Search and Rescue Radar Transponder (SART)
Search and Rescue Radar Transponder known as the SART are portable devices capable of transmitting locating signals which indicate the location of mobile unit in distress on the ships Radar screen. The SART signal is picked up by the rescue units X-Band, 9 Ghz (3cm) Navigational RADAR.
The SART signal appears on the RADAR display of a series of equally spaced dots outward on a line of bearing. There are about 12 NM of blips. These turn into arcs as the ship nears the signal on their x-band radar (The reason it is call X-Band is from WW2 when it was very secret) (or the 3 cm/9 Ghz). Generally, Search and rescue radar transponders are a means of providing locating signals in the GMDSS.
The activation of SART is simple. The SART are typically carried into survival craft and activated manually. SART are required to manually activated and deactivated.
When the SART is activated from a ship in distress or survival craft, SART provides both a audible and visual indication to alert survivors that a RADAR has triggered the SART. I guess this would give the survivors some hope that a rescue is at hand. This might be the time for survivors to attract the attention of rescue units via alerting devices.
IMO has given us some specifications for the Batteries used to power the SARTs. The SART will have sufficient battery capacity to last for 96 hours in the standby mode followed by 8 hours in transponder mode. A SART antenna is typically horizontally polarized and omni directional. This is because the 3 cm radar has an antenna that is horizontally polarized, and by the way radars, and SARTS, are the only antennas that are horizontally polarized.
The Communications Range of the SART relies on direct wave propagation, their communications range is determined primarily by transmitter power output, receiver sensitivity and antenna height above ground. It seems that the SART operators have little control over the first two but can optimize its effective range by maintaining the SART as high as possible. There is an extension mast attached to some SARTS to increase the height, providing a little more range. The height of the SART should be at least 1 meter above sea level to be effective.
The Performance Standards are set by IMO for SARTs call for a range of at least 5 miles when a SART is located 1 meter above sea level. This assumes the search vessel has a radar antenna 15 meters high. When the radar is aboard an aircraft, such as a US Coast Guard Aircraft flying a search patter at an altitude of 3000 feet should be able to detect SART at ranges up to 30 miles.
Most SART currently on market are not designed to float free or be place in the water. However, SARTs are required to sustain a drop from 20 meters into water with out damage. And have a Water tight integrity to a depth of 10 meters for 5 minutes.
On the ship the operation of the Marine X-Band Radar used to Detect the SART at its maximum range will be enhanced if the controls of the radar are properly set.
When looking for a SART the 6 or 12 N Mile range should be used. the bandwidth of the radar should be less than 5 MHz so a medium bandwidth should be selected. Check your Radar operating manual for proper radar parameters and bandwidth selection. Medium and wide bandwidths are normally with long pulse radar transmission.
In increasing the visibility of the SART in clutter condition, the radar should be de-tuned to reduce the clutter. Some radars with AFC (automatic frequency control) may not permit any manual de-tuning of the equipment. The normal gain setting for long range detection should be used, with some light background noise visible. The Anti-Sea Clutter control should be set to minimum and the Anti-Rain Clutter should be set to be used normally as to break up areas of the rain. The SART response, being a series of dots, will not be affected by the action of the anti-clutter rain circuitry.
Showing posts with label STCW. Show all posts
Showing posts with label STCW. Show all posts
Friday, December 7, 2007
GMDSS (VHF SURVIVAL CRAFT TRANSCEIVER)
VHF Survival Craft Transceiver (SCT)
GMDSS Survival Craft Transceivers (SCTs) are portable, two-way VHF transceivers capable of radiotelephone communications. These small lightweight radios are used for on-scene communications between rescue units and the survival craft. These SCT's can be used as on-board communications when the batteries are of the re-chargeable type and they are capable of operating on the appropriate frequencies.
The Survival Craft Transceivers are manufactured under IMO standards and are required to
Be operated by unskilled personnel.
Have channel 16 and one other channel
Withstand a drop of 1 meter on a hard surface
Watertight to a depth of 1 meter for 5 minutes
Power minimum of 0.25 watts (1/4 watt)
Where power exceeds 1 watt a power reduction switch to less than 1 watt must be available.
Antenna to be vertically polarized and omni-directional
Battery power capacity for 8 hours on a 1:9 duty cycle
These SCTs use phase modulation (G3E) in lieu of true Frequency Modulation (FM). The battery packs are using NiCad batteries for day-today operations some use the non-rechargeable lithium battery pack for a strictly SCT radio (These batteries are integrated into the transceiver).
The battery pack in all cases must have sufficient capacity to ensure a minimum of 8 hours of operation at the highest SCT RF power output. The batteries are based on a duty cycle of 1:9 for the non chargeable type as well as the rechargeable type. Batteries are marked with month and year of manufacture. These batteries must be replaced on or before the expiration date, there is no grace period.
The IMO has set up some specifications that we should be aware and give minimum requirements for these units. The SCT must be capable of radiating a minimum Radio Frequency (RF) power of 250 mw (milliwatts) or 1/4 watt.
Again if the transmitter of the SCT has a power excess of 1 watt then a switch must be provided to reduce the power to less than 1 was. Thus providing reduced drain on the battery. The receiver used in the SCT must have a sensitivity of less than 2 microvolts to produce a noise/signal to noise distortion (SINAD) of 12 db (decibels). What this all means is that the signal into the antenna of the receiver plus any distortion on the signal must provide noise reduction of 12 decibels within the receiver and have a reading of 2 microvolts at the antenna .
Contrast this sensitivity for the VHF Radio on the bridge having the same (SINAD) requirements but having a 0.5 microvolt signal at the antenna. This makes the SCT operating under these specifications a less sensitive receiver than the bridge radio. In effect the receiving range will be much shorter. But will be sensitive enough to provide a usable radio for the SCT and will of course cost less.
Among other requirements the IMO has stated that the Antenna on the SCT be vertically polarized. This is a requirement to keep all the antennas within the same plane to obtain maximum transfer of energy from radio to radio.
IMO has certain carriage requirements for various type of ships. At least 3 two-way VHF Survival Craft Transceivers must be provided on every Passenger ship and cargo ships of 500 tons and upwards. At least 2 two-way VHF Survival Craft Transceivers must be provided on ever cargo ships between 300 and 500 gross tonnage.
There are certain stowage requirements for the SCT and GMDSS SCTs must be stowed in such locations that they can be rapidly placed in any survival craft (other than life rafts required by the SOLAS convention. This is not to say that we cannot provide a SCT that can be fitted as a fixed two-way VHF radiotelephone installation in survival craft. These fixed installations must adhere to the same performance standards of portable SCTs as above .
There are of course some testing requirements for Survival Craft Transceivers and they must be tested at intervals not to exceed 12 months. If the SCT has rechargeable batteries be sure to let them run down then recharge the batteries prior to testing the radio. This will prevent a "memory" to be set up in the Ni-Cad battery and preventing it from fully charging.
GMDSS Survival Craft Transceivers (SCTs) are portable, two-way VHF transceivers capable of radiotelephone communications. These small lightweight radios are used for on-scene communications between rescue units and the survival craft. These SCT's can be used as on-board communications when the batteries are of the re-chargeable type and they are capable of operating on the appropriate frequencies.
The Survival Craft Transceivers are manufactured under IMO standards and are required to
Be operated by unskilled personnel.
Have channel 16 and one other channel
Withstand a drop of 1 meter on a hard surface
Watertight to a depth of 1 meter for 5 minutes
Power minimum of 0.25 watts (1/4 watt)
Where power exceeds 1 watt a power reduction switch to less than 1 watt must be available.
Antenna to be vertically polarized and omni-directional
Battery power capacity for 8 hours on a 1:9 duty cycle
These SCTs use phase modulation (G3E) in lieu of true Frequency Modulation (FM). The battery packs are using NiCad batteries for day-today operations some use the non-rechargeable lithium battery pack for a strictly SCT radio (These batteries are integrated into the transceiver).
The battery pack in all cases must have sufficient capacity to ensure a minimum of 8 hours of operation at the highest SCT RF power output. The batteries are based on a duty cycle of 1:9 for the non chargeable type as well as the rechargeable type. Batteries are marked with month and year of manufacture. These batteries must be replaced on or before the expiration date, there is no grace period.
The IMO has set up some specifications that we should be aware and give minimum requirements for these units. The SCT must be capable of radiating a minimum Radio Frequency (RF) power of 250 mw (milliwatts) or 1/4 watt.
Again if the transmitter of the SCT has a power excess of 1 watt then a switch must be provided to reduce the power to less than 1 was. Thus providing reduced drain on the battery. The receiver used in the SCT must have a sensitivity of less than 2 microvolts to produce a noise/signal to noise distortion (SINAD) of 12 db (decibels). What this all means is that the signal into the antenna of the receiver plus any distortion on the signal must provide noise reduction of 12 decibels within the receiver and have a reading of 2 microvolts at the antenna .
Contrast this sensitivity for the VHF Radio on the bridge having the same (SINAD) requirements but having a 0.5 microvolt signal at the antenna. This makes the SCT operating under these specifications a less sensitive receiver than the bridge radio. In effect the receiving range will be much shorter. But will be sensitive enough to provide a usable radio for the SCT and will of course cost less.
Among other requirements the IMO has stated that the Antenna on the SCT be vertically polarized. This is a requirement to keep all the antennas within the same plane to obtain maximum transfer of energy from radio to radio.
IMO has certain carriage requirements for various type of ships. At least 3 two-way VHF Survival Craft Transceivers must be provided on every Passenger ship and cargo ships of 500 tons and upwards. At least 2 two-way VHF Survival Craft Transceivers must be provided on ever cargo ships between 300 and 500 gross tonnage.
There are certain stowage requirements for the SCT and GMDSS SCTs must be stowed in such locations that they can be rapidly placed in any survival craft (other than life rafts required by the SOLAS convention. This is not to say that we cannot provide a SCT that can be fitted as a fixed two-way VHF radiotelephone installation in survival craft. These fixed installations must adhere to the same performance standards of portable SCTs as above .
There are of course some testing requirements for Survival Craft Transceivers and they must be tested at intervals not to exceed 12 months. If the SCT has rechargeable batteries be sure to let them run down then recharge the batteries prior to testing the radio. This will prevent a "memory" to be set up in the Ni-Cad battery and preventing it from fully charging.
GMDSS (EPIRB 2)
EPIRB'S
Because the duty cycle of the transmitter is so short it will reduce the drain on the battery and the time between transmit cycles will allow other EPIRBs to transmit simultaneously while the satellite is passing overhead. The EPIRB identification is digitally encoded hexadecimal signal which provides the serial number of the EPIRB and this allows SAR to consult the database for the name of the vessel. And as previously mentioned the newer ones may have the position inserted in the message.
The EPIRB also contains a low power homing transmitter (25 milliwatt) that emits a continuous signal on 121.5 MHz. This allows the SAR units to "home" in on the beacon. Most of the EPIRBs also have a strobe light to proved on-scene units with a visuallD of the EPIRB. As mentioned the 121.5 MHz signal is also picked up by other satellites like the NOAA.
The Federal Communications Commission requires that each EPIRB be registered. This registration is done by the card enclosed when the EPIRB is purchased. There is no fee and the card is sent to NOAA directly. They in turn make the registration data base available to all SAR organizations world wide. There is a proof of registration label that is to be .attached to the EPIRB.
GMDSS REQUIREMENT, ships are required to meet certain ship radio equipment general requirements which:
a) Includes a Satellite EPIRB capable of transmitting a distress alert through the polar orbiting satellite service in the 406 MHZ band;
b)The EPIRB must be installed in an easily accessible position, ready to be manually released and capable of being carried by one person into a survival craft. It must also be capable of floating free if the ships sinks and automatically activated when afloat;
c)The EPIRB must be capable of manual activation and deactivation;
Shipboard personnel preparing to abandon ship should retrieve the 406 MHZ EPIRB from the bracket and take to the survival craft for manual activation.
The EPIRB must be capable of automatically activating after floating free from the mounting bracket. It must able to float free from the sinking ship at a depth not to exceed 4 meters (at a list of up to 45 degrees) these float free operations are done by a hydrostatic Automatic Release Mechanism (ARM) on the EPIRB mounting bracket.
