The name of the technology “fax” is shortened from “facsimile” which means “an exact copy”. This is exactly what it is used for – to make copies of documents and send them remotely through a telephone line. The document, which is going to be sent is scanned, the image is then separated in rows (around 1mm which is about 1/25 inches) and every line is separated in dots. At the output of the scanner we receive electrical signals which are proportional of the coefficient of the reflection of every dot. These signals are sent to a modem (MOdulator-DEModulator) which is transferring them as a sequence of modulated signals. These signals are sent over a phone line and received by another modem on the other side of the connection. The receiving modem is demodulating the signals and the image is restored using a printing device.
Fax machines are like copy machines where the scanning and printing engine are separated from each other and communicate via telephone lines. There are various models of fax machines with different qualities and features. They alll communicate through strict fax standards, which is how they are able understand each other.
Usually the biggest difference in fax machines is the printing device. In the early days of the fax machine, the most popular method was thermal paper. The construction of such printing device is very simple and they are very economical. The shortcomings are that the paper itself is expensive and it fades relatively fast with time, so it’s not very suitable for long term storage. As Inkjet and Laser printers became the printing device of choice, they replaced thermal paper.
The protocols of fax transmission and that of modems over telephone line are very similar to each other. This made possible the invention of the “fax modem” which are devices which demodulate fax signals and transfers them through a computer. The computer can then take the fax, save it as a digital document (TIFF, PDF, etc.), or alternatively, print it through one of its printers. In this setup, a computer can work like a typical fax machine.
The fax to e-mail services work similarly – a fax modem demodulates the fax signal, it is converted to a digital document, and than attached to an e-mail. The advantage of this process is that it is up to the recipient if they wish to print the file or store it.
With today’s technology it is very easy to integrate microcomputers into fax machines. Multifunctional machines are now very common. They integrate fax, copy machine, printer and scanner - all in one device.
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