How to increase the signal power of a wi-fi card?

I use an atheros card that requires ath9k driver. Are there any tools that can be used to increase the signal power of the wi-fi card?

Solution 1:

Found the commands in the iwconfig man pages:

sudo iwconfig wlan0 txpower 15

or

sudo iwconfig wlan0 txpower 30mW

Solution 2:

If your issue is getting signal in your home or business only, perhaps you want to consider dealing with the other side of the equation (the AP or router). I have replaced the standard rubber duck antennas on my AP with higher gain equivalent... also, if you can often add on an external antenna to your computer side wifi device.