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How Exactly Do Fax Machines Work ?

Source : thinktel

Like a cross between a telephone & printer, fax machines copy documents in one location & print them out at another, even thousands of miles apart. Before the ubiquity of computers & high-speed internet & when the opposite options were mail or courier. A fax could relatively quickly transmit medical records to doctors, photos to newspapers & invoices to clients. But how exactly do fax machines work?

“Basically, a fax machine scans a picture or a document line by line, then transmits that scan to a receiver where it’s printed out & reproduced,” said Jonathan Coopersmith, the author of Faxed: The Rise and Fall of the Fax Machine (Johns Hopkins University Press, 2015) & professor of history at Texas A&M University. Faxes operate telephone lines today, but early faxes (short for facsimile machines) used telegraph lines which transmitted text messages using codes of long & short pulses just like Morse Code. In fact, the fax was invented in 1843, three decades before the telephone. Faxes have kept an equivalent fundamental design & function since that time but the mechanics have changed, Coopersmith said.

In 19th century, fax machine stylus moved over a document that was held in place. Each document had a message that was written ink coated with a dry resin referred to as shellac powder. “As your stylus goes, most of the line are going to be blank, but it hits shellac which raises the stylus & sends a beep to mention there’s something here, there’s black here,” said Coopersmith. Now-a-days, faxes optically scan documents without physically touching them. These machines shine a light which reflects-off of the black (or printed) areas of the surface, but not the white (or blank) areas.

But how do really faxes ask each other? Before sending a document, the 2 faxes in several locations have a quick conversation called a handshake, to verify there’s really a fax machine on the other end, explained Abe Lopes, owner of Ace Copy Inc., an office equipment repair shop based in Newark, New Jersey. “That’s why you hear the ‘deh-leh-lehhh’ sound, the small dial tones,” he said.

Fax machines split a page-up into a grid of many tiny squares almost like pixels. In real time, the sending fax reads one line of squares at a time & uses beeps to inform the receiving fax whether the squares are black or white (represented by ones & zeroes, respectively), Lopes said. “As the paper is fed through the sending fax, the receiving fax is functioning simultaneously,” he said. “One fax is sending ones & zeroes, on & off signals while the opposite receives it & translates it back to black & white to print out.”

The key to a functioning fax has two separate telephone lines, Lopes said. One line for the particularly for phone & another for the fax. “If the fax uses the same line as phone and someone picks-up the phone in the middle which will interrupt & knock-off the transmission,” he said. It means paper jams, starting over or both.

Although fax machines could seem to be outdated today compared with the convenience of attaching a PDF to an email or collaborating on a Google Doc, many medical offices & small businesses still believe on faxes. And there is home use too. That’s how Coopersmith became fascinated with faxes. His mother in the US enjoyed using one to communicate with friends in Russia & Thailand. “How neat,” he thought. “Here’s a technology so simple my mother can use it yet, so complicated, it can communicate around the world.”

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