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Like a cross between a telephone and a printer, fax machines copy documents in one place and print them in another, even thousands of miles away. Before the ubiquity of computers and the high-speed Internet, and when the other options were regular mail or a courier, a fax machine could transmit medical records to doctors, photos to newspapers, and invoices to customers relatively quickly. But how do faxes work?
“Basically, a fax scans an image or document line by line, then transmits that scan to a recipient where it’s printed and reproduced,” said Jonathan Coopersmith, author of “Faxed: The Rise and Fall of the Fax Machine” ( Johns Hopkins University Press, 2015) and professor of history at Texas A&M University. Faxes today work on telephone lines, but early faxes (short for fax) used telegraph lines, which transmitted text messages using long and short pulse codes, such as Morse code. In fact, the fax was invented in 1843, three decades before the telephone. Fax machines have retained the same basic design and function ever since, but the mechanics have changed, Coopersmith said.
In the 19th century, a fax stylus would move over a document that was held in place. Each document had a message written in ink coated with a dry treated resin known as shellac powder. “As the stylus goes, most of the line will be blank, but then it hits the shellac, which lifts the stylus and sends a beep to say there’s something here, there’s black here,” Coopersmith told LiveScience. .com. Today, faxes scan documents optically without physically touching them. These machines emit light, which reflects off the black (or printed) areas of the surface but not the white (or blank) areas.
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But how do faxes communicate with each other? Before sending a document, the two faxes in different locations have a quick conversation, called a handshake, to confirm that there is indeed a fax on the other side, explained Abe Lopes, owner of Ace Copy Inc., a ‘ office equipment repair shop based in Newark, New Jersey. “That’s why you hear the little sound ‘deh-leh-lehhh’, the little tones of the dial,” he told LiveScience.
Faxes divide a page into a grid of many small, pixel-like squares. In real time, the sending fax machine reads one line of squares at a time and uses beeps to tell the receiving fax whether the squares are black or white (represented by ones and zeroes, respectively), Lopes said. “While the paper is being fed through the sending fax, the receiving fax is working at the same time,” he said. “One fax sends ones and zeros, on and off signals, while the other receives it and translates it to black and white for printing.”
The key to a working fax is to have two separate phone lines, Lopes said. One line for the actual telephone and another for the fax. “If the fax uses the same line as the phone and someone picks up the phone in the middle, that will interrupt and stop the transmission,” he said. This means paper jams, starting over, or both.
While faxing today may seem outdated compared to the convenience of attaching a PDF to an email or collaborating on a Google document, many doctors’ offices and small businesses still rely on faxes. And there is also home use. This is how Coopersmith became fascinated with faxes. His mother in the United States enjoyed using one to communicate with friends in Russia and Thailand. How nice, he thought. “This is such a simple technology that my mother can use, but so complicated that it can communicate all over the world.”
Originally published in Live Science.
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