Finally, I had time to switch on George G’s EM device and make a few initial recordings. In the screenshot below, you can see that at the 10-second mark, I switched on the device. You can see the strong spectral lines at the odd harmonics of the power mains (60 Hz in North America). This is a good sign. When I feel reasonably confident in my use of Audacity (OS X audio software), then I will establish once and for all whether VLF radio frequencies are not responsible for the Worldwide Hum. I’ll keep you posted.