A poster on Radio Reference has linked to a video showing a trunking control channel that was being received in the Springfield, TN area (north of Nashville). The video can be seen here:
http://www.youtube.com/watch?v=Ik2GFMKF6sc&feature=youtu.be
There is all manor of speculation over what this is. It is clearly a P25 signal, probably a control channel for a P25 trunking system, but the radio is not displaying the System ID or Site. This is not uncommon on federal P25 trunked sites, as they sometimes utilize a message format that scanners cannot display properly. The trunking information is still viewable with a program like Unitrunker or PRO96COM.
406.9125 MHz is the only site information available, and it's showing a P25 NAC of N005. One posted on the thread seems to indicate that it comes in full strength north and east of Nashville. One suggestion is the Old Hickory dam, but I'm not sure the Army Corps of Engineers would be running a UHF P25 trunked system. Others have suggested a federal prison facility, but there really aren't any near Nashville.
UPDATE!
Further information reveals that this is most likely part of a new P-25 UHF trunked system being built out for the Tennessee Valley Authority (TVA). The control channel mentioned above reveals the following:
406.9125 MHz
System ID = 372
WACN = 00001
Site = 505
Reports are that Harris is building this new system throughout the TVA area of responsibility.
