SCI-TECH & AGRI

Fax and telegram

QUESTION: What is the difference between the working systems of fax and telegram?

K.Rathnam Chetty, Chitoor, A.P.

ANSWER: Though the essential purpose of both the fax and telegram, is the transmission of some information from one place to another, the profile, and the technical arrangements in these two equipment are much different.

Fax: This is the abbreviation for `facsimile auto transmission'. The equipment consists mainly of electronic circuits for scanning a matter, written, typed or printed on a paper. This scanning is done by a device called `magic eye'. Along with the scanning process, the information gathered by the magic eye is converted into electric pulses. This much is the transmission portion. The machine on the receiving portion has been designed to convert electrical pulses into corresponding letters/ figures.

To transmit the contents of a document, machines have to be used both at the transmitting and receiving ends. They have to be connected by a telephone line. For sending the contents, the document is placed in the space provided in the fax machine. The telephone number of the distant end fax is dialled from the sending side, as if for a telephone call. If the machine at the distant end is normal, a specific tone is heard, which means that the fax there is ready to receive the contents. We can then press the `start key'. The operation of this key triggers the mechanism for scanning and converting into pulses, and sending these pulses along the telephone line to the other end.

At the receiver side, there is arrangement to get a print of the matter received through the telephone line. In the earlier type of fax machines, the paper used for getting the print was thermal paper. The property of the thermal paper is that, the chemical coating provided on it gets melted and leaves black spots in portions which are subjected to low heat as a result of passage of electric pulses, so as to form the shapes of the letters/ figures/ digits etc.

In the latest type of machines, however, the usage of plain paper is becoming more popular, where inking arrangements have to be provided separately.

The word `telegram has' its origin from the words `tele and gram'. `Tele' — means distance and the `gram' stands for `write'. Naturally, therefore the combination of these two indicates `write at a distance'. The method employed to write at a distance has undergone many changes ever since it was invented during the latter half of the 19th century. To begin with, a single mechanical wire was drawn in between two places. By using a battery, a key and a sounder, at both the ends, it was possible to create a mechanical sound at the other end by the simple stroke of the key at one end. The sounds were produced by the skilful operation of the key, making dots and dashes (._) distinguishable by the time interval between two sounds. Different combinations of these dots & dashes were earmarked for alphabets, digits and other characters required for the transmission of a message, data etc. A system, namely Morse Code has been internationally accepted and continues to be in use still, adopting this dot and dash combination.

However, in tune with the various technological advancements, easier, faster and more reliable methods have since been introduced, say, teleprinter/ telex, etc.

The wireless telegraphy also has been widely used. In these systems, instead of dots and dashes, electric pulses are formed by a relay mechanism, which is controlled by the operation of a key board of letters. The pulses so generated, are converted into voice frequencies and transmitted along carrier wave channels. At the receiving end we are able to get a print of the message.

K.K. Narayanan Nair, Ernakulam, Kerala

Recommended for you