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External antenna for Clear USB & Clear CPE Modems

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  • External antenna for Clear USB & Clear CPE Modems

    Also applicable to other 2.5GHz WiMax devices that don't have an external antenna connector.

    Typically what we do in such cases is we use a coupled antenna adapter such as: http://www.rfwel.com/shop/?target=pr...roduct_id=1815. Then you can use any high gain 2.5ghz wimax antenna (i.e you can use the same procedure you would for the Clear USB modem

    There are however some short-comings to this approach including:
    • Multi-Antenna Diversity & MIMO Gain:
      One thing to realize is that since WiMax uses multiple-antenna techniques (the Clear CPE has 2 internal 7dBi antennas and the Clear USB has 2 internal 2.8dBi antennas) using an inductively-coupled antenna solution would only practically allow for use with a single-antenna. As such the performance in certain situations would not be as good as if you had used multiple antennas. On one hand if you can mount the outdoor antenna to provide a clear line of sight to the clearwire base station then you really dont benefit much from multiple antenna diversity techniques which rely on multipath propagation (multipath propagation makes the channels from the transmit antennas to the receive antennas uncorrelated which yiels the highest MIMO diversity gain). However if you have a lot of multipath interference then MIMO is needed to combat this and boost performance. Again the best way to tell which case applies to you is actually to try it out and measure the received signal strength (RSS) before and after to determine if this improves. A good RSS (or more correctly a good signal-to-noise ratio SNR) is one of the ingredients of getting higher speed (since it allows a higher order modulation with better spectral efficiency such a 64-QAM).
    • Antenna coupling loss:
      Modems that have external antenna connectors (and use an antenna diplexer to select between internal and external antennas) always provide a better coupling than using this approach.

    KF7RCQ
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