MODEMS local test system in duplex telephone line - converts transmitters frequencies using modulator and local oscillator

摘要

The local test system, for moderns (3) in a duplex telephone line, has a local converting oscillator (14) and a modulator (15) to convert the transmitter (1) frequency into another frequency band. The modulator output is connected to the receiver (2) input. An inverter (16) is connected to the receiver output. For a modern operating in the band 1,080Hz to 1,750 Hz, the local oscillator frequency is 2,830GZ and can be varied at least 200Hz about this centre frequency.