Installation, maintenance, testing and fault-finding practices
Maintenance regime
GMDSS maintenance may be by at-sea maintenance, shore-based maintenance, or equipment duplication, as allowed by the flag administration. The maintainer's role is to keep the installation compliant and available, not merely to repair after failure. Daily, weekly, and monthly checks are logged: DSC self-test, radiotelephony check, battery voltage and charger current, EPIRB test, SART test, NAVTEX or EGC reception, and antenna inspection. Annual surveys and performance tests are separate from these operational checks. Records should show the test, result, date, and any defect action.
Fault-finding method
Divide the fault by function: power, control, receiver, transmitter, antenna, and interconnection. Confirm the power source and fuses first, then the antenna and feedline, then the radio's configuration such as MMSI and channel. Use a dummy load and power meter for transmitter tests. Compare receive performance on a known signal. For DSC, a test call to a coast station is more informative than a self-test alone because it exercises the complete path.
Worked example
A VHF DSC radio shows a transmit-fail indication, but voice on channel 16 works. Check the antenna SWR at channel 70, inspect the coax and connector, confirm the MMSI and channel 70 selection, and attempt a DSC test call to a coast station. If receive is good and DSC transmit fails while voice transmits, suspect the DSC modulator, control board, or shared antenna path. The reasoning: a shared antenna fault would usually affect voice too, so the fault is more likely in the DSC transmit chain or configuration.
Traps
Do not make test transmissions on channel 16, 2182 kHz, or DSC distress frequencies. Do not use a distress priority in a test. Do not replace a battery without checking the charger and load. Do not assume an annual survey replaces daily checks. Do not log a test as satisfactory without recording the result. Do not adjust an antenna tuner or transmitter without confirming the dummy load and frequency.
Key facts
Maintenance options include at-sea, shore, and duplication. Daily and weekly checks must be logged. Self-test does not prove the full transmit path.