Edwin Sherman - Advanced Marine Electrics and Electronics Troubleshooting

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Proper installation of communications equipment, position-finding GPS-based systems, and radar is serious business. Boatowners rely on this gear to ensure their safety and, if necessary, call for help, perhaps in a life-threatening situation. Such equipment is vital to the safe operation of a boat, in contrast to, for example, installing a CD player. Yes, a CD player is a piece of electronic equipment, but if the boatowner can't hear the latest Alan Jackson CD while underway, it's not a crisis. So, please, as you read through the material that follows, approach your work as though you might be helping to save someone's life. Don't cut corners.

Communications systems on boats used to entail perhaps just a VHF radio. But nowadays most boaters consider SSBs, cell phones, satellite TV and/or Internet access basic requirements. And of course, all this additional equipment means more work for marine technicians!

VHF radio is the most common of all marine electronic equipment used for boat-to-boat and boat-to-land communication. It operates in the frequency range of 156 MHz to 174 MHz. In recent years, features such as digital selective calling (DSC), global positioning system (GPS), and the Global Maritime Distress and Safety System (GMDSS) have expanded the use and functionality of VHF radios by incorporating the ability to transmit time, position, and ownership information in the event of an emergency. While improving safety at sea, these features have altered the VHF's traditional installation procedure, so we'll review the installation process.

In the United States, the transmitting power for marine VHF is limited by the FCC to a maximum of 25 watts. Canadian regulations mirror the U.S. regulations in this area. (Land-based units can have much higher power under the regulations.) I have found that

TABLE 14-1 Line-of-Sight Distance, D1 + D2, for VHF Radios1

estimating 1 statute mile per watt of transmitting power is a fairly reliable rule of thumb for the expected range of a VHF radio. For example, a 5-watt handheld VHF would have a 5-mile range, and so forth.

With transmitting power limited by law, one of the only practical methods of increasing a VHF radio's effective range is to locate the antenna higher. Since VHF operates on a line-of-sight basis, raising the antenna extends its range by extending the effective horizon (see ).

We will look further at issues relating to the antenna and the coaxial cable that connects it to the radio in .

Since low voltage to the radio will dramatically affect its performance, proper wiring using the correct gauge to ensure minimum voltage drop, and high-quality termination points, are critical to the installation.

Installation guidelines:

• Use the wire gauge as specified by the manufacturer for the DC power feed and negative return.
• Install wiring to keep voltage drop to the maximum of 3% based on ABYC standards.

Line-of-sight transmit/receive distances for VHF radio. (Reprinted with permission from Boatowner's Illustrated Electrical Handbook, second edition, by Charlie Wing)

The wiring and cable connections to a VHF radio. Notice the interface with the GPS receiver via an NMEA cable link.

• Follow Standard E-11 to determine the appropriate wire size to use. Remember that wire size is based on the length of the wire run from the power source to the VHF radio (see the ABYC voltage drop table, page 43).

DSC is integrated into all new VHF radios and is a part of GMDSS. The interface between the VHF radio and GPS receiver allows position information to be transmitted in the event of a DSC emergency call; all you have to do is push the emergency button now found on all new radio sets to transmit your boat's exact position and time data to the U.S. Coast Guard.

Installation guidelines:

• Use an NMEA-approved cable attachment to link your VHF radio to the GPS unit (see above illustration). (This interface may be part of your boat's network; see for more on networking.)
• Follow the manufacturer's recommendations for the exact terminal connections.

As the last step to a fully capable DSC installation, the boatowner must acquire a Maritime Mobile Service Identity (MMSI) number. Once entered, this nine-digit number becomes the permanent identifier for your boat. When DSC is activated, the MMSI will provide rescue personnel with pertinent boat and owner information along with time and position data.

In the United States, you can get an MMSI from the FCC for a fee, or for free by contacting BoatU.S. ( www.boatus.com/mmsi ) or Sea Tow ( www.seasmartvhf.com ). In Canada, all applications for MMSI numbers must be

submitted to the Canadian government directly via Industry Canada. To learn more about their process, go to http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/en/sf01032e.html .