On Tue, Jul 20, 2010 at 11:02:47PM +1200, Tom Parker wrote: > The 400mW Ubiquiti device seems a good choice for a smaller number of > laptops over a wider area, but I'm no expert on these things. How many > walls can the TL-WR741ND penetrate?
Impossible to predict. It depends on the materials used in the walls, the thickness relative to the wavelength, the humidity, and the structure holding the wall. The floor and ceiling construction also has a significant impact on signal propagation; they are in the Fresnel zone. > Is a higher transmit power only > really relevant if you're talking to an equally powerful partner? As a general rule yes, but there are a few exceptions. 400mW isn't that much greater than 200mW; radio power doubling does not double the range. Despite it being specified for a maximum that is larger than the laptop, the access point may moderate the power it uses according to the signal level reports it receives from the laptop. In other words, while it might say 400mW, it might not use it if it does not need to. Where there is contention in the medium with other access points at considerable distance that cannot be coordinated, the higher power of the beacon may overcome the noise experienced by the nearby laptops. When there is a significant difference in receive signal levels between each end of the link (AP vs laptop), and the AP has the power or height advantage, then in the perimeter of coverage the laptop will be able to see that the AP exists, report a good signal strength, but will not be able to communicate with it. > Is the > building penetration limited by the less powerful laptop? Yes. But really the ultimate test is a site survey with the equipment chosen, including all the laptops. A network behaves quite differently once all the laptops are in use. If there is too much noise or contention, eventually a better design is a very low power access point in each room. But this becomes costly in cabling. -- James Cameron http://quozl.linux.org.au/ _______________________________________________ Server-devel mailing list [email protected] http://lists.laptop.org/listinfo/server-devel
