I gave up using a USB dongle for my desktop (which was operating on the 5Ghz band with an AC enabled router - drop outs, reduced connection speeds were the order of the day. Ended up buying an internal network card with external aerial. The desktop hasn't moved and the aerial is just plonked on it's lid - hidden under the desk. Far superior performance though. No drop outs, etc and have come to the conclusion that USB dongles are best used with a laptop.

I agree I have yet to find a USB dongle that works great, they are usually average.

5ghz now at 300m using the asus n53 dongle so it was just the dongle and that is downstairs varying from 270 to 300m, so this is now solved.