Introduction to Marine VHF Radio

Although IMMARSAT (International Maritime Sattelite Network) / http://en.wikipedia.org/wiki/Inmarsat) and HF Radio (http://en.wikipedia.org/wiki/High_frequency) is used for over the horizon long distance marine communications across the world, VHF is still the backbone for line of sight marine communications worldwide.
Marine VHF radio is installed on all large ships and nowadays most motorized small craft even in India . It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours, locks, bridges and marinas, and operates in the VHF frequency range, between 156 to 174 MHz. Although it is widely used for collision avoidance, its use for this purpose is contentious and is strongly discouraged by some countries.
A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels. Channel 16 (156.8 MHz) is the international calling and distress channel . Channel 9 can also be used in some places as a secondary call and distress channel. Transmission power ranges between 1 and 25 watts, giving a maximum range of up to about 60 nautical miles (111 km) between aerials mounted on tall ships and hills, and 5 nautical miles (9 km) between aerials mounted on small boats at sea-level. Frequency modulation is used.

In the Indian Maritime scenario Channel 16 (156.800 MHZ) and Channel 10 (156.500 MHZ) is used for routine port traffic control operations including maritime Search and Rescue.

Modern day marine VHF radios have a variety of features in addition to basic transmit and receive capabilities. All fixed mount marine VHF radios produced nowadays have some level of DSC calling capability. A number of the more expensive units are capable of acting as a hailer when connected to a hailer horn, can work with optional voice scramblers, and a few even have the ability to use a Bluetooth headset. A large number of unbiased independent reports on both fixed mount and handheld marine VHF radios can be seen at Marine Electronics Reviews.

Marine VHF mostly uses "simplex" transmission, where communication can only take place in one direction at a time. A transmit button on the set or microphone determines whether it is operating as a transmitter or a receiver. The majority of channels, however, are set aside for "duplex" transmissions channels where communication can take place in both directions simultaneously.

Each duplex channel has two frequency assignments. This is mainly because, in the days before mobile phones and satcomms became widespread, the duplex channels could be used to place calls on the public telephone system for a fee via a marine operator. This facility is still available in some areas, though its use has largely died out. In US waters, Marine VHF radios can also receive weather radio broadcasts, where they are available, on receive-only channels wx1, wx2, etc.

Amateur Station/HAM on board ships in India as per WPC Rules :

(1) The Central Government may on receipt of an application authorise establishment, maintenance and working of an amateur station on board a ship registered in India. Applications for such authorisation shall be accompanied by a written approval of the master or owners of the ship concerned.

(2) The establishment, maintenance and working of amateur stations on board ships shall, in addition to the conditions specified , be subject to such other conditions as the Central Government may determine from time to time and such conditions, among others, shall include the following, namely:-

(i) The amateur station on board ship shall be operated only while the ship is in International waters or Indian territorial waters. Its operation within the territorial waters of another country shall be in conformity with laws and regulations of the country concerned.

(ii) It shall not be operated whilst the ship is in any harbour in India.

(iii) The callsign allotted to such stations shall have suffix `MS' followed by the callsign of the ship in case of radiotelegraphy or the official name of the ship in case of radiotelephony.

(iv) The amateur station on board a ship shall discontinue operation at any time on request of an officer of the Central Government, the Master or Radio Officer of the ship or any land station.