Method and apparatus for receiving disparate sequences of spaced tone bursts

摘要

This invention pertains to a method and arrangements that provide automatic detection of sequences of signals which previously required listening by operators in telephone systems to identify them. In a telephone system, certain information is transmitted using preselected signal sequences of tone bursts and silent intervals. These signal sequences are subjected to interference by speech and noise occurring in the telephone system. An arrangement is disclosed which reliably recognizes and identifies these signal sequences notwithstanding the apparent modification thereof due to the interference. In the process of recognizing these signal sequences, a three-stage recognition test is utilized to classify the durations of tone bursts and silent intervals in the signal sequences that occur. The validity of the signal sequence is checked by detecting inconsistent durations within the sequences. This feature is also utilized to indicate faulty apparatus used to generate these signal sequences. A dual arrangement is also disclosed wherein signal levels of a particular signal sequence in different transmission paths in telephone systems indicate the origin of the sequence. A level comparison which is successful for a preselected portion of the total duration of the signal sequence provides a margin of tolerance for interference in the sequence.