Using to test if you are transmitting

We get this question often.... How do I know that I am transmitting my signal? I don't see myself on or other websites


Each Vesper Marine transponder has the ability to tell you if it is transmitting. On a WatchMate 850 and WatchMate Vision, look for the warning symbol (triangle with exclamation point). On the 850 it appears in the lower left corner of the main screen. On Vision it is in the header bar on the left. If this symbol is NOT present then your transponder is transmitting. For an XB-8000, look for the green LED. If the green LED is showing solid, then it is transmitting.

Now, you know the the transponder is transmitting.... but how do you know that your antenna system is doing it's job? All three transponders have a VSWR meter and this is a good indicator. On the 850 and Vision it's on the screen in the AIS Status page. For the XB-8000 and Vision you can also see this on our iPhone app. And finally, for all three transponders you can see if on the Status page of the vmAIS PC & Mac application.

The VSWR meter isn't a calibrated instrument, but it's pretty good as an indicator of antenna system quality. If the meter shows a low VSWR then that means your antenna system is doing it's job and radiating your signal. If the VSWR is in the mid-high region then antenna system probably could stand some improvement. If the meter is in the red zone (or far to the right on the 850) then your antenna system is not doing it's job and needs attention.

The most common antenna system problems are:

1. Connectors - these are notoriously difficult to put on. Check for shorts or opens.

2. Cables - make sure all cables are proper 50 ohm shielded antenna cable.

3. Antenna - some VHF antennas do not have enough bandwidth to cover 162 MHz (where AIS lives). When possible, choose an AIS-tuned antenna.

4. Antenna & cables - these can get water into them and they will fail. If they are old or of unknown origin, then suspect them.


Ok, so what about

Sites like, shipfinder and others work by crowd-sourcing AIS data. People install AIS receivers and forward the received data to the internet. There are lots of gaps in the coverage and the quality of AIS receivers and their locations varies tremendously. Many are only single channel receivers and some aren't even near the water.

Also, these systems depend on the internet and a full time connection being available at all times to the receive stations.

As a result, there are limitations to what these systems can do. They are a useful check for sure. But they are not a definitive or reliable indicator of transmission capability.

If you don't see yourself, check to see if other boats near you are being seen? Check how long ago their position reports were made? When you are stationary, your transponder will send a position every 3 minutes. If the receiver is a single channel model, it will take up to 6 minutes for it to receive your signal.


What's the best way to know it's transmitting?

Do the antenna system checks above and if all that looks good then do what radio operators have always done.... call for a radio check.... call a friend on a nearby boat or a passing ship and ask them. But keep in mind the expected range and also the interval that your transponder will be transmitting (every 3 minutes when you are stationary).


They see me but don't see my boat name

AIS information is transmitted in multiple messages. Your position is sent frequently (every 30 seconds when moving and every 3 minutes when stationary), but your boat name, size, callsign, etc. is only sent once every 6 minutes. All Vesper Marine AIS receivers and transponders are two channel. But if the other boat or shore station receiver is a single channel model, then it can take up to 12 minutes for it to receive your details.


Are there any other ways to confirm?

Have a look at the AIS Status page (Advanced on Vision). You'll see TX counts for each channel. These will increase every time your transponder transmits and you can see it happening on the schedule above. It will alternate channels between transmissions and you'll see this too. Finally, your vessel details takes two messages to send, so you'll see it jump by two every 6 minutes and that's a confirmation that your boat's details have just been transmitted.



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