3Terms, Definitions and Abbreviations

3Terms, Definitions and Abbreviations

- 1 -RTCM Paper 233-2008-SC101-231



2Normative references

3Terms, definitions and abbreviations



4General and operational requirements


4.2Classes of Radio



4.5Operating Frequencies

4.6Controls and indicators


4.7.1Call functions

4.7.2MANUAL calls

4.7.3Distress calls

4.7.4Distress Call Acknowledgement

4.7.5Incoming calls

4.8Watchkeeping Facilities


4.8.2Scanning (Dual Watch) provisions


4.10Microphone and loudspeaker

4.11Safety precautions


4.12.1Primary Batteries

4.12.2Secondary (Rechargeable) Batteries


4.14Warm up

4.15Internal Memory

5Technical requirements

5.1Switching time

5.2Class of emission and modulation characteristics

5.3Facilities for DSC transmission and reception (to be updated once Class D/H and ITU-R M.493 finalised)



5.3.3Clear channel transmission

5.3.4Automatic acknowledgement

5.3.5Automatic re-transmission of distress calls

5.4Ships identity – MMSI and Group MMSI

5.5Position information

5.5.1Internal navigation device performance

5.5.2Internal navigation device timing

5.6Alarm circuits for incoming calls (may need updating once Class D/H finalized)

5.6.1Distress and urgency

5.6.2Other categories

5.6.3Cancellation of alarms

5.6.4Acoustic alarm power

5.7Multiple watch facilities

5.7.1Scanning characteristics (to be updated to address single Rx channel requirements)

5.8Built-in test

6General conditions of measurement

6.1Power Supply

6.2Warm-up Period


6.4Additional Facilities / Supplemental Devices

6.5Audible and Visual Indications

6.6Preparation of VHF Radio for type-approval testing

6.7Measurements and Observations

6.8Test Conditions

6.8.1Normal test conditions

6.8.2Extreme test conditions

6.8.3Arrangements for test signals applied to the receiver input


6.8.5Normal test modulation

6.9Arrangements for test signals applied to the transmitter input

6.10Test channels

6.11Equipment Class

6.12Performance Check

6.13Performance Test

6.14Pre-conditioning and Post Examination for Environmental Tests

6.15Sequence of Tests

6.15.1Environmental Tests

6.15.2Electrical Performance Tests

7Environmental tests

7.1Dry Heat Test

7.2Damp Heat Test

7.3Low Temperature Test

7.4Vibration Test

7.5Bump Test (only applies to Class 3 Radios)

7.6Drop Test

7.7Thermal Shock (only applies to Class 3 Radios)

7.8Immersion Test

7.9EMC Tests

7.10Operational Life Test

7.10.1Test Method

7.11Buoyancy Test (only applies to Class 2 Radios and Class 3 Radios declared tofloat)

7.12Corrosion Test (only applies to Class 3 Radios)

7.13Solar Radiation Test (only applies to Class 3 Radios)

7.14Oil Resistance Test (only applies to Class 3 Radios)

7.15Compass Safe Distance Test

7.16Miscellaneous Tests

7.16.1Controls and Indicators


7.16.3General Construction

7.16.4Exterior Finish



8Transmitter Tests

8.1Frequency error


8.1.2Method of measurement


8.2Carrier power


8.2.2Method of measurement

8.2.3Limits, Normal and extreme test conditions

8.3Frequency deviation


8.3.2Maximum permissible frequency deviation

8.3.3Reduction of frequency deviation at modulation frequencies above 3kHz

8.4Sensitivity of the modulator, including microphone


8.4.2Method of measurement


8.5Audio frequency response


8.5.2Method of measurement


8.6Audio frequency harmonic distortion of the emission


8.6.2Method of measurement


8.7Adjacent channel power


8.7.2Method of measurement


8.8Transient frequency behaviour of the transmitter


8.8.2Method of measurement


9Receiver Tests

9.1Harmonic distortion and rated audio frequency output power


9.1.2Methods of measurement


9.2Audio frequency response


9.2.2Method of measurement


9.3Maximum usable sensitivity


9.3.2Method of measurement


9.4Cochannel rejection


9.4.2Method of measurement


9.5Adjacent channel selectivity


9.5.2Method of measurement


9.6Spurious response rejection


9.6.2Method of measurement


9.7Intermodulation response


9.7.2Method of measurement


9.8Blocking or desensitization


9.8.2Method of measurement


9.9Receiver noise and hum level


9.9.2Method of measurement


9.10Squelch operation (not applicable to radios with Digital Squelch)


