6 – 11Chapter 6 Principle of Operation (Fax)Version 1 2008.02.014. FAX System (Overview)A FAX (abbreviation of facsimile) is a device that sends and receives image data using either an analogor a digital telephone line. The following describes the analog line system (For G3, see 6. FAXStandards).The three basic units of a FAX are the scanner (for reading the image), the control circuit, and theprinter.The scanner splits the image into a fine grid, then reads the brightness (white/black) of each cell. Thisoperation is called scanning. The white/black information is converted to a digital signal: bright cellsbecome 1, dark cells 0.The digital signal from a scanned image is subjected to DA conversion (modulation) by the controlcircuit to enable transmission over an analog telephone line. After conversion, the data is sent as ananalog signal. The sound audible during transmission is image data that has become an analog signal,that is, an audio signal.The analog signal arriving over the telephone line is then subjected to AD conversion (demodulation)by the control circuit of the receiving FAX machine, and restored to a digital signal.The black/white information obtained from the AD conversion is sent to the printer, where black cellsare reproduced on the paper at the positions where they were on the original.Gnb06027KAFAX System (Overview)Image scanner Control circuit Control circuit PrinterScanning PrintingDAconversionADconversionTelephone lineOriginalDigital signal Analog signal Digital signalPrinting
