DLP-MT-LPCOM9-VHF Test call
In this learning path you will learn about Very High Frequency (VHF). Test call will be carried out
What does VHF radio stand for?
How does VHF radio work?
VHF radio is widely used for short-range communication between ships, coast stations, and aircraft. It is also the primary means of distress, urgency, and safety calls in the GMDSS. VHF radio has several advantages, such as high clarity, low interference, low power consumption, and easy installation
Marine VHF radio explanation
Marine radio was the first commercial application of radio technology, allowing ships to keep in touch with shore and other ships, and send out a distress call for rescue in case of emergency. Guglielmo Marconi invented radio communication in the 1890s, and the Marconi Company installed wireless telegraphy stations on ships beginning around 1900. Marconi built a string of shore stations and in 1904 established the first Morse code distress call, the letters CQD, used until 1906 when SOS was agreed on. The first significant marine rescue due to radio was the 1909 sinking of the luxury liner RMS Republic, in which 1,500 lives were saved. This and the 1912 RMS Titanic rescue brought the field of marine radio to public consciousness and marine radio operators were regarded as heroes
The first marine radio transmitters used the longwave bands. During World War I amplitude modulation was developed, and in the 1920s spark radiotelegraphy equipment was replaced by vacuum tube radiotelephony allowing voice communication. Also in the 1920s, the ionospheric skip or sky wave phenomenon was discovered, which allowed lower power vacuum tube transmitters operating in the shortwave bands to communicate at long distances.
Types of equipment
Sets can be fixed or portable. A fixed set generally has the advantages of a more reliable power source; higher transmit power, a larger and more effective antenna and a bigger display and buttons. A portable set (often essentially a waterproof, VHF walkie-talkie in design) can be carried on a kayak, or to a lifeboat in an emergency, has its own power source and is waterproof if GMDSS-approved. A few portable VHFs are even approved to be used as emergency radios in environments requiring intrinsically safe equipment (e.g. gas tankers, oil rigs, etc.).
Voice-only
Voice only equipment is the traditional type, which relies totally on the human voice for calling and communicating. Many lower priced handheld units are voice only as well as older fixed units.
Digital selective calling
DSC equipment, a part of the Global Maritime Distress Safety System (GMDSS), provides all the functionality of voice-only equipment and, additionally, allows several other features:
The ability to call another vessel using a unique identifier known as a Maritime Mobile Service Identity (MMSI). This information is carried digitally and the receiving set will alert the operator of an incoming call once its own MMSI is detected. Calls are set up on the dedicated VHF channel 70 which DSC equipment must listen on continuously. The actual voice communication then takes place on a different channel specified by the caller.
A distress button, which automatically sends a digital distress signal identifying the calling vessel and the nature of the emergency
A built in GPS receiver or facility to connect an external GPS receiver so that the user’s location may be transmitted automatically along with a distress call.
When a DSC radio is bought new the user will get the opportunity to program it with the MMSI number of the ship it is intended to be used on. However to change the MMSI after the initial programming can be problematic and require special proprietary tools. This is allegedly done to prevent theft.
Watch this video in real VHF test call on board ORTZE EA2421 equipment
Performing a VHF marine radio check
All fixed marine radios since 1999 have DSC capability. Since 2011 these radios must also have a DSC test call capability. Marine radios transmitting and successfully receiving a response from a DSC test call can be expected to operate acceptably in the voice mode as well.
They detail the procedure:
To perform a DSC Test Call, enter the MRCC coast station group identity “002249999” or other vessel, ORTZE “224496000” into the radio’s DSC station memory. Once entered and stored, a DSC test call can be made by executing the following three steps:
- Select “Test Call” from the radio’s DSC menu,
- Select the USCG number entered into memory, and
- Transmit the call.
The radio display should indicate when that test call is acknowledged and display the acknowledging station’s nine-digit identity. That identity may be different than the group identity previously entered into memory. The DSC call was to the group of all Rescue 21 stations, only a local individual station will answer and that MMSI will be displayed.
The MRCC specifically recommends against using channel 16 for VHF checks CH# 16 is for emergency traffic. VHF CH# 9 may be used for radio checks but is discouraged in favour of using automatic DSC test calls for radio checks.
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