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Why is my CSA300 not transmitting?


The transponder is rigged with a Comar AST 300 class B antenna splitter and I have an Alarm ID of 01 and states TX malfunction.

The AST 300 indicates when VHF TX is active, but I have not seen any indication of AIS TX per conclusion. I am not transmitting since I am not registering on other vessel’s sets.

The VHF set it is partnered with is a Simrad Shipmate RS8300, stand alone VHF radio.


There are 2 possible reasons why you are not transmitting:

  1. If the MMSI number has not been entered or entered incorrectly this could be the cause of you not transmitting your vessel data. Refer to How do I enter the MMSI number  for  information on how to do this.
  2. IMO regulations state that Class A AIS transceivers must be connected to their own VHF antenna so we would advise against using a VHF antenna splitter as described in your setup.

Resolution: Customer did not have an MMSI number, once obtained and entered correctly he was able to transmit his position to other vessels.

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