Batteries, power supplies, antennas and equipment maintenance/fault finding
Batteries and reserve power
GMDSS batteries are usually lead-acid or VRLA. Capacity is in ampere-hours (Ah); usable capacity is reduced by age, temperature and discharge rate. The reserve source must be independent of the main and emergency generator, supply the required radios and emergency lighting, and be tested and logged. Check terminals for corrosion, electrolyte level (flooded types), ventilation, and charge voltage. A battery that shows 'fully charged' at rest may still fail under load; a load test is the real check.
Antennas and fault finding
VHF range depends on antenna height, coax loss and connectors. A high VSWR suggests a corroded connector, water ingress, poor ground or a damaged antenna. MF/HF needs a suitable antenna and tuner/ATU; a mismatch can reduce output or damage the transmitter. DSC faults often trace to missing GPS input, wrong MMSI, or an antenna fault rather than the DSC controller.
Worked example
A VHF set transmits on Ch16 but range is very short and the case feels warm. Reasoning: check the antenna and coax first-VSWR, connector corrosion, centre conductor, ground-then the set's output. A DSC fault is not indicated because Ch16 voice works. Replacing the radio without checking the antenna would waste time and may not fix the fault.
Traps
Do not test a battery only by looking at the charger. Do not bypass a fuse or use automotive cable for a GMDSS feed. Do not key an MF/HF transmitter without an antenna/load. Do not assume a 'transmit' light means RF is reaching the antenna.