RCTC Reviews

Tech Talk

The scoop on the newly available DSC VHF Marine Radios. These could save your boat and your life someday.

Executive summary: The cost the same as regular VHFs. You buy one and get an MMSI number from the FCC (fairly easy and currently free when done online). Install the radio on your boat. Program the MMSI number you got from the FCC. If you have a GPS then connect the two NMEA 0183 data wires from your GPS to the DSC VHF radio. When you push the distress button this radio automatically contacts the Coast Guard and sends your position (if you remembered to hook up your GPS and it is turned on). The bad news is the Coast Guard currently doesn't have their own DSC radios along the Hudson river yet; however other boats with DSC radios can also see the distress call and your position. You can also use DSC radios to call other VHF DSC radios like dialing a person's cell phone number.

This VHF DSC rig cost only about$100 on E-bay

Detailed description: This was originally written by Chuck Husick but I updated out of date info.

Marine VHF radio advertisements increasingly mention something called Digital Selective Calling. If you are considering buying a new fixed-mount VHF radio, you need to know what DSC can do for you and how it works.

DSC was designed to automate the transmission and reception of emergency radio communications, such as mayday calls on both VHF and HF/SSB marine radios. The emergency signaling performance of VHF/DSC is outstanding. In addition, it very significantly simplifies all routine radio communication, substituting direct, telephone number-like calling for today's often frustrating voice calls on Channel 16.

VHF/DSC radios exchange digital messages on Channel 70, on which all voice calls are prohibited. In order to ensure that the brief digital messages are heard, all VHF/DSC radios have two separate receivers, with one always tuned to Channel 70. Each digital message contains: the calling vessel's unique, nine-digit Mobile Marine Service Identification number (MMSI), a call category identifier (Mayday, Securitay, Pan-Pan, routine, etc.) and the vessel's precise position from a connected GPS or Loran. A complete digital message is sent in about a third of a second. Mayday messages are sent automatically by pressing the radio's "EMERGENCY" button. Once sent, mayday calls automatically repeat until acknowledged by an answering DSC radio.

DSC radios also automatically alert their users to reception of a distress message by sounding an audio tone and by showing the MMSI of the vessel in distress and its precise position on the radio's readout. The Coast Guard's DSC response message will switch the radio on the vessel in distress to the working channel they have chosen for voice communication (typically, Channel 22A). The channel change is automatic, no one on the calling vessel need touch the radio. The positive identification of the vessel in distress, knowledge of its precise location and the ability to immediately establish voice communication, even in the absence of a trained radio operator, save lives

To function properly, every DSC radio must have a unique MMSI. At present, MMSIs are available free. BoatU.S. is cooperating with the FCC and Coast Guard so that MMSIs can be issued to unlicensed VHF/DSC radios on recreational boats with NO payment , but this probably will not last forever. It takes about 10 minutes to fill out the FCC form including emergency contact information and boat description. The FCC then automatically assigns the MMSI number and e-mails it to you .

There are two classes of VHF/DSC radios. The basic specification "D" radios provide all emergency signaling functions, but none of the more advanced user benefits. Specification "A" radios (which meet the stringent specifications for large ships) do a great deal more. The "A" radios have telephone-like keypads and present a great deal of information on their LCD display screens. Using DSC to communicate with another station is similar to using a telephone. The MMSI of the station being called is entered into the keypad or recalled from the radio's MMSI/telephone number memory. The user selects the desired voice communication channel and presses the "Send" or "Enter" key.

The called radio announces the incoming call with a beep and automatically transmits an acknowledgment of receipt to the calling radio. Communication proceeds on the preselected voice channel. The same procedure is used when placing calls via the marine operator to shoreside telephones. Some "A" DSC radios, such as the Ross DSC 500, provide additional features, for example, listing calls received (time of call and MMSI or name) when the radio is unattended.

Should you buy a DSC radio? The emergency signaling value of the DSC system won't be fully effective until completion of the Coast Guard's DSC system, still about four years away. Part of the DSC-equipped marine operator ship-to-shore system is operating, with work proceeding on the remainder.

Commercial towing companies and increasing numbers of your fellow boaters are installing VHF/DSC radios. Even before the Coast Guard's system is complete, communications between class "A" DSC stations will be remarkably improved. Within the next few years, the emergency signaling value of a class "D" DSC radio will become significant. By that time, a DSC radio should be on board every boat. Quality marine radios last a long time. Don't buy just for the present; the future will be here before you know it.

Chuck Husick is an engineer, pilot, sailor and the former president of Chris Craft Boats.

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