MacOS – Wifi problem in OSX 10.7.1 after wake from sleep

If you were to run the Wireless Diagnostic tool each time the network dropped, you might be able to look over the logs once you have 5 to 10 events and see if you can determine a pattern. It's hidden in the folder /System/Library/CoreServices/ and also available if you hold the option key and click on the wireless icon in the menu bar.

Once the tool runs and deposits the diagnostic data on your desktop - you might run it a second time and use the Utilities window to see if you can see interference or other issues on the Performance view.

That section where the noise jumped up was when I turned on our Microwave.

This might be a case of using channels which are not allowed in your region. The wikipedia page on WLAN channels notes region limitations.

For example, in the US, in the 2.4 GHz spectrum you're only allowed to use channels 1-11, not 12, 13 and 14, while other regions may allow these.

In the 5 GHz spectrum, many countries only allow channels 34-165, or some subset of those (e.g. the US allows 36, 40, 44, 48-116, 132-165). Actually, you'll also note that not all channels in the ranges are listed (e.g. there's a big gap from 64-100, and a gap of 2 or 4 between most successive available channels) so its not necessarily obvious in the 5 GHz range if a channel is excluded in your region.

Anyway, the thing to do is check what region your devices (Access Point & Laptop) are set to, and either adjust them to be the same, and/or set your AP to use a channel common to both regions (e.g. 1-11 in the 2.4 GHz range or 48-64 in the 5 GHz range).