Abstract: A method and apparatus for communicating over a track circuit which includes an interference signal. The invention includes sampling the interference signal on the track circuit at a predetermined sampling frequency to produce a sampled interference signal, detecting interference at a predetermined first sub-carrier frequency based on a fast Fourier transform of the sampled interference signal, forming a vector signal corresponding to a predetermined second sub-carrier frequency related to the predetermined sampling frequency and different from the predetermined first sub-carrier frequency, performing an inverse fast Fourier transformation on the vector signal to form a series communication signal, coupling the series communication signal to the track circuit, sampling the series communication signal on the track circuit at the predetermined sampling frequency from a sampled communications signal, and recovering the vector signal based on a fast Fourier transform of the sampled communication signal.

Abstract: A method and apparatus for on-line diagnostics, particularly for use in power circuits of a DC-DC converter is described. Signals are sensed at selected strategic test points in a circuit and compared with stored expected signals for those points under normal operating conditions. Whenever the signals sensed at the selected test points do not correlate with the corresponding expected signals, the sensed signal is compared with abnormal signals stored in the memory associated with known failure conditions for that test point. Whenever the sensed signal matches closely with a signal for a known failure condition, an indication of the particular failure is logged into memory. If the sensed signal does not match a known failure condition, an indication of an unknown failure condition is logged into memory. Failure information can later be retrieved by maintenance personnel at a convenient time or can be displayed on an operator's display during operation.