RECALLING Article 15(j) of the Convention on the International Maritime Organization concerning
the functions of the Assembly in relation to regulations and guidelines concerning maritime safety,
RECOGNIZING the improved navigational information which radar beacons and transponders can
provide for the safety of navigation,
HAVING CONSIDERED the recommendation made by the Maritime Safety Committee at its
(a) the Recommendation on the Marine Uses of Radar Beacons and Transponders set out in
Annex l to the present resolution and considers that Recommendation as the IMO policy
document on the subject;
(b) the Recommendation on Operational Standards for Radar Beacons set out in Annex 2 to
the present resolution;
(c) the Recommendation on Transponders set out in Annex 3 to resolution;
2. RECOMMENDS Member Governments to ensure that:
(a) the use of radar beacons and transponders conforms with Annex l to the present resolution;
(b) radar beacons conform to operational standards not inferior to those contained in Annex 2
to the present resolution;
(c) transponders conform to the recommendations contained in Annex 3 to the present
3. REVOKES resolution A.423(XI).
Annex 1 Recommendation on the marine uses of radar beacons and transponders
The uncontrolled provision of radar beacons and transponders could cause degradation of ships'
navigational radar and ARPA* displays, produce incompatibilities among devices developed for
different uses, or necessitate a succession of modifications to ships' radar displays to accommodate
progressive developments of radar beacons and transponders.
To avoid these possibilities, the following recommendations are made concerning the appropriate
applications for radar beacons and transponders, where an operational requirement for such a device
exists, and concerning measures for general administration of radar beacons and transponders.
The technical criteria and operation of radar beacons and transponders are similar. However, the
terms "radar beacon" (racon) and "transponder", as used in this recommendation, are understood to
have the following meanings:
- Radar beacon (racon): A receiver-transmitter device associated with a navigational mark
which, when triggered by a radar, automatically returns a distinctive signal appear on the
display of the triggering radar, providing range, bearing and identification information. The
terms "radar beacon" and "racon" should be reserved exclusively for this use and include
devices mounted on fixed structures, or on floating aids anchored at fixed positions, for
navigational purposes. The racon itself is considered a separate aid to navigation, whether
used alone, or mounted on another aid to navigation (such as a visible mark).
- Transponder device in the maritime radio determination service which transmits automatically
when interrogated, or when a transmission is initiated by a local command. The
transmission may include a coded identification signal and/or data. The response may be
displayed on a radar PPI, or on a display separate from any radar, or both, depending upon
the application and content of the signal.
* In this recommendation "radar display" includes ARPA display.
2 General operational characteristics
2.1 Radar beacons2.1.1
A radar beacon in the maritime radionavigation service* is a device which will:
- be triggered automatically by the transmissions of any radar operating in the appropriate
frequency band; and
- transmit a response immediately on receipt of the triggering pulse for display as part of the
normal picture of the triggering radar.
Where a radar beacon incorporates a user-selectable mode, so that a user can control the
presentation of a radar beacon response, it will also:
- be triggered automatically by the transmission of a suitably configured radar in the vicinity
operating in the appropriate frequency band and using its own user-selectable facility; and
- transmit a response so that it can:
- be shown on the radar display in a manner distinct from that used for radar
- be shown on the radar display or other display without other information, or
- not be shown on the radar display.
In special circumstances, a radar beacon not being used for general navigational purposes may
operate exclusively in the user-selectable mode.
A transponder is a device which can provide for:
- ship radar target identification and echo enhancement with the proviso that such
enhancement should not significantly exceed that which could be achieved by passive means
on the radar display of an interrogating ship or shore station;
- radar target correlation with voice or other radio transmission for identification on the radar
display of an interrogating ship or shore station;
- user-selectable presentation of transponder responses either superimposed on the normal radar
display, or free of clutter and other targets; and
- transfer of information pertinent to avoidance of collision or other hazards, manoeuvre,
manoeuvring characteristics, etc.
* In accordance with the Radio Regulations, maritime radionavigation service means radionavigation
service intended for the benefit, and for the safe operation, of ships
3 Operational use
Radar beacons should be used only for radionavigational purposes*, for example:
- ranging on and identification of positions on inconspicuous coastlines;
- identification of positions on coastlines which permit good ranging but are featureless;
- identification of selected navigational marks both seaborne and land-based;
- landfall identification;
- as a warning device to identify temporary navigational hazards and to mark new and
- bridge marking;
- leading lines;
- identification of offshore structures;
- marking important features in channels.
Radar beacons used at locations where clutter from land, sea, ice or weather could mask their
response may, at the discretion of the Administration concerned, incorporate a user-selectable
Where an operational requirement exists for a responding device, other than for radionavigational purposes, a transponder should be used. Examples of requirements suitable for
- identification of certain classes of ships (ship-to-ship) and towed devices;
- identification of ships for VTS and other shore surveillance purposes;
- search and rescue operations;
- identification of individual ships and data transfer;
- establishing positions for hydrographical purposes.
