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 aerial 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 water-proof 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.).
Marine radios can be "voice-only" or can include "Digital Selective Calling" (DSC).
Voice-only equipment is the traditional type, which relies totally on the human voice for calling and communicating.
Digital Selective Calling 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:
- a transmitter can automatically call a receiver equipped with Digital Selective Calling, using a telephone-type number known as a Maritime Mobile Service Identity or MMSI. The DSC information is sent on the reserved Channel 70. When the receiver picks up the call, his active channel is automatically switched to the transmitter's channel and normal voice communication can proceed.
- a distress button, which automatically sends a digital distress signal identifying the calling vessel and the nature of the emergency
- a connection to a GPS receiver allowing the digital distress message to contain the distressed vessel's position
The MMSI is used for sea-going vessels and consists of a nine digit number identifying a VHF set or group of sets. The left hand digits of MMSI indicate the country and type of station. For example, here are MMSI prefixes of four station types:
- Ship : 232, 233, 234 or 235 are the United Kingdom – e.g. a UK ship : 232003556
- Coast : 00 – e.g. Solent Coastguard : 002320011
- Group of stations : 0 – e.g. 023207823
- Portable DSC equipment : for UK 2359 - e.g. 235900498
For use on the in-land waterways within continental Europe, a different automatic identification (ATIS) is compulsory. The alphanumeric call sign is translated into a 10-digit number for this purpose. This, and the use of channels, is regulated, most recently by the Basle convention.
Read more about this topic: Marine VHF Radio
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