Radio Survey

Article 53 of the International Telecommunication Union Radio Regulations states that all stations in the Maritime Mobile and the Maritime Mobile-Satellite service shall be capable of offering four levels of priority in the following order: Distress, Urgency, Sasfey, Routine.

There are several types of Maritime Mobile Service: Ship Stations, Coastal radio stations, Port operations stations, Aricraft stattion, Rescue Coordination Centers.

The International Telecommunication Union (ITU) has allocated various bands of frequencies throughout the radio frequency spectrum to the Maritime Mobile Service and the Maritime Mobile-Satellite Service.

All HF and all VHF marine frequencies are arranged in a channelised format. Channels are designated as either: simplex or duplex.

The ITU has allocated simplex (i.e. single frequency) frequencies in the MF, the VHF and each of the HF maritime bands exclusively for distress and safety purposes. These frequencies are protected by international agreement, and any transmission capable of causing harmful interference to distress and safety signals is prohibited.

DSC is a paging technique used to automate the initial call between two stations. The technical principles are almost identical to NBDP, in that tone information is transmitted from one DSC system to another over a radio link.

DSC is used in the MF, HF and VHF marine bands for distress, urgency and safety alerting.

Marine Orders requires that a 406 MHz EPIRB is tested and, if necessary has its batteries replaced at intervals specified by the manufacturer. Hydrostatic releases must be replaced by their expiry dates. These are usually marked on the release mechanism. 


406 MHz EPIRBs are to be physically examined and the self-test function checked, at least once per month.

The EPIRB is subject to annual performance tests under SOLAS regulation IV/15.9: "Satellite EPIRBs shall be tested at intervals not exceeding 12 months for all aspects of operational efficiency with particular emphasis on frequency stability, signal strength and coding" and shore-based maintenance at intervals not exceeding five years.

The purpose of an annual testing is to determine that EPIRB is operational as defined in appropriate performance standards - the International Maritime Organization (IMO) Performance Standard (A.810) and IEC standard, IEC 61097-2: COSPAS-SARSAT EPIRB – Satellite emergency position indicating radio beacon operating on 406 MHz – Operational and performance requirements, methods of testing and required test results.

The annual testing of 406 MHz satellite EPIRBs is required by SOLAS regulation IV/15.9. The volume of annual beacon testing is described in IMO MSC.1/Circular 1040. MSC/Circ.955 further recommends that annual testing of the EPIRB shall be carried out concurrently with the Annual Safety Radio Survey. Shore-based maintenance volume is described in IMO MSC/Circ.1039.

The testing should be carried out using suitable test equipment, such as EPIRB Tester, capable of performing all the relevant measurements required in these guidelines. All checks of electrical parameters should be performed in the self-test mode, if possible.

The NAVTEX system provides the automatic dissemination of local Maritime Safety Information (MSI) by Narrow Band Direct Printing (NBDP) operating in the Forward Error Correction (FEC) broadcast mode (see Section 0 for more details on FEC operation). Depending on the geographical features of its area of responsibility (in main, the length of coastline), the NAVTEX system may be chosen by Administrations as an alternative to providing such information by the Inmarsat-C EGC service.

The system provides navigational safety information, weather warnings and forecasts relevant to vessels within specified coastal areas.

Range is generally within 300 – 400 n miles.

Due to its large length of coastline and the limited communications range of the NAVTEX frequencies, Australia has no plans to provide a NAVTEX service. Coastal MSI is disseminated by Inmarsat EGC. The NAVTEX system is presently used by countries in Asia, the Middle East, Europe and North America.

Broadcasts of local MSI by land stations operating in the NAVTEX service are made on the (MF) frequency of 518 kHz. A second NAVTEX (MF) frequency of 490 kHz is available for national language broadcast. The (HF) frequency of 4 209.5 kHz is also allocated for nation NAVTEX transmissions. There is also provision for transmissions on other nationally assigned frequencies for national transmissions, which also be in language other than English. Some of these are on 424 kHz (refer to ALRS for details).

To receive NAVTEX broadcasts, a ship must be equipped with a dedicated NAVTEX receiver tuned to 518 kHz. Once switched on and programmed, the receiver will provide fully automatic operation and broadcasts will not be missed even if the bridge watch keeper is busy with other duties. Messages are received in printed form on a paper roll, and on recent models, displayed electronically with local storage.

These ‘MSLS’ or ‘MOB’ devices and systems are intended for very short-range crew retrieval applications. The MSLS is designed to allow for self help from the vessel or organisation where there is a risk of crew falling overboard by sounding an alert from the onboard receiver.

They are not part of the GMDSS, but may use frequencies which can be detected by both GMDSS vessels and non-GMDSS vessels.

One example is a device transmitting on VHF Ch.70 using DSC, having an integral GNSS receiver, and transmits periodically, an automated Distress-priority alert and DSC message with the associated text ‘MAN OVERBOARD’. The DSC message contains the GNSS position and time, which will be displayed on the vessel’s VHF DSC receiver. The units may also be fitted with an alerting light flashing at not-less than 20 flashes/min. If fitted, the light shall be capable of operating at least 6 h, which is also the main battery operation requirement. It may also be capable of being water activated.

A number of devices used as Man Overboard Devices (Maritime Survivor Locating Systems/Devices) use AIS technology based on the burst transmissions defined in Annex 9 of Recommendation ITU-R M.1371. Early versions of these devices have the maritime identity of the format 970xxyyyy, but newer units starting from 2011, use the format 972xxyyyy, (see footnote 1 below the Table), which has been internationally agreed in Recommendation ITU-R M.585-6, Annex 2, Section 2.

The devices should be certified by a competent testing house that they are sufficiently compliant with the IEC 61097-14 for the purpose it is intended, or fully compliant with overseas standards, such as RTCM 11901.1 (June 2012). Additional overseas standards for these devices are under development.

Portable two way VHF radiotelephone equipment is used for communications between survival craft and rescue vessels. It may also be used for onboard communications on channels 15 and 17. Newer models automatically reduce the power to 1 W when these channels are selected. The equipment typically comprises a small hand-held transceiver with integral antenna.

The equipment is operated in the same fashion as any hand held (or ‘walkie-talkie’) type unit. Controls are provided for volume, squelch and channel operation. Transmission – reception is controlled by a ‘push-to- talk’ switch located on the side of the unit.

GMDSS vessels over 500 GRT are required to carry three portable survival craft VHF transceivers. Vessels of 300–500 GRT carry two. They are usually stored on or near the navigating bridge, for easy transport to survival craft. As the equipment uses re–chargeable batteries, the transceivers are stored in a ‘drop in’ type of battery charging cradle.

The effective radiated power should be a minimum of 0.25 W. Where the e ective radiated power exceeds 1 W, a power reduction switch to reduce the power to 1 W or less is required. When this equipment provides for on–board communications, the output power should not exceed 1 W on these frequencies.

Primary batteries should have a shelf life of at least 2 years, and if identified to be user–replaceable should be of a yellow or orange colour or marking.