Load up the sites closest to you, as we previously determined, Mace Hill 700 and Mace Hill VHF. As those air ambulances fly around, WHEN one affiliates to the Mace Hill site you will be able to hear that talk group. If there isn't a unit affiliated to that site, you won't hear anything.
Likewise, you can't just decide you want to listen to Knoxville FD from Carthage and program in the Knox Simulcast site. Unless you're within receiving distance, it won't work.
TL;DR: load the closest TACN tower site into your scanner and just listen. As you develop an ear, you'll see what talk groups are frequently found on that site.
