It has almost been one year since my last post, so it is really time to write something again 🙂 .
The transmit power of a radio within an access-point is being represented based on power-levels within the Cisco controller world. I have already written a post about these power-levels and how the configured gain of the antenna is related in the past. But did you know that besides the gain, the regulatory domain and specific channel also the input power of the access-point itself might influence the actual transmit power?
With the 3800 serie access-points the radios cannot be enabled when the run on regular PoE, this behavior is different with the 3700 serie. The 3700 access-point will work, but with one receive and one transmit antenna disabled. Besides that also the transmit power changes. Below some calculation examples based on an 3702I-E access-point. So, my advice is to always verify on the cli of the controller with the “show advanced 802.11x txpower” so you can, besides the power-levels, also see the dBm values which the represent.
| Input power | Antennas | Channel | Max. EIRP | PL1 | PL2 | PL3 | PL4 | PL5 | PL6 | PL7 | PL8 |
| PoE | Rx: 3, Tx: 3 | 36 | 23 dBm | 17 dBm | 14 dBm | 11 dBm | 8 dBm | 5 dBm | 2 dBm | – | – |
| 132 | 30 dBm | 17 dBm | 14 dBm | 11 dBm | 8 dBm | 5 dBm | 2 dBm | – | – | ||
| PoE+ | Rx: 4, Tx: 4 | 36 | 23 dBm | 18 dBm | 15 dBm | 12 dBm | 9 dBm | 6 dBm | 3 dBm | – | – |
| 132 | 30 dBm | 23 dBm | 20 dBm | 17 dBm | 14 dBm | 11 dBm | 8 dBm | 5 dBm | 2 dBm |
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