Propagation distance of AIS.

[srm]

Its all very interesting receiving AIS from x00 miles away. However, the bottom line is how far away is our TX being consistently received so that potential threats are aware of our existence. It seems that information is a bit harder to come by.
Possibly "belts and braces" but I also have a dual band radar transponder/target enhancer mounted at my mast top.

 

[MathiasW]

Most of the things that affect tx in a negative or positive way apply equally to rx. The physics is such that there is a lot of symmetry between sending and receiving. Hence, when you receive well, in all likelihood, you will also transmit well.

 

[srm]

Hence, when you receive well, in all likelihood, you will also transmit well.

I think AIS Class A TX at 12.5 W, while Class B max TX is 2.0 W, so the symmetry argument tends to fall down there. (Though I seem to remember have heard of radio amateurs successfully reflecting very low power VHF signals off the moon).
However, as a youngster (and even more foolish than now) I discovered that our old TV set would get a good picture if I put my finger in the antenna socket which suggests that the RX antenna is not as critical as the TX.

 

[MathiasW]

I think AIS Class A TX at 12.5 W, while Class B max TX is 2.0 W, so the symmetry argument tends to fall down there. (Though I seem to remember have heard of radio amateurs successfully reflecting very low power VHF signals off the moon).
However, as a youngster (and even more foolish than now) I discovered that our old TV set would get a good picture if I put my finger in the antenna socket which suggests that the RX antenna is not as critical as the TX.

Not really. Sure, their signal will reach farther than mine, but I can still gauge my system with other class B devices and when I see those in 20 nm distance, I can with confidence assume a class A device will see me as well in that distance, if not father because of the higher position of their antenna. And no, I do not think that the class A devise will see me in 600 nm, even though I can see it.

So, the trick is to use other class B vessels and the symmetry argument to get an idea of one's own range.

I would be more worried that class A devices have the capability of disregarding all class B devices and not have them appear on the screen at all...