Telemetry and Foldback
Many stations use subcarriers for internal purposes, such as getting telemetry back from a remote transmitter, often located in a difficult-to-access area at the top of a mountain. A station's engineer can carry a decoder around with him and know anything that's wrong, as long as the station is on the air and he is within range. This is the essence of a wireless transmitter/studio link.
On wireless studio/transmitter links (STLs), not only are the broadcast station's subcarriers transmitted, but other remote control commands as well. Thus, the STL's total bandwidth may actually be even wider than the station's. This is also used sometimes when transmitting more than one station at a time.
Interruptible foldback, such as for remote broadcasting, is also possible over subcarriers, though its role is limited.
Read more about this topic: Subcarrier