DSC VHF - it doesn't get any better than this!

Radio communications have made tremendous advances in the past few yearsand no where is this more evident than in DSC VHF radios, explains Frank Lanier.

Imagine sending a Mayday over your VHF radio telling not only where you are, but what the problem is with the touch of a button, or how about using your VHF to call a specific vessel and pass information without everyone else listening in?  Such are the promises of DSC (Digital Selective Calling) VHF radio and while some of its advertised advantages are still a bit in the future, others are available now and ready to enhance your boating experience.  

Since 1999 the international Safety of Life at Sea (SOLAS) Convention has required most vessels 300 gross registered tonnes and larger (cruise ships, cargo vessels, etc.) on international voyages to carry DSC-equipped radios.  DSC is currently used on VHF, MF and HF maritime radios as part of the GMDSS (global marine distress and safety) system, with Channel 70 (VHF) and 2187.5 KHz (MF) being reserved exclusively for DSC safety and distress calls.

DSC radios are currently required on all SOLAS-regulated ships, which consequently are no longer required to maintain a live 2182 kHz radio listening watch. The long-term goal of some countries (the US for example) is to do the same with VHF Channel 16.  In Australia channel 16 is the VHF voice distress channel with 67 as a supplementary voice distress channel.  VHF DSC alerts are monitored on Channel 70.    

Although there is no such official VHF (or MF) DSC shore infrastructure in Australia, there are a number of volunteer marine rescue (VMR) stations that have installed VHF DSC, which can provide local checks along with vessel to vessel alerting.

DSC is arguably the greatest technological advancement to hit VHF marine radio in decades.  When properly registered with a Mobile Maritime Service Identity (MMSI) number (more on this later) and interfaced with a GPS or LORAN unit, DSC radios have the capability to operate much like an EPIRB in an emergency.  They transmit encoded vessel and owner information, position, and the nature of distress (if entered) at the push of a button and continue to do so automatically until answered by another DSC-equipped shore unit or vessel.

DSC radio also has the ability to make private ‘direct dial’ calls to other DSC radios.  Enter the MMSI number of the radio you want to call and only that radio will receive your message—just like a phone call.  Calls can be directed to a specific group or set of DSC radios (all VMR stations, for example), receivers in a specific geographic area, or all receivers in radio range—a useful feature when the individual identity of a unit being called is unknown.

Another neat trick (when connected to a chart plotter) is the ability to locate another DSC-equipped vessel at the push of a button.  Your friend finds that perfect, uncrowded anchorage and sends you his coordinates via DSC; it appears on your chartplotter (privately and encoded) followed by a dialogue box that pops up, asking if you want to navigate there.  If part of a group or fleet of boats, some DSC radios can also be set to answer an automatic ‘polling’ mode by sending constant updates on vessel position so you know just where everyone is—does it get any easier?

Types of DSC radios

The two main flavours of VHF DSC radios (as they pertain to recreational boaters) are Class A and Class D. Both can send and receive digitally-encoded distress calls on channel 70. However, Class A radios are higher-end units with additional functions and features, such as listing calls received (time and MMSI or name) even when the radio is unattended.  Class D radios (the type most recreational boaters buy) meet the basic DSC essentials and while they don’t have all the bells and whistles, they’re less expensive.  Radios simply claiming to meet SC-101 requirements have even less functionality and are not recommended, the big negative being they don’t have the two separate receivers found in Class A & D radios, which allow constant monitoring of channel 70 (the DSC distress channel) while also monitoring normal working channels or weather channels.

Desirable features to look for when selecting a DSC radio include message retrieval, caller ID functions, or even call waiting.  Another thing to check out is the number of MMSI numbers it can store.  Some radios don’t have much capacity in this regard, which could be a negative factor if you have lots of boating buddies.  
Construction-wise, chose a unit with a sufficiently sized display screen.  The smaller the screen, the harder it’ll be to enter or read displayed information—smaller screens also require more key scrolling when viewing larger messages.  Other things to consider include the amount of screen background lighting and key pad size (smaller keys make for more difficult data entry).  One way to get a feel for how difficult a smaller screen and key pads can be to operate is by comparing a potential purchase with use of a typical cell phone, in the dark, while on a pitching, rolling boat.

DSC Operation

In Australian waters, channel 70 should  be used for VHF DSC alerts.   As there are still a number of non-DSC equipped vessels, once you send an alert, you should monitor channel 16 for a response.  If no response is received, try sending a  voice distress call on channel 16.  It’s a good idea to include your MMSI in that distress alert so stations know that you sent the DSC alert (otherwise they may think there are separate two distress calls, which could lead to confusion
and delays).   Similarly, if you receive a DSC alert generated by someone else, you should switch

to Channel 16 and acknowledge their call by voice, signaling “Received MAYDAY”.  In the event that you don’t receive an acknowledgement to your DCS alert on channel 70, or your voice distress call on 16, you may want to try your nearest VHF repeater station (21, 22, 80, 81, 82).   Repeater startions are located up and down the coast.

Registration

Australian Maritime Safety Authority (AMSA) allocates and issues MMSI numbers to Australian vessels and coast stations.  An MMSI is a unique nine-digit code entered into your DSC-capable radio transceiver and/or AIS transceiver to identify your vessel or coast station. You only need one MMSI per vessel, as you use the same number for all DSC and AIS transceivers onboard.  

All large commercial vessels subject to the SOLAS Convention must carry DSC equipment appropriate to their area of operations.  DSC radios are not required on small recreational and fishing vessels; however, it should be a consideration if operating offshore or cruising overseas.  

As marine VHF transceivers now operate under a Class Licence, for VHF-only installations there is no requirement for an official call sign and maritime ship station licence, but the operator must have a minimum of a Marine Radio Operator’s VHF Certificate of Proficiency.

For an Australian MMSI number for MF or HF radios, you must have an ACMA Maritime Ship Station licence number and call sign, as well as a Marine Radio Operator’s Certificate of Proficiency or a GMDSS General Operator’s Certificate of Proficiency.  

More information: MMSI registration can be completed at www.amsa.gov.au/mmsi