More information would help us help you.
What firmware are you using on the RT-N53? What customizations have you enabled in the router? What features other than wireless/wired routing are you using (eg. USB disks, etc.)?
Which device(s) are dropping the connection? What O/S are they running (and is the O/S up to date)?
Have you updated the driver on each device?
What steps have you taken to try to fix this issue?
Have you tried a reset to defaults of the router and also use a new ssid (to force a re-association with each of your devices)?
So many words, so little info you provide...
I would recommend the Auto setting and not 'N' only, for starters. Still need more info.
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