Chapter 10 Principle of Operation
10.4 FAX System (Overview)
10-10
10.4 FAX System (Overview)
A FAX (abbreviation of facsimile) is a device that sends and receives image data using either an analog or a
digital telephone line. The following describes the analog line system (For G3, refer to "10.6 FAX Standards
(ITU-T Recommendations)").
The three basic units of a FAX are the scanner (for reading the image), the control circuit, and the printer.
The scanner splits the image into a fine grid, then reads the brightness (white/black) of each cell. This opera-
tion is called scanning. The white/black information is converted to a digital signal: bright cells become 1, dark
cells 0.
The digital signal from a scanned image is subjected to DA conversion (modulation) by the control circuit to
enable transmission over an analog telephone line. After conversion, the data is sent as an analog 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 cells are
reproduced on the paper at the positions where they were on the original.
KjA10007XA
FAX System (Overview)
Image scanner Control circuit Control circuit Printer
Scanning Printing
DA
conversion
AD
conversion
Telephone line
Original
Digital signal Analog signal Digital signal
Printing
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