Over a month ago I was working north of Atlanta and found what appeared to be a multi-site, P-25 trunked system in the federal 406-420 MHz UHF band.
There are two UHF systems in the Atlanta metro area currently - a 4 site Motorola Type II system operated by the Federal Protective Service and used by Dobbins Air Reserve Base, and another Motorola Type II system operated by the Bureau of Prisons.
This new system is showing that it has 4 networked sites on the air. The site info I have so far:
System ID - 3B9
WACN - BEE00
NAC - 3B1
Site 101 - 406.1125, 407.8125, 409.3000, 410. 0375
Site 102 - 408.8375
Site 103 - 406.7750, 408.4375, 408.6375
Site 104 - 408.8375
(Yes, both sites 102 and 104 show the same frequency for the control channel. They must be located far enough apart to re-use some frequencies.)
Traffic monitored so far has only used two talk groups, TG 100 and TG 200. The users are still unknown but traffic so far is mostly security checks to various building numbers. Radio procedure sounds possibly military. Also the broadcast band plan of the trunked system shows a 380 MHz channel level, so more circumstantial evidence of it being possibly DoD.
While there are several US Army installations around the Atlanta area, including Fort McPherson and Fort Gillem, they were reported to be using the FPS trunked system. Monitoring of the FPS trunked system showed no connectivity or patches to this P-25 system.
More information as it becomes available.