Analysis Of Transmission Characteristics For Audio Jointless Digital Track Circuit

At present, urbans rail transit development continuous, track circuit has attracted more and more attention because it’s an importance part as urban rail transit. Audio jointless digital track circuit has been more and more widely used because this track circuit can obviously increase the information communication and reliability betwreen train and ground. Currently, Chinese audio jointless digital track circuit mostly import from abroad, so we should analyze the audio jointless digital track circuit and improve the technology of track circuit to avoid being controlled by other countries.Some signal equipments of other countries are unable to satisfy the demand of urbans rail transit develops and the Chinese audio jiontless digital track circuit became experiment, to study the transmission characteristics of the domestic jointless track circuit is necessary. Some methods had been givend according to the practical application of track circuit and the transmission characteristics analysis software had been designed according to track circuit application research of transmission characteristics in the thesis. Analysis software can realizes the transmission parameters could meet requirements of the normal and shunt states, and if some parameters are changed we can find the influence of this change for transmission characteristics.Firstly, the jointless track circuit development history and the advantages and disadvantages of transmission characteristics are introduced. The thesis introduces the basic theories of four-terminal network then the transmission line model of track circuit is established. The thesis also analyze the frequency characteristic of the track circuit and analyze the compensation capacitor, ballast impedance and rail impedance by the factors that can affect the transmission characteristics of track circuit.Secondly, on the base of the analysis of audio jiontless track circuit, to establish mathematical model of audio jiontless track circuit which include normal, shut and signaling states. Based on analyzing and calculating the normal state of audio jointless digital track circuit, every voltage and current of transmission and the adjustment resistance are numerated in this thesis. Then every shunt points on the track circuit are checked that every shunt points are reliably, with no "dead section". At last, the cab signaling state is analyzed to make sure that the current in track could meet the requirements of cab signaling and the voltage of equipments are in the normal range.Finally, on the base of analyzing track circuit, audio jointless digital track circuit analysis software is implemented by the Graphical User Interfaces (GUI) tool in MATLAB. Observ-ing the change of the track circuit transmission characteristics when the parameters changed, for example the change in voltage and current.