Fax System (Overview) - Dell 3115cn Service Manual

Color laser printer

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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, see 6. FAX

The three basic units of a FAX are the scanner (for reading the image), the control circuit, and the

The scanner splits the image into a fine grid, then reads the brightness (white/black) of each cell. This

operation 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.

FAX System (Overview)

Image scanner

Version 1 2006.11.21

Control circuit

Digital signal

Chapter 6 Principle of Operation (Fax)

Control circuit

Telephone line

Analog signal

Digital signal

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