Product and Software: This article applies to all Aruba controllers and ArubaOS versions.
In ArubaOS 2.x and earlier, the software had provided few steps for control of the AP tx-power. There are five output levels (plus one addition level of "no output" by changing it to air-monitor):
Level 0 – 0 dBm (1 mW)
Level 1 – 11 dBm (12.5 mW)
Level 2 – 14 dBm (25 mW)
Level 3 – 17 dBm (50 mW)
Level 4 – 20 dBm (100 mW)
Since ArubaOS 3.x, the software has been enhanced to allow the administrator to configure tx-power with 0.5 dBm granularity. All command line options have been changed to use the dBm value only. When ARM assignment is not used, the allowable range of power settings starts from 0.0 dBm and goes up to 30 dBm in steps of 0.5 dBm.
The concept of power level in ArubaOS 2.5 has been phased out except in ARM power assignment. We are still limited to choosing from 0, 11, 14, 17, and 30 dBm only. This restriction will be changed in ArubaOS 3.3.
When the user tries to configure or read from the current setting of 30 dBm, this does not really mean the AP is generating 1 Watt of power. In fact, 30 dBm means the AP is operating at the max EIRP permitted by country code regulation. EIRP is basically the sum of tx-power and transmitter antenna gain minus any cable loss.
To understand EIRP and antenna gain, you can compare a light bulb with 10 Watts to a laser beam with the same power. The laser can deliver its 10 Watts in a single direction and cause more damage than the bulb.
To learn more about your current country code and the power constraints applied to your AP, enter the following command:
show ap debug driver-log ap-name <ap-name> | include dB
351 94318.77108 wifi1: External Antenna Gain Set to 0.0 dB for 2.4 GHz (Configured Value: 0.0 dB)
353 94318.77356 wifi1: Internal Antenna Gain Set to 2.0 dB for 2.4 GHz
355 94318.77661 wifi1: Tx Power (Config: 15.0 dBm, Set: 15.0 dBm), Actual EIRP 17.0 dBm, Max EIRP 33 dBm, TPC Red 16
382 150528.661085 wifi1: External Antenna Gain Set to 0.0 dB for 2.4 GHz (Configured Value: 0.0 dB)
385 150528.661131 wifi1: Internal Antenna Gain Set to 2.0 dB for 2.4 GHz
387 150528.661131 wifi1: Tx Power (Config: 18.0 dBm, Set: 18.0 dBm), Actual EIRP 20.0 dBm, Max EIRP 33 dBm, TPC Red 13
The "Config" value is either from static configuration or dynamic ARM assignment. The "Set" value is actually implemented on the AP at this moment. The "Actual EIRP" value is the "Set" plus "antenna gain". The "Max EIRP" value is the country limit on the current AP channel.
For all APs using internal antennas, Aruba has carefully measured the internal cable loss plus the antenna gain and these are hardcoded into the software. For external antenna, the value is taken from the provisioned values (ant-a-gain and ant-g-gain) and it is the user's responsibility to ensure that correct values are entered.