Outdoor PTP

6 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: August 7, 2007:
  • Hi all,

    We have been asked to provide a PTP solution for a claint whom wants 24/7 surveilence across 10+ buildings using 5.8GHz equipment. Alvarion to be presise.
    They are now adding a number of additional PTP buildings to the mix.

    We werent involved in the original project, therefore at a slight disadvantage being brought in at this stage.

    However what I wanted to know is the following:
    The clint has already decided whcih buildisng will be linked to which.
    1) Should we still be performing some sort of survey to check for interfierence?
    2) I beleive we should inform Ofcom. Do we do this before install or after?
    3) Should we be using GPRS even though there is line of sight with a diatance of 5KM?

    PS: I am planning on going on the CWNA as soon as funds allow, as I am sure all this would be explained in the course.



  • If you have LoS, you shouldn't have to do much of a site survey. If there are other antennas on any of the buildings, it would be nice to know what frequency they were operating on, or run a spectrum analysis.

    5km is a pretty short link and shouldn't present any problems. You have a 15 ft Fresnel zone at that frequency which is nice and tight. Fresnel zone blockage could still cause a problem if there are other buildings infringing on that 15 ft radius from LoS.

    In the US we don't have to notify anyone (except the FAA in close proximity to airports) when using an unlicensed band such as 5.8 GHz.

    Let us know how it goes!


  • Hi Gene

    Thanks for your quick reply.

    Just out of curiosity, how did you calculate the Fresnel zone? is it purely to do with the frequency and distance? And is that is diameter or from the centre to the outer edge?

    What would you recommend using to check for any thing else operating on or near that frequency?



  • I use the Fresnel zone calculator from first mile wireless. Just google "Fresnel zone calculator" and use the first link. The only variables are frequency and distance.

    The result is the radius from the center LoS.

    I recommend Cognio spectrum analyzer to search for sources of interference. It will cost around $3000 so if it is going to be a one time job, it may be less expensive to hire out.

    The less proactive option is to perform the install and if there are any problems then troubleshoot from there. (i.e. change channels etc.)

    Let me know if there is anything I can do to help.


  • Well who ever did the site survey or recomended the solution earlier but now before you jump into connecting the sites its very much important to check the LOS if its clear or not. Although the distance is only 5 KM but if the LOS is not present then the Alvarion will not communicate. I hope the environment is not densly occupied by 5.8GHz wireless, if yes then even if you have LOS you may not get a very stable working link so check out these things. If there are 5.8 GHz link running in the near bylocation try to install your equipment with a different polarity (Horizontal or Vertical)and keep it at least 5 mtr away from any other near by radio.

    For further information do write

  • Gene and wimax, thanks for your comments.
    I have decided that I will most likely partner up with a local based company who has many years experience in designing and implementing these type of solutions.
    The main benefit is that we can shadow them for the whole project and look at taking on the next phase directly, based on what we will learn.
    This aliveates alot of pressure from me on getting it right first time.

    I will keep you's posted and let you know how we go on.

    Thanks again for your help.


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