Estimation of emission frequencies of rolling stock in running condition using Doppler shift of emission frequencies found during stationary condition

The Electromagnetic environment as encountered by Railways system comprises of emissions contribution from many sub systems including signaling, traction and communication. The Indian railway urban transport system faces much more complex environment considering emissions from other non railway sources including emission from road transport as the roads are running almost parallel to the railway tracks. Measurement of radiated emissions (RE) of moving trains in the frequency range 9 kHz-1 GHz is one of the most challenging and time-consuming preposition for assessing the Electromagnetic Compatibility (EMC) of a railway system. The concept of `Doppler shift' has been used for numerous applications in various systems. In this paper, we propose that the Doppler shift can also be utilized for estimating the emissions of a rolling stock in moving condition by knowing the speed of the rolling stock and emission measurements taken during the stationary condition. The radiated emission measurements exercise was undertaken for Mumbai suburban trains during which the emission measurements were carried out for the rolling stock during stationary as well moving condition. Knowing the speed of the rolling stock and frequency components captured during the stationary condition the probable frequency components those would appear during moving condition of rolling stock have been computed using the Doppler shift principle. The actual frequency components found during the measurement of rolling stock in moving condition were compared with the frequency components computed using the Doppler shift principle. They were found to be within the agreement considering the resolution bandwidth (RBW) of the receiver, set during actual measurements.