Why can't the adapter connect to the 5GHz network?

Question

WiFi

I purchased a Dlink DWA 582 adapter for PC. When trying to connect to a 5 GHz network, the system gives an error "Failed to connect to the selected network." Windows signal level shows 3-4 points out of 4, judging by inSSIDer, the signal level is -50 db. The adapter connects to the 2.4 GHz network, but gives out unstable 20-30 for the jump and 15-60 Mbps for the distribution.
Windows 10 Home x64, I tried both the Windows and bundled drivers, as well as from the site: ftp.dlink.ru/pub/Wireless/DWA-582/Drivers/rev.A/1....
Sercomm RV6699 router (gpon mgts) is located behind 2 walls, 5-10 meters in a straight line. The phone catches the network at the same point of 5 GHz, the results of speedtest.net are more than 100 Mbps for upload and download.
Tell me, please, what could be the problem? Changing the channel doesn't help. On channel 36 (as far as I understand it should be preferred) there are 2 more networks with a much weaker signal.
Maybe there are other firewood?
Or is there no way out except for the repeater?

Answer 1

As the practice of setting up unify plates has shown, two standards are capable of 5 GHz: n and ac. And on one of them everything is very bad, and on the other you can watch streaming in 4K. Pay attention to this.
https://www.intel.ru/content/www/ru/ru/support/art...
There are detailed speed tables here.
wi-life.ru/texnologii/wi-fi/wi-fi-standardy
And here is a description of the scheme when n can give a higher speed (MIMO).
Most likely, your adapter is trying to break at 5GHz according to the n standard, and therefore you get such a speed.