There is a replacement date label is affixed to the ARM and the ARM must be replaced by this date .
Watertight Integrity, EPIRBs are required to be watertight to a depth of 10 meters for a period of at least a 5 minutes. They must be capable of being dropped into the water from a height of 20 meters without damage and of floating upright in calm water.
Some of the newer models will activate when detected in water, salt or fresh, and automatically activate the beacon regardless of the switch position. All EPIRBs have a buoyant lanyard used as a tether to secure the beacon to a survival craft or to yourself if need be.
There are severe penalties in store for the vessel who activate either by inadvertently or on purpose (hoax or gross negligence) and the 100ierai Communications Commission will take action.
The EPIRBs should be tested and examined as part of the pre departure checks on every vessel. Check for expiration dates on both the ARM and EPIRB, and to see if the proof of registration is affixed. You can check for signal by using the small FM radio tuned to 100 MHz while the EPIRB is in the test mode. This will assure that the 121.5 MHz signal is working and we can assume that the 406 MHz transmitter is working also. Most EPIRBs are equipped with a test switch. The US Coast Guard requires a monthly test (and must be done on the first FIVE minutes of the hour). The test switch places the EPIRB into a non radiating position and signal is kept to a minimum.
The batteries in the EPIRB are to have sufficient capacity to operate the EPIRB for a minimum of 48 hours. And in all cases of survival equipment there is a month and year of replacement marked on the battery. The unit cannot be used beyond this date. The battery must be replaced at this time as there is no grace period permitted.
Because the duty cycle of the transmitter is so short it will reduce the drain on the battery and the time between transmit cycles will allow other EPIRBs to transmit simultaneously while the satellite is passing overhead. The EPIRB identification is digitally encoded hexadecimal signal which provides the serial number of the EPIRB and this allows SAR to consult the database for the name of the vessel. And as previously mentioned the newer ones may have the position inserted in the message.
The EPIRB also contains a low power homing transmitter (25 milliwatt) that emits a continuous signal on 121.5 MHz. This allows the SAR units to "home" in on the beacon. Most of the EPIRBs also have a strobe light to proved on-scene units with a visuallD of the EPIRB. As mentioned the 121.5 MHz signal is also picked up by other satellites like the NOAA.
The Federal Communications Commission requires that each EPIRB be registered. This registration is done by the card enclosed when the EPIRB is purchased. There is no fee and the card is sent to NOAA directly. They in turn make the registration data base available to all SAR organizations world wide. There is a proof of registration label that is to be .attached to the EPIRB.
GMDSS REQUIREMENT, ships are required to meet certain ship radio equipment general requirements which:
a) Includes a Satellite EPIRB capable of transmitting a distress alert through the polar orbiting satellite service in the 406 MHZ band;
b)The EPIRB must be installed in an easily accessible position, ready to be manually released and capable of being carried by one person into a survival craft. It must also be capable of floating free if the ships sinks and automatically activated when afloat;
c)The EPIRB must be capable of manual activation and deactivation;
Shipboard personnel preparing to abandon ship should retrieve the 406 MHZ EPIRB from the bracket and take to the survival craft for manual activation.
The EPIRB must be capable of automatically activating after floating free from the mounting bracket. It must able to float free from the sinking ship at a depth not to exceed 4 meters (at a list of up to 45 degrees) these float free operations are done by a hydrostatic Automatic Release Mechanism (ARM) on the EPIRB mounting bracket.
There is a replacement date label is affixed to the ARM and the ARM must be replaced by this date .
Watertight Integrity, EPIRBs are required to be watertight to a depth of 10 meters for a period of at least a 5 minutes. They must be capable of being dropped into the water from a height of 20 meters without damage and of floating upright in calm water.
Some of the newer models will activate when detected in water, salt or fresh, and automatically activate the beacon regardless of the switch position. All EPIRBs have a buoyant lanyard used as a tether to secure the beacon to a survival craft or to yourself if need be.
There are severe penalties in store for the vessel who activate either by inadvertently or on purpose (hoax or gross negligence) and the 100ierai Communications Commission will take action.
The EPIRBs should be tested and examined as part of the pre departure checks on every vessel. Check for expiration dates on both the ARM and EPIRB, and to see if the proof of registration is affixed. You can check for signal by using the small FM radio tuned to 100 MHz while the EPIRB is in the test mode. This will assure that the 121.5 MHz signal is working and we can assume that the 406 MHz transmitter is working also. Most EPIRBs are equipped with a test switch. The US Coast Guard requires a monthly test (and must be done on the first FIVE minutes of the hour). The test switch places the EPIRB into a non radiating position and signal is kept to a minimum.
The batteries in the EPIRB are to have sufficient capacity to operate the EPIRB for a minimum of 48 hours. And in all cases of survival equipment there is a month and year of replacement marked on the battery. The unit cannot be used beyond this date. The battery must be replaced at this time as there is no grace period permitted.
GMDSS (EPIRB)
The EPIRB (Emergency Position Indicating Radio Beacon) is a device normally located on the wing of the bridge in a bracket, sometimes on both wings. It could also be placed on the bulkhead on the wheel house. The device is small enough to carry to the life boat. Otherwise the unit can be left on the bulkhead and the ARM (automatic release mechanism) will release the EPIRB if the ship sinks.
GMDSS utilizes the COSPAS-SARSAT satellite system to intercept and locate signals from EPIRBs, Emergency Locating Transmitters (ELTs), and Personal Locating Beacons (PLBs). COSPAS in Russian language means Cosmicheskaya Systyema Poiska Avariynyich Sudov (Space System for Search of Distressed Vessels).
SARSA T is the acronym for: Search And Rescue Satellite Aided Tracking. Together COSPAS-SARSAT is a joint system established by organizations in the United States, Russia, Canada and France to locate EPIRBS operating on 406 and 121.5 MHZ.
Some SARSAT satellites are able to relay certain beacons that transmit on 243 MHZ (military), but not all COSPAS-SARSA T ground station (LUTs) are equipped with equipment for this frequency.
Let's look at the Space Segment of the system.
COSPAS-SARSA T relies on 6 satellites in low earth orbit (LEO) and geostationary satellites for the relay of distress alerts. COSPAS satellites orbit at an altitude of approx 1000 Km. And they complete an orbit about every 105 minutes. These SARSAT satellites orbit at an altitude of approx 850 Km and complete and orbit about every 100 minutes. (And passes from horizon to horizon in about 15 minutes.) The maximum delay a distressed vessel should experience would be a wait of about 90 minutes for the satellite to be in range. The current COSPAS-SARSAT constellation is comprised of 3 COSPAS and 3 SARSAT satellites. With 6 satellites, the delay time in relaying distress alerts is reduced to an average of 90 minutes.
The COSPAS-SARSAT system operates in two basic coverage modes:
a) Real time Mode; and
b) Store and forward mode.
The121.5 MHZ beacons operate in the real-time mode, the 121.5 MHz signal is transmitting continuously. The signal is sent so that any passing aircraft will receive the signal on the emergency receiver in each aircraft. The satellite can calculate the position of the 121.5 MHz beacon but may require two passes.
There are other satellites that have 121.5 MHz receivers such as the NOM weather satellites. These satellites can receive the signal but have no way of knowing where the signal is located. They will notify the ground station that there is a signal but that is the only information, there is no position information on the signal.
The 406 MHZ portion of the EPIRB is sending a signal with a message indicating the registration number of the EPIRB and the satellite will compute the location by the use of the doppler effect. This signal is sent in bursts with digital information contained in the burst. If the Satellite is not in view of the EPI RB then nothing will happen. As the satellites are in polar orbit and there are only six it will be a little time before the signal is received .by the satellite.
Of the signals from the 406 MHz EPIRB the satellite can fix the position within about 2.5 miles. By comparison the 121.5 MHz beacon the fix is about 9 Miles and it may take two passes to obtain the fix.
As the satellite approached the EPIRB position, the carrier frequency transmitted by the EPIRB will increase. As the Satellite moves away from the EPJRB position, the carrier frequency will decrease. As this frequency is changed by the motion of the Satellite it is calculated and will give approximate location of the EPIRB.
GMDSS utilizes the COSPAS-SARSAT satellite system to intercept and locate signals from EPIRBs, Emergency Locating Transmitters (ELTs), and Personal Locating Beacons (PLBs). COSPAS in Russian language means Cosmicheskaya Systyema Poiska Avariynyich Sudov (Space System for Search of Distressed Vessels).
SARSA T is the acronym for: Search And Rescue Satellite Aided Tracking. Together COSPAS-SARSAT is a joint system established by organizations in the United States, Russia, Canada and France to locate EPIRBS operating on 406 and 121.5 MHZ.
Some SARSAT satellites are able to relay certain beacons that transmit on 243 MHZ (military), but not all COSPAS-SARSA T ground station (LUTs) are equipped with equipment for this frequency.
Let's look at the Space Segment of the system.
COSPAS-SARSA T relies on 6 satellites in low earth orbit (LEO) and geostationary satellites for the relay of distress alerts. COSPAS satellites orbit at an altitude of approx 1000 Km. And they complete an orbit about every 105 minutes. These SARSAT satellites orbit at an altitude of approx 850 Km and complete and orbit about every 100 minutes. (And passes from horizon to horizon in about 15 minutes.) The maximum delay a distressed vessel should experience would be a wait of about 90 minutes for the satellite to be in range. The current COSPAS-SARSAT constellation is comprised of 3 COSPAS and 3 SARSAT satellites. With 6 satellites, the delay time in relaying distress alerts is reduced to an average of 90 minutes.
The COSPAS-SARSAT system operates in two basic coverage modes:
a) Real time Mode; and
b) Store and forward mode.
The121.5 MHZ beacons operate in the real-time mode, the 121.5 MHz signal is transmitting continuously. The signal is sent so that any passing aircraft will receive the signal on the emergency receiver in each aircraft. The satellite can calculate the position of the 121.5 MHz beacon but may require two passes.
There are other satellites that have 121.5 MHz receivers such as the NOM weather satellites. These satellites can receive the signal but have no way of knowing where the signal is located. They will notify the ground station that there is a signal but that is the only information, there is no position information on the signal.
The 406 MHZ portion of the EPIRB is sending a signal with a message indicating the registration number of the EPIRB and the satellite will compute the location by the use of the doppler effect. This signal is sent in bursts with digital information contained in the burst. If the Satellite is not in view of the EPI RB then nothing will happen. As the satellites are in polar orbit and there are only six it will be a little time before the signal is received .by the satellite.
Of the signals from the 406 MHz EPIRB the satellite can fix the position within about 2.5 miles. By comparison the 121.5 MHz beacon the fix is about 9 Miles and it may take two passes to obtain the fix.
As the satellite approached the EPIRB position, the carrier frequency transmitted by the EPIRB will increase. As the Satellite moves away from the EPJRB position, the carrier frequency will decrease. As this frequency is changed by the motion of the Satellite it is calculated and will give approximate location of the EPIRB.
GMDSS (EQUIPMENT)
RADIO DISTRESS COMMUNICATIONS
DSC
2187.5 Khz ,
4207.5 Khz
6312.0 Khz
8414.5 Khz
12577.0 Khz
16804.5 Khz
RADIOTELEPHONE
2182.0 Khz
4125.0 Khz
6215.0 Khz
8291.0 Khz
12290.0 Khz
16420.0 Khz
NBDP
2174.5 Khz
4177.5 Khz
6268.0 Khz
8376.5 Khz
12520.0 Khz
16695.0 Khz
VHF Channel 70 (156.525 MHZ) VHF Channel 16 (156.800 MHZ)
DSC
2187.5 Khz ,
4207.5 Khz
6312.0 Khz
8414.5 Khz
12577.0 Khz
16804.5 Khz
RADIOTELEPHONE
2182.0 Khz
4125.0 Khz
6215.0 Khz
8291.0 Khz
12290.0 Khz
16420.0 Khz
NBDP
2174.5 Khz
4177.5 Khz
6268.0 Khz
8376.5 Khz
12520.0 Khz
16695.0 Khz
VHF Channel 70 (156.525 MHZ) VHF Channel 16 (156.800 MHZ)
GMDSS (DIGITAL SELECTIVE CALLING DSC 2)
If the GMDSS Radio Operator does not have time to select the follow on frequency/mode then the unit will default to the standard answering frequency and mode .
