How to choose your AIS post was written to help you decide how to choose an Em-trak AIS. Whether it is time to purchase your first AIS, or you are ready to upgrade and not sure how to select the right AIS to suit your needs, this page is for you.
How to choose your AIS – 2W or 5W?
Firstly, you will want to decide between 2 Watt or 5 Watt AIS. This is the transmission power of the AIS, therefore the higher power AIS will potentially transmit your position and other vessel data further. There is another reason for selecting the higher power AIS. As more vessels install AIS the available bandwidth in the VHF radio spectrum that AIS operates in becomes more congested. Older 2W units may not reliably transmit when congestion becomes too great, therefore meaning you won’t be seen. The current 5W AIS units utilise a more efficient method to transmit which means they are guaranteed a slot to transmit their data in. This ensures that you are always seen. Em-trak 5W AIS units also support “Message 27” which means that satellite based AIS stations can possibly receive your vessel data and make it available to websites like Marine Traffic. This feature can be very useful if you are travelling across oceans or in less populated areas.
Select a 2W AIS if you are budget conscious, however as time goes on the price gap is narrowing.
Models of Em-trak that include 5W output are: B951, B952, B953, B954, B400
Antenna Splitter or not?
This generally comes down to personal preference and boat type. If you have a yacht and your current VHF radio antenna is mounted at the mast top, then utilising an AIS with built in splitter is probably your best solution. As long as the quality of the antenna and cable is of high quality and connections are corrosion free, then this will provide you excellent range. The downsides of using a built-in antenna splitter are that you are reliant on a single VHF antenna for both VHF radio and AIS. There is always some “loss” associated with this, but can be overcome with a quality antenna and cable mounted on the mast top. Secondly, redundancy is reduced by using the built-in splitter. If you have a separate antenna for both VHF radio and AIS you are able to swap between antennas should one fail. Using a dedicated antenna for your AIS allows you to utilise an AIS tuned antenna as well. These antennas are specifically tuned just for the frequencies that AIS uses and are therefore more efficient than standard radio VHF antennas.
Models of Em-trak with built in VHF antenna splitter are: B923, B924, B953, B954
Useful extra features
Now that you have hopefully narrowed down your choice of AIS you can look at extra features which may make your use of AIS more than just being a black box stuck below decks. While all the models mentioned so far include both NMEA0183 and NMEA2000 connections to allow AIS data to be displayed on any compatible chart plotter, we are seeing more and more people who are using Navionics on a tablet or mobile device as their sole navigation source. Em-trak offer models which include built-in Wi-Fi and Bluetooth to allow Navionics to connect directly to the AIS and display surrounding AIS targets as well as provide a more reliable GPS position for the vessel than the tablet provides. Setup of this features is as easy as connecting the tablet to the Wi-Fi hotspot of the Em-trak AIS and inserting a single parameter in the Navionics configuration to start receiving the data. Up to 3 devices can connect at once to the AIS. This does not disable the other communication methods available.
Models of Em-trak with built-in Wi-Fi / Bluetooth are: B922, B924, B952, B954, B400
Manufacturers webpage: https://www.em-trak.com