9.10.2Method of measurement


9.11Squelch hysteresis (not applicable to radios with Digital Squelch)


9.11.2Method of measurement


9.12SC117 Tests

10DSC Transmitter Tests

10.1Modulation index


10.1.2Method of measurement


10.2Modulation rate


10.2.2Method of measurement


10.3Bit stream speed


10.3.2Method of measurement


10.4Testing of generated call sequences

11DSC Receiver Tests

11.1Dynamic range


11.1.2Method of measurement


11.2Verification of correct decoding of various types of digital selective calls


AnnexA (normative) Types of DSC Calls

A.1DSC Calls

AnnexB (informative) Intellectual Property


B.2Essential patented technologies

B.3Non-essential patented technologies

- 1 -RTCM Paper 233-2008-SC101-231


VHF-FM portable marine radiotelephone equipment with Digital Selective Calling (DSC) and Global Navigation Satellite System (GNSS) location functions


This document specifies the minimum functional and technical requirements for VHF-FM portable marine radiotelephones, equipped with Digital Selective Calling (DSC), and Global Navigation Satellite System (GNSS) functions. These radios are intended to be used on small vessels which may not be equipped with a fixed radio installation. Their purpose is to provide basic distress and routine calling functions with a simple user interface to make them easy to use by persons who are not completely familiar with DSC radio operation.

Since the envisioned user of these radios may not have access to accurate position and navigation information, the radio is equipped with a GNSS processor which is intended to encode a distress call with location information.

Since users may not be familiar with DSC functionality, manufacturers that add additionalfunctions not required under this standard, should strive to maintain a simple user-friendly interface. Any additional DSC functions must comply with the requirements of ITU-R M.493.

VHF Radios that meet this standard are divided into three classes:

Class 1A General Purpose radio designed for use on smaller vessels, but where it is unlikely that the radio will be dropped overboard, this radio will not float without additional buoyancy aids.

Class 2A General Purpose radio designed for use on small vessels, where it is possible that the radio may be dropped overboard, this radio will float without any additional buoyancy aids.

Class 3A radio intended to comply with IMO SOLAS requirements that could potentially be used in a Survival Craft in an emergency that may in due course become a part of the GMDSS. The manufacturer shall declare whether this radio will or will not float without additional buoyancy aids.

2Normative references

The following referenced documents are indispensable for the application of this document to the extent specified herein. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 60945 - Maritime navigation and radio communication equipment and systems general requirements - methods of testing and required test results (2002-08)

ITU Radio Regulations, Appendix S18: 1998, Table of transmitting frequencies in the band 156 - 174 MHz for stations in the maritime mobile service

ITU-R Recommendation SM.332-4: 1978, Selectivity of Receivers

ITU-R M.493-11 - Digital selective-calling system for use in the maritime mobile service

ITU-R Recommendation M.821-1: 1997, Optional expansion of the digital selective-calling system for use in the maritime mobile service

ITU-R Recommendation M.1084-4: 2001, Interim solutions for improved efficiency in the use of the band 156 -174 MHz by stations in the maritime mobile service

ITU-T Recommendation E.161: Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network

ITU-T Recommendation O.41: 1994, Psophometer for use on telephone-type circuits

ITUTRecommendationV.11: 1996, Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10Mbit/s

3Terms, definitions and abbreviations



The term “integral” where used in this standard indicates that the feature or function is a permanent part of the equipment and cannot be removed or disconnected from it without the use of tools.


The term “shall” (or “must”) is used to describe attributes which are considered mandatoryby RTCM in order to meet the standard. The term "should” is reserved for recommended provisions. There is no intent to prevent a law, regulation, contract, or other document referencing this standard from amending the provisions herein for the purposes of that instrument.

NOTE: The documentation provided with equipment which is claimed to meet this standard but which has been exempted from any mandatory feature, must explain the deviation from this standard.


DSCDigital Selective Calling

EMCElectro Magnetic Compatibility

EUTEquipment Under Test

FMFrequency Modulation

GMDSSGlobal Maritime Distress and Safety System

GNSSGlobal Navigation Satellite System

IECInternational Electrotechnical Commission

IMOInternational Maritime Organisation

ITUInternational Telecommunication Union


PEPPeak Envelope Power

PERPPeak Effective Radiated Power

PLLPhase Locked Loop

RFRadio Frequency

RMSRoot Mean Squared

RTCMRadio Technical Commission for Maritime Services

SOLASSafety Of Life At Sea

TTFFTime To First Fix

VHFVery High Frequency

4General and operational requirements


The manufacturer shall declare that compliance to the requirements of clause 4 is achieved and shall provide relevant documentation if requested.

