AIS transmitter range

[Yealm]

I’ve just moved my AIS from using an aerial on the pushpit to a masthead aerial with VHF splitter (Raymarine 100).

I understand that this significantly improves the range of receiving signals. But will the transmit range also increase- ie does the increased aerial height overrule the reduction in transmit power due to the splitter?

I’d like to feel confident that ships can see me at over 20 nm away.

 

[RichardS]

I’ve just moved my AIS from using an aerial on the pushpit to a masthead aerial with VHF splitter (Raymarine 100).

I understand that this significantly improves the range of receiving signals. But will the transmit range also increase- ie does the increased aerial height overrule the reduction in transmit power due to the splitter?

I’d like to feel confident that ships can see me at over 20 nm away.

As you've fitted an active splitter (with a power connection) it will cause a negligible reduction in signal, and some active splitters actually increase the signal.

The increase in propagation provided by the extra height will be far more than any signal degradation.

Richard

 

[Yealm]

Many thanks

As you've fitted an active splitter (with a power connection) it will cause a negligible reduction in signal, and some active splitters actually increase the signal.

The increase in propagation provided by the extra height will be far more than any signal degradation.

Richard

 

[Yealm]

ps can I test the transmitter by seeing if it’s picked up by the internet eg Marine Traffic? Or is that not reliable for displaying TypeB ?And if it is reliable, how many minutes does it take to appear?

 

[johnalison]

ps can I test the transmitter by seeing if it’s picked up by the internet eg Marine Traffic? Or is that not reliable for displaying TypeB ?And if it is reliable, how many minutes does it take to appear?

I think it would be hard to extrapolate from shore aerials to ships'. My family have tracked me, with a splitter, from Lowestoft to Ijmuiden on the internet, though sometimes with a gap in the middle. I feel that if I can pick up ships from around 40 miles, which is usual, then my transmissions should be good for a fair proportion of that.

 

[lpdsn]

I’d like to feel confident that ships can see me at over 20 nm away.

I wouldn't depend upon that, but then again I don't think you have to as ships seem to make ColRegs decisions closer in. I can generally pick up large vessels at just over 20 nm. Large ferries are the best and I can get close to 30nm. Fishing vessels other yachts small coaster are less. Hills and islands have a big effect. That's with a masthead aerial. 19.7m air draught (without the aerial). Shore stations may well be able to detect you further away.

 

[Prasutigus]

Hi Yealm, may I politely enquire why you want ships to 'see' you from 20 miles away?

 

[EdWingfield]

I’d like to feel confident that ships can see me at over 20 nm away.

Ships don't look further than 20M. Why should they?

 

[LadyInBed]

My AIS antenna is at the top of my mizzen, when I tested the AIS crossing Biscay saw that I can pick up ships at 50nM. I very seldom range out the chart plotter to more than about 10nM except when plotting a goto so as long as others can see me from my horizon I don't care about anything that has fallen off the edge of the world!

 

[GHA]

Hi Yealm, may I politely enquire why you want ships to 'see' you from 20 miles away?

Well offshore I've been told they get my steel boat on radar close to 20 miles away, and seem happy about it. Any ship maneuvers to give me more sea room is usually done before the ship appears over the horizon. Nothing wrong with trying the get the best signal going out as possible, not every vessel will have a good receiving setup.

 

[Yealm]

The further the better - giving a good comfort zone - I assume range will be less in certain conditions.

Hi Yealm, may I politely enquire why you want ships to 'see' you from 20 miles away?

 

[mikegunn]

AIS class B transmissions, which most of us yachties who have transponders will be using, are at a max power of 2 Watts. This, in ideal conditions will have a range of 5 to 6 miles. Class A transmissions put out by commercial and large boats are at 12.5 Watts. This should and generally does give a significantly greater range. So generally we will see the big-uns before they will see us. But as Bill Gates might have said, were he a sailor, 5-6 miles should be enough for anyone.

 

[EdWingfield]

The further the better - giving a good comfort zone - I assume range will be less in certain conditions.

Chill out baby. We are supposed to be de-stressing at our ages.

 

[dom]

AIS class B transmissions, which most of us yachties who have transponders will be using, are at a max power of 2 Watts. This, in ideal conditions will have a range of 5 to 6 miles.

How do you get to 5-6 miles and are you taking into account the format of an AIS transmission? I think you’ll find it is in practice a much longer distance than that from a masthead antenna to a ship.

 

[GHA]

How do you get to 5-6 miles and are you taking into account the format of an AIS transmission? I think you’ll find it is in practice a much longer distance than that from a masthead antenna to a ship.

Several hundred km if you count the class B signals which get picked up by the satellites

 

[lpdsn]

Several hundred km if you count the class B signals which get picked up by the satellites

That's good. Wouldn't want to be hit by a satellite so glad they have plenty of time to avoid us.

 

[GHA]

That's good. Wouldn't want to be hit by a satellite so glad they have plenty of time to avoid us.

 

[doug748]

ps can I test the transmitter by seeing if it’s picked up by the internet eg Marine Traffic? Or is that not reliable for displaying TypeB ?And if it is reliable, how many minutes does it take to appear?

Hi, You have probably found out by now but, yes, Marine Traffic will pick up your B signal. It will also keep hold of it even when switched off so you can put it up for 15 minutes and go home to find it still find it logged 24 hours later.

 

[Salty John]

AIS (VHF) transmitter range is a combination of your VHF horizon and the VHF horizon of the other station.
Your VHF horizon is 1.4 x root of antenna height above sea level in feet. Answer is in nautical miles. Eg: 49' antenna height, 1.4 x 7(root of height) = 9.8 nm. Add that to the horizon of the other station or vessel and you have range. To an identical vessel range would be 19.6 nm. To a big ship with antennas very high above sea level range would be more; to smaller, low down, vessels it would be less.
This assumes good antenna, connections and cable size and type.

 

[Yealm]

That’s great- thnaks!

AIS (VHF) transmitter range is a combination of your VHF horizon and the VHF horizon of the other station.
Your VHF horizon is 1.4 x root of antenna height above sea level in feet. Answer is in nautical miles. Eg: 49' antenna height, 1.4 x 7(root of height) = 9.8 nm. Add that to the horizon of the other station or vessel and you have range. To an identical vessel range would be 19.6 nm. To a big ship with antennas very high above sea level range would be more; to smaller, low down, vessels it would be less.
This assumes good antenna, connections and cable size and type.