I did one better.

Following your thought that it might be the antenna I looked at various Linksys wireless routers around the property and saw that they have the same connection type for the antenna's. I removed the Nevo antenna and conneted a Linksys antenna in its place on the NC50 and the connection is now fine. So it looks like the problem is the faulty Nevo antenna as you suggested.

Any idea where I can get a replacement antenna from or how much it will cost. ?

Thanks TF.