4.2Classes of Radio

Three classes of radio are permitted as defined below:

Class 1 – General Purpose not required to float

Class 2 – General Purpose required to float

Class 3 – Full SOLAS Compliance


The equipment shall, as a minimum include a handset which includes

–a VHF radiotelephone transmitter;

–a VHF radiotelephone receiver;

–a DSC encoder;

–a DSC decoder; and

–a integral GNSS Receiver.


The mechanical and electrical construction and finish of the equipment shall conform in all respects to good engineering practice, and the equipment shall be suitable for hand-held use on board vessels.

All controls shall be of sufficient size to enable the usual control functions to be easily performed and the number of controls should be the minimum necessary for simple and satisfactory operation.

Adequately detailed operating instructions shall be provided with the equipment.

Class 3 radios shall be predominantly highly visible yellow or orange in color. Class 1 and 2 radios maybe any color other than yellow or orange.

4.5Operating Frequencies

The equipment shall be capable of operating on single frequency and two-frequency channels with manual control (simplex).

As a minimum, Class 1 and Class 2 radios shall be able to operate on all the international VHF channels[check definition] defined in appendix S18 to the Radio Regulations. Additional VHF channels outside those defined by appendix S18 to the Radio Regulations may also be provided, but means shall be provided to block any of these additional channels, as may be required by appropriate Administrations [add footnote for US channels].

Class 3 radios shall be capable of operation on the frequency 156.800 MHz[1] (VHF channel 16) and on at least one additional channel as defined in Appendix S18 to the Radio Regulations. In addition Class 3 radios may operate on other single- frequency (simplex) voice communication only channels as defined in the Radio Regulations.

It shall not be possible for the user to unblock any blocked channels. (See also ITU-R Recommendation M.1084-4.)

The equipment shall be so designed that use of channel 70 for purposes other than DSC is prevented.

It shall not be possible to transmit while any frequency synthesizer used within the transmitter is out of lock.

It shall not be possible to transmit during channel switching operations.

4.6Controls and indicators

The user shall not have access to any control which, if wrongly set, might impair the technical characteristics of the equipment.

The following controls or functions shall be provided:

– DISTRESS BUTTON (see 4.7.3): the default shall be an undesignated distress message;

– CALL / ENTER BUTTON (see 4.7.1): the default (initial display) shall be an individual call. When in other parts of the Menu this button functions as Enter/Accept/OK for that menu function;

– CANCEL / CLEAR: to revert to the initial display or to silence the aural alarm and visual indication used to indicate receipt of a DSC alert. The cancel function shall take place automatically after a maximum of 5 min of inactivity;

– a means of easily entering an MMSI for calling and manual position information. If a numeric key pad is provided this shall conform to ITU-T Recommendation E.161;


– on/off control with a visual indication that the installation is in operation;

– a manual non-locking push-to-talk switch to operate the transmitter with a visual indication that the transmitter is activated and facilities to limit the maximum transmission time to 5 min;

– an audiofrequency power volume control;

– a squelch function;

The equipment shall have means to select manually a channel and shall indicate the designator of the channel at which the installation is set.

All electronic displays, including the channel designator, distress button and numeric keypad (if fitted), shall be legible irrespective of the external lighting conditions for at least 5 seconds upon activation of any control.

Channel 16 shall be distinctively marked. Selection of channel 16, shall be by readily accessible means (e.g. a distinctively marked key). Selection of Channel 16 by any means shall automatically set the transmitter output power to maximum. This power level maysubsequently be reduced by manual user control if required.

If a switch for reducing transmitter output power to no more than 1 W, on both telephony and DSC, with a visual indication that low power is selected is not provided then High and Low transmitter power settingsfor each channel shall be automatically selected as required by the Radio Regulations. Transmission of DSC distress calls shall always be at full power.


4.7.1Call functions

The facilities for coding and composition of calls shall be so arranged that it is possible for the operator quickly and precisely to enter a call. The types of DSC calls provided in this equipment are specified in annex A.

The CALL function (see 4.5) shall permit selection of the following functions:

– INDIVIDUAL: for making a call to a specific MMSI;

– TEST: for making a DSC Test Call

– OTHER: for equipment housekeeping functions.

