I am trying to repurpose an old Linksys E4200 v1 as an access point.
The problem is that wireless 'n' mode is not available on either radio0 or radio1, only '802.11bg'.
Issue is present on openwrt 18.06.8 & 19.07.3
I have tried changing the country code to 00 - world, driver default, GB and US and given the device a reboot after each change, I have also confirmed g speeds by running a speedtest and I am being capped at around 24Mbps which is near enough max for g networks. I'm not realy sure where to look now.
BCM4718A1 is only supported by b43, but b43 doesn't have any kind of support for HT modes, which would be required for achieving throughputs above 54 MBit/s (and no, there is no hope for this to change in the future). If you need more performance, you'll have to look for a better supported router (there are quite a few nice devices on the used market for rather little money).
The freshtomato code has support for the USB 5Ghz radio on the E3200, but performance is limited. On mine, I get about 81Mbps on the 5Ghz and CPU is at 99% usage (known issue).
I think tomato is the only firmware that supports the USB 5Ghz radio. It's not on dd-wrt and openwrt.
AFAIK, pedro is actively maintaining the code as he has already released 5 versions in 2020. Most of the maintenance is in updating all the busybox components.
AFAIK, dd-wrt has some $$$ arrangement with broadcom to use their closed sourced drivers. I have no idea, though, whether those drivers ever get updated by broadcom or not.