LROCP Course Quick Revision Sheet

Certificate Scope: LROCP covers Marine VHF, MF, and HF Single Sideband (SSB) stations. SROCP is restricted entirely to VHF frequencies.

Frequency Groups & Ranges:

• VHF Band: 156 MHz – 174 MHz (Short-range line-of-sight communication up to 20–30 NM depending on antenna elevation).
• MF Band: 1605 kHz – 4000 kHz (Medium-range propagation up to 100–150 NM).
• HF Band: 4000 kHz – 27500 kHz (Long-range skywave refraction spanning thousands of NM).

Propagation Types: VHF travels via line-of-sight surface waves. HF relies on skywave propagation, bouncing between the ionized layers of the atmosphere and the earth's surface.

Solar Variability: Daylight hours ionize the upper layers, making higher frequency HF bands (8, 12, 16 MHz) highly effective over long distances. At night, lower frequencies (4, 6 MHz) are required to prevent signals from escaping into space.

Core Transceiver Controls:

• Squelch: Controls the background audio mute circuit threshold to filter out empty ambient white noise/static.
• Volume vs RF Gain: Volume changes speaker output levels. RF Gain sets internal antenna pre-amplifier sensitivity thresholds.
• Dual Watch: Allows continuous background monitoring of Channel 16 while working on a secondary operational channel.

Simplex vs Duplex: Simplex channels share a single frequency for both transmitting and receiving—only one operator can speak at a time. Duplex paths split communication across two separate frequencies, enabling ship-to-shore telephone integration channels.

Emission Configuration: Maritime regulatory standards require **Upper Sideband (USB)** voice modulation mode for all single-sideband channels in the MF/HF bands.

Antenna Matching Couplers: Because HF wavelengths are large, an automated physical antenna tuning unit (ATU) is required to electronically match the physical antenna wire length to the transmitting frequency to prevent power reflection damage.

MMSI Address Format: A Maritime Mobile Service Identity is a unique 9-digit digital address. All official **Coast Shore Stations** are identified by two leading zeros: 00XXXXXXX. Standard shipboard identities do not contain leading zeros.

DSC Frequency Matrix:

• VHF Band DSC: Channel 70 (156.525 MHz).
• MF Band DSC: 2187.5 kHz.
• HF Band Core DSC Watch: 8414.5 kHz (supported by secondary channels 4207.5, 6312.0, 12577.0, and 16804.5 kHz).

406 MHz Core System: Modern EPIRBs transmit coded digital parameters to the COSPAS-SARSAT satellite constellation on **406.0 MHz**. They include a low-power secondary **121.5 MHz** transmitter to act as a homing beacon for rescue aircraft and vessels.

Deployment: Float-free units use a **Hydrostatic Release Unit (HRU)** that automatically triggers and releases the beacon at water depths between 1.5 and 4 meters.

Radar SART (9 GHz): Operates strictly in the marine radar **X-band**. When scanned by a rescue ship's radar, it displays a line of **12 evenly spaced dots** along its radar bearing line. As the ship approaches, these dots widen into arcs and eventually form full concentric circles.

Inmarsat Satellites: Relies on geostationary orbit (GEO) space segments positioned 36,000 km over the equator. Because of earth's curvature, coverage is ineffective in extreme polar gaps above 70°–76° North or South latitude.

Enhanced Group Call (EGC): A broadcast data service that automatically pushes Maritime Safety Information (MSI), such as weather warnings and nav alerts, to ships within specific ocean regions.

GMDSS Area Definitions:

• Sea Area A1: Inside VHF DSC coastal radio tower footprints (20–30 NM).
• Sea Area A2: Inside MF DSC coastal footprints, excluding Area A1 (approx. 100–150 NM).
• Sea Area A3: Open-ocean blue water zones covered by geostationary satellites between 70°N and 70°S.
• Sea Area A4: Extreme polar gaps left by geostationary satellites. Requires high-power HF DSC systems.

Legal Authorization: A distress signal can only be authorized by the master, skipper, or individual in command of the vessel.

Command Word Summary:

• MAYDAY Grave and imminent danger to a vessel or life. Requires immediate assistance.
• PAN PAN Urgency condition regarding the safety of a vessel or person. Used for scenarios like serious mechanical failure or medical emergencies.
• SECURITE Navigational hazard notices, floating logs, failed reef markers, or severe storm warnings.

Control Codes: The phrase **SEELONCE MAYDAY** enforces absolute radio silence on a frequency handling emergency traffic. **PRUDONCE** signals a transition to restricted, cautious usage. **SEELONCE FEENEE** announces that emergency operations have concluded and normal radio operations can resume.