i've looked through the manual, and trawled the web interface
but no where can I change the frequency that this router is on,
when I look at the channel selection only get channels in the 2.4GHz band, can't set it to 5GHz anywhere....

any ideas?

i've set it t 'n' only - and green-field too, still can't find an option

You need to set the wireless to 80211a + 11n, that puts it into 5ghz mode

thanks, totally correct.

Steve