I'm about the same latitude as you, over in Huntsville Al. I listen to Atlanta and Memphis quite a bit, although there is a mountain between me and Atlanta. I rarely hear Atlanta controllers. Wikimaps says Memphis is about 185 miles from me, and so maybe another 75 from you, so good Dxing there. I gather from your commentary that the various sectors have their own local transmitters. I was always under the impression that all the transmitters and controllers were housed at the same facility. It does seem like I hear mostly Huntsville, though. I'm using a 1/2 wave dipole cut for 125mhz and hear quite a bit of air traffic.
That's a negative! At the scope, the controllers have control for three or four transmit/receive stations. All of the sectors have their established locations though, such as ZTL has 124.375 listed as "Foothills- High"
Since Foothills is a high sector, the controller rarely has problems receiving other aircraft, so they almost never switch transmitter location. I have only heard Foothills changed once in 4 years.
Now ZTL's 133.100 and 134.800 do change often. They are "based" at MOUNT OGLETHORPE. Their other transmit/receive stations are Foothills and Stone Mountain, along with the home station. The controllers can receive on all three, but can only transmit on one at a time. I do hear them at Foothills a lot.
But, TRACON and local control can't change their locations, since it's all at the same place, and a TRACON sector only handles a certain direction.
And another thing is for UHF, they usually don't change the transmit location, although they can, they usually don't. The VHF and UHF are both independent.
Edit: Also, the controller can recive on all the stations of his/hers.
Sometimes at night, when a class CHARLIE's tower and TRACON closes, they will setup a RCO, or remote control outlet, so that when the aircraft comes up on the ground frequency, he's talking to center or flight service, picking up his clearance. This is because the airport may not have a proper center frequency for the location, if one at all. And so that aircraft in the air won't be stepping on unheard aircraft on the ground.
Hope this helps!
73s
Caleb