I'm happy with my router, a Belkin RT3200, onto which I
installed openwrt. However, my little fanless desktop can't
get a decent speed connection, although everyone
gets adequate speeds.

The Belkin RT3200 / Linksys E8450 is a dual-band IEEE
802.11ac/ax router based on MediaTek MT7622BV and MediaTek
MT7915E.

My mini has this internal wireless adapter:
02:00.0 Network controller: Broadcom Inc. and subsidiaries BCM43228 802.11a/b/g/n
and the Panda wireless USB dongle model PAU0A with the
MT7610U chip.

 

Bus 001 Device 002: ID 0e8d:7610 MediaTek Inc. WiFi
 


OK. We need numbers here. What are thery doing and what are ththey doing?

There are actually a lot of wifi speeds. I think they go


    b
    g
    n
    a
    ax


in order of slow to fast. There's also channel crowding. First, investigate. How old is everything?Sometimes the router is oldest & slowest and your ISP will often post out a router rather than do a service call. How old is your box? Your wifi dongle? 

 

BTW, Broadcom & Mediatek are high on my list of things never to buy. Broadcom just rebadge Cypress parts & Mediatek have no kernel approved coder. 

For 2.4Ghz, there's a channel crowding problem, and the channels overlap. Run

 

sudo iwlist <your_wifi> scan |grep Channel 

 

and you should get to see what channels are in use, and pick yourself an empty spot with a few blank channels on each side.. Wifi is directional. Moving your aerial will increase/desrease your speed. Handiest test is speedtest.net, where you get a progress bar for a few seconds per test that allows you to try a few positions. Keep your signal path away from metal. 2.4Ghz has the Channel crowding issue, 5GHz is reflected more, and you want the low end of the range to minimize that. Also the channels allowed vary from place to place. It loses signal going through walls or glass more than 2.4GHz does.