With the DSC system we can indicate the Priority of these Communications, Distress, Urgency, Safety or Routine. When using the "All Ships" Distress mode then the radios will set up on the Highest Priority .
If the GMDSS Radio Operator does not have time to enter all the extra information by keying it into the equipment, the nature of the distress will be "UNSPECIFIED" on the screen or on the printed record.
If a distress alert is received the bridge alarm will sound. The DSC will display, or print the alert message, including the MMSI of the calling station. The rest of the total message will print, priority of communications, time of receipt, Follow on communications, and time of receipt.
To insure that someone will hear the distress alert, the call is repeated a second time. In VHF the call is repeated a second time, if it is not answered the first time. In the case of MF/HF the distress alert is sent out on the six DSC frequencies and then there is a timed wait (to see if someone answers the alert) then this sequence is repeated. If there is no answer then the GMDSS Radio Operator can repeat the distress alert a second time.
The receiving station will acknowledge the DSC call with an DSC "Acknowledge" and will move to the new working frequency. If the sending station did not have time to insert the variable individual messages then the method of communications will be Radiotelephone.
To increase the probability of reception for DSC distress calls, it is wise to repeat the alert several times until you obtain a response, at regular intervals .
It is wise to wait form 3 to 5 minutes to allow the coastal station time to answer and/or notify the Coast Guard or other authority before answering the alert. Relaying the distress alert might do more harm to the radio waves and good. Due to HF propagation you might not be in the range of another station that may be answering the distress alert.
With the DSC system we can indicate the Priority of these Communications, Distress, Urgency, Safety or Routine. When using the "All Ships" Distress mode then the radios will set up on the Highest Priority .
If the GMDSS Radio Operator does not have time to enter all the extra information by keying it into the equipment, the nature of the distress will be "UNSPECIFIED" on the screen or on the printed record.
If a distress alert is received the bridge alarm will sound. The DSC will display, or print the alert message, including the MMSI of the calling station. The rest of the total message will print, priority of communications, time of receipt, Follow on communications, and time of receipt.
To insure that someone will hear the distress alert, the call is repeated a second time. In VHF the call is repeated a second time, if it is not answered the first time. In the case of MF/HF the distress alert is sent out on the six DSC frequencies and then there is a timed wait (to see if someone answers the alert) then this sequence is repeated. If there is no answer then the GMDSS Radio Operator can repeat the distress alert a second time.
The receiving station will acknowledge the DSC call with an DSC "Acknowledge" and will move to the new working frequency. If the sending station did not have time to insert the variable individual messages then the method of communications will be Radiotelephone.
To increase the probability of reception for DSC distress calls, it is wise to repeat the alert several times until you obtain a response, at regular intervals .
It is wise to wait form 3 to 5 minutes to allow the coastal station time to answer and/or notify the Coast Guard or other authority before answering the alert. Relaying the distress alert might do more harm to the radio waves and good. Due to HF propagation you might not be in the range of another station that may be answering the distress alert.
GMDSS (DIGITAL SELECTIVE CALLING DSC)
DIGITAL SELECTIVE CALLING (DSC)
One of the keys to a successful GMDSS system is the use of DSC or Digital Selective Calling. We have come into the computer age on the High Seas! By using DSC we can call other ships and change their frequency to an operating frequency by one call. We can call a ship or all ships to indicate special messages to each. To do this we had to set up a new series of call signs for each ship. It seems like we have a lot of call signs for our ship, Radio call (WABX), SECAL call (11122), Ships Name (SS Neversail), and now we have another call sign. I guess it's a world of call signs.
This new call sign is called a Maritime Mobile Service Identity number (MMSI). It is a nine digit number and the first three digits to denote the ships state of registery. The United States is assigned 366 and 367, while Norway uses 257 and 258. The rest of the digits (six) are the individual ships identity. Example: 367112233.
The number system also needs to have a group station identity and we place a zero in front of the country identifier and the remaining five digits denote a group of ships, such as all OILCO Tankers. Example: 036711223.
Coastal Station have their own special identity and it has two zeros prior to the country identifier. Example: 003671122. A Coastal Group would have the following group of digits: 002673344 (the 3344 would denote a group of coastal stations).
We have shown the ship/station call numbers in decimal format, DSC uses a sequence of seven unit binary combinations to transmit the number. It is only by the use of binary codes that true digital communications and the reliability is achieved. While DSC calls are important for distress alerting and acknowledgment, the system is valuable for handling other routine communications.
This digital system is used on MF, HF and VHF communications. It is used for automated position reporting as in the US Coast Guard Vessel Traffic Service areas.
The DSC system will permit the establishment of communications without manual listening watch requirements. By this means we will no longer have to have a manual listing watch on VHF channel 16 nor on MF 2182 KHz .
There has been frequencies set aside for guarding these DSC calls so that the equipment will be able to respond to distress calls without an operator at the radio console. We can scan these frequencies automatically without operator intervention. The GMDSS system bring into the network the NBDP so that a printed message can be used for distress and this is automatically printed. Some of the frequencies use in DSC and NBDP are:
VHF DSC Channel 70 (156.525 Mhz)
MF DSC 2187.5 KHz
HF DSC 4207.5; 6312; 8414.5; 12,577 and 16,504.5 KHz
MF NBDP 2174.5 KHz
HF NBDP 4177.5; 6268; 8376.5; 12,520 and 16,695 KHz
It should be noted that channel 70 (156.525 KHz) was a intership frequency but in 1986 this frequency was set aside for Digital signaling only and is not to be used for voice conversations .
The message sent via Digital Signaling Calling includes as basic information, the MMSI number of the station sending, time of call, location of ship and one or several messages concerning the nature of the distress . This information could be "Sinking, Grounding, Fire, Taking on Water, etc . When this message arrives at the receiver it will sound an alarm and print out the message on a printer (if the printer is on line). The GMDSS Radio Operator can then silence the alarm and take what actions is necessary.
One of the nice features of the DSC method is that the "follow on" communications, the channel to "work" the alert, can be programmed by the calling person and when the alert communications is established, the mode and frequency will automatically be set-up on the receiving ships radio.
One of the keys to a successful GMDSS system is the use of DSC or Digital Selective Calling. We have come into the computer age on the High Seas! By using DSC we can call other ships and change their frequency to an operating frequency by one call. We can call a ship or all ships to indicate special messages to each. To do this we had to set up a new series of call signs for each ship. It seems like we have a lot of call signs for our ship, Radio call (WABX), SECAL call (11122), Ships Name (SS Neversail), and now we have another call sign. I guess it's a world of call signs.
This new call sign is called a Maritime Mobile Service Identity number (MMSI). It is a nine digit number and the first three digits to denote the ships state of registery. The United States is assigned 366 and 367, while Norway uses 257 and 258. The rest of the digits (six) are the individual ships identity. Example: 367112233.
The number system also needs to have a group station identity and we place a zero in front of the country identifier and the remaining five digits denote a group of ships, such as all OILCO Tankers. Example: 036711223.
Coastal Station have their own special identity and it has two zeros prior to the country identifier. Example: 003671122. A Coastal Group would have the following group of digits: 002673344 (the 3344 would denote a group of coastal stations).
We have shown the ship/station call numbers in decimal format, DSC uses a sequence of seven unit binary combinations to transmit the number. It is only by the use of binary codes that true digital communications and the reliability is achieved. While DSC calls are important for distress alerting and acknowledgment, the system is valuable for handling other routine communications.
This digital system is used on MF, HF and VHF communications. It is used for automated position reporting as in the US Coast Guard Vessel Traffic Service areas.
The DSC system will permit the establishment of communications without manual listening watch requirements. By this means we will no longer have to have a manual listing watch on VHF channel 16 nor on MF 2182 KHz .
There has been frequencies set aside for guarding these DSC calls so that the equipment will be able to respond to distress calls without an operator at the radio console. We can scan these frequencies automatically without operator intervention. The GMDSS system bring into the network the NBDP so that a printed message can be used for distress and this is automatically printed. Some of the frequencies use in DSC and NBDP are:
VHF DSC Channel 70 (156.525 Mhz)
MF DSC 2187.5 KHz
HF DSC 4207.5; 6312; 8414.5; 12,577 and 16,504.5 KHz
MF NBDP 2174.5 KHz
HF NBDP 4177.5; 6268; 8376.5; 12,520 and 16,695 KHz
It should be noted that channel 70 (156.525 KHz) was a intership frequency but in 1986 this frequency was set aside for Digital signaling only and is not to be used for voice conversations .
The message sent via Digital Signaling Calling includes as basic information, the MMSI number of the station sending, time of call, location of ship and one or several messages concerning the nature of the distress . This information could be "Sinking, Grounding, Fire, Taking on Water, etc . When this message arrives at the receiver it will sound an alarm and print out the message on a printer (if the printer is on line). The GMDSS Radio Operator can then silence the alarm and take what actions is necessary.
One of the nice features of the DSC method is that the "follow on" communications, the channel to "work" the alert, can be programmed by the calling person and when the alert communications is established, the mode and frequency will automatically be set-up on the receiving ships radio.
GMDSS (INMARSAT)
INMARSAT Systems
One of the major problems with communications at sea was the problem of atmospheric interference, static crashes, fading of signals, unreliable communications on certain frequencies, that would interfere with emergency communications. The IMO (International Maritime Organization) realizing this as a major problem looked to the major global satellite communications system of the INMARSA T Organization to the answer.
INMARSAT acronym for INternational MARitime SATellite, an organization of member countries established in 1979. When INMARSAT first started its operation it leased capacity on existing satellites. In the initial operations were just concerned with the maritime station. Soon they expanded in the aeronautical and land users. The system soon grew and INMARSAT then launched their own satellites. Maritime now uses about half of the operation of INMARSAT.
INMARSAT divided the world into four regions: Atlantic Ocean Region East; Atlantic Ocean Region West; Indian Ocean Region and Pacific Ocean Region. There are satellites for each region and some spares to assist each region. The satellites are in geostationary orbit at about 22,000 miles in the sky. The chart shows the location and some of the spares for each ocean region. The satellite has a footprint of about one third of the earth with some overlap. Each satellite provides coverage based on a maximum line of sight distance of 72 degrees from it's Geographical Position (GP).
This means that the polar regions are not covered by the INMARSAT system
There are on the surface of the earth about 34 Land Earth Station
(LES) which provide the link between the ship and the terrestrial telecommunications networks. We sometimes call these station Coastal Earth Station (CES). In the United States commercial stations have the intertie to land line communications. In the U.S.A COMSAT Mobile· Communications is one provider while lOB Mobile Communications, lately purchased by a Canadian firm call
STRATOS Communications and they operate the LESs.
The next satellite is the INMARSAT-B and is a digital version of the INMARSAT A. The use of digital technology uses less bandwidth and power and thus lowers cost of communications. The antennas are some what smaller than the "A" and so installation costs are lower.
INMARSAT-B supports direct-dial telephone, fax, telex and High Speed Data. It is assumed that INMARSAT B will replace the A. INMARSAT B does not support EGC for the reception of MSI. If your ship has only the "A" then there can be a EGC receiver as a stand alone unit or you could use the INMARSAT-C to receive MSI. The "B" has a single button to alert the shore station of a distress alert, but must input the position data.
INMARSAT-C is a digital only system and does not support voice and is a "store and forward" type of system, Le., it is a "one-way" type of transmission. The ship will transmit a message and then the shore station will transmit the response of the sending ship station. TELEX type messages can be sent but not in "real-time" mode. Faxes can be sent by the ship to the LES and they in turn will retransmit it on the land line system.
An advantage of the "C" is the small size and small omni directional antenna. No power hungry gyros to move the antenna following the satellite, a power saving. The antenna is a small diameter device and is fixed on the mast. The latest "C" has a built in GPS and can include the position when sending out an distress alert call.
