Mike1970 wrote

Tried to set it to channel 100, 104, 108, 112, 116 etc. but could not connect.

If you can't associate with the WLAN on channel 100 and above, maybe your client device doesn't support those channels.

This frequency band is the only band which might be used by outdoor APs, so legacy indoor devices often restrict their radio to the indoor-only channels (channels 32 to 68 are allowed only indoors in the EU, channels 96 to 144 are allowed indoors and outdoors).

I disabled the Wifi on the ISP modem because I did read elsewhere that the EAP245 refuses tro connect on a DFS channel when radar waves are detected.

This is what Dynamic Frequency Selection (DFS) is all about: weather and military radars have priority over Radio LAN (RLAN) and that's why an AP needs to release and avoid further use of a channel for a defined time when a radar is being detected by the AP on this channel.

The AP then needs to switch to another channel, the client device wil follow.

According to ETSI / ECC regulations EN 301 893 / ECC/DEC/(04)08 following applies to the use of channels 96 to 144:

Channel access and occupation rules: WAS/RLANs operating in the bands 5470 - 5725 MHz shall use mitigation techniques that give at least the same protection as the detection, operational and response requirements described in EN 301 893 to ensure compatible operation with radiodetermination systems (radars). Such mitigation techniques shall equalise the probability of selecting a specific channel for all available channels so as to ensure, on average, a near-uniform spread of spectrum loading. The equipment shall implement an adequate spectrum sharing mechanism in order to facilitate sharing between the various technologies and applications. The adequate spectrum sharing mechanism can be e.g. LBT (Listen Before Talk), DAA (Detect And Avoid) or any other mechanism providing a similar level of mitigation.

Note that indoor channels 50 to 68 also require the use of DFS in the EU, even if those channels are allowed only for indoor use.

Maybe I missed something, but would like to use higher channels because it seems the signal is more powerfull, but usesless when devices cannot connect.

According to ETSI / ECC regulations EN 301 893 / ECC/DEC/(04)08 the following applies to the use of channels 96 to 144:

Transmit power / Power density: Max. 1 W e.i.r.p. Max. 50 mW/MHz e.i.r.p. density in any 1 MHz band. WAS/RLANs operating in the band 5470 - 5725 MHz shall either employ transmitter power control (TPC), which provides, on average, a mitigation factor of at least 3dB on the maximum permitted output power of the systems; or if transmitter power control is not in use, the maximum permitted e.i.r.p. and the corresponding e.i.r.p. density limits shall be reduced by 3dB.

Note that 80 MHz channel width in the 5 GHz band will acquire 16 channels at once (instead of only 4 at 20 MHz channel widh), this means that all or some of those channels will overlap with those used by other APs nearby. Therefore, throughput can vary significantly if nearby APs compete with your AP for AirTime (i.e. if they want to acquire those channels which your AP wants to use at the same time - one AP has to wait until the channel is released by the other).