How to find and revert driver update? (WinUpdate broke WiFi channels 12+13)

Question

tl;dr: How to revert to previous device driver version?

I have a Acer Aspire One (AO751h) netbook, with Atheros WiFi adapter, dual-booting Ubuntu 10.04.2 and Windows XP Home. Ubuntu works fine - wifi was supported out of the box; with XP, it also used to work without any effort on my part.

Since sometime in March 2011, in Windows, the wifi stopped seeing anything on channels 12 and 13: as if they don't exist at all (previously it worked without issue). Since our AP at work is at channel 13, I can no longer connect (the AP doesn't show up in Windows' Wireless Networks list or in NetStumbler). With Ubuntu, there is no problem: the AP is visible, associates and works at normal speed. With Windows, APs on channels 1-11 are visible, associate and work at normal speed.

It seems to me that Windows Update, in its infinite wisdom, has pushed new WiFi drivers, which were built for the U.S. (FCC limits WiFi to channels 1-11 in the USA, channels 1-13 are allowed in most of the world). Since I am in the EU, this means there are legitimate APs that I can't connect to, which is rather limiting (and annoying). Windows' regional settings shows my location as Czech Republic (which hasn't been relocated to USA recently, IIRC), so that shouldn't be the issue.

(as for malware: The system is used as an unprivileged user, actively avoiding IE and other malware gateways, patched, firewalled, w/ antivirus+antimalware; there haven't been any new installs, no new processes - looks clean.)

For now, I'm just trying to revert the driver update, but all I see in the Installed programs is a long list of "KBxxxxxx" items, without any indication of "updated wifi driver". How can I find which update contains the new driver, so I can uninstall it? And, will this be enough to get the older driver back, or do I need to trawl the Web for the old driver?

Edit: I've moved the AP in question to channel 11 temporarily, and it works there, so we can rule out sudden device incompatibility; alas, 1) I don't have a mandate to keep it there (as it interferes with other APs, plus the paperwork) and 2) that's a doorstop measure, hardly a solution.

Answer 1

A quick and easy fix may just be to perform a system restore, which will roll back any driver updates.

Even easier, may be to go into Device Manager, into the properties for the wireless device and click the Roll Back Driver button, if it is an option.

Answer 2

Channels are limited based on your chosen 'region'. For example, different channels are allowed in the US compared with the EU. Installing an updated driver probably reset that selection.

Fortunately, this is normally a setting that you can choose in your wireless card's configuration utility. (Or at least it has been for my ralink/atheros chipsets)

Try loading that utility up if you have it installed (not the windows wireless one) and seeing if you can select your region. It'll be quite obvious what dropdown it is as it'll most likely have a list of channels next to it.

If you don't have a utility like that, try looking on the manufacturer's website.

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Here's an example:

This is from ralink's old utility. Note the "Country Region Code" dropdown middle left.