Thread: AIS Questions
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Old 04-12-2021, 04:30 PM
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Join Date: Aug 2012
Location: Brigantine, NJ
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Originally Posted by abbor View Post
I recommend a standalone AIS transponder. AIS transponders integrated in VHF's are CSTDMA, standalone transponders are available both as CSTDMA and SOTDMA. SOTDMA is the same transmission scheme as used in AIS Class A. SOTDMA Class B has 5W transmit power, is transmitting every 5s and has guaranteed slots in congested areas. CSTDMA has 2W transmit power, transmits every 30s and don't have guaranteed slots, it's just checking if the air is not used by other AIS transponders before transmitting.

The differences between CSTDMA and SOTDMA are explained here:

While it's a little more expensive, I plan on adding a Cortex SOTDMA combo VHF/AIS transponder on my new to me 43' Sport Fish. I had the Vesper XB8000 on my last boat and was very impressed with it, but wanted the higher transmit power in SOTDMA. I need to add another VHF anyway (for redundancy) and the boat already has a 2nd, unused antenna.