I've got an old PC with debian on it, which works as some kind of router. It is set up as wireless access point using hostapd. I want to setup multiple access points, one on old wifi card with 2.4hz, and one on new one with 5hz. I wonder if there is a way to do that?
Yes it is possible.
The major difficulty lies in persuading hostapd to use 5GHz channels. This is mostly an issue with regulatory domain: you must set a country where such communication is legal. But I found it impossible to change the "world" domain built into the in-kernel version of my driver. In my case, I ended up recompiling the ath9k driver, with a modification intended to make it disregard completely the EEPROM code.
I ended up writing a concise yet complete summary of the steps involved here