Frequency multiplexed telephone line status equipment - has single demodulator, voice frequency filter and voice energy circuit

摘要

A measuring equipment is used to determine the status of a telephone line using frequency division multiplexing. It has a single demodulator which analyses successively and repeatedly the telephone lines. The equipment has a demodulator connected to an oscillator and to the telephone line. The multiplexed signal has one channel converted within a frequency band of -2 kHz to +2 kHz. A low pass filter with a cut-off at about 2 kHz gives a signal which is the superposition of two halves of the voice frequency band. A squaring circuit, an integrating circuit and a comparator are used to detect the presence or absence of a signal for the channel sampled.