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Adding an antenna to an access point

  • 15-06-2004 7:32pm
    #1
    Stky10
    Registered Users, Registered Users 2 Posts: 1,165 ✭✭✭


    Just checking something here.....

    Lets say that I have an access point with an omnidirectional antenna attached as standard. Is there any point in removing these antennas and fitting a higher gain omnidirectional antenna??.

    My understanding is that I'd have to add a lossy connector or long cable between the AP and antenna so as to act as a loss comparible to the extra gain of the new antenna so as to be within legal power limits, and so the extra gain of the new antenna would not result in any extra distance or effect.

    Just checking this, cos a very senior designer in an
    international telecomms company I'm dealing with
    seems to think differently.

    I realise that replacing an omnidirectional antenna with a semi (or bi)-directional antenna would provide extra distance because the signal would be focused, but replacing an omni with an omni shouldnt work right???


Comments

  • #2
    jmcc
    Registered Users, Registered Users 2 Posts: 7,456 ✭✭✭jmcc


    Originally posted by Stky10
    Lets say that I have an access point with an omnidirectional antenna attached as standard. Is there any point in removing these antennas and fitting a higher gain omnidirectional antenna??.
    It depends on how much higher the gain of the new omni is compared to the old one.
    My understanding is that I'd have to add a lossy connector or long cable between the AP and antenna so as to act as a loss comparible to the extra gain of the new antenna so as to be within legal power limits, and so the extra gain of the new antenna would not result in any extra distance or effect.
    Technically speaking, the losses incurred are probably going to be greater than the effective gain of the new omni. The legal aspect over the power limits (EIRP) is an afterthought. Coaxial cable is lossy at wifi frequencies. So the loss from the connectors and the cable are probably going to make the whole exercise futile.
    I realise that replacing an omnidirectional antenna with a semi (or bi)-directional antenna would provide extra distance because the signal would be focused, but replacing an omni with an omni shouldnt work right???
    Replacing an omni with an omni should work but you are always going to have some loss in the equation. Directional antennas are probably better

    You could use some of those wiremesh and foam constructions around each omni to provide an sort of directional effect. (They are in the O'Reilly book "Wireless Hacks" but I cannot remember the URL for the actual site with the details of the mod.

    Regards...jmcc


  • #3
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 92,615 Mod ✭✭✭✭Capt'n Midnight


    you can use a parabolic reflector to concentrate the beam in one direction.

    if you change the omni (you need to open the AP - warranty void and figure out what connector is on the inside if any) then you will get a flatter beam. ie. you may get a stronger signal in the garden at the expense of the signal upstairs.

    Legal limits - 100mW EIRP - ie no part of the beam can look stronger than a 100mW point source.

    So it depends on the AP's power - eg: smartbridges have a "dial a power" option - you tell it your antenna gain and the limit and it adjust power to suit.


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