FCC Element 9 Practice Questions: GMDSS Radio Maintainer License (2026)

VHF-DSC and MF/HF-DSC servicing

Element 9 expects a maintainer to know the marine VHF plan cold. Channel 16 at 156.800 MHz is the international calling and distress voice frequency, Channel 70 at 156.525 MHz is reserved exclusively for Digital Selective Calling, and Channel 13 at 156.650 MHz is the low-power bridge-to-bridge navigation-safety channel. Marine VHF channels are assigned on a 25 kHz raster, and a duplex channel uses a fixed 4.6 MHz offset between the ship transmit and receive halves so public-correspondence channels can pass traffic both ways at once. Moving to MF and HF, the assigned figures matter for keeping signals inside their channels: single-sideband voice, J3E, occupies about 2.8 kHz of bandwidth with 3.0 kHz channel spacing, while J2B SITOR or NBDP is a narrowband telex signal fitting in about 300 Hz with 500 Hz channel spacing. GMDSS MF/HF transmitters must hold frequency within a tight 10 Hz tolerance so DSC, SITOR and SSB signals decode reliably in their narrow assigned channels.

• Channel 16 (156.800), Channel 70 (156.525, DSC only) and Channel 13 (156.650, bridge-to-bridge).
• VHF channels use 25 kHz spacing and a 4.6 MHz duplex transmit-receive offset.
• GMDSS MF/HF transmitters must hold frequency within a 10 Hz tolerance.

Satellite terminals, EPIRBs and power sources

The satellite and beacon sections are core maintainer territory. Inmarsat-C ship terminals receive in the L-band from 1530.0 to 1545.0 MHz and transmit from 1626.5 to 1645.5 MHz, the standard maritime mobile satellite pairing, and the low noise amplifier, or LNA, sits at the antenna to receive and amplify the very weak satellite signal while adding minimal noise, which sets the receiver's overall sensitivity. On the beacon side, COSPAS-SARSAT satellites detect, time-tag and relay 406 MHz beacon data and let a ground LUT derive position from LEOSAR Doppler shift, but they provide no follow-on SAR communications. The magnet in an EPIRB mounting bracket holds the beacon's reed switch open so a manual-activation EPIRB stays inhibited while stowed, and the beacon floats free to arm when it leaves the bracket; the primary battery must be replaced every 5 years or after any use. Power source knowledge is practical throughout: a single nickel-cadmium cell has a nominal 1.2 volts, a higher electrolyte temperature gives a lower specific gravity reading on a lead-acid battery, and cell reversal happens on deep discharge when the current forced through an exhausted weak cell by the healthier cells charges it backwards.

Networks, tests and installation

The final sections treat a GMDSS console as part computer and part radio installation. A maintainer is expected to troubleshoot ordinary shipboard computing: a defective graphics card is not a likely reason a document will not print, because the graphics card drives the monitor rather than the printer, whereas a frozen print queue, empty cartridge or paper jam are genuine printing faults. A blank monitor points to the display path, a bad video card, a faulty 15-pin video connector or no power to the monitor, and the BIOS performs four core jobs: the power-on self test, the bootstrap loader, the BIOS drivers and BIOS Setup. Installation questions reward sound RF and mechanical practice. The best method for grounding an Inmarsat-C terminal is a copper strap brazed from the steel terminal to the ship's steel hull, because a wide bonded conductor gives far lower RF impedance than a thin wire. When installing a full-duplex VHF radiotelephone, the most important consideration is maximum separation between the transmitting antenna and the duplex receiver antenna, since the two operate at once on different frequencies and the transmitter would otherwise desensitise or overload the receiver. And when locating a depth-finder transducer, the most important factor is an area not subject to cavitation, because cavitation bubbles scatter the ultrasonic beam and cause dropouts.