It's called VORTAC (VOR/TACAN)
It's just a navigational aid for pilots. Spits out a radio frequency that their equipment can pick up and point them in the right direction. I believe the aircraft side would use a DME (distance measuring equipment).
AirNav: Navaid information
VXV
VOLUNTEER VORTAC
KNOXVILLE, TN
Location
Lat/Long: 35-54-17.419N / 083-53-41.015W (35.9048386/-83.8947264)
Elevation: 1290.0 ft.
Variation: 03W (1985)
Operational Characteristics
Type: VORTAC
Class: H-VORTAC
Frequency: 116.40
TACAN channel: 111X
Altitude code: H (high)
Hours of operation: 24
Voice ID: no
Morse ID: ...- -..- ...-
Station call name: NASHVILLE RADIO
NOTAM facility: TYS
FSS:
FSS hours of operation: 24
Technical Characteristics
Accuracy: NOS
Monitoring: Internal monitoring plus status indicator
at control point
Owner: FEDERAL AVIATION ADMIN
Operator: FEDERAL AVIATION ADMIN
Common system usage: yes
For public use: yes