I have ALFA AWUS036NH network adapter on raspberry pi model 2B running the latest raspbian. ALFA AWUS036NH should be capable of delivering up to 2W of power according to specs. Following some tutorials on the web and tweaking the CRDA database, I'm able to set TX power up to 33dbi (2W).
#iwconfig wlan0 txpower 33
I've installed USB power meter to measure the actual current consumption of the raspberry. Raspeberry with peripherals attached, but without the network card, uses about 400mA. When I plug in the network adapter, current usage increases to 600mA, which is comparable to most other network cards.
My understanding, that at least 400mA at 5V is required to transmit 2W. However, there are no changes in current usage when I change the TX power via iwconfig. The network adapter is connected to a network, so it is transmitting something. iwconfig output confirms the new TX setting.
Why the usb power does not change when I change TX power via iwconfig? Could it be that there is an internal "limiter" inside the network adapter?