Maritime Safety Information (M.S.I.):
Navtex-1: Operations:
How is mutual interference on 518 kHz among NAVTEX stations avoided?
How is mutual interference on 518 kHz among NAVTEX stations avoided?
(C). Transmissions scheduled on a time-sharing basis, power limited and station assignment codes are geographically separated.
Although, NAVTEX stations are constantly sending information, they do not broadcast at night, since atmosphere layers change and the radio wave propagation increases in scope. So, they transmit at daytime only.
The 518 kHZ frequency is for English only broadcasts. Regional stations are also broadcasting on 490 kHz or even 424 kHz in local languages, other than English.
For great overview of NAVTEX, please see MySea Time site article on 20 Navtex Question (and answers) to Make Naxtex Your Friend For Life
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When do NAVTEX broadcasts typically achieve maximum transmitting range?
When do NAVTEX broadcasts typically achieve maximum transmitting range?
(D). Middle of the night
Medium Frequency (MF) of 518 kHz or 490 kHz can reach up to 200 nautical miles during the day. But, at night it can reach up to 400 nautical miles.
The MF uses ground bounce of radio waves which attenuates energy with every bounce, BUT on salt water, the propagation scope increases dramatically.
For overview of MF, please see Wikipedia's article on Medium frequency
Some of the energy absorbing layers, which limit radio wave propagation, disappear during the night, allowing MF to have a significantly larger broadcast scope.
For more information about the radio wave focused atmospheric layers composition, please see Wikipedia's article on Ionosphere
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What should a GMDSS Radio Operator do if a NAVTEX warning message is received but it contains too many errors to be usable?
What should a GMDSS Radio Operator do if a NAVTEX warning message is received but it contains too many errors to be usable?
(A). Do nothing. Vital NAVTEX messages will be repeated on the next scheduled broadcast.
NAVTEX messages are categorized as vital, important, or routine. When vital message is transmitted, other stations cease transmissions. If other stations do not stop in time, messages can be distorted.
The important messages are send at the subsequent open time slot. And, routine messages are sent during scheduled broadcasts.
For more information, please see gmdsstesters.com article on NAVTEX System
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Which of these cannot happen when a paper model NAVTEX receiver runs out of paper?
Which of these cannot happen when a paper model NAVTEX receiver runs out of paper?
(B). The system will automatically change from receiving MSI by NAVTEX to receiving it by SafetyNETTM so that no messages will be lost.
I believe in the answer is SafetyNET(tm) for trade mark.
As example NAVTEX operations manual with illustrations, please see NAV-7 NAVTEX Receiver User Manual 35-821N Iss1 NAV-7 Orolia
For comprehensive info, please see pdf INTERNATIONAL SafetyNET Services
For Inmarsat info on SafetyNET(tm) pdf booklet, please see International SafetyNET Handbook
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Which of the following is the primary frequency that is used exclusively for NAVTEX broadcasts internationally?
Which of the following is the primary frequency that is used exclusively for NAVTEX broadcasts internationally?
(B). 518 kHz
The 518 kHZ frequency is for English only broadcasts. Regional stations are also broadcasting on 490 kHz or even 424 kHz in local languages, other than English.
For great overview of NAVTEX, please see MySea Time site article on 20 Navtex Question (and answers) to Make Naxtex Your Friend For Life
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What is the transmitting range of most NAVTEX stations?
What is the transmitting range of most NAVTEX stations?
(C). Typically 200-400 nautical miles (360-720 km).
Medium Frequency (MF) of 518 kHz or 490 kHz can reach up to 200 nautical miles during the day. But, at night it can reach up to 400 nautical miles.
The MF uses ground bounce of radio waves which attenuates energy with every bounce, BUT on salt water, the propagation scope increases dramatically.
For overview of MF, please see Wikipedia's article on Medium frequency
Some of the energy absorbing layers, which limit radio wave propagation, disappear during the night, allowing MF to have a significantly larger broadcast scope.
For more information about the radio wave focused atmospheric layers composition, please see Wikipedia's article on Ionosphere
Last edited by markadlerdallas. Register to edit
Tags: none