AIS through satellites.

[Orion Jim]

I have not found a splitter to be an issue after two years of use, coastal and at sea, with my Garmin class B AIS.

[GILow]

Originally Posted by Orion Jim

I have not found a splitter to be an issue after two years of use, coastal and at sea, with my Garmin class B AIS.

Plenty of people have no problems with them at all, but a significant number have sudden and unexpected failures or random problems. I’ll give them a miss.

[Nicholson58]

It seems that there be some misconceptions here. Unless there has been a radical change since we bought our Watchmate 850.

Satellites do not “see you”. Your AIS sees the satellite by way of its GPS receiver.

Your AIS transmits it’s position by VHS frequency to any Receiver in range. Class B is about five watts. Think of this as equivalent to a hand held VHS, about five miles. Some very good receivers and shore stations may get this signal farther away. If your AIS is well offshore Or away from a repeater then you have disappeared from view. It may be that shore stations do not find you instantly when you return to range, however, shipboard receivers see you in accordance with their update rate and your transmit rate.

Class A AIS transmitters are much more powerful and can be detected farther away.

Our dedicated AIS antenna is 80 feet up. We detect class B At 3-8 miles. We have detected class A at 80 miles. If your class B is on the low end of power or your antenna is compromised then you may not be seen.

[SVHarmonie]

Originally Posted by Nicholson58

It seems that there be some misconceptions here. Unless there has been a radical change since we bought our Watchmate 850.

Satellites do not “see you”. Your AIS sees the satellite by way of its GPS receiver.

Your AIS transmits it’s position by VHS frequency to any Receiver in range. Class B is about five watts. Think of this as equivalent to a hand held VHS, about five miles. Some very good receivers and shore stations may get this signal farther away. If your AIS is well offshore Or away from a repeater then you have disappeared from view. It may be that shore stations do not find you instantly when you return to range, however, shipboard receivers see you in accordance with their update rate and your transmit rate.

Class A AIS transmitters are much more powerful and can be detected farther away.

Our dedicated AIS antenna is 80 feet up. We detect class B At 3-8 miles. We have detected class A at 80 miles. If your class B is on the low end of power or your antenna is compromised then you may not be seen.

Sorry... wrong... All you have to do is look at Marinetraffic.com, and you’ll know that AIS broadcasts are pick up by satellite.

There most certainly are satellites that can pick up AIS signals from space. There are several commercial services that sell the resulting data to ship owners. Like this one: https://insights.spire.com/maritime-...api-from-space

AIS signals are line of sight, and satellites most certainly are in your line of sight, and not all that far away. Class A transmitters are easy for the “eyes in the sky”, Class b with lower power transmitters, a bit more difficult.

Oh, Class A transmitters ar 12.5 W and Class B are 2W

[seandepagnier]

if you are using a vhf dipole how can it aim at satellites overhead?

Maybe a dual helix antenna like for weather satellite will work?

[sailjumanji]

Why do you care whether satellites or a website are tracking your location? The primary purpose of AIS is collision avoidance, but it also makes communication with ships and other AIS-equipped boats much easier as you can identify them by name without binoculars, and they can see you, and communications are usually more efficient (think passing protocols, etc.) Whether you show up on a website is less important than showing up on nearby ship's chartplotter.

Also, AIS is line of sight, just like VHF. Are you serious about "putting the antenna on its side?" I hope not. If you want to be seen better, put the antenna higher up. For best performance, use the VHF antenna at the top of the mast and a powered splitter. Vesper makes a very good one - and SP-160 - that I used on my last boat and this one as well. Not all splitters are created equal, but this one has good specs and a track record of performance.

[SVHarmonie]

Originally Posted by boat_alexandra

if you are using a vhf dipole how can it aim at satellites overhead?

Maybe a dual helix antenna like for weather satellite will work?

Nobody uses a dual helix antenna for AIS, yet satellites see every Class A and many Class B transmitters. Those are facts.

Maybe the error in your assumption is that satellites are not always directly overhead????

[El Pinguino]

Everything seems to be working fine...

[sailjumanji]

Originally Posted by El Pinguino

Everything seems to be working fine...

That says position received 18 hrs ago.

[tek-noid]

Lots of interesting data re S-AIS vs T-AIS here https://storymaps.arcgis.com/stories...79f8d857b317f6

[El Pinguino]

Originally Posted by tek-noid

Lots of interesting data re S-AIS vs T-AIS here https://storymaps.arcgis.com/stories...79f8d857b317f6

An interesting link...
This can be found in the references at the end of it https://help.marinetraffic.com/hc/en...MarineTraffic-

and in that link we find this...
'Signals from vessels that sail in remote areas can only be covered using Satellite AIS. The positional updates provided by this service may vary from a few minutes up to several hours (regardless of how often the subject vessel transmits positions). On average, we get one position update per hour for ocean-going vessels equipped with a Class-A AIS transponder.'

[Jubilee39]

4. Although never designed for the purpose, VHF signals can also be detected by satellites.
This enables AIS signals to be detected mid ocean hundreds of miles from any land based receiver.
The drawback: Due to the nature of satellite orbits and their trajectories, satellite AIS receivers
cannot pick up AIS messages as frequently as terrestrial receivers which are in a fixed position.
Also, VHF signals received by satellite do not use time slots, meaning that satellite detected AIS
data provides valuable but less granular vessel position records than land based receivers.

This is from marine intelligence website

[El Pinguino]

Originally Posted by sailjumanji

That says position received 18 hrs ago.

Oh no it doesn't....

This - below - is just out of the ether....

[sailjumanji]

Originally Posted by El Pinguino

Oh no it doesn't....

This - below - is just out of the ether....

Well, go back and look as the original one you posted said last update was 18 hours ago. Now you got an update. Great. Wait 18 more hours and maybe you will have another. That's why I don't get excited about satellite AIS. What good is it? In 18 hours, I will have sailed 120-150 nm.

[GILow]

Originally Posted by El Pinguino

Oh no it doesn't....



This - below - is just out of the ether....

It took its sweet time, but yep, there we are. Thanks for finding that, I was too scared to look this morning.