In the above the "Distress" button will generate a signal to the Rescue Coordination Center. And to the rescuers.
Another satellite system is the INMARSAT-M system. The use of this system is mainly by Mobile units using digital telephone system as well as slow speed fax. This system is one that uses little bandwidth and low power and costs are lower than A.
One of the major problems with communications at sea was the problem of atmospheric interference, static crashes, fading of signals, unreliable communications on certain frequencies, that would interfere with emergency communications. The IMO (International Maritime Organization) realizing this as a major problem looked to the major global satellite communications system of the INMARSA T Organization to the answer.
INMARSAT acronym for INternational MARitime SATellite, an organization of member countries established in 1979. When INMARSAT first started its operation it leased capacity on existing satellites. In the initial operations were just concerned with the maritime station. Soon they expanded in the aeronautical and land users. The system soon grew and INMARSAT then launched their own satellites. Maritime now uses about half of the operation of INMARSAT.
INMARSAT divided the world into four regions: Atlantic Ocean Region East; Atlantic Ocean Region West; Indian Ocean Region and Pacific Ocean Region. There are satellites for each region and some spares to assist each region. The satellites are in geostationary orbit at about 22,000 miles in the sky. The chart shows the location and some of the spares for each ocean region. The satellite has a footprint of about one third of the earth with some overlap. Each satellite provides coverage based on a maximum line of sight distance of 72 degrees from it's Geographical Position (GP).
This means that the polar regions are not covered by the INMARSAT system
There are on the surface of the earth about 34 Land Earth Station
(LES) which provide the link between the ship and the terrestrial telecommunications networks. We sometimes call these station Coastal Earth Station (CES). In the United States commercial stations have the intertie to land line communications. In the U.S.A COMSAT Mobile· Communications is one provider while lOB Mobile Communications, lately purchased by a Canadian firm call
STRATOS Communications and they operate the LESs.
The next satellite is the INMARSAT-B and is a digital version of the INMARSAT A. The use of digital technology uses less bandwidth and power and thus lowers cost of communications. The antennas are some what smaller than the "A" and so installation costs are lower.
INMARSAT-B supports direct-dial telephone, fax, telex and High Speed Data. It is assumed that INMARSAT B will replace the A. INMARSAT B does not support EGC for the reception of MSI. If your ship has only the "A" then there can be a EGC receiver as a stand alone unit or you could use the INMARSAT-C to receive MSI. The "B" has a single button to alert the shore station of a distress alert, but must input the position data.
INMARSAT-C is a digital only system and does not support voice and is a "store and forward" type of system, Le., it is a "one-way" type of transmission. The ship will transmit a message and then the shore station will transmit the response of the sending ship station. TELEX type messages can be sent but not in "real-time" mode. Faxes can be sent by the ship to the LES and they in turn will retransmit it on the land line system.
An advantage of the "C" is the small size and small omni directional antenna. No power hungry gyros to move the antenna following the satellite, a power saving. The antenna is a small diameter device and is fixed on the mast. The latest "C" has a built in GPS and can include the position when sending out an distress alert call.
In the above the "Distress" button will generate a signal to the Rescue Coordination Center. And to the rescuers.
Another satellite system is the INMARSAT-M system. The use of this system is mainly by Mobile units using digital telephone system as well as slow speed fax. This system is one that uses little bandwidth and low power and costs are lower than A.
GMDSS (NARROW BAND DIRECT PRINTING NBDP)
Narrow Band Direct Printing (NBDP)
NBDP is the printing of all messages which will give us a printed record of the communications. If the ship is involved in a distress situation it would be nice to have a printed record of all communications that took place during the operation.
Narrow Band Direct Printing (NBDP) is a term we use to describe a method of sending information over the radio and having it printed. In some publications it is called TELEX, a system used on land line communications between offices.
One of the disadvantages of using NBDP for communications is that a skilled keyboard operators are required. An advantage is that there is a written hard-copy of all communications. NBDP communications uses digital signals on the links between communicators.
A NBDP circuit uses teleprinters, like an electric typewriter, or now days using a computer terminal. The message is formatted in the word processing program and then transferred to the "line" section for transmitting. Teleprinters use the CCITT ITA NO.2 code (International Telegraph Alphabet Code) for communicating. Each keyboard character is composed of a 5-element code. This code is only able to provide us with 32 combinations, and the "shift" key allows 26 more combinations.
All data communications uses some form of error checking so we use a 7 -unit code. We add a "space" element and a "mark" element to form this 7 bit code. Space is generally accepted to mean a logic zero (0) and Mark as a logic one (1). These special codes are used to provide a system of checking for errors. We use this as a "parity" checking system.
To further aid in error checking we can use the FEC (forward error checking) system to assist us in providing non-error communications. FEC frames are sent over the air and they include a "parity" information and this is check on receipt at the receiving station. If an error in the checksum is noted then the receiving station will not accept the frame .
NBDP is the printing of all messages which will give us a printed record of the communications. If the ship is involved in a distress situation it would be nice to have a printed record of all communications that took place during the operation.
Narrow Band Direct Printing (NBDP) is a term we use to describe a method of sending information over the radio and having it printed. In some publications it is called TELEX, a system used on land line communications between offices.
One of the disadvantages of using NBDP for communications is that a skilled keyboard operators are required. An advantage is that there is a written hard-copy of all communications. NBDP communications uses digital signals on the links between communicators.
A NBDP circuit uses teleprinters, like an electric typewriter, or now days using a computer terminal. The message is formatted in the word processing program and then transferred to the "line" section for transmitting. Teleprinters use the CCITT ITA NO.2 code (International Telegraph Alphabet Code) for communicating. Each keyboard character is composed of a 5-element code. This code is only able to provide us with 32 combinations, and the "shift" key allows 26 more combinations.
All data communications uses some form of error checking so we use a 7 -unit code. We add a "space" element and a "mark" element to form this 7 bit code. Space is generally accepted to mean a logic zero (0) and Mark as a logic one (1). These special codes are used to provide a system of checking for errors. We use this as a "parity" checking system.
To further aid in error checking we can use the FEC (forward error checking) system to assist us in providing non-error communications. FEC frames are sent over the air and they include a "parity" information and this is check on receipt at the receiving station. If an error in the checksum is noted then the receiving station will not accept the frame .
GMDSS (DISTRESS AND SAFETY COMMUNICATIONS)
Distress and Safety Communications
When we speak of Distress traffic we want to include all messages relating to the immediate assistance for a ship in distress as well as any Search and Rescue (SAR) communications and those on-scene communications. These communications should be conducted on the designated frequencies.
As would be expected Distress traffic has absolute priority over all other communications. We as GMDSS Radio Operators are required to monitor and copy in the station log all the traffic even if the ship is not directly involved, until it is clear that no assistance is required. No transmissions are to be made until all distress traffic has been cleared and you are given permission to resume normal traffic.
The radio telephone distress signal is spoken as MAYDA Y. And in the radiotelegraph method (includes NBDP, SITOR) the distress signal is SOS
Another form of traffic we should be aware of is the Urgency TRAFFIC, this signal indicated that the calling station has a very urgent message to transmit concerning the safety of a ship, aircraft, or other vessel, or some person on board a vessel or within sight. The Urgency signal is PAN PAN (pronounced "pon pon") and the telegraphic (includes NBDP, SITOR) signal is XXX.
A third traffic category is called Safety traffic. This would indicate to the mariner that the station sending the signal is preparing to transmit a message concerning the safety of navigation or giving important meteorological warnings. The radio telephone safety signal is Securite (Secur-a-tay). The telegraphic signal (includes NBDP, SITOR) would be TTT (three "T')
One might use this signal to indicate a hazzard effecting other shipping. Suppose you are leaving a dock and there is a bend in the river and ships in the bend of the river could not observe your ship as you back into the channel. A security message could be send on VHF to alert another ship out of sight that your ship is entering the channel.
In the US we generally use channel 13 to pass this information on to the ships in the area.
The transmitting of a distress alert should include the ships positions its identity, the problem, the ships course and speed, time of the transmitting of the alert. And of course, the type of assistance needed.
The distress alerting is intended to inform a SAR (Search and Rescue) organization that the ship is in distress. This would normally be directed to the Rescue Coordination Center (RCC). The alert will also notify other ships in the immediate area of the ship in distress. Shore/Ship distress alerts will inform ships about distress incidents as appropriate to their position.
Sometimes when an operator becomes aware of another mobile unit in distress, action must be taken to initiate and transmit a distress relay. When the mobile unit in distress is not in a position to transmit a distress alert or when the master of a ship not in distress determines that further assistance is needed, they them will do a distress relay. However, these ships doing the relay must indicate that they are themselves not in a distress situation.
On some of the GMDSS radio equipment there is a automatic distress relay programmed in the radio set. The Coast Guard is recommending that all these automatic relay devices be disabled.
The US Coast Guard recommends that all automatic distress reply from the equipment be disconnected.
The distress alert sent via Satellite(the COSPAS-SA TSART system) will be acknowledged by an RCC ashore. Ship stations may acknowledge distress alerts transmitted by Digital Selective Calling (DSC), but such acknowledgment is deferred several minutes to allow an RCC time to respond.
When we acknowledge Distress Alerts via Radiotelephone we should use the following format:
1.The distress signal MAYDAY.
2.The call sign (said three times) and name of the vessel sending the Distress.
3.The words THIS IS.
4.The call sign of the station acknowledging receipt of the distress alert spoken three times.
5.The words RECEIVED MAYDAY.
When we acknowledge a Distress Alert via NBDP (Narrow band
direct printing), we should stay with this method:
1. The distress signal MAYDAY.
2. The call sign and name of the vessel sending the Distress.
3. The word DE meaning "this is"
4. The call sign of the station acknowledging receipt of the distress alert.
5. The signal RRR MAYDAY
All ship board station receiving a distress alert must inform the Master or person responsible for the ship of the contents of any distress alert as soon as possible.
It is important the ship station should defer acknowledgment of a distress alert for a short period of time. This will allow the receipt and acknowledgment by a coast station. If a ship acknowledges receipt for a distress alert must, as soon as possible, inform a RCC via coastal radio station or via INMARSAT.
Ships that acknowledge receipt for distress alerts must, as soon as possible, inform a RCC via a coastal radio station or via INMARSAT. If the ship receives the distress alert via High Frequency radio then there should be a wait of 3 - 5 minutes before relaying the alert, IF there is no acknowledgment by a coastal station. It should be noted that you may receive the HF signal on one frequency and the coastal station may receive the alert on another frequency and due to propagation of the radio waves, you may not be able to hear the acknowledgment of the coast station.
If the Distress Alert is received via Medium Frequency (MF) on 2187.5 KHz then if you do not hear an acknowledgment within the 3 - 5 minute period you could then acknowledge the alert via radio on 2182 KHz.(SSB). If this attempt is unsuccessful the acknowledgment should be attempted using DSC on 2187.5 KHz.
If the Distress alert is received via VHF (using DSC on Channel 70 [156.525 MHz]), the VHF radio will, by the action of the DSC system, tune the receiving radio to Channel 16. The acknowledgment, by radiotelephony, will then be sent on Channel 16 (156.800 MHz). (As all VHF radios have been switched to Channel 16.) If there is no response to the acknowledgment then an acknowledgment could be sent on Channel 70 via DSC. It might be noted that some VHF station cannot acknowledge distress alerts on Channel 70.
When we speak of Distress traffic we want to include all messages relating to the immediate assistance for a ship in distress as well as any Search and Rescue (SAR) communications and those on-scene communications. These communications should be conducted on the designated frequencies.
As would be expected Distress traffic has absolute priority over all other communications. We as GMDSS Radio Operators are required to monitor and copy in the station log all the traffic even if the ship is not directly involved, until it is clear that no assistance is required. No transmissions are to be made until all distress traffic has been cleared and you are given permission to resume normal traffic.
