How Does A Fax Machine Work?

This might seem like a basic question, but here it is: How does a fax machine work?

Most of us tend to think of a fax machine as an invention that has only been around for a few years. Magically, it seems, these indispensable office machines are able to send and receive documents around the world without the documents ever actually leaving the office. But, as high-tech as this sounds, the truth is that the fax machine was first invented in 1843! Of course today’s fax machines are far more complex and efficient than their ancestors, but the basics remain essentially the same.

So how exactly does your fax machine work? While it can get quite technical, the basics of sending a fax are quite simple. The process begins by scanning the document into the fax machine so that it can be transmitted to the recipient on the other end via telephone line. This is accomplished by using a photo-diode sensing array.

The photo-diode sensing array is simply a device that has hundreds, sometimes thousands, of tiny sensors. The sensors detect light and dark spots on the document being scanned. The blank areas of the document will be recorded as white dots while the text and images will be recorded as black dots. (Some fax machines complicate matters by sending color faxes, but the principle is the same.)

That information about light and dark areas of the page is converted into sound to be transmitted over the phone line, as with a modem. So, every letter, image, and blank space on the document being faxed becomes a bit of electronic information. This information is sent through the phone lines to the receiving fax machine where it is reassembled from sound back into white and black dots again by the receiving fax machine. Then, the document is then reproduced as a copy of the original.

A modern fax machine sends and receives a minimum of 100 lines per inch, and a maximum of 400 lines per inch the high-resolution modes available on some models. Higher resolution means clearer images, but there’s more information to transmit over the phone line — so it will take longer to transmit the page. Of one fax machine can’t handle a particular speed or feature (such as color) the machines will “negotiate” a transmission standard that both can handle and “fall back” to that standard. Therefore, any fax machine should be able to transmit to any other fax machine, even one that’s 10 or 15 years old.

Indeed, the fax machine has been with us for a lot longer than most of us would believe but the technology has dramatically improved the speed and quality of the documents so vital to business today. It may not be magic that transports a spitting image copy of the original document anywhere on the globe with a receiving fax on the other end, but it is amazing how images can be transformed into sound, then reassembled again.