If INDIVIDUAL is selected, either a MANUAL call (see 4.7.2) or a DIRECTORY call shall be selected. The DIRECTORY list shall have a facility for at least 10 entries. Their MMSIs shall be programmable.

4.7.2MANUAL calls

The MANUAL call facility shall permit the entry of an MMSI. If the called station is a coast station (i.e. MMSI commencing 00) no further information shall be requested from the operator. If the called station is a ship station the equipment shall request input of a channel number. The equipment shall assist the operator by suggesting a suitable inter-ship channel suitable for the vessels area of operation.

NOTE In Appendix S18 of the Radio Regulations channels 6, 8, 72 and 77 are reserved solely for inter-ship communications. Channels 9, 10, 13, 15, 17, 67, 69 and 73 may also be used for inter-ship communications but are also available for port operations and ship movement.

4.7.3Distress calls

It shall only be possible to transmit distress DSC calls by means of a single dedicated button which is used for no other purpose. This button shall not be any key of ITU-T Recommendation E.161 digital input panel. This button shall be red in color and marked “DISTRESS”. Where a non-transparent protective lid or cover is used, it shall also be marked “DISTRESS”. The cover shall be protected against inadvertent operation with a spring loaded lid or cover permanently attached to the equipment by, for example hinges. It shall not be necessary for the user to remove seals or to break the lid or cover in order to operate the distress button.

The operation of the distress button shall generate a uniquevisible and audible indication. The distress button shall be kept pressed for at least 3 s in order to initiate a distress call. A flashing light and an intermittentacoustic signal shall start immediately. After the 3 s, the transmission of the distress alert isinitiated and the indication shall become steady.

The distress alert initiation shall require at least two independent actions. Lifting the protectivelid or cover is considered as the first action. Pressing the distress button is considered asthe second independent action.

The nature of distress shall be the undesignated distress.

Initiation of a distress call shall automatically have priority over any other operation of theequipment. The equipment shall automatically select channel 70 and the maximum transmitterpower.

The distress call shall automatically be transmitted five times in succession with no intervalsbetween the individual calls so that bit synchronization between the transmitter and receiverof the call can be maintained. Each call shall include the appropriate dot pattern. If position is not available from the internal GNSS Receiver then the distress call shall still be transmitted, but with default position.

Following the distress call sequence, a DSC expansion message giving enhanced positionresolution according to ITU-R Recommendation M.821-1 shall be transmitted.

If position is not available from the internal GNSS Receiver then the DSC expansion message shall still be transmitted, but with default position. The radio shall automatically monitor the status of the internal GNSS Receiver output for a period of at least [5] minutes after the transmission of a distress call. If during this time a position (or updated position) is provided by the GNSS Receiver then the radio shall automatically repeat the distress call sequence followed by another DSC expansion message giving the position (updated position).

Check updated call status if send another call before / after acknowledgement

After the transmission of the distress call sequence, including the DSC expansion message,the equipment shall wait for a period of xx seconds to receive a distress acknowledgement beforeautomatically tuning to channel 16 and selecting the maximum transmitterpower.

4.7.4Distress Call Acknowledgement

Where no distress acknowledgement is received, the equipment shall automatically re-transmit the distress call attempt after a random delay of between 3,5 and 4,5 minutes from the beginning of the previous call.

This sequence shall be continued until a distress acknowledgement has been received, or until the automatic transmission of the distress call is discontinued manually.

4.7.5Incoming calls

The DSC equipment shall be provided with suitable facilities for converting incoming calls with relevant address content to visual form in plain language.

In the case of incoming distress and urgency calls the radiotelephone shall automatically switch to channel 16 and automatically select the maximum transmitter power. For other calls the user shall be provided with a visual indication that a channel change is requested and if the user acknowledges the call then the radio shall automatically change to that channel.

4.8Watchkeeping Facilities


The VHF radiotelephone equipment shall be provided with dual watch facilities on at least channels 16 and 70 but transmission of DSC shall always take precedence. Other scanning or tri watch facilities may be included in the radio but are not mandatory.

NOTE Might miss DSC Rx Calls due to dual watch / scanning, what if anything do we want to do about this?

Need to sort out DUAL WATCH features after sending distress call vs before sending etc.

4.8.2Scanning (Dual Watch) provisions

Equipment shall as a minimum comply with the following:

– Facilities for the automatic sequential change of any additional channels may be provided;

– the priority channel ischannel 70 this channel shall be sampled even if there is a signal on the additional channel (channel 16) and on which the receiver will lock during the time a signal is detected;