Cisco 8821 Manual page 81

If Channel width is set to Auto for an access point, then that access point will use the value specified for Default 5 GHz
channel width if applicable for that access point model.
The channel width can also be configured on a per access point basis overriding the default.
2.4 GHz radios utilize 20 MHz channel width and can not be configured for 40 MHz channels.
It is recommended to utilize the same channel width for all access points.
When using Cisco Meraki access points it is recommended to select Auto for the channel and transmit power.
When Auto is selected for 2.4 GHz channels, only channels 1, 6, and 11 will be utilized.
Configure the access point transmit power level assignment method for either 5 or 2.4 GHz depending on which frequency band
is to be utilized.
Individual access points can be configured with static channel and transmit power for either 5 or 2.4 GHz radios, which may be
necessary if there is an intermittent interferer present in an area. While other access points can be enabled for Auto and work
around the access points that are have static channel assignments.
Note: Cisco Meraki access points do not support Dynamic Transmit Power Control (DTPC), therefore the Cisco Wireless IP
Phone 8821 and 8821-EX will utilize the maximum transmit power supported for the current channel and data rate.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
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