Basically when it comes to the marine radio bands, the marine radio telephony service, which is also known as high frequency (HF) ship to shore, has operated on short wave radio frequencies using single side band since voice communication was introduced in the field of marine communication.
Single side band, shortly called SSB, is used in the marine field because the short wave bands are crowded with many users and it permits a single voice channel to use a narrow range of radio frequencies or bandwidth (about 3.5 KHZ). Sometimes the longest wave bands (nearly 20MHZ) at which it works best is also used, but in this case the ionosphere weather can dramatically change and alter communications.
Very High Frequency (VHF):
The proper use of VHF radio communication is necessary in the marine field to contribute to the safety of life at sea and efficiency of navigation. Any misuse may cause communication interference and can cause potential danger to safety at sea.
The most famous VHF channel for distress at sea are channel 16 and channel 70, and anyone who wants to use VHF can tune it to their respective operating frequencies. Also for normal communication, VHF channel 13 and VHF channel 6 can be used.
- In channel 16, the VHF should be tuned to 156.800 MHZ.
- In channel 70, the VHF should be tuned to 156.525 MHZ.
- In channel 13, the VHF should be tuned to 156.650MHZ.
- In channel 6, the VHF should be tuned to 156.300 MHZ.
GMDSS (Global Maritime Distress Safety Signal):
GMDSS is a global communication service based upon an automated system having both satellite and terrestrial components to produce an alert when the ship is in distress. This system includes two subsystems named Morse Telephony and Radio Telegraphy System.
In Morse Telegraphy the system works on 500 KHZ when the signal has to be transmitted from cargo ship of 1000 GT and for all passenger ships, and in case of Radio Telegraphy System the system works on 2182 KHZ and 1526.80MHZ for all cargo ships of 300 GT and over and also for passenger ships.
In general the IMO states that the receiver should be tuned throughout the bands between 1605 KHZ and 27.5 MHZ. This tuning should be either continuous, or by incremental steps, or by selection of a number of spot frequencies.
The following frequencies should be readily accessible to the operator.
For Radio Telephony, the carrier frequencies are 2182.0 KHZ, 4125.0 KHZ, 6215.00 KHZ, 8219.00 KHZ, 12290.00 KHZ, and 16420.00 KHZ.
For NBDP, the carrier frequencies are 2174.50 KHZ, 4177.5 KHZ, 6268.00 KHZ, 8376.5 KHZ, 12520.00 KHZ, and 16695 KHZ.
For DSC (Digital Selective Calling), the frequencies are 2187.50 KHZ, 4207.5 KHZ, 6312.00 KHZ, 8414.5 KHZ, 12577.00 KHZ, and 16804.5 KHZ.
The transmitter should also be able to transmit all the above frequencies allocated to the maritime mobile service in the frequency band between 1605.00 KHZ and 27.5 MHZ. The same condition as stated above will apply to the transmitter.
Radio Watch Keeping at Sea (SOLAS Regulation):
All ships while at sea should keep a continuous watch on the following frequencies to receive any distress signal from another ship or to receive any distress and safety alert form shore based services. Keep continuous watch on
- VHF DSC channel 70
- DSC MF 2187.50 KHZ (for receiving ship’s distress signals and safety alerts)
- DSC distress and safety frequencies 2187.5 KHZ and 8414.5 KHZ and also on at least one of the distress and safety HF DSC frequencies 4207.5 KHZ, 6312 KHZ, 12577 KHZ,Or 16804.5 KHZ according to the time of day and the geographical position of ship relative to the nearest DSC coast station.
Credits: IMO regulation and SOLAS regulation