Marine Glossary

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radiofacsimile

Facsimile is graphic data transferred by electrical signals from one place to another. The "graphics" can be pictures or text, but the text is just a picture of the words, it is not actual words and letters such as transmitted by teletype or ascii computer files.

I believe the term "facsimile" implies that the main information is conveyed by an analog signal, such as the color white being a high pitch tone, black as a low pitch tone, and a uniform distribution of grays in between. Somehow the signal is received as a voltage level whose height determines the color.

Digital information, on the other hand, is transferred as numbers or letters. White might be 10 and black 0, or some such thing. And the number itself transferred as a fixed voltage level being either on or off a certain number of times or in a certain pattern. (See discussion of analog vs. digital signals in G427.)

The "electrical" transmission can be by radio signals or by wires (telephone lines). The abbreviation FAX applies to any or all of these processes or products. Generally the phrase "fax machine" applies to a land based instrument tied to phone lines. However, the same fax machine can be tied to a cellular phone or to a satellite communications system, in which case they can head offshore on a vessel. Both the cellular phone rig and the satcom system are actually communicating by radio signals, but these applications are usually not called radiofacsimile.

Radiofacsimile is usually restricted to the types of machines designed to be used directly with a radio receiver. When the receiver works in the marine band, they are called marine radiofacsimile.

Many vessels use these machines only for receiving weather maps. This type of machine is called a weather fax. It can receive other information besides weather maps, such as text, weather reports, other marine safety information, and even stock quotes or world news if you know the proper frequencies to tune to. ART-16 discusses the nuts and bolts of using this type of machine.

Fax map means a weather map transmitted by radiofacsimile.

Radiofacsimilie maps are broadcast from coast guards, navies, and other agencies of many countries on the marine band in the high frequency range (see Radio Primer). Use of the maps is covered in ART-16 and RES-1.

Ham operators refer to these maps as WEFAX.

See INMARSAT for a discussion of the transmission of similar information via satellites.

The worldwide schedule of fax map broadcasts is given in RES-3.