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Old 24-04-2018, 14:39   #1
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Weak AIS Signal?

About 15 boats left Coffs today, many with AIS. I see them on my screen and on Marine Traffic. But why doesnít Marine Traffic see me? And in the past when Iíve asked other boats they say my signal comes and goes.

Iíve noticed it usually only picks me up when pulling into a major port but other boats are more readily seen in the Marine traffic system with more recent updates. I have the XB-8000 on a 45í mast. Am I just not as tall as the others? Iím usually the smallest boat...

Any thoughts/tests would be nice.

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Thanks,
austin

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Old 24-04-2018, 15:03   #2
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Re: Weak AIS Signal?

Where is your boat located? Are you using an antenna splitter (and what kind)? What kind of coax are you using between the antenna and your transponder / splitter? What kind of antenna? How far off can you usually see Class-A equipped vessels?
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Old 24-04-2018, 15:09   #3
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Re: Weak AIS Signal?

IME most likely cause is a poor connection between the AIS and antenna. Could be a poor connector installation, corrosion, a cut in the cable when it got installed in the mast....

Have you looked at the SWR on the status page in the app? That may show an antenna problem. It's not definitive, but if it doesn't show something very close to 1:1 then there's definitely a problem. However, SWR won't pick up things that just attenuate power (corrosion, etc.).

Since it is just a VHF whip, you can borrow one and put it up just on deck with an inexpensive pre-made cable. If switching cable and antenna helps then you know the problem lies there.
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Old 24-04-2018, 15:14   #4
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Re: Weak AIS Signal?

Quote:
Originally Posted by Paul Elliott View Post
Where is your boat located? Are you using an antenna splitter (and what kind)? What kind of coax are you using between the antenna and your transponder / splitter? What kind of antenna? How far off can you usually see Class-A equipped vessels?

Thanks for the questions...

1: Leaving Coffs, was in the middle of that group shown in first image.

2: Yes, Vesper Marine, Same as the AIS unit

3: Not sure, how would I know, what kinds of coax are there? Itís what was in the boat for VHF originally.

4: I think itís just a aluminum pointed rod, about 3ft tall Maybe, itís atop the mast.

5: Good question... itís been a while, but a good distance 5-10nm (I can look back at some of my logs) But this distance has seem to become shorter and maybe less reliable.

Could something just be loose or bad connection? Or is it an all or nothing thing?

My setup looks like this...
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Old 24-04-2018, 15:32   #5
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Re: Weak AIS Signal?

Since you are using your same antenna as your main VHF, the next question has to be, How is your VHF transmission range?

With a 45 foot height, you ought to be out 20-30 miles.

If the best you can do on seeing a Class A vessel is 10 miles, something is definitely wrong. With a 30 foot height, I get 25 to 50 miles range of detection on a Class A.
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Old 24-04-2018, 15:40   #6
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Weak AIS Signal?

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Originally Posted by billknny View Post
Since you are using your same antenna as your main VHF, the next question has to be, How is your VHF transmission range?



With a 45 foot height, you ought to be out 20-30 miles.


I just checked with Coffs Harbour, currently 15NM to the south and he said heís reading me 4/5
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Old 24-04-2018, 15:42   #7
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Re: Weak AIS Signal?

If you look at the corrosion on the antenna connector in your photo, and then imagine it 10 times worse up the mast out in the elements...

Could also be the connection of the antenna to its own coupler. How old is the antenna? How good/old is any waterproofing applied over the connector at the masthead?
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Old 24-04-2018, 15:46   #8
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Re: Weak AIS Signal?

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Originally Posted by theway View Post
My setup looks like this...
Attachment 168669
That white coax jumper between the transponder and the splitter looks pretty funky. The insulation has pulled out of the metal sleeve. This may not indicate a problem, but it is possible that the shield connection has corroded or pulled free. The SWR test that Dsanduril mentioned should tell you if this is the case. In any case, I would replace that cable, using fresh connectors.
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Old 24-04-2018, 15:47   #9
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Re: Weak AIS Signal?

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Originally Posted by Dsanduril View Post
If you look at the corrosion on the antenna connector in your photo, and then imagine it 10 times worse up the mast out in the elements...

Could also be the connection of the antenna to its own coupler. How old is the antenna? How good/old is any waterproofing applied over the connector at the masthead?


That looks like corrosion to you? I guess Iím not sure what new looks like, seems fine compared to the others, but Iíll take it off and have a look at the actual connection.

The antenna is at least 8yrs Iíve had the boat and probably many more before that 10-30yrs

Iíll check out the connection at the top the next time Iím up. Fairly soon.
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Old 24-04-2018, 15:49   #10
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Re: Weak AIS Signal?

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Originally Posted by Paul Elliott View Post
That white coax jumper between the transponder and the splitter looks pretty funky. The insulation has pulled out of the metal sleeve. This may not indicate a problem, but it is possible that the shield connection has corroded or pulled free. The SWR test that Dsanduril mentioned should tell you if this is the case. In any case, I would replace that cable, using fresh connectors.


Ahhh, yes I see that. Iíll give it an inspection.
Thanks.
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Old 24-04-2018, 15:52   #11
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Re: Weak AIS Signal?

And Iím noticing the the vessels that I did see near me have disappeared... I can only see those within 4nm on my chart plotter.

...but radio Check was good at 15nm

Makes me think itís a AIS connection, perhaps the white wire
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Old 24-04-2018, 16:04   #12
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Re: Weak AIS Signal?

Hereís the white cable from the transponder end... seems clean...

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Old 24-04-2018, 19:19   #13
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Re: Weak AIS Signal?

take the antenna cable off the splitter and connect it direct to the AIS. see if you range increases. (you'll loose the VHF, don't transmit it while testing AIS)

you should be picking up boats 40 miles away.

if it doesn't get better. as posted above. buy an antenna with cable already on it. plug it in down below, hold it/ lean it against something non metal. and try it. see if it's better.

you should have a spare antena on the boat anyways if you only have one on the mast. if the mast breaks off. plug spare into radio, and use use radio.
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Old 24-04-2018, 20:07   #14
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Re: Weak AIS Signal?

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Originally Posted by smac999 View Post
take the antenna cable off the splitter and connect it direct to the AIS. see if you range increases. (you'll loose the VHF, don't transmit it while testing AIS)
Excellent suggestion!
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Old 24-04-2018, 20:20   #15
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Re: Weak AIS Signal?

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Originally Posted by smac999 View Post
take the antenna cable off the splitter and connect it direct to the AIS. see if you range increases. (you'll loose the VHF, don't transmit it while testing AIS)

you should be picking up boats 40 miles away.

if it doesn't get better. as posted above. buy an antenna with cable already on it. plug it in down below, hold it/ lean it against something non metal. and try it. see if it's better.

you should have a spare antena on the boat anyways if you only have one on the mast. if the mast breaks off. plug spare into radio, and use use radio.


Thanks...
Trying now.
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