I have a draytek vigor 2850Vn

I'm getting abysmal wireless range. Using the WiFi analyser on my phone I am getting -70dbm less than 5m away with clear line of sight. I can't connect a pc wirelessly from the next room, about 3m with a wooden partition wall as the only thing between. I can't connect ect a PS3 either.

There are other WiFi devices nearby but not many and I'm on the most open channel. I have a Netgear router sitting next to it for testing to rule out interference. I get better signal from that and it's got a smaller aerial.

Any thoughts on a possible cause other than the device being faulty