When searching for a wireless card, people often want to find one with the best range. Most often, this decision is solely limited to the transmit power of the card. While transmit power is one factor in determining range, there are others that ought to be considered when determining overall range.
As 802.11b/g uses 2.4 ghz, which operates like any other radio frequency signal, we can use the basics of RF signal propagation to determine range. There are five basic components which effect signal propagation:
*Transmit antenna gain
*Frequency and distance (path loss)
*Receiving antenna gain
There are other factors which effect signal loss as well: cable losses, RF opaque materials in the signal path, etc.
Because wireless communication is a two way process, we may also have to include the same five factors in reverse. While 'transmit power' referred to your wireless card, on the return trip 'transmit power' refers to the access point. Likewise, 'receiver sensitivity would refer to your card as opposed to the access point, and so on.
The point of this post is to demonstrate that your 250mw or 300mw or 600mw card may have significant power out, but that is only one of the factors that determine range.
This is meant to be a very basic primer in wireless ranging. There are very detailed range equations out there. If you're interested, Google "Friis transmission equation" and go from there.