This is a never fixed openwrt showstopper, with a simple solution. In gargoyle it exist up to 1.5.5 and maybe in 1.5.6.
Try: Switch regulatory domain to germany / europa. Now try to set channel 12 or channel 13, they did not exist in the slider. This comes from a buggy regulatory.bin.
Solution is here: http://smorgasbord.gavagai.nl/tags/hack/
Here Ceivik posted a working wget trick in comment-7
http://smorgasbord.gavagai.nl/2010/09/w ... ment-40596
Please insert the fixed regulatory.bin in further releases.
Hanselan-DE