If you look at a new
marine radio, you will notice a red button marked “DISTRESS”
protected by a spring- loaded cover to prevent it from being
accidentally pressed. This button tells you that the radio has DSC, (Digital Selective Calling). DSC is an advanced, computerized form
of VHF and MF radio designed for marine use. New radios with DSC
capability are replacing the VHF and the MF type of radios that have been
in use for more than half a century. They have all of the capabilities of
the earlier radios and a number of new features that can add dramatically
to the safety aspects and the usefulness of marine communications.
DSC automates many
aspects of radio communication. Without using a microphone, a
user can make a distress call just by pressing one button on the radio.
DSC will then automatically supply the Coast Guard (Canadian or US) and
other vessels in the area with your identification and your location. You
can even dial in the reason for the distress call. DSC will automatically
repeat the distress call until it is acknowledged. These digital
communications result in visual messages being displayed on a receiver’s
display screen much like information displayed on a computer's monitor.
DSC radio can make
distress calls, urgency calls, safety and all ships calls as
well as routine calls (the usual person to person type calls we make using
non-DSC radios) using only buttons on the radio's keyboard. They can also
digitally make position requests (asking other vessels their exact
location) and polling calls (who is within communication range?).
In the same way that
your telephone rings when you receive incoming calls an alert
will sound if there is a call for you or if there is a priority call such
as a distress, urgency or safety message. Eventually, there will be no
need to monitor Channel 16. In Canada, the requirement that compulsorily
fitted vessels monitor Channel 16 has been dropped. Such vessels are now
only required to monitor digital data on Channel 70 and MF frequency
2178.5 kHz. However, a large number of vessels are still not equipped with
DSC radio, so it is desirable that Channel 16 still be monitored. The
Coast Guards in both Canada and the US are still monitoring Channel 16 and
will do so for the foreseeable future.
If you make a digital call of any kind using
DSC, your radio transmits the message on Channel 70; thus relieving
congestion on Channel 16. This digital call is sent at ‘computer speed’,
taking only a moment of air time.
All DSC equipped marine
radios can be connected to a GPS, so your radio ‘knows’ your
exact location and the exact time and sends out this information with a
distress call. This can truly be a lifesaver, it takes the "search" out of
search and rescue.
DSC calls can be made
directly to another vessel without broadcasting; it is much
more private, like making a phone call. Remember, a DSC call does not use
Channel 16. If the call is directed to an individual station, then that
signal is sent on Channel 70 and only that station receives the call. The
call can include the channel number on which you want to hold an ordinary
conversation. Channel 70 is only used for digital communication; you
cannot use voice on that channel.
You can store numbers
that connect you to other vessels (like storing phone numbers
on a cell phone). Your radio can keep a log of calls.
DSC radios are available in four categories,
Class A, Class B, Class D and SC-101.
They differ in their features and cost.
Class A and Class
B radios are designed for commercial vessels. They are pricey
and are not usually of interest to pleasurecraft owners.
Class D
radios are designed for commercial boats that are not required to carry
Class A or Class B equipment and for recreational boaters. They are not as
expensive as Class A or B. At the time of writing, prices for a Class D
radio can be as low as $400. Most models cost about $500 to $1000. If the
price of a Class D radio is within your budget, we recommend that you use
this type of DSC radio.
SC-101 is the
low cost, entry level standard for DSC radios. By International law, it
cannot be used on commercial vessels, but may be used on recreational
boats. This class of DSC radio is very limited in capability. These can
cost as little as $200.
What do you get for your
money?
One
difference between lower cost radios is the methods used to enter data.
Better radios tend to have a keyboard method of inputting information
rather than turning dials. There is one very important difference
between a SC-101 radio and a Class D. A true Class D radio has two
receivers, one of which constantly monitors Channel 70. An SC-101 radio
has only one receiver. If you are tuned to a different channel or if you
are transmitting, then the single receiver cannot receive on Channel 70.
Some units have a quick change feature in which they momentarily listen
to Channel 70 then return to the channel you are tuned to. This is still
not as good a system as having dual receivers built in, one always
listening to Channel 70.
A Class D unit will not miss any calls
arriving on Channel 70 because it constantly monitors that channel. Like
anything else, you get what you pay for.
VHF-DSC has the same range as ordinary VHF as
well as the same power restrictions, but it is more efficient than
ordinary VHF.
MMSI
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Digital Selective Calling
