How to get Tx-Power of wifi adapter in MacOS?
The Tx- Power is coded in to Firmware and has a maximum allowed by law. (FCC in the US)

Apple did offer the possibility to change the Tx-Power in its older version of Airport utility Ver 5.6



You can download it and try.

The 802.11n (5th Generation) - Airport Extreme card is set to

20 dBm (nominal) Output Power.


The iwconfig does not actually report the output power of the antenna. That is not possible. An antenna can not measure its own output, but a secondary antenna can. The iwconfig power output is a misnomer, it reports the power going in to the circuit that powers the antenna.