Subelement C: Satellite Systems— Topic :
Question 31C3
Element 9 (GMDSS Maintainer)An Inmarsat-C terminal will not “LOG IN” and shows an “Antenna not connected” alarm. What action would you take?
Explanation
An "Antenna not connected" alarm on an Inmarsat-C terminal typically indicates a break or high resistance in the coaxial cable connecting the terminal to the antenna unit. Many satellite terminals provide DC power and control signals up the coax to the LNA/antenna, and also perform a continuity check.
Shorting one end of the coax and measuring resistance from the other end is a direct way to test the cable's integrity. A good cable, when shorted, should show very low resistance (ideally less than one ohm). High resistance indicates a break, damage, or poor connection within the cable, preventing proper signal transmission and potentially DC power delivery, thus triggering the alarm.
Changing satellites (B) will not fix a physical cable connection issue. Replacing the antenna unit (C) is premature without first verifying the cable, which is a common point of failure. The AZ-EL board (D) controls antenna pointing, which is unrelated to a fundamental "Antenna not connected" alarm.
Related Questions
31C1 An Inmarsat-C terminal shows a “No Receive Signal” alarm. There is no voltage on the antenna center pin. What is the most likely cause?31C2 An Inmarsat-C terminal will not “LOG IN”. A test antenna cable with a new ADE attached in view of the satellite allows the terminal to “LOG IN”. What steps would you take?31C4 The antenna goes past the AZ EL of the satellite but does not initialize but you can manually point the antenna at the satellite and acquire signal. What is the most likely problem?31C5 The antenna creeps up and down after initialization. What action would you take?31C6 The antenna tries to initialize then points straight up and stops. What is the most likely problem?