Few days ago i saw specifications of the recent revision of raspberry pi 3 B+ witch apparently claims it to have a dual band WiFi in 5GHz and 2.4GHz. my Lenovo laptop also has a dual band WiFi and as i run windows 10, i can use 5GHz to connect to a router and meanwhile broadcast a Hotspot access point on 2.4 GHz at the same time.
Is this also possible for the raspberry pi 3 B+ because it is claimed to have a dual band WiFi card?
From my reading of the specification it doesn't look possible unfortunately although I have not tried it. If you use the 'iw list' command you should get a lot of output detailing the hardware capability with the interesting section being 'valid interface combinations' which gives this output:
* #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
total <= 3, #channels <= 2
* #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
total <= 4, #channels <= 1
In both of the combination lines it states only one managed interface is possible, ie. it is only possible to connect to one wifi network at any one time. In the second line it looks possible to have both a managed connection and an access point (AP) but it also places the restriction that only one channel can be used and since a completely different set of channels are available between the 2.4GHz range and the 5GHz range then that means the two bands cannot be used at the same time so, for example, you cannot connect to a 5GHz network and broadcast an access point on the 2.4GHz network.
I would really like to be proved wrong but reading that capability I think it's not possible so I haven't tried it.
