On 10/26/2010 12:11 AM, Joseph Sinclair wrote:
As for antenna size, a 2.4GHz antenna is generally going to be most efficient
at 1/4 it's wavelength of 12.5cm. Most small devices have an antenna of about
that size (around 1.2 inches), and there's little or no advantage to using
anything larger.
The larger antennae on some access points and bridges are usually dipole (2
antennae at 3.125cm each in opposition around a common centroid) and aren't
actually any better at receiving signal, but they feed into a much higher gain
amplifier stage using a differential amplifier which has better signal-to-noise
ratios at the cost of using more power (and requiring a dipole antenna).
Ah, not quite.
While a quarter-wave antenna is the smallest self-resonant length, even a
vertical dipole has higher gain (releases more power and recovers more signal)
from the plane orthogonal to the antenna. Stacking dipoles can give you even more
gain. (as well as more rejection to signals further away from that plane.) Adding
more antennas and creating a phased array can net you even more gain.
Two things that are more important here:
1) Not all WiFi hardware are created equal. I've seen SMC PCMCIA cards with 14dB
more sensitive receivers than a similar Linksys product, and a lot more output
power capability too.
2) A quick survey of the area should be performed to see what other devices are
using the spectrum, and which channel will provide the greatest freedom from
interference from these other devices. (An Android phone running a suitable
application is very handy for this. :-) )
For a quick comparison of 802.11 hardware, I've found the Seattle Wireless site
to be a good source of information.
http://www.seattlewireless.net/HardwareComparison
--
KevinO
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