Signal Oscar Tango

A radio transmission in the vicinity of Jury Street Metro Station. The large antenna tower near the station entrance can be turned on after unlocking the gate. Once the power is restored, it begins broadcasting morse code. The station generating the transmission is under a manhole cover within sight of the antenna.

Morse code translation:

CQ CQ CQ DE OT OT OT K

This translates to "calling anyone, this is Oscar Tango, over".