802.11 is half duplex, that is it sends then it listens. When it sends, it takes the output from the wireless card and amplifies it. The amplifiers generally have a fixed gain either in dBm or in watts.
The power gain in dBm is calculated by taking 10XLOG(pwr/0.001). The pwr is the power output of your card and the 0.001 is one milliwatt, the little m in dBm. So, if your card puts out 1 milliwatt, your gain is zero or 0 dBm. If your card puts out 2 milliwatts, your gain is 3 dBm, and if your card put out 4 milliwatts, your gain is 6 dBm. 10 dBm gain is a 10 fold increase in power and a 20 dBm gain is a 100 fold increase in power. So, if your card puts out 30 mW and your amplifier has a 20 dBm gain, your amplifier would send 3 watts to the antenna. On the receive side it works the same way. A receive signal, lets say -60 dBm or 1E-9 watts (0.000000001 watts) goes through the same 20 dBm amplifier and comes out as a one hundred times increased signal of -40 dBm or 1E-7 watts (0.0000001). There is a TX/RX switch to switch the transmit and receive signals. The receiver sensitivity on WLAN card is generally around -75 dBm or so. So you can see how a amplifier can help receive a marginal signal. The inverse of this is the gain on the transmit side may give you more distance, but raises the noise level of the RF environment much as the car behind you with the 1000 watts amplifier and the huge woofers rattles your mirrors. Amplifiers can help, but you need to know what your trying to do. For more information see: http://www.maxim-ic.com/appnotes.cfm/appnote_number/614 Later... Larry The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift. --Albert Einstein -- NYCwireless - http://www.nycwireless.net/ Un/Subscribe: http://lists.nycwireless.net/mailman/listinfo/nycwireless/ Archives: http://lists.nycwireless.net/pipermail/nycwireless/
