RYA SRC/VHF flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

GMDSS Sea Area A1

Sea area within VHF DSC coverage of at least one coast station, typically 20-30 nautical miles offshore. Vessels operating here need VHF DSC, a 406 MHz EPIRB and an MSI receiver.

GMDSS Sea Area A3

Sea area beyond A2 but within Inmarsat geostationary satellite coverage, roughly between 70°N and 70°S. Requires Inmarsat or HF DSC equipment in addition to A1/A2 equipment.

Channel 16 purpose

156.800 MHz. The VHF distress, safety and calling channel. Initial contact is made here, then traffic moves to a working channel. Routine conversation on channel 16 is not permitted.

Channel 70 restriction

156.525 MHz. Reserved exclusively for Digital Selective Calling. Voice transmission on channel 70 is prohibited, and a DSC watch on this channel must be maintained.

Squelch control function

Suppresses receiver output when no signal is present, silencing background noise between transmissions. Set it just above the threshold where noise disappears; too high a setting blocks weak signals.

MAYDAY call content

Spoken three times, then THIS IS and vessel name three times, then name and call sign, position, nature of distress, assistance required, persons on board, other information, OVER.

PAN PAN meaning

Urgency signal spoken three times. Concerns the safety of a vessel or person but no immediate grave danger. Has priority below MAYDAY but above all routine traffic.

DSC distress key operation

Lift the protective cover and press and hold the DISTRESS key for about five seconds until the alert transmits. The alert carries the vessel MMSI and, if GPS is connected, position and time.

MMSI structure

Nine digits. A ship station MMSI begins with the three-digit MID identifying the flag state; group MMSIs begin with 0; coast station MMSIs begin with 00.

Routine DSC call sequence

Enter the called station's MMSI, select category ROUTINE and propose a working channel. Send the call, wait for the DSC acknowledgement, then both stations switch to the working channel for voice.

SRC certificate

Short Range Certificate: the operator qualification for VHF DSC radio under the ITU Radio Regulations. It is personal to the holder and is required in addition to the ship radio licence.

SILENCE MAYDAY instruction

Order issued by the station controlling distress traffic imposing radio silence on all other stations. It remains in force until lifted by the words SILENCE FINI.

406 MHz EPIRB function

Transmits an alert to the Cospas-Sarsat satellite system containing the vessel identity and, with built-in GPS, a position. The 121.5 MHz signal is used for local homing by rescue units.

SART radar response

A Search and Rescue Transponder operating on 9 GHz. When interrogated by X-band radar it paints a line of twelve dots on the radar display, helping locate a survival craft.

MAYDAY RELAY use

Used by a station transmitting a distress on behalf of a vessel unable to transmit itself. The relay repeats the original vessel's identity and distress details.

Radio horizon formula

Range in nautical miles is approximately 1.23 times the square root of antenna height in feet, or 2.2 times the square root of height in metres, for each antenna.

NAVTEX frequencies

518 kHz for international maritime safety information, 490 kHz for national broadcasts and 4209.5 kHz. Messages are received and displayed automatically within about 200 nautical miles of a coast station.

Dual watch function

Monitors channel 16 plus one selected working channel alternately. Tri-watch additionally monitors the DSC channel 70, so distress alerts are not missed while working elsewhere.

SECURITE signal meaning

Safety signal spoken three times, preceding a broadcast about navigation safety or weather. It has lower priority than MAYDAY and PAN PAN but takes precedence over routine traffic.

DSC distress acknowledgement

Sent by a coast station by DSC, normally followed by a voice MAYDAY acknowledgement on channel 16. Ship stations should not acknowledge unless able to assist and no coast station has responded.

ATIS requirement

Automatic Transmitter Identification System: transmits the vessel identity after each voice transmission on inland waterways in some countries. Must be switched off when operating at sea.

EPIRB battery life

Typically 48 hours of transmission at minus 20 degrees Celsius. Check the expiry label and run the self-test monthly; replace the battery before the stated expiry date.

Abandon ship radio actions

Take the EPIRB and SART into the survival craft, activate the EPIRB, and switch on the SART once clear of the vessel so rescuers can locate the craft.

MF distress frequencies

2182 kHz for voice distress, safety and calling, and 2187.5 kHz for MF DSC distress alerts. These extend alerting range beyond VHF to roughly 100 nautical miles.

MID meaning

Maritime Identification Digits: the first three digits of an MMSI identifying the flag state, for example 232 to 235 for the United Kingdom and 244 to 246 for the Netherlands.

Group MMSI

A nine-digit MMSI beginning with 0, assigned for calling a group of stations such as a fleet or race committee rather than a single vessel.

EPIRB registration duty

The beacon must be registered with the national authority, linking it to the vessel and emergency contacts. Details must be updated on change of owner, flag, name or MMSI.

Antenna height advantage

Range depends mainly on antenna height, not transmitter power. Doubling height extends the radio horizon, so a masthead antenna greatly outperforms a low-mounted one.

Reserve source of energy

A dedicated battery required under GMDSS to power radio equipment if main power fails, for a specified period such as one hour for VHF. It must be charged and tested regularly.

MAYDAY RELAY format

MAYDAY RELAY spoken three times, THIS IS and the relay station three times, then MAYDAY and the distressed vessel's name and call sign, followed by the original distress details.

False alert cancellation

Transmit by DSC and by voice on channel 16, stating the vessel name and CANCEL MY DISTRESS ALERT, with the reason. Prompt cancellation prevents an unnecessary search and rescue response.

AIS-SART

A locating device transmitting position and identity on AIS frequencies, appearing on AIS displays rather than radar. It complements the radar SART and needs no radar interrogation.