The radio telephone distress signal is spoken as MAYDA Y. And in the radiotelegraph method (includes NBDP, SITOR) the distress signal is SOS
Another form of traffic we should be aware of is the Urgency TRAFFIC, this signal indicated that the calling station has a very urgent message to transmit concerning the safety of a ship, aircraft, or other vessel, or some person on board a vessel or within sight. The Urgency signal is PAN PAN (pronounced "pon pon") and the telegraphic (includes NBDP, SITOR) signal is XXX.
A third traffic category is called Safety traffic. This would indicate to the mariner that the station sending the signal is preparing to transmit a message concerning the safety of navigation or giving important meteorological warnings. The radio telephone safety signal is Securite (Secur-a-tay). The telegraphic signal (includes NBDP, SITOR) would be TTT (three "T')
One might use this signal to indicate a hazzard effecting other shipping. Suppose you are leaving a dock and there is a bend in the river and ships in the bend of the river could not observe your ship as you back into the channel. A security message could be send on VHF to alert another ship out of sight that your ship is entering the channel.
In the US we generally use channel 13 to pass this information on to the ships in the area.
The transmitting of a distress alert should include the ships positions its identity, the problem, the ships course and speed, time of the transmitting of the alert. And of course, the type of assistance needed.
The distress alerting is intended to inform a SAR (Search and Rescue) organization that the ship is in distress. This would normally be directed to the Rescue Coordination Center (RCC). The alert will also notify other ships in the immediate area of the ship in distress. Shore/Ship distress alerts will inform ships about distress incidents as appropriate to their position.
Sometimes when an operator becomes aware of another mobile unit in distress, action must be taken to initiate and transmit a distress relay. When the mobile unit in distress is not in a position to transmit a distress alert or when the master of a ship not in distress determines that further assistance is needed, they them will do a distress relay. However, these ships doing the relay must indicate that they are themselves not in a distress situation.
On some of the GMDSS radio equipment there is a automatic distress relay programmed in the radio set. The Coast Guard is recommending that all these automatic relay devices be disabled.
The US Coast Guard recommends that all automatic distress reply from the equipment be disconnected.
The distress alert sent via Satellite(the COSPAS-SA TSART system) will be acknowledged by an RCC ashore. Ship stations may acknowledge distress alerts transmitted by Digital Selective Calling (DSC), but such acknowledgment is deferred several minutes to allow an RCC time to respond.
When we acknowledge Distress Alerts via Radiotelephone we should use the following format:
1.The distress signal MAYDAY.
2.The call sign (said three times) and name of the vessel sending the Distress.
3.The words THIS IS.
4.The call sign of the station acknowledging receipt of the distress alert spoken three times.
5.The words RECEIVED MAYDAY.
When we acknowledge a Distress Alert via NBDP (Narrow band
direct printing), we should stay with this method:
1. The distress signal MAYDAY.
2. The call sign and name of the vessel sending the Distress.
3. The word DE meaning "this is"
4. The call sign of the station acknowledging receipt of the distress alert.
5. The signal RRR MAYDAY
All ship board station receiving a distress alert must inform the Master or person responsible for the ship of the contents of any distress alert as soon as possible.
It is important the ship station should defer acknowledgment of a distress alert for a short period of time. This will allow the receipt and acknowledgment by a coast station. If a ship acknowledges receipt for a distress alert must, as soon as possible, inform a RCC via coastal radio station or via INMARSAT.
Ships that acknowledge receipt for distress alerts must, as soon as possible, inform a RCC via a coastal radio station or via INMARSAT. If the ship receives the distress alert via High Frequency radio then there should be a wait of 3 - 5 minutes before relaying the alert, IF there is no acknowledgment by a coastal station. It should be noted that you may receive the HF signal on one frequency and the coastal station may receive the alert on another frequency and due to propagation of the radio waves, you may not be able to hear the acknowledgment of the coast station.
If the Distress Alert is received via Medium Frequency (MF) on 2187.5 KHz then if you do not hear an acknowledgment within the 3 - 5 minute period you could then acknowledge the alert via radio on 2182 KHz.(SSB). If this attempt is unsuccessful the acknowledgment should be attempted using DSC on 2187.5 KHz.
If the Distress alert is received via VHF (using DSC on Channel 70 [156.525 MHz]), the VHF radio will, by the action of the DSC system, tune the receiving radio to Channel 16. The acknowledgment, by radiotelephony, will then be sent on Channel 16 (156.800 MHz). (As all VHF radios have been switched to Channel 16.) If there is no response to the acknowledgment then an acknowledgment could be sent on Channel 70 via DSC. It might be noted that some VHF station cannot acknowledge distress alerts on Channel 70.
GMDSS (NAVTEX)
With NAVTEX Distress alerts, navigation and weather warnings cannot be rejected.
The same providers of the NAVTEX also provide information to the SafetyNET. Navigational warnings are provided daily to NAVAREA IV at 1000 and 2200 hours UTC. NAVAREA XII is broadcast over POR satellite at 1030 and 2230 UTC.
The COMSAT CES at Santa Paula, California provides MSI service to the Pacific Ocean Region and MSI service to Atlantic Ocean Region EAST and WEST.
By-the-way there are special receivers that may interfaced to INMARSAT-A or B to allow for EGC in addition to the normal communications, to allow for receiving the SafetyNET.
A third method of receiving Maritime Safety Information is High Frequency Radio.
If we look at the FCC rules in 47 CFR 80.1123 (b) we find that while at sea, all ships must maintain radio watches for broadcasts of maritime safety information on the appropriate frequency or frequencies on which such information is broadcast for the area in which the ship is navigating.
This would mean that if your ship is in the area not served by INMARSAT then you must set up watches on those frequencies that would be in use in that area. Of course this does not mean that if, in any sea area, you cannot use the HF frequencies to receive MSI in lieu of any other method. On HF radio there are special frequencies for reception of MSI via NBDP. The IMO GMDSS Master Plan Publication identifies HF Coastal Radio Stations that broadcast MSI via NBDP. It seems reasonable that HF NBDP is required in sea area A4 outside of NAVTEX service areas.
The same providers of the NAVTEX also provide information to the SafetyNET. Navigational warnings are provided daily to NAVAREA IV at 1000 and 2200 hours UTC. NAVAREA XII is broadcast over POR satellite at 1030 and 2230 UTC.
The COMSAT CES at Santa Paula, California provides MSI service to the Pacific Ocean Region and MSI service to Atlantic Ocean Region EAST and WEST.
By-the-way there are special receivers that may interfaced to INMARSAT-A or B to allow for EGC in addition to the normal communications, to allow for receiving the SafetyNET.
A third method of receiving Maritime Safety Information is High Frequency Radio.
If we look at the FCC rules in 47 CFR 80.1123 (b) we find that while at sea, all ships must maintain radio watches for broadcasts of maritime safety information on the appropriate frequency or frequencies on which such information is broadcast for the area in which the ship is navigating.
This would mean that if your ship is in the area not served by INMARSAT then you must set up watches on those frequencies that would be in use in that area. Of course this does not mean that if, in any sea area, you cannot use the HF frequencies to receive MSI in lieu of any other method. On HF radio there are special frequencies for reception of MSI via NBDP. The IMO GMDSS Master Plan Publication identifies HF Coastal Radio Stations that broadcast MSI via NBDP. It seems reasonable that HF NBDP is required in sea area A4 outside of NAVTEX service areas.
GMDSS (NAVTEX)
If a NAVTEX receiver becomes inoperative, the MSI broadcasts can be copied by using HF NBDP, INMARSAT-C SafetyNET or copy NAVTEX broadcasts on NBDP on 518 Khz on your MF/HF receiver. However you will not get the reject/select feature as you would have on the NAVTEX receiver . The frequency of 4209.5 KHz using NBDP and FEC is used in some European areas . The IMO as established some performance standards for NAVTEX receivers. The receiver has three main parts. The receiver section is designed for one frequency only (518 Khz); a small computer to process the message and a printing device to allow display of the message on paper.
Some units are designed to store at least 30 message header ID .
These messages are saved in the memory for about 70 hours and will be erased from the memory. If there is a lot of traffic when the memory section is filled then the oldest message will be deleted to make way for the newest. The station ID and items in the memory should remain in the unit for at least 6 hours when the power is off.
One nice thing about the receiver is that if a character is garbled then the receiver will print a star (*). The message will still be readable under some severe radio conditions. A message will be considered received if the character error rate is below 5% .
If a message is received from a Search and Rescue operation there will be an alarm sound at the position from which the ship is normally navigated. It may then be reset at the receiver.
There is a second system of receiving the MSI (Maritime Safety Information) and that is the SafetyNET. This network is a product of the IMARSAT Corporation and is a free service to the Maritime Industry. This service is an automated service using the INMARSAT-C system. This service is authorized by the IMO, within the auspices of the GMDSS, providing safety service for mariners. The coverage is as for INMARSA T coverage that is, from about 70 degrees North to 70 degrees South. Out side of
NAVTEX and beyond 70 degrees we must use HF Radio.
Some of the services of SafetyNET include:
Shore to ship distress alerts and urgent information from RCC
Meteorological warning and forecasts compiled by the National Weather Center
Navigational warning and electronic chart corrections from Hydrographic Office
International Ice Patrol information for the North Atlantic Ocean
Some units are designed to store at least 30 message header ID .
These messages are saved in the memory for about 70 hours and will be erased from the memory. If there is a lot of traffic when the memory section is filled then the oldest message will be deleted to make way for the newest. The station ID and items in the memory should remain in the unit for at least 6 hours when the power is off.
One nice thing about the receiver is that if a character is garbled then the receiver will print a star (*). The message will still be readable under some severe radio conditions. A message will be considered received if the character error rate is below 5% .
If a message is received from a Search and Rescue operation there will be an alarm sound at the position from which the ship is normally navigated. It may then be reset at the receiver.
There is a second system of receiving the MSI (Maritime Safety Information) and that is the SafetyNET. This network is a product of the IMARSAT Corporation and is a free service to the Maritime Industry. This service is an automated service using the INMARSAT-C system. This service is authorized by the IMO, within the auspices of the GMDSS, providing safety service for mariners. The coverage is as for INMARSA T coverage that is, from about 70 degrees North to 70 degrees South. Out side of
NAVTEX and beyond 70 degrees we must use HF Radio.
Some of the services of SafetyNET include:
Shore to ship distress alerts and urgent information from RCC
Meteorological warning and forecasts compiled by the National Weather Center
Navigational warning and electronic chart corrections from Hydrographic Office
International Ice Patrol information for the North Atlantic Ocean
GMDSS (NAVTEX)
A dedicated NAVTEX receiver is used to receive incoming message and then prints the information. The receiver has the capability to select a number of special messages by using a predetermined code. These codes are set into the receiver by the radio operator and will determine what type of messages will be printed.
Each station in the NAVTEX system has a unique transmitter identification, these determine the area they will provide MSI. The Identification is a unique letter from A to Z. There is also a special letter to determine the type or category of message. There are additional letters to have a specific functions in the message. The first line of the message is:
ZCZC FV01
These are designated as: Start signal [ZCZC] then; B1 B2 xy Second group of four
B1 = The station code as "F" above
B2 = The subject matter code.
xy = the serial number of the message, starting with 01
The B1 designator is the station obtained form IMO Master Plan of Shore-Based Facilities; Publication 117, Radio Navigational Aids, list many of the active NA VTEX stations worldwide.
The B2 designator is the Subject matter of the message and is shown in the table below.
The xy characters are the serial number of the category of message and if this is a "OO" then it is for distress and will be sent immediately.
There are several Categories of MSI. Navigational Warnings, Distress Alerts, and Meteorological Warnings.
The first to discuss is Navigational Warnings. Under this title we will consider some of the following: buoys out of position, new wrecks, floating debris, oil rig moves, naval gunfire exercises, unlit buoys .
The second is Meteorological Warnings and these consist of messages concerning: gale force winds, severe weather conditions requiring immediate transmission.
And third are Distress Alerts these messages are the first details of any distress situation will often be broadcast as MSI upon receipt. Additional information will be transmitted as distress traffic and on those designated frequencies.
