Electromagnetic Compatibility, Interference and Operational Safety
EMC and interference
Electromagnetic compatibility means radio equipment works without causing or suffering harmful interference. Common sources on board are LED drivers, solar regulators, battery chargers, inverters, radar, AIS and badly grounded cables. Symptoms include noise on VHF, reduced range, distorted DSC or unexpected alerts. Good practice includes antenna separation, shielded cables, bonding of metal structures, ferrite chokes on power leads and filters on noisy equipment.
Operational safety
Treat antenna systems as live when transmitting. Do not touch an antenna or open a feedline during transmission; RF exposure and high voltage are real hazards. Ventilate battery compartments because charging can release explosive gas. Use approved chargers and fuses. Before maintenance, switch off and isolate the equipment, and never transmit with the antenna disconnected unless the set is designed for it.
Worked example: Ch 16 becomes noisy whenever the cabin LED lights are switched on. Fit a ferrite choke to the LED power lead, check the lamp driver for shielding and increase separation between the VHF antenna and the lighting cable. The reasoning: the LED driver is a broadband switching noise source, and the fix is to stop the noise reaching the antenna rather than to increase transmitter power.
Operational traps
Do not ignore interference; it can mask a distress call or trigger a false DSC alert. Do not transmit close to persons, especially with a handheld or a whip antenna. Do not assume a metallic hull is automatically a good RF ground. Do not use automotive chargers or unfused leads on GMDSS equipment.