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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."

21 of 227 comments (clear)

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

    War surfing!!!

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

    so how did they overcome the earth horizon limitations?

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

      so how did they overcome the earth horizon limitations?

      Poles.

    2. 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.

      --
      There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
    3. Re:physics by jhines0042 · · Score: 5, Funny

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

      --
      42 - So long and thanks for all the fish.
    4. 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.

    5. 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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  3. 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
  4. 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!"

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

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

  6. 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?

  7. 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.

      --
      There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
  8. 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?

  9. 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.

  10. 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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  11. 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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  12. 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... '

    --
    If Jesus wants me it knows where to find me.
  13. 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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  14. 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".