When Alberto was parting the Red Sea this morning, and turning it green, he noticed that the wireless had gone sketchy.
When I checked it out, the ethernet light was definitely blinking, indicating that it was getting signal. So this was not the usual case of bad cable/connector which is a known problem for our wireless (one of these days we should probably relay that ethernet cable....but not today). After power cycling and replugging the ethernet cable, the light for the 2.4GHz wireless was blinking, but the 5GHz wasn't. Since the wireless still wasn't working, I checked the advanced configuration settings, as described by Yoichi's wiki page: 40m Network Page
The settings had the 5GHz disabled, while Yoichi's screenshots of his settings showed it enabled. Immediately after enabling the 5GHz, I was able to use the laptop at Alberto's length measurement setup to get online. I don't know how the 5GHz got disabled, unless that happened during the power cycle (which I doubt, since no other settings were lost), but it's all better now.