I found the parameter: chanbw (integer) Specifies a narrow channel width in MHz, possible values are: 5 , 10 , 20
My case is even more special, because I'd like to be able to set a different value from the pre-defined ones and even non-integer values like 6.25 MHz.
I know it is possible since this OpenWRT-based product has this feature: https://doodlelabs.com/products/industrial-iot-radio-platform/
It says: "Software defined channel size of 3~40 MHz for efficient re-use of spectrum", and I know it can be continuously (with non-integer values) adjusted.
But I don't know which hardware is used.
Hope someone help me finding this answer.
Honestly, I think the 3-40MHz does refer to Wi-Fi. Furthermore, Doodle claims to be able to adjust the guard interval lengh as well, suitable for bigger coverage areas.
Anyway, I found this hack, which allows changing the BW by reducing the chipset clock speed: