VPI II Overview - Alstom

Non-Vital Subsystem5.5. TRAIN TO WAYSIDE COMMUNICATIONS BOARDSThe Non-Vital Train-to-Wayside Communications Modem board is the wayside part ofthe Train to Wayside Communications (TWC) system. TWC is a two-waycommunication link consisting of a transmitter/receiver set (transceiver) aboard the trainand a similar set in wayside systems. The system provides communication between thecar-carried equipment and the wayside equipment for the transfer of routing, dispatchinformation and for monitoring by central control. This board demodulates analogfrequency information into a digital form and passes it on to the NVP board (CSEX2 orCSEX3 board). It also takes digital information from the NVP board and converts it toanalog frequency form to be transmitted to the train.As with the CSEX board series, the TWC board series has evolved over the years ofapplication to reach higher levels of integration and functionality. The present boardassemblies supporting the TWC function are the 31166-119 series.5.5.1. NVTWC-FSK (Non-Vital TWC FSK) Board 31166-119-XXThe Non-Vital TWC FSK board provides true Frequency Shift Keying TWC. Theincoming TWC messages are keyed such that the logic 1 and logic 0 frequencies arebased symmetrically around some base frequency (example: 9650 ± 150 Hz). Thisboard uses 4 Phase Lock Loops (1 per channel) to decode the incoming signals. Theoutput of the phase lock loops are then reformatted so that they can then be sent to theCSEX board. Firmware on board validates the received message before it is sent to theNVP to reduce or eliminate the effects of noise-induced errors.Figure 5-8. NVTWC-FSK BoardP2511G, Rev. Jan/06 5–17 ALSTOM Signaling Inc.