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27-09-2018, 13:32
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#1
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Registered User
Join Date: Jun 2014
Posts: 9
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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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27-09-2018, 13:53
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#2
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Registered User
Join Date: Jun 2013
Location: canada
Posts: 4,642
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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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27-09-2018, 15:05
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#3
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Moderator Emeritus
Join Date: Sep 2006
Posts: 4,663
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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.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
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28-09-2018, 12:31
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#4
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Registered User
Join Date: Jul 2012
Location: New Bern, NC
Boat: Shannon 43 Ketch
Posts: 246
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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
__________________
Smooth sailing and fresh warm breezes,
Tony & Lisa
sv Marite
'87 Shannon 43' Ketch
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28-09-2018, 12:53
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#5
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Moderator Emeritus
Join Date: Sep 2006
Posts: 4,663
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Re: Intermittent AIS signal
Quote:
Originally Posted by svMarite
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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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.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
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28-09-2018, 17:39
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#6
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,420
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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.
b.
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02-10-2018, 03:59
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#7
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Registered User
Join Date: Mar 2014
Location: Sydney, Australia
Boat: Lightwave 38' Catamaran - now sold
Posts: 557
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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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02-10-2018, 15:06
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#8
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Registered User
Join Date: Jul 2011
Location: UMR mm 283 /winter in Kansas
Boat: Bayliner 3870 41' oal.
Posts: 945
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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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02-10-2018, 17:25
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#9
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,155
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Re: Intermittent AIS signal
Quote:
Originally Posted by River Cruiser
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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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.
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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02-10-2018, 22:41
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#10
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Moderator Emeritus
Join Date: Sep 2006
Posts: 4,663
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Re: Intermittent AIS signal
Quote:
Originally Posted by Jim Cate
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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- 0-2 kts: every 3 minutes
- Greater than 2 kts: every 30 seconds
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
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04-10-2018, 14:53
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#11
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Registered User
Join Date: Jul 2011
Location: UMR mm 283 /winter in Kansas
Boat: Bayliner 3870 41' oal.
Posts: 945
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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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05-10-2018, 23:36
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#12
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Registered User
Join Date: Sep 2018
Location: Washington State
Boat: Steamboat, 25 ft
Posts: 89
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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?
__________________
"Science, my lad, is made up of mistakes, but they are mistakes which
it is useful to make, because they lead little by little to the truth" - Jules Verne
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06-10-2018, 03:09
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#13
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,155
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Re: Intermittent AIS signal
Quote:
Originally Posted by Sir_Crabs_A_Lot
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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typical low gain sailboat antennae are not subject to this effect. There must be another source.
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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