The Emmaus test site video (test area #3) should be pretty representative
of the "main.net" system ... test area #4 is the Amperion OFDM system.
There could be others that might have different "signatures" ...

Just as a mnor correction, test area #4, in Briarcliff Manor, NY, is an Ambient
system. The Amperion system is also OFDM and has a very similar sound. I found
it easily in Whitehall, PA, once I drove into the test area.

73,
Ed Hare, W1RFI