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Old 27-09-2018, 13:32   #1
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Intermittent AIS signal

We have a 10 year old Raymarine AIS 500. Other boaters have reported to us that we are visible on their chartplotter only intermittently, that is, it on for a minute, then off, over and over (not sure of exactly timing though). We have checked it out while docked and not seen this behavior. Somebody told us that this it normal, due to congestion on the radio band used by AIS. Does this sound normal to anyone here? We have checked all the antenna connections to the AIS and everything seems solid.
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Old 27-09-2018, 13:53   #2
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Re: Intermittent AIS signal

Possible bad antenna And the unit is shutting off for high vswr.

Also it could be losing gps signal. Then it won't transmit. It will still receive.

Or the unit is just failing.

If yiu are close to the other boats you should be seen. Generally if they cut boats it will be the furthest ones away. Some cut off at 100 targets. It's pretty normal to see 100-150 targets in my area. But the ones 30-40 miles away will get cut if the screen has a limit.



You need the computer software to plug into pc to see what's going on.
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Old 27-09-2018, 15:05   #3
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Re: Intermittent AIS signal

Where are you located? Class-B AIS essentially uses timeslots that are left over after all the Class-A transponders transmit. So it's possible that you are being shut out by a lot of Class-A traffic. But this is pretty rare, and if other nearby Class-B transponders aren't showing the same behavior smac999 (above) is probably correct.
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Old 28-09-2018, 12:31   #4
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Re: Intermittent AIS signal

What jumped out at me was the comment "10 yrs", check connections for corrosion, especially clean antenna connectors as carbon has probably built up, a pencil eraser works well.
Next is the CG just published a study of LED interference, check that too
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Old 28-09-2018, 12:53   #5
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Re: Intermittent AIS signal

Quote:
Originally Posted by svMarite View Post
What jumped out at me was the comment "10 yrs", check connections for corrosion, especially clean antenna connectors as carbon has probably built up, a pencil eraser works well.
Next is the CG just published a study of LED interference, check that too
LED interference will affect reception, but not transmission of AIS (or any radio signal.)

Here's that USCG report: https://www.dco.uscg.mil/Portals/9/D...-16-091109-630

Good info, but it's what we've been saying here for years.
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Old 28-09-2018, 17:39   #6
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Re: Intermittent AIS signal

If it was OK before but is not any more then a bad cable / connector or antenna may be the fault. Check one item at a time and test.


It is very easy to rig another antenna with a new piece of cable and new connectors and test this by just running the cable out of the hatch and onto the rail.


Let us know how it goes.


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Old 02-10-2018, 03:59   #7
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Re: Intermittent AIS signal

I have seen this with other boats, disappearing, then appearing, over and over again all day as we sail near each other. No idea what AIS they have, but it certainly was not caused by congestion.
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Old 02-10-2018, 15:06   #8
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Re: Intermittent AIS signal

My class B will transmit once every 2 minutes while cruising, normal speed is 6 to 7 mph. I have 2 mfd on the flybridge one is connected to my SH GX2150 vhf, that one picks up the transmission and the icon moves to the boat position icon. Then as I move the AIS icon remains stationary until the next transmission and it jumps ahead.
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Old 02-10-2018, 17:25   #9
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Re: Intermittent AIS signal

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My class B will transmit once every 2 minutes while cruising, normal speed is 6 to 7 mph. I have 2 mfd on the flybridge one is connected to my SH GX2150 vhf, that one picks up the transmission and the icon moves to the boat position icon. Then as I move the AIS icon remains stationary until the next transmission and it jumps ahead.
I believe that at such speeds a class B should transmit every 30 seconds. Mine (Vesper Vision) does, and so do all the others I see on my display.

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Old 02-10-2018, 22:41   #10
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Re: Intermittent AIS signal

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I believe that at such speeds a class B should transmit every 30 seconds. Mine (Vesper Vision) does, and so do all the others I see on my display.
  • 0-2 kts: every 3 minutes
  • Greater than 2 kts: every 30 seconds
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Old 04-10-2018, 14:53   #11
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Re: Intermittent AIS signal

I probably go slow enough at times to be in the 3 minute group puting along against the current
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Old 05-10-2018, 23:36   #12
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Re: Intermittent AIS signal

The signal from a VHF antenna spreads out horizontally, so on a sailboat that's heeled, one side will shoot up in the air and the opposite side into the water. This might be why it drops out intermittently, but is ok at the dock?
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Old 06-10-2018, 03:09   #13
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Re: Intermittent AIS signal

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Originally Posted by Sir_Crabs_A_Lot View Post
The signal from a VHF antenna spreads out horizontally, so on a sailboat that's heeled, one side will shoot up in the air and the opposite side into the water. This might be why it drops out intermittently, but is ok at the dock?
typical low gain sailboat antennae are not subject to this effect. There must be another source.

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