• Hi,
    I would be interested in hearing peoples thoughts on why and in which situation you would use a 6dbi rubber duck omni instead of a 2.2 dbi one.
    Bearing in mind that if you are restricted in maximum EIRP to 100mW. It seems to me that from a pure coverage area asect there isn't anything between them (i.e. if using 2.2dbi you can set the radio to about 17dbm outut and if using the 6dbi set the radio to 14dbi).

    Apart from the fact that you would have a better client/AP power match when using the 6dbi (as most clients will have 30mW power outputs) I can't think of any other reason.

    Perhaps you get a better "quality" signal with the 6dbi?????

    What are your exeriences out there lease?

  • Let's say that no matter what antenna you use that, in conjunction with output power setting, the EIRP is the same.

    What difference would different gain antennas make? Plenty.

    The only reason that an antenna has more "dBi" than another is because of the shape of the signal it produces.

    Imagine a ball of dough. Now, push down on it a bit. That is the coverage shape of a 2.2dBi antenna. Now, push down on it some more. That is a higher gain omnidirectional antenna. See the difference? The higher the gain of the omni antenna, the more coverage it has to the sides of the antenna. However, you lose signal elsewhere, in this case, up and down.

    Antenna choice is sometimes a compromise. For every gain you make, you lose is another direction.

    Let me know if there is more information or better explanation that I can make.


  • Gene,
    Thanks for your input.

    What you say is fine, and I appreciate the change in the doughnut shape as the gain increases.

    However, if I wasn't worried about loosing gain above and below the doughnut, i.e. I am still well within the beam width for the area I want covered. Then is there any reason to go for 6dbi rather than 2dbi.
    i.e. suppose I am roughly horizontally inline (level with or I can bend the antenna towards the area to be covered) with the antenna. Since my EIRP has to be limited to 20dbm, is there any difference (in this scenario) in choosing one antenna over the other??

    Obviously, if I wanted good coverage on a floor above, then I might consider the 2dbi antenna (thicker donought), but if not then surely there isn't much between choosing one or the other!!

  • Again, lets say that you max out at 20dBm with either antenna and only need coverage on the horizontal plane. Would the 6dBi antenna be any different? Yes!

    In respect to the "shape" of the signal transmitted, that is also the shape of signal it can receive. So, an antenna with a more narrow signal shape will receive less interference from outside sources.

    Let me know if there is anything else I can do!


  • Gene,
    O.K. That makes sense.
    thanks for your help.

    Incidently, which one would you tend to use, I mean generally if you had no real issues with noise/interference in practice do you find peole tend to use 6dbi rather than 2dbi?

    Once, again thanks for your input

    (Is there anyone else who could relay some of their own exeriences of why they choose one rather than another in some of their work??

  • Hi Dianuj,

    I`d certainly be more inclined to go for the reduced gain. The gain of an antenna works both ways. It both increases (or decreases) the output (forward gain)which allows a better received signal at the distant end, and also increases (or decreases)the quality of the receive signal due to the sensitivity. This means in theory that with the higher gain antennas, you don`t need as many of them to cover the same area. If the noise/interference (both outbound and inbound) isn`t an issue, then the lower gain (dbi) may also help in avoiding any other potential future interference problems.

    Obviously, with a good site survey, the differences would be mapped, but in my view, the increase in costs through perhaps having to install more hardware to cover the same area is offset by the reduction in problems with RF planning. (Within reason of course).

  • Hi david,
    Thanks, What you say makes good sense.

  • Dianuj,

    As Gene pointed out, the shape of the coverage is different. It's not that one antenna is "better" than another, more that it depends on what you're trying to cover that will determine which is more appropriate.

    In general, I would recommend the 6dBi rubber duck for general coverage. This improves coverage range on a single floor and permits clients to use a lower TX power level - which affects battery life.
    br /> In a typical multi-floor office environment, designing for voice where call continuity through stairwells is desired, then the 2.2dBi antenna positioned near the stairwell will carry the client from one floor to another better than the 6dBi. But in open space, the 6dBi provides greater coverage. In my experience, 802.11b voice clients in a dense environment struggle when dependent on an AP on a floor above or below, so "flattening" coverage is preferred vs. a "3D" model.

    Use the propagation pattern of the different antennas to optimize coverage for your environment - you may find value in using several different models in the same design.

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