B - Operations – Transporting – 61 – L
Patent
B - Operations, Transporting
61
L
346/32
B61L 21/00 (2006.01) B61L 23/00 (2006.01)
Patent
CA 1149918
(Case No. 7033) ABSTRACT OF THE DISCLOSURE A frequency modulated track circuit arrangement in which a transmitter supplies an FSK signal to the rails, with side frequencies deviating by equal amounts from a central carrier frequency and alternating at a preselected modulation rate. The receiver apparatus includes first and second verification circuit networks coupled to the rails through a band pass filter network which passes only the correct side band fre- quencies based on the central frequency of the transmitter. The first verification network demodulates only the correct side frequencies and decodes the resulting signal to produce an output only if the modulation rate is correct. The second verification network comprises an amplifier with a predeter- mined threshold level based on the known attenuation of the transmitted signal by the track circuit and produces an output only if the track signal equals or exceeds this threshold level. The two network outputs, only if both are present, activate an AND gate which supplies an output signal to a delay circuit element which energizes the associated track relay only if the duration of the verification outputs exceeds the preset delay period which eliminates very short noise pulses possibly having true characteristics.
342152
Fetherstonhaugh & Co.
Wabco Westinghouse Compagnia Italiana Segnali S.p.a.
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