* Radar beacons should not be used to enhance the detection of marine craft. ** It is noted that to ensure compatibility of the user-selectable mode of radar beacons with marine
radars, international operating and technical specification are being studied by CCIR. On completion of the
work of CCIR, consideration should be given to the need to include optional standards for a user-selectable
mode in appropriate shipborne equipment.
4 General administration of radar beacons and transponders
4.1 All radar beacons should be authorized by an Administration or by a competent navigation
authority. Before authorizing or approving the setting up of a radar beacon, account should be
taken of the density of such devices in the particular area and the need to prevent degradation of
ships' radar displays.
4.2 Except in the case of SAR transponders (see resolution A.530(13)), transponder systems
designed to respond in a frequency band used by marine radars should be authorized by an
Administration. Before giving such authorization, account should be taken of the effect such
transmissions would have on ships' radars.
Annex 2 Recommendation on operational standards for radar beacons
1.1 Radar beacons should conform to the following minimum operational standards.
1.2 Radar beacons should be operationally compatible with navigational radar and ARPA equipment
which conforms to the performance standards recommended by the Organization.
2 Operating frequencies
2.1 Radar beacons designed to operate on a wavelength of 3 cm should be capable of being
interrogated by any navigational radar equipment operating on any frequency between 9,320 MHz
and 9,500 MHz and respond within this frequency band.
2.2 Radar beacons designed to operate on a wavelength of 10 cm should be capable of being
interrogated by any navigational radar equipment operating on any frequency between 2,900 MHz
and 3,100 MHz and respond within this frequency band.
3 Transmitter tuning characteristics
The tuning characteristics of the transmitter should be such that the beacon response can
appear on a radar display* in a recognizable form at least once every 2 mins.
4 Operating range
The operating range should be compatible with the navigational requirements for the radar
beacon at its location.
5 Response characteristics
5.1 On receipt of an interrogating signal, the radar beacon should commence its response in such
time that the gap on the radar display between the radar target and the beacon response does not
normally exceed approximately 100 m. In certain cases, the operational use of radar beacons may
be aided by increasing this delay slightly. Under such circumstances, the delay time should be as
short as practicable and the details should be shown in appropriate navigational publications.
5.2 The duration of the response should be approximately 20% of the maximum range requirement
of the particular radar beacon, or should not exceed 5 miles, whichever is the lower value. In
certain cases, the duration of the response may be adjusted to suit the operational requirements for
the particular radar beacon.
5.3 The leading edge of the response should be sufficiently sharp to permit satisfactory range
6 Identification coding
6.1 Identification coding should normally be in the form of a Morse letter. The identification
coding used should be described in appropriate navigational publications.
6.2 The identification coding should comprise the full length of the radar beacon response and,
where a Morse letter is used, the response should be divided with a ratio of 1 dash equal to 3
dots and 1 dot equal to 1 space.
6.3 The coding should normally commence with a dash.
7 User-selectable mode
7.1 Radar beacons may be provided with a user-selectable mode. In this mode the radar beacon, in
addition to satisfying the response characteristics set out in section 5, should be capable of
transmitting a response after receipt of an interrogating signal from a suitably configured radar
using its own user-selectable facility.
7.2 The characteristics of the interrogating signal and the response should conform to the
appropriate CCIR Recommendations.
7.3 Radar beacons provided with a user-selectable mode should, unless operating exceptionally only
in the user-selectable mode, be capable of responding to interrogations from both normal radar
signals and special interrogating signals with a minimum of interruption in response to any user.
Radar beacons should be designed to provide high availability when installed permanently in a marine environment.
* In this recommendation "radar display" includes ARPA display.
Annex 3 Recommendation on transponders
1 The design of transponder systems should ensure that there is no significant degradation in the
use of radar beacons, and the response of a transponder should not be capable of being interpreted
as being from a radar beacon of any type.
2 Where a transponder is to be used with a marine navigational radar or ARPA, any modifications
necessary to the radar or ARPA should not degrade its performance; they should be kept to a
minimum, be simple and be compatible with a user-selectable beacon facility.
3 Transponders should not be used to enhance the detection of marine craft, except for search and
rescue or when specially authorized by Administrations for safety * purposes. Transponders used
for search and rescue purposes should be capable of transmitting signals which will appear on a
radar or ARPA display as a series of equally spaced dots (resolution A.530(13)).
* This application of transponders should be strictly limited in accordance with guidelines prepared by
the Administration concerned. For all cases a local notice to mariners should be issued before such
transponders are used.