Worldwide Communications via MF/HF marine SSB radio
Marine MF/HF SSB (Single Side Band) radio is a popular means of communication for the independent cruising yachtsmen and a must if you are planning to do bluewater cruising to the Caribbean, Pacific or Mediterranean.
The range of SSB is up to several thousand miles and calls between yachts are free and there are coast stations broadcasting weather bulletins and even providing low cost SSB email service.
Marine MF/HF SSB transceivers like the Icom M801E, M802, M803 and GM800 have built-in Digital Selective Calling (DSC) capabilities, which allows sending and receiving of distress, urgency and safety communications between other ships and to and from a coastguard.
DSC can also be used for individual routine inter-ship calling between two ships/yachts and routine DSC group calling between a number of ships/yachts within a designated group.
It is mandatory for all ocean going ships to have a marine MF/HF SSB DSC transceiver on board and the regulation states that the DSC equipment must be tested daily, which is an internal test using the built in self test feature of the equipment and week by means of a live DSC test call to another station.
Having DSC capability to summon help from other ships within a wide area is a major safety feature to anyone spending time at sea.
There are a number of procedures and regulations involved in using a marine radio and therefore in the UK it is a legal requirement that the radio operator holds a GMDSS Long Range Certificate (GMDSS LRC) or a General Operators Certificate (GOC).
Medium Frequency (MF) radio
Medium Frequency (MF) radio uses on frequencies between 300 kHz to 3000 kHz and propagates (travels) along the ground, this is called ground wave propagation.
Depending on the transmit power will depend on the range, with a 400 watts transmitter a range up to 200 miles can be achieved. A good rule of thumb is 1 Watt per half mile, so a 100 watt transmitter can be received up to 50 miles during daylight hours.
At night-time MF radio waves refract (bend) at the ionosphere (called sky-waves) and a range of several hundreds miles can be achieved.
High Frequency (HF) radio
High Frequency (HF) radio uses frequencies between 3 MHz to 30 MHz which lies between medium-wave (MF) and VHF radio.
HF radio waves can refract (bend) at the ionosphere giving coverage over hundreds or even thousands of miles and therefore ideal for long distance communications.
MF/HF radio propagation
Low frequencies follow the curvature of the earth and this type of propagation is called Ground Wave, while higher frequency radio waves can also refract off the Ionosphere this type of propagation is called Sky Wave. Sky Wave propagation can suffer from areas where no signal, (called a dead zone) which usually occurs when close to a transmitting station.
A good simple rule during daytime is 100 miles per MHz:-
MF/HF Range Freq.
Why Single-Sideband Radio
modulation (SSB) is a very powerful and spectrum efficient form of
communications compared to AM or FM forms of modulation, as an SSB
transmission does not contain carrier wave like AM or FM
When pressing the microphone button on a SSB transceiver is pressed nothing is transmitted and very little DC power is taken by the transceiver.
When the radio operator talks into the microphone the SSB transmits just the voice information and the transmit output power changes and so does the DC power along with the voice peaks.
Therefore to obtain maximum power output the radio operator should talk at a constant level holding the microphone no more than 2 to 3 cm (1 inch) from your mouth because the quieter or further away from the microphone the less power is transmitted.