Article by Capt. Steve Katz
RADIO CHECK
~ PART II ~
Last week we reviewed the basics of the VHF marine radio, how it works and how to be sure it is working properly. Now that we have a good working radio, let’s review some of the popular features in today’s modern VHF radios.
One of the most underused and misunderstood features is Digital Selective Calling or DSC. Before we can review what it is and how to use it, we need to understand the Maritime Mobile Service Identity (MMSI) number. Every marine VHF radio sold in the USA is mandated to have DSC and therefore capable of being programmed with a MMSI number. The MMSI number is a unique 9-digit number assigned to your vessel, like a phone number for your boat. The MMSI number also provides personal information to the United States Coast Guard from your MMSI registration in the event of an emergency distress broadcast. The MMSI number is free and available on-line through BoatUS.com and other approved organizations. You can get a free number if you are a boater who only uses their VHF radio for recreation purposes and are not required by law to carry a VHF and you do not make international voyages or communications. If you do not qualify for the Boat US MMSI registration, you will need to register with the FCC to obtain a MMSI number and a legally required Ship Station License.
Once you get your MMSI number, you can program it into your VHF radio(s) on your boat. Be careful entering the numbers. If you make a mistake, you may not be able to change it Older VHF’s generally allow an MMSI to be entered twice, but many newer models are limited to one MMSI attempt. Further re-programming or clearing out of old MMSI numbers requires factory authorized service.
If you have a handheld VHF radio, you may want to register it to a second MMSI number whose contact information can be easily updated if or when you take your handheld VHF onto another boat.
We are almost ready to explain the DSC function, but we have one more item to take care of. We need to connect the VHF radio to a position source. Using a NMEA0183 or NMEA2000 interconnection, a VHF radio can easily be connected to a GPS receiver/chart plotter or other position enabled navigation device. In 2011, USCG Rear Admiral R. E. Day indicated “Of the roughly 100 digital selective calling (DSC) distress alerts we are now receiving each month, approximately nine out of 10 do not have position information and approximately six out of 10 have not registered their Maritime Mobile Service Identity.” This is an important feature that should be correctly implemented on all VHF radios. To make it even easier, ICOM and Standard Horizon both now offer VHF radios with built in GPS receivers, eliminating the need for an additional connection.
Now that your VHF radio has a MMSI number and position data, you can use the DSC feature! The DSC feature allows many types of digital calls, such as allowing you to call a fellow boater (private call) using their MMSI number. Instead of a “shout out” to your buddy with everyone listening on channels 16, 68 or some other channel, your call goes directly to your buddy's radio, though you need their MMSI number in advance.
DSC calls are a digital transmission on channel 70, often with longer range than traditional voice calls. The recipient will hear an alert tone and can digitally acknowledge the request. They will then tune to a pre-set working frequency to continue the conversation traditionally.
Making a DSC call is an effective way to privately get the attention of a fellow boater so you can converse with them normally on a traditional channel. DSC does not enable a private or digital conversation.
Contacting a friend with their MMSI is a great way to confirm your DSC system is working properly. Another way to test the DSC feature is to make a test call to the USCG and here is their procedure; “For VHF DSC radios equipped with the Test Call feature, test transmissions should be made to the US Coast Guard MMSI 003669999 to receive an automated VHF DSC test response. You must use the “Test Call” category of your radio because “Individual” category calls to this address will not receive an automated response. For older radios not having a test call capability, testing can only be performed by using a routine individual call to a fellow boater. Under no circumstances shall a DSC distress alert be sent to test your radio. It is a violation of the rules and can result in heavy fines.”
Since this digital calling works so well and has a good range, it makes for a great emergency distress calling feature. The small red cover on the front of most VHF radios is covering the distress button; this is the modern mayday call. If you have an emergency and need immediate help, instead of the traditional way of calling on channel 16, you can push the button to get help. Using an ICOM M506 as an example, here is how to place an automatic distress call:
(1) While lifting up the key cover, hold down the distress button for 3 seconds until you hear 3 short beeps and then one long beep.
(2)Wait for an acknowledgment on Channel 70 from a coast station.
(3)After the acknowledgement is received, channel 16 is automatically selected.
(4) Hold down the “Push to Talk” button and transmit.the appropriate information”.
A DSC distress call automatically transmits your MMSI number and your current location to the receiver, usually the USCG, so they immediately know who you are and where you are. A DSC distress call also goes out to other boaters in your listening area.
The USCG uses a nationwide computer system called Rescue 21 to record, manage and respond to DSC distress calls. Rescue 21 is a billion dollar program started over 10 years ago. After testing and analysis conducted in July 2014, the Coast Guard determined that Rescue 21 provides over 90 percent coverage for direction finding and 94 percent coverage for voice and DSC communications within 20 miles of the U.S. coastline if the caller is using a 1-watt handheld radio. The coverage increases to 95 percent or higher if the caller is using a stronger transmitter.
Testing also found that the Rescue 21 system is extremely reliable. The report stated that the system is functional more than 99 percent of the time. As a result, missed calls due to system failure are unlikely. Rescue 21 also covers the shorelines of Hawaii, Puerto Rico, Guam, the U.S. Virgin Islands and the Northern Marianas Islands of Saipan, Tinian and Rota.
While this may seem like a complicated topic, once the initial VHF set-up work is complete, the use of DSC and automated distress call is very simple. Be sure to get the MMSI numbers of your fellow boaters and try the DSC.
Update: In last week’s article, I mentioned Sea Tow's Automated Radio Check Service on VHF channel 26; this system is currently not operational in Ocean City, MD, but expects to be soon.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers.
