| 摘要 |
<p>A railway signalling receiver for electrical signals carried by railway lines is disclosed. The receiver comprises a sensing device co-operating with the railway lines to sense the signals, a sampling device operative in the time domain to continuously sample a sensed signal, a data memory for storing a plurality of sample values, computing circuitry for performing a discrete Fourier transform on the stored sample values, a data memory for storing the results of the transformation and circuitry responsive to the final results of the transformation in the frequency domain to identify the sensed signal. In such apparatus for receiving and detecting a frequency shift keyed transmission the receiver is connected to a heterodyne circuit, a low-pass filter is arranged to pass the difference frequency components and to exclude the sum frequency components in the heterodyned output which is connected to the computing circuitry for performing a discrete Fourier transform on the difference frequency components. The invention provides discrimination against noise and interference which if not dealt with effectively in the railway context can seriously affect the safety of the railway system. Also, the invention operates stably over a large temperature range, does not drift with age and can be applied to numerous applications with minimum modification.</p> |
