Fri Apr 06, 2007 2:30 am
There is no theoretical limit to the gain of what antenna you can attach, only a practical one. The higher the gain of an antenna, the narrower the angle it covers.
A 0db antenna covers an area roughly spherical, between 2dB and 15db you have the option of omni-directional or sector. Omni-directional antennae cover a area roughly doughnut shaped, getting squashed flatter the higher the gain. Sector antennae cover a smaller and smaller arc the higher the gain.
You can get antennae with gains of 26dB and more, but you usually have to turn down the power of the wireless in order to keep within legal limits, e.g. in the UK legal EIRP @ 2.4GHz is 20dBi, so ignoring cable loss using a 26dBi antenna would require the wireless to be set to -6db. In the US higher power limits apply, max EIRP @ 2.4GHz is 36dBi (assuming you're using a narrow beam angle antenna), so the wireless card could be set to 10dB. Don't think that you can just buy a high power card and high gain antenna and set both to Max, you'd likely be exceeding 52dBi which I'm fairly certain is illegal pretty much everywhere.
In wireless options set TX power to manual, then in the TX power tab select "card rates" and then enter the max value for your card, e.g. 100mW = 20dB, 200mW = 23dB. However, as said before you have to determine what the max EIRP is for your location, the TX power of the wireless plus the gain of your antenna minus any cables losses must not exceed the legal EIRP otherwise you will interfere with other users and likely end up with some enforcement officer turning up on your doorstep.
Regards
Chris Macneill