In this thesis, a novel diagnostic system has been developed to increase the realibility of leaky feeder communication systems in underground mines. The new system is based on three main parts: 1) Diagnostic Receiver Unit (DRU) located in the control room above ground; 2) several Diagnostic Transponder Units (DTU) connected to amplifiers, Power Supply Units (PSU), fans and sensors; and 3) Communication protocol that was designed for this specific system. The amplifiers, PSU, fans, and sensors in the system cascade will be able to communicate freely with the control room through the leaky cable to send information about their current conditions, and receive configuration messages. A new concept is also presented that provides energy saving in mines; Ventilation-on-Demand where the fans will operate according to the current situation of each section in the mine. This is made possible through a series of interrupt messages that is sent from the DTU attached to the fan/sensor to the DRU in the control room.