The Alfa AWUS1900 uses the Realtek RTL8814AU chipset, so it needs an OpenWRT driver package with name similar to kmod-rtl8812au. I could not find such a driver on my Brume, nor Slate routers.
You may have better luck with a wifi adapter using the MediaTek MT7612U chipset, which works on my both my Slate and Shadow routers. It seems not so easy to find 3rd-party USB wifi adapters that work with OpenWRT.
I do not work for and I do not have formal association with GL.iNet
In my region, I can only get Beryl or Slate, which are basically priced about the same. I guess I have no option of ordering Brume, so I have no choice but to order the Beryl… and hope that it will be integrated with AWUS036ACM.
I can also get the GL.iNET GL-MT300N-V2, but I think it will be too weak.
Speaking of adapters, I was planning to order the AWUS036ACM this evening, but i noticed that There are TWO version of the adapter, one in Blue Packaging, the other is in White packaging.
Do you happen to know in which box did your adapter came in?
I bought a cheap, generic version with MT7612U chipset for <1/2 the price of the Alfa branded adapter. There are several generic products on Amazon if you search for “MT7612U” on their website. I am in Canada and different markets/countries may have different products.
From the photos, it looks like the Blue box one has a USB cable with a cradle to mount the adapter standing up, whereas the White box only has a blue USB extension cable. My generic version includes the USB cable with a cradle.
Note that there may still be some issues with these Mediatek chipsets. I am currently testing MT7610U with plain OpenWRT (not GL.inet firmware) so I can’t compare directly to @wcs2228 as I think he is testing MT7612U with GL.inet firmware. But vanilla OpenWRT had some bugs with the MT7610U in version 21, and while it’s improved in version 22, I still haven’t verified a lack of major problems.
I am currently testing an Alfa AWUS036ACHM which is designed for high power and long range, but, it is only a 1x1:1 unit.