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When you configure a MikroTik Access Point (AP) to operate in the 5 GHz band with the 802.11ac standard and notice that the connection is “dropped” or limited to 802.11n for all connected devices, even when some are 802.11 capable ac, this may be due to several factors.

Below we explore some of the most common reasons why this could happen:

1. Access Point Configuration

• Wireless Mode: If the AP is configured to use a mode that supports both standards (n/ac), but is somehow configured to preferentially or limited to 802.11n, all devices will connect using that standard. Make sure the AP's wireless mode is configured correctly to allow 802.11ac.
• Channel Bandwidth: 802.11ac requires wider channel widths (80 MHz or even 160 MHz) to achieve its maximum speeds. If the channel width is configured to support only up to 40 MHz, this may limit performance to what is typical for 802.11n.

2. Device Compatibility

• Client Devices: Even if the AP supports 802.11ac, all connected client devices must also support 802.11ac to use that standard. If there are devices that only support 802.11n, they will connect using that standard. However, this should not degrade the connection of ac to n devices.

3. Interference and Environmental Conditions

• Interferences: The presence of interference in the 5 GHz band can affect the performance and stability of 802.11ac connections, which could cause the system to opt for a more stable, but slower, connection using 802.11n.
• Distance and Obstacles: 802.11ac, while offering higher speeds, has a shorter range and is more susceptible to attenuation by obstacles than 802.11n. In weak signal situations, devices may “decide” to use 802.11n for its better penetration and range.

4. Network settings

• Guest Network or Specific Configurations: Check to see if you have configured a guest network or specific settings that limit the connection to 802.11n for compatibility or security reasons.

Solutions

• Check AP Configuration: Make sure the AP is configured to allow 802.11ac connections and that the channel width is adequate.
• Update Firmware: Ensure that both the AP and client devices are updated with the latest firmware, which may include compatibility and performance improvements.
• Evaluate the Environment: Consider performing spectrum analysis to identify and mitigate potential interference. Also, try relocating the AP or devices to improve the signal.

If after these checks the problem persists, it may be helpful to consult the MikroTik documentation or technical support to ensure that there is no underlying problem with the AP's hardware or software.