2.4g is just terrible and you are very unlikely to ever get speed on it.
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Wireless scanners like InSSIDer cannot pick up wireless interference from domestic appliances in range of your hub like A\V Streaming devices, Baby Monitors, Chordless phones, Microwave ovens, Plasma TVs, Security systems etc.
It might be worth checking for such devices nearby bearing in mind they do not have to be in your home to interfere, a Toyota Prius parked outside can interfere for example.