Choosing the WiFi radio channel

The Mac doesn't select the channel. It selects the network for which it senses the strongest apparent signal on either the 2.4GHz or 5GHz bands depending on what's available at the moment it seeks to logon and the order of remembered networks in your list of Preferred Networks in System Preferences. You can only control the available channel(s) in the AP.

Have you scanned your WiFi environment to see what channels are actually being used and how congested they may be? You can do this on your Mac. Turn on WiFi, allow your Mac to connect to a network. Then Option-Click the WiFi icon and select Open Wireless Diagnostics. Then in the menu strip at the top of your screen click Window > Scan. The results can inform your decisions about what channels to enable or disable in your AP.

While I don't know how complex your environment is, or how congested it may be, in general keep in mind that on 2.4GHz only channels 1, 6 and 11 do not overlap. On 5GHz generally the higher the channel the better; I stick with channels 149-153-157-161-165 and within that your selections will be limited by the bandwidth you have chosen (20, 40 or 80 MHz). And although 80MHz bandwidth sounds great, in practice you are likely to achieve faster overall throughput at 20 or 40 MHz bandwidth. Even in my generally uncongested environment, I have found channel 161 @ 40MHz to work optimally. YMMV, however.

First things to look for in Wireless Diagnostics are 1) what channels are used the most and 2) what channels are unused. If you are going to manually select a channel, choose an unused channel if at all possible or at least stay away from the most used channels.

Regarding 5GHz channels in Europe, these are the basic choices (without regard to channel congestion):

• 20MHz bandwidth - 36, 40, 44, 48, 149, 143, 157, 161
• 40MHz bandwidth - 38, 46, 151, 159
• 80 MHz bandwidth - 42, 155

If you use 40Mhz or 80 MHz bandwidth, watch out for possible overlapping 20Mhz channels that may be in use in your environment. It is also technically possible to use other channels in the 5GHz band but there are complex issues with them beyond what I could explain here.

It appears the Aruba defaults to 80MHz bandwidth; I suggest reducing that to 40MHz in the setup. The wider the bandwidth the greater the loss in signal power and the greater the opportunity for channel overlap.

This article is a good place to start exploring WiFI channel selection: Channel Planning Best Practices for Better Wi-Fi

rmsmendes wrote:

I then re-enabled all the channels on the Wi-Fi antennas, it stuck to channel 100. But I definitely don't understand how, having a wide number of different channels available, some much stronger than the others,

macOS isn't even close of guaranteeing that the channel selected on Wi-Fi is the best available.

see: Channel Set to Auto

Each band of your router is divided into multiple, independent communication channels, like lanes in a street. When channel selection is set to automatic, your router selects the best Wi-Fi channel for you.

If your router doesn't support automatic channel selection, choose whichever channel performs best in your network environment. That varies depending on the Wi-Fi interference in your network environment, which can include interference from any other routers and devices that are using the same channel. If you have multiple routers, configure each to use a different channel, especially if they are close to each other.

ref: Recommended settings for Wi-Fi routers and access points