsd.edu/news/021101.html

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    8. Re:physics by Allnighterking · · Score: 3, Interesting

      OK in a sense they don't have to. First, 72 miles isn't that great a curve to deal with and second once you get into this frequecy range there are a number of Technics available for "bouncing" signal off of the Troposphere for really long shots. (100's even 1000's of miles) However for this one this technic isn't required.

      Try this.. Draw a circle on a piece of paper. Then Draw two lines out from the center of the circle at right angles extend those two lines through the circle and beyond. You will notice that sooner or later it will be possible to draw a line from the top of those two original lines that will no longer intersect the circle itself. This is the same reason you see two things One very tall MicroWave (2.4 gig is in the MicroWave band) with dishes that look like the are pointed down. (The picture you drew will show you the angles. ) Of course there are limits, like how high you can get the antenna (Mountains help) and note that the longer the shot the larger the antenna should be (concentration of more signal) but you should be able to recieve cleanly down to -90dbm0 no problem (or even lower).

      Factors that will affect the signal are. Atmospheric conditions (two antennna's swaying in the wind is the simplest example) Sun Spots buildings or trees in the line of site, and frequency. 2.4ghz can shoot further than say 7ghz can just as low frequency radio goes through the earth rather than around it. In general the rule of thumb is any time the thickness of a material exceeds the length of a single cycle the radio wave is blocked. (yes this is true of all wave transmissions and yes some materials can be made that are transparent, but I did say "in general").

      Doing a 72 mile shot over water isn't really that remarkable. At 7ghz I've seen 50+ shots over water. (Despite the statement at the end of the article shots over water are IMPROVED not inhibited by the water in the microwave range. )
      If anything the neat part or even unique part is that they did it at such a low cost.

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  4. The first use... by yunfat · · Score: 5, Funny

    Watson: Did you get it?

    Bell: Yes, send more porn.

    --
    "Smokey, this isn't Nam, there are rules." -Walter
    1. Re:The first use... by roalt · · Score: 3, Funny
      Sorry Mr Bell,

      this is all I got...

      Signed Watson

  5. Very Useful by jaavaaguru · · Score: 3

    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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  6. With Error Correction? by coupland · · Score: 5, Funny

    "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!"

  7. What, no pics? by JUSTONEMORELATTE · · Score: 5, Funny

    Great read, but somehow I picture something like this mounted on a 40' mast.
    --

  8. What happens if... by Cap'n+Canuck · · Score: 5, Funny

    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?

  9. Aluminum Vs. Silicon by n9fzx · · Score: 4, Informative
    More proof that a cheap $2 aluminum dish will beat a $200 silicon power amplifier any day -- and it uses the spectrum more efficiently!

    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...

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    ...-.-
    1. Re:Aluminum Vs. Silicon by afidel · · Score: 4, Informative

      Dishes with this kind of signal amplification are not cheap, notice the $3,000 price quote. Assume $1,000 for the 2 proxim AP's this leaves over $2,000 for the dishes. Even with free AP's I decided the 25 mile link to my ISP's hq would not be worth it because of the cost of dishes. Fibre may be cheap to rent in some instances but the cost of running a 72 mile aquatic link would have been astronomical compared to the cost of this link. Also this has almost nothing to do with last mile problems specifically because this is a point to point link with a $3,000 price tag. No home user is going to shell out a $3,000 setup fee. Point to multipoint links are feasible with different kinds of antennas and they do partially solve the last mile problem, but Ma Bell has been darn good at beating back competition over the years.

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      There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
    2. Re:Aluminum Vs. Silicon by RollingThunder · · Score: 3, Interesting

      $2000 for dishes and the towers they're mounted on.

      That's dead cheap for a large tower, especially if you have to pay a company to build it for you.

    3. Re:Aluminum Vs. Silicon by mosch · · Score: 3, Insightful

      or perhaps they already had access to a tall building, or some cliffs, thus obviating the need for a large tower.

  10. And one guy on a 2.4GHz phone... by Insightfill · · Score: 3, Funny

    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.

  11. How long... by Gruneun · · Score: 5, Funny

    before a Corona commercial shows the guy on the beach adjusting the dish and using it as a shade umbrella?

  12. In further news by Brigadier · · Score: 5, Funny



    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.

  13. DX by Goody · · Score: 3, Informative

    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 .

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  14. Before you ask, the horizon is still a problem. by Art+Popp · · Score: 5, Informative

    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....

    1. Re:Before you ask, the horizon is still a problem. by GigsVT · · Score: 4, Informative

      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....

      Heh, to an unlicensed operator, who is probably violating all kinds of ERP FCC limits? Not a chance.

      If anything, the only thing hooking up with hams will do is convince you to get licensed, because they likely won't talk to you much until you do, especially if they think you are going to violate FCC rules and possibly cause QRM.

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    2. Re:Before you ask, the horizon is still a problem. by Art+Popp · · Score: 3, Informative

      Heh, to an unlicensed operator, who is probably violating all kinds of ERP FCC limits?

      It's really two questions.

      To an unlicensed operator?

      Yes, of course they will help unlicensed people. They were all unlicensed until they became hams, and most of them know it. I've had help on piles of radio projects from those nice folk, and returned the favors when they wanted to interface 'puters to their "rigs."

      ...who is probably violating all kinds of ERP FCC limits?

      Who said anything about violating ERP (Effective Radiated Power) limits for FCC rules. The fellow in the article specifically mentioned abiding by those rules.

      As for QRM (abbr. for interference), how much QRM is generated from a 1 watt tight-beam microwave hop.

      This issue is quite different from that of CB radio enthusiasts that transmit at 300 times (yes, times) the FCC limits for that band, stomp all over the adjacent ham band with horrible amounts of interference, and then ask the hams for help when they've blown the finals on their tube amps. Yes, that category of CBer is often treated poorly at ham gatherings. And appropriately so.

      Amateur radio isn't called called Amateur because they're beginners. It's Amateur because it's "not for profit." These fellows invest inordinate amounts of time and money participating in a community of radio enthusiasts, and if you are trying to stay within the rules and and achieve long distance radio communication there will be no end to the help/advice/parts available from them.

  15. Re:2 foot antenna? by Loki_1929 · · Score: 3, Funny

    You really want a 2 foot microwave antenna broadcasting right next to your head?

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  16. Isn't this in violation of FCC Part 15.247? by GMontag · · Score: 5, Interesting

    (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?

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  17. link to HPWREN web site by NspktrGdgt · · Score: 3, Informative

    here's a link to more information via HPWREN's web page: hpwren San Clemente

    --
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    Assistant Director, IT Services
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  18. Don't laugh... by thatguywhoiam · · Score: 5, Funny
    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.

    .. this used to happen to me.

    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... '

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  19. Re:Isn't this in violation of FCC Part 15.247? by afidel · · Score: 3, Insightful

    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.

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  20. Re:Isn't this in violation of FCC Part 15.247? by DustMagnet · · Score: 5, Informative
    You are allowed more than 6dB gain. You just need to read a little more of the rules you quoted.

    (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.

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  21. In other news... by r_j_prahad · · Score: 5, Funny

    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".

  22. Re:Isn't this in violation of FCC Part 15.247? by LWATCDR · · Score: 3, Insightful

    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?

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  23. What about the 802.11a stuff they are doing? by LWATCDR · · Score: 3, Informative

    the 802.11b link was interesting but I want to know more about there 10mile+ 45mb 802.11a links.

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    See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
  24. Re:2 foot antenna? by alienw · · Score: 3, Informative

    Dude, many cellphones transmit at more than 5 watts. And they're right next to your brain when they're on.