OpenWrt on Raspberry Pi4 using 802.11n on 2.4 GHz?

Is there a way to make the built-in radio of the Raspberry Pi4 running OpenWrt provide 802.11n wifi on 2.4 Ghz?

The wan connection is provided by the built-in Ethernet port and I want lan on the built-in radio

From Luci, I go to Network, Wireless, then tap Edit on AP configuration. Under Operating Frequency I select Mode and N, Band 2.4 GHz, and Channel Auto.

Then Save, Save and Apply, then reboot. The wireless signal is absent. Same configuration, but I choose Legacy instead of N in the Mode box and it works.

Is this some limitation in the RP4 hardware that the community knows about? Is there a way to edit the /etc/config/wireless file to make it use 801.11n at 2.4 GHz that Luci won't do? Or am I doing something else wrong? When I try such edits, the radio is just disabled.

Anyone know the answer for sure? Or a workaround? 802.11ac works fine at 5 GHz, but I have a computer that has only a 2.4 GHz wireless card I'm trying to use.

Under 'Legacy" the wireless connection is limited to 65.0 Mbit/s with effective throughput much lower than that. Checking the connection in Windows Properties, it says the connection is "Wi-Fi 4, (802.11n) 65 Mbps."

I'm thinking that's just the way it is and my hardware is limited. Any advice appreciated.

https://openwrt.org/meta/infobox/broadcom_wifi

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Interesting. Why then can I set it up as an 801.11ac wireless using 5 Ghz and it works with that protocol and frequency? The driver for that is supported? Or is the 2.4 GHz chip a Broadcom and the 5 GHz chip something else? I thought it was just the one radio in the RP4.

Can non-open source drivers be installed on OpenWrt? Is there a licensed one I could use?

The onboard WLAN chipset works, but isn't very capable or fast. It's dual-band, but not concurrent dual-band, so you can choose only a single band/ channel to work with - either 2.4 GHz XOR 5 GHz. There are no valid interface combinations (so no 'repeater mode'), it can only handle a (fairly) limited number of connected clients, range and throughput are very much on the low end.

If you want decent wifi, keep the onboard radio disabled and connect (even) a (cheap) dedicated Wifi router/ AP running OpenWrt configured as https://openwrt.org/docs/guide-user/network/wifi/dumbap.

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Interesting to learn these new little details. I want to avoid any dongles so I'll have to settle for the lower speed, and just use 802.11ac at 5 GHz - getting about 50 mbps throughput on a 500 mbps internet connection when I'm 15 feet from the router. The Pi 4 is not my main router, I'm just going for the simplest portable router setup possible with only the drivers and packages needed.

Internet connects to the built-in Ethernet Port and built-in wireless provides the Wi-Fi LAN connection. I added OpenVPN too which I can toggle on and off easily and the commercial VPN services are providing me about the same download speed as the RP 4 can handle. So I've got my cigarette pack sized router with VPN.

I have another micro-SD card with the built-in wireless setup to connect to the internet and the built-in Ethernet provides the LAN with optional OpenVPN and it's a cigarette pack sized wireless bridge. Throughput about the same.

Anyway, my question has been answered and thanks to all for the replies.

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