E-22
Uniden UM725 Radio Owner’s Manual
All ships call
Group
call
Individual
call
All ships call
DIGITAL SELECTIVE CALLING (DSC)
WHAT IS DSC?
Digital Selective Calling (DSC) is a standard that allows you to quickly and easily call
specific radios or groups of radios using their unique MMSI (Maritime Mobile Service
Identity) number. The four basic call types are:
x
Distress Calls – Use in emergencies only! The Distress message alerts all ships that
you need assistance and sends your current position.
x
Individual Calls – Calls a single station using the User MMSI. Use when you want to
talk to another station
x
Group Calls – Calls all ships with the same Group MMSI. Use to talk with your whole
group at the same time.
x
All Ships Calls – Calls all ships within range of your radio. Should only be used for
safety warnings (e.g., debris in the water) or urgent situations.
HOW DOES DSC WORK?
The DSC standard dedicates a VHF channel—channel 70—to digital transmissions only.
Because digital transmissions require less bandwidth than voice transmissions, channel
70 avoids the problems of busy voice channels. The radio uses channel 70 to transmit
your MMSI number to the other station along with a voice channel.
If the other station accepts your call, both radios automatically switch to the requested
voice channel so you can talk to the other station.
DSC also provides a system for automated distress calls. At the touch of a key, the radio
can transmit your MMSI number, the nature of your distress, and your current position
based on data from your GPS receiver. The radio repeats the distress call every few
minutes until it receives an acknowledgement. Much like familiar "contacts" and "group
text" functions of modern phones, your UM725 lets you save individual contacts in your
Individual Directory and groups in your Group Directory.
Suppose you are coordinating safety for a
sailboat race. Before the race starts, you
instruct all the racers to enter your group MMSI
number into their radios. During the race:
x
Throughout the race, you use group calling
to update the racers on the time, race
status, and any course corrections.
x
A power boat full of spectators comes too
close to the race path. You use individual
calling to contact the power boat and advise
them to stay clear of the race.
x
You see a rowboat entering the area, but
since it doesn’t have a radio, you can’t
communicate with the rowboat. You use all
ships calling to alert all the other ships in the
area of the possible danger
.
