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  1. #1
    New Lounger
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    Why two Antennas on built in internet card?

    I want to get an extension cable for my internet card antenna so I can place the antenna outside for better reception of a weak Wi-Fi signal. The built in card has two screw on type antennas. Somebody please tell me why there are two, and if I have to put extensions on both antennas to make it work. Also, is this a good idea?

  2. #2
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    Hello Strawboss,

    the two antennas provide RF diversity. It's a mechanism that improves reception inside a building or where there are multiple reflections which may cause a reduction in signal strength at one antenna. The recent 802.11N spec allows for multiple antennas for both physical and electrical diversity. It is more often referred to as MIMO (Multiple In - Multiple Out).

    If you are going to run an RF extension cable to an outside point to improve reception you need to consider the length of the cable run. Much more than a few metres and the cable losses may well be greater than the improved signal strength, depending on the grade of co-ax used.

    For example, if your cable run is long and you loose say 10dB in the co-ax but only gain 7dB in an omnidirectional antenna, you will have half the power input to the wireless card and make things worse.

    A short cable run may only have a couple of dB loss and a directional antenna can have 15dB or more gain depending on design. In that scenario you have 20 times the signal strength input at the wireless card.

    The best improvement will be to run two short cables and a single MIMO enabled antenna as shown in the Wikipedia article referred to above, thereby continuing to enjoy the benefits of MIMO.

    However, if the cable run to your proposed outdoor antenna is lengthy, I would recommend placing an external antenna and a short high quality RF cable run to an inside Wireless access point. From there you can run Ethernet or a Powerline connection to your PC and do away with the wireless card in the machine altogether.
    Last edited by Tinto Tech; 2012-06-14 at 08:25.
    In God we trust; all others must bring data.

    - William Edwards Deming. 1900 - 1993

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    Strawboss (2012-06-14)

  4. #3
    New Lounger
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    Lounger, thank you so much. This information is exactly what I was looking for.

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