Subject Matter of NA VTEX Messages
A Navigational Warnings
B Meteoroloaical Warnings
C Ice Reports
D SAR Information
E Meteorological Forecast
F Pilot Service Messages
G Decca Messages
H Loran Messages
I Omeaa Messages
J SATNAV messages
K Other Electronic Navigation Messages
L Navigational Warnings in addition to A (Overflow from A)
M-U Reserved
V Fishing Vessels
Y Reserved
Z No messaaes to transmit
These station and subject matter designators are programable into the NAVTEX receiver and allows the operator to choose only the safety messages pertinent to the sailing area and other item of interest. The other designators not programmed in the receiver will be rejected.
A typical SafetyNET MSI broadcast is shown below. Please note the following on the message:
Date and time of the message in UTC .
The identifier of the CES send the message
A unique number identifying the message
The priority of the message
The nature of the message
Each station in the NAVTEX system has a unique transmitter identification, these determine the area they will provide MSI. The Identification is a unique letter from A to Z. There is also a special letter to determine the type or category of message. There are additional letters to have a specific functions in the message. The first line of the message is:
ZCZC FV01
These are designated as: Start signal [ZCZC] then; B1 B2 xy Second group of four
B1 = The station code as "F" above
B2 = The subject matter code.
xy = the serial number of the message, starting with 01
The B1 designator is the station obtained form IMO Master Plan of Shore-Based Facilities; Publication 117, Radio Navigational Aids, list many of the active NA VTEX stations worldwide.
The B2 designator is the Subject matter of the message and is shown in the table below.
The xy characters are the serial number of the category of message and if this is a "OO" then it is for distress and will be sent immediately.
There are several Categories of MSI. Navigational Warnings, Distress Alerts, and Meteorological Warnings.
The first to discuss is Navigational Warnings. Under this title we will consider some of the following: buoys out of position, new wrecks, floating debris, oil rig moves, naval gunfire exercises, unlit buoys .
The second is Meteorological Warnings and these consist of messages concerning: gale force winds, severe weather conditions requiring immediate transmission.
And third are Distress Alerts these messages are the first details of any distress situation will often be broadcast as MSI upon receipt. Additional information will be transmitted as distress traffic and on those designated frequencies.
Subject Matter of NA VTEX Messages
A Navigational Warnings
B Meteoroloaical Warnings
C Ice Reports
D SAR Information
E Meteorological Forecast
F Pilot Service Messages
G Decca Messages
H Loran Messages
I Omeaa Messages
J SATNAV messages
K Other Electronic Navigation Messages
L Navigational Warnings in addition to A (Overflow from A)
M-U Reserved
V Fishing Vessels
Y Reserved
Z No messaaes to transmit
These station and subject matter designators are programable into the NAVTEX receiver and allows the operator to choose only the safety messages pertinent to the sailing area and other item of interest. The other designators not programmed in the receiver will be rejected.
A typical SafetyNET MSI broadcast is shown below. Please note the following on the message:
Date and time of the message in UTC .
The identifier of the CES send the message
A unique number identifying the message
The priority of the message
The nature of the message
GMDSS (MARITIME SAFETY INFORMATION MSI)
MARITIME SAFETY INFORMATION (MSI)
Maritime Safety Information (MSI) is a one of the functional requirements of GMDSS ships. The International Maritime Organization and International Hydrographic Organization established the World Wide Navigational Warning Service (WWNWS) and has established 16 NAVAREAs worldwide.
Search and Rescue information will come from the U.S. Coast Guard. And, the National Weather Service will provide weather and Ice monitoring.
As indicated in IMO Master Plan of Shore-Based Facilities (this publications must be carried on board each ship under the GMDSS rules) MSI can be received by three different systems: NAVTEX, SafetyNET and High Frequency NBDP.
As indicated in FCC rules 47 CFR 80.1085 GMDSS compulsory vessel must provide a radio facility for the receipt of MSI. If ship is engaged on voyages in any area of INMARSAT coverage in which International NAVTEX service is NOT established or provided, equipment to receive Enhanced Group Galling (EGG) over the Safety NEPM or HF Radio must be provided. In areas where INMARSAT does not cover then HF NBDP would be the approved method.
The NAVTEX system which is one system of three to obtain MSI. This system is a terrestrial (land radio station)system using Narrow Band Direct Printing (NBDP) with Forward Error Correction (FEC) the same as SITOR. The world wide frequency 518 Khz (0.518 MHZ) and the radio receiving range is about 200 to 400 Nautical Miles offshore.
NAVTEX carries information for all sizes and types of vessels. The English language is used as the world wide language. Frequency 490 Khz is available for a country to use their own language on the broadcasts on this worldwide NAVTEX frequency and is NBDP using mode FEC. The system uses the present NAVAREAs as regions for the transmissions. By MARITIME SAFETY INFORMATION (MSI)
Receipt of Maritime Safety Information (MSI) is a one of the functional requirements of GMDSS ships. The International Maritime Organization and International Hydrographic Organization established the World Wide Navigational Warning Service (WWNWS) and has established 16 NAVAREAs worldwide.
Search and Rescue information will come from the U.S. Coast Guard. And, the National Weather Service will provide weather and Ice monitoring.
As indicated in IMO Master Plan of Shore-Based Facilities (this publications must be carried on board each ship under the GMDSS rules) MSI can be received by three different systems: NAVTEX, SafetyNET and High Frequency NBDP.
As indicated in FCC rules 47 CFR 80.1085 GMDSS compulsory vessel must provide a radio facility for the receipt of MS/. If ship is engaged on voyages in any area of INMARSAT coverage in which International NAVTEX service is NOT established or provided, equipment to receive Enhanced Group Galling (EGG) over the SafetyNEPM or HF Radio must be provided. In areas where INMARSAT does not cover then HF NBDP would be the approved method.
The NAVTEX system which is one system of three to obtain MSI.
This system is a terrestrial (land radio station)system using Narrow Band Direct Printing (NBDP) with Forward Error Correction (FEC) the same as SITOR. The world wide frequency 518 Khz (0.518 MHZ) and the radio receiving range is about 200 to 400 Nautical Miles offshore.
NAVTEX carries information for all sizes and types of vessels. The English language is used as the world wide language. Frequency 490 Khz is available for a country to use their own language on the broadcasts on this worldwide NAVTEX frequency and is NBDP using mode FEC. The system uses the present NAVAREAs as regions for the transmissions. By using geographical separation, minimum transmitter power and sharing of time on these frequencies interference is kept to a minimum.
Maritime Safety Information (MSI) is a one of the functional requirements of GMDSS ships. The International Maritime Organization and International Hydrographic Organization established the World Wide Navigational Warning Service (WWNWS) and has established 16 NAVAREAs worldwide.
Search and Rescue information will come from the U.S. Coast Guard. And, the National Weather Service will provide weather and Ice monitoring.
As indicated in IMO Master Plan of Shore-Based Facilities (this publications must be carried on board each ship under the GMDSS rules) MSI can be received by three different systems: NAVTEX, SafetyNET and High Frequency NBDP.
As indicated in FCC rules 47 CFR 80.1085 GMDSS compulsory vessel must provide a radio facility for the receipt of MSI. If ship is engaged on voyages in any area of INMARSAT coverage in which International NAVTEX service is NOT established or provided, equipment to receive Enhanced Group Galling (EGG) over the Safety NEPM or HF Radio must be provided. In areas where INMARSAT does not cover then HF NBDP would be the approved method.
The NAVTEX system which is one system of three to obtain MSI. This system is a terrestrial (land radio station)system using Narrow Band Direct Printing (NBDP) with Forward Error Correction (FEC) the same as SITOR. The world wide frequency 518 Khz (0.518 MHZ) and the radio receiving range is about 200 to 400 Nautical Miles offshore.
NAVTEX carries information for all sizes and types of vessels. The English language is used as the world wide language. Frequency 490 Khz is available for a country to use their own language on the broadcasts on this worldwide NAVTEX frequency and is NBDP using mode FEC. The system uses the present NAVAREAs as regions for the transmissions. By MARITIME SAFETY INFORMATION (MSI)
Receipt of Maritime Safety Information (MSI) is a one of the functional requirements of GMDSS ships. The International Maritime Organization and International Hydrographic Organization established the World Wide Navigational Warning Service (WWNWS) and has established 16 NAVAREAs worldwide.
Search and Rescue information will come from the U.S. Coast Guard. And, the National Weather Service will provide weather and Ice monitoring.
As indicated in IMO Master Plan of Shore-Based Facilities (this publications must be carried on board each ship under the GMDSS rules) MSI can be received by three different systems: NAVTEX, SafetyNET and High Frequency NBDP.
As indicated in FCC rules 47 CFR 80.1085 GMDSS compulsory vessel must provide a radio facility for the receipt of MS/. If ship is engaged on voyages in any area of INMARSAT coverage in which International NAVTEX service is NOT established or provided, equipment to receive Enhanced Group Galling (EGG) over the SafetyNEPM or HF Radio must be provided. In areas where INMARSAT does not cover then HF NBDP would be the approved method.
The NAVTEX system which is one system of three to obtain MSI.
This system is a terrestrial (land radio station)system using Narrow Band Direct Printing (NBDP) with Forward Error Correction (FEC) the same as SITOR. The world wide frequency 518 Khz (0.518 MHZ) and the radio receiving range is about 200 to 400 Nautical Miles offshore.
NAVTEX carries information for all sizes and types of vessels. The English language is used as the world wide language. Frequency 490 Khz is available for a country to use their own language on the broadcasts on this worldwide NAVTEX frequency and is NBDP using mode FEC. The system uses the present NAVAREAs as regions for the transmissions. By using geographical separation, minimum transmitter power and sharing of time on these frequencies interference is kept to a minimum.
GMDSS (TABLES SEA AREAS)
GENERAL EQUIPMENT REQUIREMENTS FOR ALL GMDSS SHIPS
VHF Radio Installed in the Wheelhouse
DSC Distress Alerts on Channel 70
Voice on channels: 6, 16, and 13
Dedicated DSC VHF Watch Receiver on Channel 70
Search and Rescue Radar Transponder (SART)
NAVTEX Receiver
Satellite 406 MHZ EPIRB
EQUIPMENT REQUIREMENTS FOR SEA AREA A1
All general Equipment requirements, and Capability to initiate transmission of a ship-to-shore distress alert from the position where the ship is normally navigated via:
• VHF using DSC, or MF using DSC (if engaged on voyages with coverage of an MF coast station equipped with DSC), or
• HF using DSC, or
· INMARSAT (if within INMARSAT coverage), or
· Satellite 406 MHZ EPIRB -This requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated.
EQUIPMENT REQUIREMENTS FOR SEA AREA A1 & A2
All General Equipment requirements, and
Capability to initiate transmission of a ship-to-shore distress alert from the position where the ship is normally navigated via:
MF using DSC on 2187.5 khz and 2182 khz Radiotelephone. (A dedicated 2187. 5 khz DSC watch receiver may be separate from or combined with the above MF installation.)
Satellite 406 MHZ EPIRB - this requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated, or
HF radio using DSC, or
INMARSAT (if within INMARSAT coverage).
Ships must be capable of transmitting and receiving general radio communications using radiotelephony or Narrow Band Direct Printing via:
MF radio installation operating on frequencies between 1605 - 4000 Khz, or
HF radio installation operating on frequencies between 4000 - 27,500 Khz, or INMARSAT Ship Earth Station
EQUIPMENT REQUIREMENTS FOR SEA AREA A1& A2 & A3
All General Equipment requirements, and
An MF/HF radio capable of transmitting and receiving on all Distress Frequencies between 1605 Khz - 27500 Khz using DSC, NBDP and Radiotelephone. It must be possible to initiate transmission of Distress alerts from the position where the ship is normally navigated.
Equipment capable of maintaining a DSC watch on 2187.5 Khz, 8414.5 khz and at least one other HF DSC frequency. It must be possible to select any HF DSC frequency at any time. This watch equipment may be part of the above MF/HF radio installation.
An MF/HF radio capable of transmitting and receiving general radio communications using NBDP and radiotelephone on working frequencies between 1605 Khz and 27500 Khz. This equipment may be part of the above MF/HF radio installation.
