I have a specific desktop which seems to have consistently high packet loss and ping regardless of what connection it is using. I'm connecting via wifi and this computer usually has a ping to my router of around 800ms and packet loss of around 20%. I've tried different wireless adapters, and even using the usb tethering on my phone, and they all have the same result.
The computer is running Windows Server 2008 R2 and Arch Linux, and the problem only exists on Windows for usb tethering. I can't test with the wifi adapters on Linux, as there are no drivers for them.
It is also not a locational or hardware problem. My laptop can connect without issue from the same position, either by using its own wireless adapter, a usb adapter which has issues in the desktop but is fine in the laptop, or usb tethering through my phone.
I've tried disabling 11n on my router so I know it's connecting by 11g, and it had the problem, and I tried setting it to 11n and it had the problem.
I've no idea on how to diagnose this. I can't find anything in my network settings which look likely to be the cause.