Fax demodulator

A fax demodulator is a device used to intercept fax messages by listening in on a telephone line or radio signal.

Function

A typical fax transmission requires a two-way conversation between two modems.
Each modem may be part of a “fax machine” incorporating an image scanner and a printer.

Application

A demodulator can only be used to observe a conversation between two fax modems, usually to record the image transmitted.
It cannot be used to receive a fax transmission in the usual sense, because a sending modem cannot transmit an image without first negotiating a connection with a receiving modem.