Means of initiating a Distress alert via Satellite 406 MHZ EPIRB - This requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated, or
An INMARSAT Ship Earth Station
EQUIPMENT REQUIREMENTS FOR SEA AREAS A 1 & A2 & A3 & A4
All General Equipment Requirements, and
An MF/HF radio capable of transmitting and receiving on all distress frequencies between 1605 khz - 27500 Khz using DSC, NBDP and Radiotelephone. It must be possible to initiate transmission of Distress alerts from the position where the ship is normally navigated.
Equipment capable of maintaining a DSC watch on 2187.5 khz, 8414.5 khz and at least one other HF DSC frequency. It must be possible to select any HF DSC frequency at any time. This watch equipment may be part of the above MF/HF radio installation.
An MF/HF radio capable of transmitting and receiving general radio communications using NBDP and radiotelephone on working frequencies between 1605 khz and 27500 Khz. This equipment may be part of the above MF/HF radio installation.
Means of initiating a Distress alert via Satellite 406 MHZ EPIRB -This requirement and the general equipment can be med with a single 406 MHZ EPIRB close to the position where the ship is normally navigated.
VHF Radio Installed in the Wheelhouse
DSC Distress Alerts on Channel 70
Voice on channels: 6, 16, and 13
Dedicated DSC VHF Watch Receiver on Channel 70
Search and Rescue Radar Transponder (SART)
NAVTEX Receiver
Satellite 406 MHZ EPIRB
EQUIPMENT REQUIREMENTS FOR SEA AREA A1
All general Equipment requirements, and Capability to initiate transmission of a ship-to-shore distress alert from the position where the ship is normally navigated via:
• VHF using DSC, or MF using DSC (if engaged on voyages with coverage of an MF coast station equipped with DSC), or
• HF using DSC, or
· INMARSAT (if within INMARSAT coverage), or
· Satellite 406 MHZ EPIRB -This requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated.
EQUIPMENT REQUIREMENTS FOR SEA AREA A1 & A2
All General Equipment requirements, and
Capability to initiate transmission of a ship-to-shore distress alert from the position where the ship is normally navigated via:
MF using DSC on 2187.5 khz and 2182 khz Radiotelephone. (A dedicated 2187. 5 khz DSC watch receiver may be separate from or combined with the above MF installation.)
Satellite 406 MHZ EPIRB - this requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated, or
HF radio using DSC, or
INMARSAT (if within INMARSAT coverage).
Ships must be capable of transmitting and receiving general radio communications using radiotelephony or Narrow Band Direct Printing via:
MF radio installation operating on frequencies between 1605 - 4000 Khz, or
HF radio installation operating on frequencies between 4000 - 27,500 Khz, or INMARSAT Ship Earth Station
EQUIPMENT REQUIREMENTS FOR SEA AREA A1& A2 & A3
All General Equipment requirements, and
An MF/HF radio capable of transmitting and receiving on all Distress Frequencies between 1605 Khz - 27500 Khz using DSC, NBDP and Radiotelephone. It must be possible to initiate transmission of Distress alerts from the position where the ship is normally navigated.
Equipment capable of maintaining a DSC watch on 2187.5 Khz, 8414.5 khz and at least one other HF DSC frequency. It must be possible to select any HF DSC frequency at any time. This watch equipment may be part of the above MF/HF radio installation.
An MF/HF radio capable of transmitting and receiving general radio communications using NBDP and radiotelephone on working frequencies between 1605 Khz and 27500 Khz. This equipment may be part of the above MF/HF radio installation.
Means of initiating a Distress alert via Satellite 406 MHZ EPIRB - This requirement and the general equipment can be met with a single 406 MHZ EPIRB close to the position where the ship is normally navigated, or
An INMARSAT Ship Earth Station
EQUIPMENT REQUIREMENTS FOR SEA AREAS A 1 & A2 & A3 & A4
All General Equipment Requirements, and
An MF/HF radio capable of transmitting and receiving on all distress frequencies between 1605 khz - 27500 Khz using DSC, NBDP and Radiotelephone. It must be possible to initiate transmission of Distress alerts from the position where the ship is normally navigated.
Equipment capable of maintaining a DSC watch on 2187.5 khz, 8414.5 khz and at least one other HF DSC frequency. It must be possible to select any HF DSC frequency at any time. This watch equipment may be part of the above MF/HF radio installation.
An MF/HF radio capable of transmitting and receiving general radio communications using NBDP and radiotelephone on working frequencies between 1605 khz and 27500 Khz. This equipment may be part of the above MF/HF radio installation.
Means of initiating a Distress alert via Satellite 406 MHZ EPIRB -This requirement and the general equipment can be med with a single 406 MHZ EPIRB close to the position where the ship is normally navigated.
GMDSS (EQUIPMENT)
GMDSS EQUIPMENT
Under GMDSS rules and regulations all ships 300 gross tons or over, are required to carry specific communications equipment based upon their Sea Area of Operation. Different equipments and subsystems are used in the GMDSS System to ensure availability in time of need, each subsystem has its own limitations with respect to geographical coverage and services provided. General equipment is required on all GMDSS ships as a basic configuration. Additional equipment is required as a ship travels within the Sea Areas (not NAVAREAS).
All GMDSS equipment (except INMARSA T ship earth stations) must Type Accepted by the Federal Communications Commission. It might be noted that INMARSAT terminals are commissioned by the INMARSAT Organization through an Earth Station after the equipment is installed.
GMDSS equipment is required to conform with the general requirements of CFR 80.1101 (a) and the specific performance requirements in CFR 80.1101 (b).
GMDSS equipment must be specifically authorized for GMDSS use, 'and except for existing 406 Mhz EPIRBs, must have a label affixed to the equipment.
The following tables will indicate the proper equipment to be used in the various Sea Areas (these may be reproduced to have a handy table available):
Under GMDSS rules and regulations all ships 300 gross tons or over, are required to carry specific communications equipment based upon their Sea Area of Operation. Different equipments and subsystems are used in the GMDSS System to ensure availability in time of need, each subsystem has its own limitations with respect to geographical coverage and services provided. General equipment is required on all GMDSS ships as a basic configuration. Additional equipment is required as a ship travels within the Sea Areas (not NAVAREAS).
All GMDSS equipment (except INMARSA T ship earth stations) must Type Accepted by the Federal Communications Commission. It might be noted that INMARSAT terminals are commissioned by the INMARSAT Organization through an Earth Station after the equipment is installed.
GMDSS equipment is required to conform with the general requirements of CFR 80.1101 (a) and the specific performance requirements in CFR 80.1101 (b).
GMDSS equipment must be specifically authorized for GMDSS use, 'and except for existing 406 Mhz EPIRBs, must have a label affixed to the equipment.
The following tables will indicate the proper equipment to be used in the various Sea Areas (these may be reproduced to have a handy table available):
GMDSS (FREQUENCY AND DISTANCE)
Here is a chart estimating the frequency to be used to communicate with another station at a given distance.
4MHZ Good choice for communications up to approximately 200 miles throughout the day. Longer range communications may be possible in late afternoon. Short range communications (up to 200 Miles) should slowly deteriorate but may continue through the night.
6MHZ Good choice for long range communications around midnight. A ship off the coast of New York should easily be able to contact any coastal radio station in the continental US.
8 MHZ This band offers shorter propagation during the day and conditions conducive to long range propagation conditions at night.
12 MHZ Late afternoon and evening hours offer maximum long range communications. Communications between stations less than 100 miles may be possible in the early morning hours.
16 MHZ Late afternoon and evening hours offer maximum long range communications. Communications over "short" distances (500 miles) are possible throughout the day but should gradually deteriorate and become impossible on
this frequency at niqht.
22 MHZ
During period of high solar activity, this band can support worldwide communications with relative low power transmitters.
4MHZ Good choice for communications up to approximately 200 miles throughout the day. Longer range communications may be possible in late afternoon. Short range communications (up to 200 Miles) should slowly deteriorate but may continue through the night.
6MHZ Good choice for long range communications around midnight. A ship off the coast of New York should easily be able to contact any coastal radio station in the continental US.
8 MHZ This band offers shorter propagation during the day and conditions conducive to long range propagation conditions at night.
12 MHZ Late afternoon and evening hours offer maximum long range communications. Communications between stations less than 100 miles may be possible in the early morning hours.
16 MHZ Late afternoon and evening hours offer maximum long range communications. Communications over "short" distances (500 miles) are possible throughout the day but should gradually deteriorate and become impossible on
this frequency at niqht.
22 MHZ
During period of high solar activity, this band can support worldwide communications with relative low power transmitters.
GMDSS (EQUIPMENT)
GMDSS EQUIPMENT
Under GMDSS rules and regulations all ships 300 gross tons or over, are required to carry specific communications equipment based upon their Sea Area of Operation. Different equipments and subsystems are used in the GMDSS System to ensure availability in time of need, each subsystem has its own limitations with respect to geographical coverage and services provided. General equipment is required on all GMDSS ships as a basic configuration. Additional equipment is required as a ship travels within the Sea Areas (not NAVAREAS) .
All GMDSS equipment (except INMARSA T ship earth stations) must Type Accepted by the Federal Communications Commission. It might be noted that INMARSAT terminals are commissioned by the INMARSAT Organization through an Earth Station after the equipment is installed .
GMDSS equipment is required to conform with the general requirements of CFR 80.1101 (a) and the specific performance requirements in CFR 80.1101 (b) .
GMDSS equipment must be specifically authorized forGMDSS use, and except for existing 406 Mhz EPIRBs, must have a label affixed to the equipment.
Under GMDSS rules and regulations all ships 300 gross tons or over, are required to carry specific communications equipment based upon their Sea Area of Operation. Different equipments and subsystems are used in the GMDSS System to ensure availability in time of need, each subsystem has its own limitations with respect to geographical coverage and services provided. General equipment is required on all GMDSS ships as a basic configuration. Additional equipment is required as a ship travels within the Sea Areas (not NAVAREAS) .
All GMDSS equipment (except INMARSA T ship earth stations) must Type Accepted by the Federal Communications Commission. It might be noted that INMARSAT terminals are commissioned by the INMARSAT Organization through an Earth Station after the equipment is installed .
GMDSS equipment is required to conform with the general requirements of CFR 80.1101 (a) and the specific performance requirements in CFR 80.1101 (b) .
GMDSS equipment must be specifically authorized forGMDSS use, and except for existing 406 Mhz EPIRBs, must have a label affixed to the equipment.
GMDSS (RADIO WAVES)
The Radio waves leave the antenna and travel skyward and they will reach the first layer, the D-Layer at low frequencies this layer seems to want to dampen the lower frequencies and these wave cannot reach the other higher layers. The radio waves collide with the free ions in doing so use up some of the energy of the radio wave.
As the radio frequency is increased the wave length become shorter and fewer collisions will take place and the radio wave will continue through this layer and on to the next layers. As the density is lower the higher we go the less ions and less collisions and these layers affect the radio wave in a different manner. It now tends to bend some of the radio wave back toward the earth. The angle that the radio wave is entering the layers is going to affect the angle that the radio wave is "reflected" back to the earth.
During the daylight hours the D-Layer will absorbs most signals that reach the ionosphere. As frequency increases the energy that is absorbs becomes less and signals are passed on through to the other layers. The E-Layer will reflect some of these radio waves and the signal will be reflected at a greater distance from the transmitter.
If the radio signal is increased further in frequency the E-Layer then becomes less of a absorber and the signal then passes on through to the F-Layers and there they are reflected back to earth and those higher frequencies are received at greater distances from the transmitter.
As we increase the frequency of the radio wave, the F-Layers will have less effect on the radio wave and those waves will pass through the FLayers and continue on into space. As in the sketch above we find that the radio wave using the E-Layer will travel about 2000 Km (or about 1300 miles) and the F-Layer to about 4000 Km (or about 2500 miles) The Radio waves also leave the antenna and travel skyward and they will reach the first layer, the D-Layer at low frequencies this layer seem to want to dampen the lower frequencies and thus these wave cannot reach the other higher layers. The radio waves collide with the free ions in doing so use up some of the energy of the radio wave.
