My Pi4 also shows all 5GHz nets, you can check which bands are supported by running sudo iw list | grep MHz; if the 5GHz bands show, the adapter supports it. If you want to check whether or not it’s Volumio, just run sudo iwlist wlan0 scan | grep SSID:, all nets scanned by the adapter should show (and should be visible in Volumio as well).
As for my previous post, the Pi3 does indeed not support 5GHz
I tried iwlist scan wlan0 and the list it returned contained only 2.5 GHz networks. I verified it by using a wifi scanner app on my phone. I have 2 Pi 4s running Volumio and both are within 15 feet of the router. Signal strength is -52 dBM for the 5GHz network in my house measured near the Pi on my desk. When I was running Moode on both of these Pi 4s, forgive the mention of a competing product, they saw 5GHz networks without a problem.
Tried looking for Frequency and SSID (grep -e “Frequency” -e “SSID”) and discovered that the Pi saw a couple of 5GHz networks neither of which were mine. It didn’t see my main router or the wired access point downstairs. Interesting.
The antenna of the Pi isn’t the best and since 5GHz is heavily impacted by any structure in between, you might not get the same results as mobile devices. You could try a USB WiFi adapter, that might yield better results
There are two things that puzzle me. First, my 5GHz network has the strongest signal of any 5GHz network visible to my desktop, tablet, and phone. Second, on both Pi 4s, both Raspbian and Moode detect my 5GHz network. I also have a Pi 3B not running Volumio that detects the 5GHz network. It’s not the end of the earth. The 2.5 GHz band is fine for streaming music. At the Pi 4 on my desk 2.5 GHz signal strength is -49 dBm. The 5 GHz strength is -54 dBm. Either would work if I had the choice. I just find it peculiar that Volumio is the only Pi software I’ve tried that doesn’t detect my 5GHz network. BTW, I’ve tried to use the manual entry of the SSID in the network configuration. It fails. The good thing is that I’m retired and have the time to spend chasing first world problems like this.
Thanks. That appears to be it. The wpa_suppliant config file had no country code specified. I added a line specifying US and the 5 GHz networks are available. I was able to connect to the one I wanted.