Marine Communication Equipment
For standard marine radio communication principally three
kinds of equipment are used:
- VHF transceivers for short-range (up to 50 Km) communications
- HF-SSB transceivers for long-range (up to 5000 Km) communications
- Satellite transceivers for world-wide communications
A transceiver is a combined transmitter-receiver communication unit,
in which some of the hardware (e.g. the user controls) is combined
to reduce cost and complexity.
VHF equipment is relative cheap and most user friendly.
HF-SSB equipment is more expensive and technically more
difficult to manage.
The distance over which communication can be conducted,
strongly depends on the radiation performance of the antenna used.
This includes high-quality matched cabling between transmitter and
antenna as well as a careful grounding installation.
Additionally to the HF-SSB bands that are reserved for marine
communication there are also the HF-SSB bands that are used by
radio amateurs (HAM radio).
If a valid HAM licence and associated call sign are available, also these
HF-bands can be used to establish radio connections with other HAM
stations on ships or on land. This offers an additional communication
channel to obtain weather forecasts or technical (marine) information.
Today's marine radio sets for use on VHF are very user friendly with only
three basic controls:
- a control to select the frequency for transmitting and receiving, using
simple channel numbers (Ch.),
- a control to set the audio volume level for the received signal (VOL),
- and a third control to set the squelch level (SQL), which silences
the normal background noise when no signal is being received.
Other controls that may be found on the VHF set allow to quickly shift to the
distress and calling channel (16) or to scan a variety of channels.
The IMO regulations require that every VHF set be
capable of operating on Channels 16 and a working channel, but today,
all sets, even the small hand-helds, can tune to all marine channels (about 58 channels
in the range of 156.0 MHz to 164.0 MHz).
Many channels are appointed to specific types of communication such as ship-to-ship
communication or distress communication. Here is a
list of the VHF channels and the different types of communication allocated to them.
Notice, that there is no strict international agreement on the usage of these
channels and that especially in the USA there are some exceptions to this scheme.
See the VHF marine radio channels recommendations issued by the USCG for details.
Maritime VHF communication with Digital Selective Calling (DSC)
is an integrated part of the Global Distress and Safety System (GMDSS) introduced
by the IMO in 1991 in order to improve the safety of live at sea
(primary for commercial shipping).
In order to participate in the GMDSS a VHF tranceiver will have to be equipped
with a DSC controller enabling Digital Selective Calling.
This is important also for pleasure yachts, since after the introduction of
GMDSS, the IMO has discontinued the permanent watch obligation on the distress
channels (for both commercial shipping and the coast stations).
Today (2007), almost all newly build maritime VHF sets have DSC capability.
But in order to use the DSC feature, the equipment must be registered with the
national telecommunications authorities.
Through registration, the DSC radio station will obtain a unique calling number
and call sign.
In most countries also an operator's certificate is required to use DSC featured
VHF radio transceivers.
Other restrictions concerning on-board VHF radio
equipment include the following:
- Mounted VHF sets may have the maximum allowable HF power output
of 25 W, with a required low-power mode of 1 W.
Hand-held VHF radios may have up to 5 W transmission power and
also a required low-power mode of 1 W.
- National regulations usually prohibit the use of hand-helds on shore
or the use of regular marine channels for on-board communications.
- All radio equipment that can transmit a radio signal must be "Type
Approved" by national telecommunications authorities.
This should be no problem when purchasing new sets because "Type Approval"
is required before equipment may be offered for sale (e.g. in Europe this is
documented through the "EC sign" on the outside of the transceiver).
However, when crossing national borders with the equipment or when
"Type Approved" equipment is imported, a supplementary inspection by the
local telecommunications authorities may be required.
- The "Type Approval" of a radio set is certified in a document that will
be delivered with the equipment at purchase and must be kept on board.
HF - SSB Transceiver
Transceivers for AM-SSB communications are larger and more complicated to
handle than those for VHF. SSB equipment is mainly used for long-range communication.
The maximum RF power is usually 150W. As on VHF transceivers all AM-SSB transceivers
have an instant 2182kHz selection capability. This is the distress and calling
frequency in the MF radio band.
The range of SSB communications is dependent on sky waves, so it is extremely
sensitive to atmospheric and ionospheric interference. Transmission conditions
can vary strongly on a seasonally, daily and even hourly basis.
With additional hardware including a radio modem,
a text decoder and a printer, SSB equipment can also be used to pull down
weather faxes around the world and gain an up-to-date and accurate picture
of the weather systems and forecast for the region.
Some SSB coast stations with internet connections
also offer a simple data communication service for mariners enabling the
on-board transmission and reception of E-mail. This requires a radio modem
and a PC-based software coder-decoder. Due to the limited audio bandwidth,
the data rate (characters per second) is limited to about 1200 baud allowing
for only text-based E-mail without binary attachments. For more information
on this service and on the required hard- and software, please link to
For operating an AM-SSB radio station, a stations licence
and an operating permit are required.
Also regard that in some countries (e.g. USA) it is not allowed to use
SSB transceivers for short-range communication.
In the specification of radio equipment for AM there
is a system of abbreviations to specify the type of communication.
The abbreviation consists of a 3-character code, which is a result of
the World Administrative Radio Conference held in 1979 (WARC-79).
Here are some examples of this code:
- F1B: Modulation format for data transmission
(e.g. SITOR: SImplex Telex Over Radio or also RTTY: Radio Tele TYpe)
- H3E: SSB with carrier (carrier can be used for homing in by Search and Rescue)
- J3E: SSB with suppressed carrier (no homing possible)
The first character specifies the type of modulation of the main carrier:
N - unmodulated carrier
A - Double side band
H - Single side band - full carrier
R - Single side band - reduced carrier
J - Single side band - suppressed carrier
B - Independent side bands
F - Frequency modulation
G - Phase modulation
P - Sequence of unmodulated Pulses
K - Amplitude modulated pulses
L - Width modulated pulses
M - Phase modulated pulses
Q - Sequences of pulses modulated during the period of the pulse
The second character specifies the nature of signal modulation of the main carrier:
0 - no modulation
1 - a single channel containing digital information without the use of a modulating sub-carrier
2 - a single channel containing digital information with the use of a modulating sub-carrier
3 - a single channel containing analogue information
7 - two or more channels containing digital information
8 - two or more channels containing analogue information
The third character specifies the type of information to be transmitted:
N - no information transmitted
A - telegraphy for aural reception
B - telegraphy for automatic reception
C - facsimile
D - Data transmission
E - Telephony
F - Television (video)
W - Combination of the above
The four geo-stationary INMARSAT satellites form the
space segment of the GMDSS system.
In this scope, two different standards can be used for maritime communication:
- INMARSAT-B for direct-calling telephone, data and telex communication, and
- INMARSAT-C for telex communication.
Since the INMARSAT-B standard requires a large directional satellite antenna,
which must be continuously kept aligned to the communication satellite,
this communication standard is not feasible on small pleasure yachts.
The communication standard INMARSAT-C is based on narrow-band telex communication
and requires only a simple omni-directional antenna.
This communication type will allow world-wide telex communication but no
The required equipment for INMARSAT-C telex communication consists of a small
satellite transceiver and a PC-based telex station using the PC-screen and keyboard
for printing and writing text-based telex messages.
Since recently, also Email service has become feasible with this equipment.