DLP-MT-LPCOM10-VHF Safety and Distress call

Marine radio was the first commercial application of radio technology, allowing ships to keep in touch with shore and other ships, and send out a distress call for rescue in case of emergency. Guglielmo Marconi invented radio communication in the 1890s, and the Marconi Company installed wireless telegraphy stations on ships beginning around 1900. Marconi built a string of shore stations and in 1904 established the first Morse code distress call, the letters CQD, used until 1906 when SOS was agreed on. The first significant marine rescue due to radio was the 1909 sinking of the luxury liner RMS Republic, in which 1,500 lives were saved. This and the 1912 RMS Titanic rescue brought the field of marine radio to public consciousness and marine radio operators were regarded as heroes

The first marine radio transmitters used the longwave bands. During World War I amplitude modulation was developed, and in the 1920s spark radiotelegraphy equipment was replaced by vacuum tube radiotelephony allowing voice communication. Also in the 1920s, the ionospheric skip or sky wave phenomenon was discovered, which allowed lower power vacuum tube transmitters operating in the shortwave bands to communicate at long distances.

Types of equipment

Sets can be fixed or portable. A fixed set generally has the advantages of a more reliable power source; higher transmit power, a larger and more effective antenna and a bigger display and buttons. A portable set (often essentially a waterproof, VHF walkie-talkie in design) can be carried on a kayak, or to a lifeboat in an emergency, has its own power source and is waterproof if GMDSS-approved. A few portable VHFs are even approved to be used as emergency radios in environments requiring intrinsically safe equipment (e.g. gas tankers, oil rigs, etc.).

Voice-only

Voice only equipment is the traditional type, which relies totally on the human voice for calling and communicating. Many lower priced handheld units are voice only as well as older fixed units.

Digital selective calling

DSC equipment, a part of the Global Maritime Distress Safety System (GMDSS), provides all the functionality of voice-only equipment and, additionally, allows several other features:

The ability to call another vessel using a unique identifier known as a Maritime Mobile Service Identity (MMSI). This information is carried digitally and the receiving set will alert the operator of an incoming call once its own MMSI is detected. Calls are set up on the dedicated VHF channel 70 which DSC equipment must listen on continuously. The actual voice communication then takes place on a different channel specified by the caller.

A distress button, which automatically sends a digital distress signal identifying the calling vessel and the nature of the emergency

A built in GPS receiver or facility to connect an external GPS receiver so that the user’s location may be transmitted automatically along with a distress call.

When a DSC radio is bought new the user will get the opportunity to program it with the MMSI number of the ship it is intended to be used on. However to change the MMSI after the initial programming can be problematic and require special proprietary tools. This is allegedly done to prevent theft.