MF/HF RT radio is often known as SSB radio. It is a transmitting-receiving system often referred to as a Transceiver (Tx/Rx), which allows the operator to either transmit or receive information by voice. MF/HF radios use SSB modulation for voice communication.
One of the greater disadvantages of an MF/HF RT radio is that it is not able to "address" a particular radio. A voice broadcasted over MF/HF RT radio can be heard by all other MF/HF radios within range.
Because of that MF/HF radios integrate an MF/HF DSC Controller. Its function can be regarded as a cross between a normal telephone and a radio. The DSC functions via the DSC Controller or Modem, which simply sends a burst of digital code on the MF/HF DSC frequencies, will automatically “ring” another MF/HF radio. This is feasible because each MF/HF DSC Controller has been allocated a unique MMSI number that acts like a telephone number.
The main components of a MF/HF radio consist of:
* A receiver (Rx) with an earphone and/or loudspeaker;
* A Transmitter (Tx) with a microphone – the microphone and the earphone are often combined into a single handset;
* A MF/HF DSC controller;
* A radio telex system (option);
* An antenna enabling both simplex and duplec operation;
* Power supply - often a 12 V or 24 V battery.
Medium Frequencies (MF) designated for marine communication range between 1605 kHz to 3800 kHz and are called "t" band.
High Frequencies (HF)designated for marine communication range between 4000 kHz to 27500 kHz and are called "u" band. This is divided into the following sub-bands: 4, 6, 8, 12, 16, 18/19, 22, 25/26 MHz. Only the first five are used for distress and safety communication.
and Others ... : Furuno FS1575, JRC JSS 2150/2250/2500