Study on centre-fed boundless track circuits

An equivalent circuit diagram for a track circuit with one transmitting end and two receiving ends is presented. Two-port network models are developed under normal, shunt and broken rail modes of operation. Shunt sensitivity and broken rail sensitivity are studied in relation to each of the receivers. An abstract synthesis algorithm is devised and used to determine the optimal end-input impedances. The maximum length of the boundless track circuits of the Sofia Underground is determined.