Series frequency train decoder for telephone system - has bank of programmable passband filters in parallel and administration circuit identifying digital output of each of filters

摘要

The appts. is used e.g. in a telephone network, for decoding messages such as indicator, or call codes transmitted in the form of a signal series having a set frequency corresponding to a respective character of the message. A battery of discrete band-pass filters is mounted in parallel to receive the signal series. Each filter is tuned to a different frequency corresponding to one possible characteristic in the message to produce an indication of recognition when a corresponding tuned frequency is present at the battery input. An administration circuit in turn identifies each filter providing one such indication of recognition and produces a respective characteristic digital signal to obtain a set of such digital signals which reproduce the message transmitted by each signal series. The filters are programmable.