DSC VHF—Better than a Cell Phone

Don't have DSC? It's time to get it. Since the installation of the new Rescue 21 emergency communication system last December, DSC will not only save your life, it also will simplify it.

Since the installation of the new Rescue 21 emergency communication system last December, DSC will not only save your life, it also will simplify it.

The Call That Saved Your Life

Digital selective calling (DSC) works by transmitting a hailing signal on channel 70, which is reserved for digital transmissions. Its advantages in emergencies are overwhelming. The complete Mayday call, including the identity of your boat and its precise position, is sent in about one-third of a second. Once initiated, your call will be automatically repeated until the Coast Guard answers. If you wish, the signal can include the specific nature of your distress and the number of people on board. Because it’s digital, the message transmitted on channel 70 can get through to the Rescue 21 system when conditions make voice calls difficult. Once your Mayday call is received, it will be automatically recorded and will alert the crew on every boat with a VHF/DSC radio in range of your transmitter (up to 200 square miles).


One Call Does It All

DSC hailing is also revolutionizing routine radio communications by providing cell phone-like convenience for ship-to-ship and ship-to-shore communications, without the cellular range limitations and cost. Enter the DSC “phone number (the MMSI-maritime mobile service identity number) of the station you wish to call or select the MMSI from those stored in your radio’s phone book, choose a working channel and press enter. There is no need to hail the other station on channel 16 or to discuss which channel to use. If the called radio is on and within range it will acknowledge your call and switch to the working channel you selected. The called radio can also tell you its precise position, a great advantage when arranging a rendezvous. When traveling with other vessels you can set up a group calling number, simplifying communication with the entire flotilla and facilitating the silent exchange of position reports.

Class A Versus Class D


Any DSC-capable VHF radio can provide emergency signaling, but to take full advantage use one with two receivers, one always tuned to channel 70. Commercial vessels are required to use a Class A DSC radio that can receive signals on channel 70 even while transmitting voice messages on a working channel. A recreational vessel International Class D set is less expensive.

However, all Class D radios are not equal in their DSC capabilities. The International (ITU) Class D specification requires two separate receivers, one always tuned to channel 70, the other free to listen to channel 16, all working channels and the weather channels. A unique U.S.-only Class D single receiver radio may have fine features and specifications, but it will be incapable of receiving DSC hailing calls on channel 70 while a signal is being received on any other channel.

The U.S.-only Class D specification was developed to allow production of less expensive radios. The price difference between the U.S.-only and ITU Class D radios has decreased significantly and will likely continue to do so.


A New Wave of Radios

A number of dual-receiver International Class D VHF/DSC radios are available, at prices between $200 and $800, including the Icom M602, Standard Horizon Quantum Series GX 3500S, Phantom series PS2000 and the Uniden 525 and 625. The Icom M602 and Standard GX 3500S provide alphanumeric keypads that simplify data entry when storing DSC calling information in the radio’s calling directory memory.

We recently tested the newest of these radios, the Uniden 625, and were impressed by a number of its unique features, some previously unavailable in a VHF radio. The most obvious difference between the model 625 and other VHF sets, including Uniden’s own model 525, is its use of a color LCD screen. One of its most valuable features is the cross-track screen that automatically appears when a Mayday call is received. The LCD immediately displays the bearing, distance and time required to reach the vessel in distress. The cross-track display is automatically updated to provide continuing course guidance. The display can also be used when receiving routine DSC calls, making a rendezvous with a buddy about as simple as it can be.


All Class D VHF/DSC radios automatically log received distress calls, typically in a 20-message capacity memory. The 625 has a separate 100-capacity DSC calling directory that makes hailing other stations as easy as using a telephone. DSC hailing calls received when the radio is unattended are logged in a 100-call capacity memory. The DSC hailing menu includes all possible designations, including position polling and group calling. The 625 has any number of other neat features, including a self-test mode, voice-scrambler option, and the option of programming same and fips codes so that only those weather alert signals that apply to the area in which the vessel is navigating are announced.

With new Class D VHF/DSC radios available for as little as $200, and the Coast Guard’s Rescue 21 going online, it’s time to jump on board. All it takes is 1) install a VHF/DSC radio; 2) obtain your unique identification number (available free of cost); 3) enter the MMSI in the radio’s memory; 4) connect the radio to your GPS; and 5) spend a few minutes learning how and when to use the red button. Then tell your congressman and senator that continuing the funding needed to complete the system is high on your list of what the Federal Government needs to do.

You can obtain your mmsi at no cost from BoatU.S. by calling (800) 563-1536 or by visiting and from SeaTow at

Uniden 625: While most of the new Class D DSC/VHFs have similar features, the Uniden 625 we tested combines a 100-call capacity memory, a 35W hailing amplifier, an optional voice scrambler and up to four wireless handsets with a 150-foot-plus range, making it well suited for a large yacht. The two receivers in the 625 score very well, meeting 90dB spurous response and 80dB adjacent channel rejection specifications. One of the nicest features is a color cross-track screen that automatically shows the bearing, distance and time it will take to reach the calling vessel, making a rendezvous with another yacht a simple affair. $300;

ICOM M602: The Class D Icom M602 has an alphanumeric keypad that greatly simplifies many operations, including entering data into the radio’s 100-address call memory. The radio also gets superior reception-a good choice if your area is prone to interference. $570;

Standard Horizon QuantumGX3500S: An alphanumeric keypad on this Class D VHF makes it easy to enter the MMSI. Its speaker is powered by a 4.5W amplifier with a separate 30W amplifier for the loud hailer and fog horn functions. $500;