As the radio frequency is increased the wave length become shorter and fewer collisions will take place and the radio wave will continue through this layer and on to the next layers. As the density is lower the higher we go the less ions and thus less collisions and these layers affect the radio wave in a different manner. It now tends to bend some of the radio wave back toward the earth. The angle that the radio wave is entering the layers is going to affect the angle that the radio wave is "reflected" back to the earth. These various layers will change as the sun moves overhead and will cause changes in the distance we can communicate. There is no guarantee that the radio waves will behave in the same manner on each day. In order to be sure that we can communicate with some reliability we can consult various document that will predict with some accuracy what will happen to the radio waves at a certain frequency and time of day.
One way we can check on these predictions is to tune to Radio Station WWV which is the product of National Bureau of Standards in Bolder, CO., and WWVH in Hawaii. These stations will transmit the solar terrestrial indices which is the indication of activities of the solar conditions. This station transmits on 2.5, 5.0, 10.0, 15.0,20.0 and 25.0 MHz. They also provide a 'time tick" to accurately set the ships clocks.
The propagation of the radio waves on the Maritime frequencies will vary depending on time of day, season, sunspot activity, etc. In general the higher frequencies are best for mid day communications over a long range, about 800 miles. Lower HF bands are the best choice for nighttime communications over the same range. Medium frequency bands are best for mid day communications over short ranges, 50 miles or so.
The best way to find the 'right' frequency is to listen to the station you want to engage in communications and if you can hear them you should be able to communicate
The antenna serves a dual purpose. It acts as a radiator of RF energy in transmit and efficient collector of weak RF energy in receive mode. To do this efficiently the size or length ofthe antenna is related to the frequency. The physical length is cut or tuned to a specific frequency in the band you will be using. The Federal Communications Commission require that all antennas on Maritime ships be in the Vertical plane. On the VHF frequencies the wave length is about two meters long and we will use a onehalf wave for the actual length of the antenna. This is about 15 or so inches for the VHF channels.
On the HF radio waves the wave length is from 160 meters to 10 meters. It would a real problem to have a vertical antenna 160 meters in length (about 450 feet high). So we use a specific length that we can put on the wheel house and still not have it hit the bridges we pass under. To this shortened vertical antenna we will have to fool the transmitter and coil up some of the length and put it in a box. This box we call an "Antenna Coupler" and this will let us to electrically make the antenna longer or shorter according to the frequency band we want to operate. Most radios have a place in the program to "tune" the transmitter, not really tuning the transmitter but adjusting the Antenna Coupler and thus making the antenna electrically longer or shorter.
As the radio frequency is increased the wave length become shorter and fewer collisions will take place and the radio wave will continue through this layer and on to the next layers. As the density is lower the higher we go the less ions and less collisions and these layers affect the radio wave in a different manner. It now tends to bend some of the radio wave back toward the earth. The angle that the radio wave is entering the layers is going to affect the angle that the radio wave is "reflected" back to the earth.
During the daylight hours the D-Layer will absorbs most signals that reach the ionosphere. As frequency increases the energy that is absorbs becomes less and signals are passed on through to the other layers. The E-Layer will reflect some of these radio waves and the signal will be reflected at a greater distance from the transmitter.
If the radio signal is increased further in frequency the E-Layer then becomes less of a absorber and the signal then passes on through to the F-Layers and there they are reflected back to earth and those higher frequencies are received at greater distances from the transmitter.
As we increase the frequency of the radio wave, the F-Layers will have less effect on the radio wave and those waves will pass through the FLayers and continue on into space. As in the sketch above we find that the radio wave using the E-Layer will travel about 2000 Km (or about 1300 miles) and the F-Layer to about 4000 Km (or about 2500 miles) The Radio waves also leave the antenna and travel skyward and they will reach the first layer, the D-Layer at low frequencies this layer seem to want to dampen the lower frequencies and thus these wave cannot reach the other higher layers. The radio waves collide with the free ions in doing so use up some of the energy of the radio wave.
As the radio frequency is increased the wave length become shorter and fewer collisions will take place and the radio wave will continue through this layer and on to the next layers. As the density is lower the higher we go the less ions and thus less collisions and these layers affect the radio wave in a different manner. It now tends to bend some of the radio wave back toward the earth. The angle that the radio wave is entering the layers is going to affect the angle that the radio wave is "reflected" back to the earth. These various layers will change as the sun moves overhead and will cause changes in the distance we can communicate. There is no guarantee that the radio waves will behave in the same manner on each day. In order to be sure that we can communicate with some reliability we can consult various document that will predict with some accuracy what will happen to the radio waves at a certain frequency and time of day.
One way we can check on these predictions is to tune to Radio Station WWV which is the product of National Bureau of Standards in Bolder, CO., and WWVH in Hawaii. These stations will transmit the solar terrestrial indices which is the indication of activities of the solar conditions. This station transmits on 2.5, 5.0, 10.0, 15.0,20.0 and 25.0 MHz. They also provide a 'time tick" to accurately set the ships clocks.
The propagation of the radio waves on the Maritime frequencies will vary depending on time of day, season, sunspot activity, etc. In general the higher frequencies are best for mid day communications over a long range, about 800 miles. Lower HF bands are the best choice for nighttime communications over the same range. Medium frequency bands are best for mid day communications over short ranges, 50 miles or so.
The best way to find the 'right' frequency is to listen to the station you want to engage in communications and if you can hear them you should be able to communicate
The antenna serves a dual purpose. It acts as a radiator of RF energy in transmit and efficient collector of weak RF energy in receive mode. To do this efficiently the size or length ofthe antenna is related to the frequency. The physical length is cut or tuned to a specific frequency in the band you will be using. The Federal Communications Commission require that all antennas on Maritime ships be in the Vertical plane. On the VHF frequencies the wave length is about two meters long and we will use a onehalf wave for the actual length of the antenna. This is about 15 or so inches for the VHF channels.
On the HF radio waves the wave length is from 160 meters to 10 meters. It would a real problem to have a vertical antenna 160 meters in length (about 450 feet high). So we use a specific length that we can put on the wheel house and still not have it hit the bridges we pass under. To this shortened vertical antenna we will have to fool the transmitter and coil up some of the length and put it in a box. This box we call an "Antenna Coupler" and this will let us to electrically make the antenna longer or shorter according to the frequency band we want to operate. Most radios have a place in the program to "tune" the transmitter, not really tuning the transmitter but adjusting the Antenna Coupler and thus making the antenna electrically longer or shorter.
GMDSS (MF MEDIUM FREQUENCY)
We will be concerned with the frequencies in the MF (medium frequency) bands, especially from 2Mhz to 3 MHz and in the HF (high frequency) bands, 3 MHz to 30 MHz.
The broadcast AM band is in the Low MF band, that is, from 550 Khz to 1500 Khz. And the broadcast FM band is in the VHF band: 88.1 MHz to 107.9 MHz band. Airplanes are in the VHF band around 118.7 MHz AM. Our VHF FM Bridge to bridge radios are in the area of 156.00 MHz FM. EPIRB's are in the UHF band and are on 406 MHz. How about our RADAR units that are on 3 Ghz (giga hertz) or in the SHF band. The INMARSAT Satellite's are in the 1.5 Ghz and 4.5 Ghz bands, SHF. So in using our GMDSS system we are in several different frequency bands.
In these band we experience different Radio Propagations, or that these radio waves act different at different frequencies. So go far and some just got to the horizon and stopped. We call this difference: radio propagation. Once the radio wave leave the antenna this radio wave travels out in space and is radiated in a circular pattern at right angles to the antenna wire. Here we see a vertical antenna, like the ones that we see on the bridge. As this Radio wave travels out and upward into the sky there are some layers of ionized particles, some thick and some thin. The radio wave tends to bounce off these layers of particles and return to earth. There are several layers at different thickness and at different altitudes. We have given these layers names.
The first layer above the earth and at about 90 to 100 miles is called the D-Layer the next is the E-Layer and is about 100 to 130 miles. Above the E-Layer is the F-Layer and at the zenith of the day this layer splits into two layers called the F1-Layer (the lower one) and the F2-Layer. This F1 and F2 layers are about 200 to 300 miles in altitude. These layers vary in altitude during the various time of the day and night. Some go a way at night.
These layers are formed by the solar radiation (mainly by ultra-violet light) and is so intense that when it strikes gas molecules they ionize the gas molecules and set a positive ion free. The free electrons actually affect radio waves. This action takes place in the Ionosphere which is from about 70 to about 500 miles from the surface of the earth. And as the title indicates this area contain these gas molecule and releases the electrons by this action and is thus called IONosphere.
The D-Layer is the lowest from 90 to 100 miles above the earth. It is present during the day when the sun is sending this radiation at its maximum. Because the density ofthe ionosphere is high at this altitude the ions and electrons will recombine quickly and after sunset the solar radiation is blocked by the earth the electrons levels fall quickly and thus this D-layer all but disappears. Just above this O-Iayer is the E-Layer and its about 100 to 150 miles above the earth. At this altitude the ions and electrons recombine quickly and act somewhat like the D-Layer and after sunset this layer also disappears.
The next layers are the F-Layers and these are the ones we use for our long distance communications. As the day starts this layer starts to split into two layers the two layers are at their maximum at the zenith of the sun. At night the two layers, F1 and F2 recombine and become the F layer. In the winter times this F layer and its children F1 and F2 are lower in the ionosphere and will effect the radio waves.
The broadcast AM band is in the Low MF band, that is, from 550 Khz to 1500 Khz. And the broadcast FM band is in the VHF band: 88.1 MHz to 107.9 MHz band. Airplanes are in the VHF band around 118.7 MHz AM. Our VHF FM Bridge to bridge radios are in the area of 156.00 MHz FM. EPIRB's are in the UHF band and are on 406 MHz. How about our RADAR units that are on 3 Ghz (giga hertz) or in the SHF band. The INMARSAT Satellite's are in the 1.5 Ghz and 4.5 Ghz bands, SHF. So in using our GMDSS system we are in several different frequency bands.
In these band we experience different Radio Propagations, or that these radio waves act different at different frequencies. So go far and some just got to the horizon and stopped. We call this difference: radio propagation. Once the radio wave leave the antenna this radio wave travels out in space and is radiated in a circular pattern at right angles to the antenna wire. Here we see a vertical antenna, like the ones that we see on the bridge. As this Radio wave travels out and upward into the sky there are some layers of ionized particles, some thick and some thin. The radio wave tends to bounce off these layers of particles and return to earth. There are several layers at different thickness and at different altitudes. We have given these layers names.
The first layer above the earth and at about 90 to 100 miles is called the D-Layer the next is the E-Layer and is about 100 to 130 miles. Above the E-Layer is the F-Layer and at the zenith of the day this layer splits into two layers called the F1-Layer (the lower one) and the F2-Layer. This F1 and F2 layers are about 200 to 300 miles in altitude. These layers vary in altitude during the various time of the day and night. Some go a way at night.
These layers are formed by the solar radiation (mainly by ultra-violet light) and is so intense that when it strikes gas molecules they ionize the gas molecules and set a positive ion free. The free electrons actually affect radio waves. This action takes place in the Ionosphere which is from about 70 to about 500 miles from the surface of the earth. And as the title indicates this area contain these gas molecule and releases the electrons by this action and is thus called IONosphere.
The D-Layer is the lowest from 90 to 100 miles above the earth. It is present during the day when the sun is sending this radiation at its maximum. Because the density ofthe ionosphere is high at this altitude the ions and electrons will recombine quickly and after sunset the solar radiation is blocked by the earth the electrons levels fall quickly and thus this D-layer all but disappears. Just above this O-Iayer is the E-Layer and its about 100 to 150 miles above the earth. At this altitude the ions and electrons recombine quickly and act somewhat like the D-Layer and after sunset this layer also disappears.
The next layers are the F-Layers and these are the ones we use for our long distance communications. As the day starts this layer starts to split into two layers the two layers are at their maximum at the zenith of the sun. At night the two layers, F1 and F2 recombine and become the F layer. In the winter times this F layer and its children F1 and F2 are lower in the ionosphere and will effect the radio waves.
Subscribe to:
Posts (Atom)