After a lot of troubles i figured out how to enable 5GHz hostapd on debian with ath9k.
First of all you need to set the correct regulatory domain. This can be done with the package
crda using the file
then you can use
iw list to see which channels are enabled for your country. Now you can set it in the hostapd config at magically it will work!
And for the speedtest:
[router] $ cat /dev/zero | nc -l -p 13337 [laptop] $ nc 192.168.0.1 13337 | pv -b -r -a > /dev/null 73.2MiB [10.6MiB/s] [10.5MiB/s]
About 10 to 11MiB/s are much much better than the 3-5MiB when using 2.4Ghz.