How to tolerably Co-locate with Cellular?

  • We need to put wireless on towers and rooftops that often already have Cellular company's antennas and transmitters located on them.
    How far away should we be from their equipment to tolerably minimize interference and electromagnetic radiation from their high wattage (40-60w)?
    Although I desire an easy answer.  It would also be nice to have a link explaining how to calculate a tolerable distance if we know their watts and frequencies.
    Thank you, -Pete

  • Find the freq, used for the cell, find out how strong any harmonic noise can be (usually low).
    Carrier at 2000 MHz with 20 Mhz channels will normally generate noise/interference from 1980 to 2020 Mhz.
    Distance needed if you are on 2.4 Ghz should be pretty low (like 2-3 meters).
    But his will alllways depend on your antennas, how narrow they are when it comes to their freq range. how many dB they will drop the signal at 2 Gh when they are working at 2.4 Ghz etc.

    There is no exact science to this. Not unless you know exactly how the other radio operates, how much noise it will create on the sidebands of it's center freq, how much the antenna will amplify the noise (if it's present). If it's amped, how much sideband noise will the amp. create, how much of it will be amped by the antenna. Does the antenna have a negative effect on this noise/freq.. And so on and so forth…......

    Your best bet is to get a spectrum analyzer and read out how good/bad it will be.
    Professional equipment should behave nicely and if you have enough distance between channels you should be in the clear. You can allways add passive channel filters to drop the interference (if any).

    Good luck :-)

  • Thanks lsf!  Very helpful info.  It's also good to hear the EM field from their 40-60watt equipment shouldn't adversely affect us if we're 2-3m away with quality antennas.  And, we do use quality channel filters.  Thanks again -Pete

  • Appart from all the right directions contained in lsf's post I would add that you should house all of your wifi equipment in a meticulously shielded, preferably aluminum, box.

    Interference first becomes evident by blocking your front-end via the antenna input path.
    When you are done with this, a RF band pass filter is not a luxury in your case in my opinion, it will still reach and de-sensitize your wifi receiver through other paths.

    One last advise, if you are deploying point-to-point links use the most directional antennas you can afford with the best front to back ratio you can buy.

Log in to reply