Multiplexing system for telephone lines - has double modulation for twelve lines with pass band filters in first modulation

摘要

A multiplexing system for telephone lines is used in carrier current equipment. It has a double modulation and is aimed at reducing the cost of first modulation filters. The system has twelve lines. It consists in transposing twelve voice frequencies bands, situated between 0.3 and 3.4 kHz, into a single frequency band of 48 kHz, between 60.6 and 107.7 kHz. It has a first modulation of two, three or four carrier waves and a second modulation to give a total modulation of twelve carrier waves. The two, three of four lines are coupled by means of a filter with, correspondingly, two, three or four pass bands with the same attenuation in each band. The gap between the carrier waves of the first modulation is equal to the voice frequency band of 48 kHz divided by the number of first modulation carrier waves. There are correspondingly six, four or three assemblies which provide a second modulation to give the twelve carrier waves after coupling and filtering.