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Old 19-08-2019, 09:37   #1
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VHS/AIS Limited Range

Hello All,

I'm hoping that the collective insight out there might be able to help me figure out a solution to a problem.

I have a Raymarine Axiom plotter, and a Raymarine AIS transceiver which were installed by me prior to the 2018 sailing season. (the AIS and VHF share the masthead antenna via a Raymarine splitter) Both performed very normally last season, and then this past winter we had the mast taken down to replace the standing rigging.

This season, both the VHF and AIS seem to only be working within a limited range of about 2 nms. I have confirmed with other vessels within that range that they can see me on AIS, and I can only raise others on the VHF within a distance somewhat longer than that range, but less than before. My handheld VHF activates the automatic radio check located about 4 miles away, but the main unit does not. Reception on the VHF seems to be normal.

I have checked all the components several times, all seem to be in normal operation, I have also checked all connections (except at the masthead) and they all are tight. (the rigger assures me it is not the masthead connection)

The only variable that I can come up with is that prior to the mast going back up, I noticed a slit in the outer cover of the coax in the exposed section at the top of the mast. The wrapping under the slit did not appear damaged, but was slightly discolored. Not having enough time to replace the coax prior to the mast re-installation, I sealed the slit with liquid electrical tape.

Is it likely that the slit is the cause of the problem? If so, do I need to replace the entire run of coax within the mast, or can a new section be spliced in at the masthead? (my understanding is that would degrade the signal)

Thanks!
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Old 19-08-2019, 11:53   #2
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Re: VHS/AIS Limited Range

My first guess would be something has changed in the connection at the antenna. When you put the mast back up, the outer sleave of the coax is no longer making a good connection. It would have been good practice to redo connectors when the mast is down. Not only redo the electrical connection, but add shrink tube to the connector. I fear the rigger is not knowledgeable enough to make that determination.

The slit, unless it got badly corroded in side, should not have caused this problem. Moving the mast and flexing the cables beyond what is normal could cause the problem. You might have to go up the mast and redo the connectors. One thing for sure is it will not hurt your system by doing so. Unless the rework was done incorrectly.
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Old 19-08-2019, 12:58   #3
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Re: VHS/AIS Limited Range

First and most obvious to eliminate is a faulty element on the way between your AIS unit and the antenna. Any of the components along the way can be faulty - also any of the connectors (this is quite common). A plain test will discover this though (it is called I think standing wave test or similar).


If the range is limited in some sectors but fine in others, it will be antenna placement.


If the connection from the unit to the mast top is sound and well built, then the AIS unit has an internal problem.


b.
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Old 19-08-2019, 13:09   #4
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Re: VHS/AIS Limited Range

Quote:
Originally Posted by Brian.D View Post
My first guess would be something has changed in the connection at the antenna. When you put the mast back up, the outer sleave of the coax is no longer making a good connection. It would have been good practice to redo connectors when the mast is down. Not only redo the electrical connection, but add shrink tube to the connector. I fear the rigger is not knowledgeable enough to make that determination.

The slit, unless it got badly corroded in side, should not have caused this problem. Moving the mast and flexing the cables beyond what is normal could cause the problem. You might have to go up the mast and redo the connectors. One thing for sure is it will not hurt your system by doing so. Unless the rework was done incorrectly.
So there in lies one dilemma. Do I go through the trouble of going up the mast and changing the connector, knowing that the slit could be part of the problem? The inner layer was discolored (rust colored) but not badly.
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Old 19-08-2019, 13:11   #5
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Re: VHS/AIS Limited Range

Quote:
Originally Posted by barnakiel View Post
First and most obvious to eliminate is a faulty element on the way between your AIS unit and the antenna. Any of the components along the way can be faulty - also any of the connectors (this is quite common). A plain test will discover this though (it is called I think standing wave test or similar).


If the range is limited in some sectors but fine in others, it will be antenna placement.


If the connection from the unit to the mast top is sound and well built, then the AIS unit has an internal problem.


b.
The only new variable is the slit in the cable, antenna placement and equipment are all the same from when it was performing well.
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Old 19-08-2019, 13:29   #6
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Re: VHS/AIS Limited Range

Did you install/replace anything else on mast top? A new wind sensor, LED, etc.
I have an Airmar wind sensor on mast top which blocks VHF reception, some LED’s will also block reception.

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Old 19-08-2019, 13:44   #7
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Re: VHS/AIS Limited Range

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Did you install/replace anything else on mast top? A new wind sensor, LED, etc.
I have an Airmar wind sensor on mast top which blocks VHF reception, some LED’s will also block reception.

Cheers
Nope, only new variable is the slit in the cable.
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Old 19-08-2019, 14:34   #8
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Re: VHS/AIS Limited Range

Radio transmit/receive problems are almost always in the antenna or it's coax cable and connections. If the coax has a damaged outer sheath, I would suspect water has infiltrated the inner conductor insulation, causing a short circuit. On some cable, that insulator is a plastic foam that can absorb water and when it does it forms a bridge between the center conductor and the shield braid. This will bleed off a lot of the rf energy causing reduced transmit range. Sounds like you need to replace the coax.
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Old 19-08-2019, 14:36   #9
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Re: VHS/AIS Limited Range

I had my vhf and ais mysteriously degrade during my Bahamas crossing last year....all of a sudden I couldn’t see any ais targets further than two NMs away...previous range was around 10... turns out it was a failed/ing antenna...a loaner from a buddy solved the problem...old antenna definitely failed, it was not the connection...
YMMV
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Old 19-08-2019, 15:44   #10
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Re: VHS/AIS Limited Range

If you can find somebody with an SWR meter you can test the antenna system. I had a similar problem about 5 years ago in the Bahamas. It ended up that the coax in the mast had gone bad. We swapped it out and everything returned to normal. The connectors on the ends looked fine but the swr reading was 4.5. Ideal is one and anything over 2 will limit your range a bit but over 3 pretty much renders your radio useless. I really never saw any obvious issue on the outside but it was still bad.
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Old 19-08-2019, 17:43   #11
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Re: VHS/AIS Limited Range

Quote:
Originally Posted by NewCatGuy View Post
So there in lies one dilemma. Do I go through the trouble of going up the mast and changing the connector, knowing that the slit could be part of the problem? The inner layer was discolored (rust colored) but not badly.
I would think if you want the problem solved that might be what you have to do. I don't think it will fix/solve itself. If it does then it will be temporary until the cable/connector moves again. This might be a good time to replace the RF cable and eliminate and future issues.
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Old 19-08-2019, 18:05   #12
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Re: VHS/AIS Limited Range

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Originally Posted by Brian.D View Post
I would think if you want the problem solved that might be what you have to do. I don't think it will fix/solve itself. If it does then it will be temporary until the cable/connector moves again. This might be a good time to replace the RF cable and eliminate and future issues.
Thanks
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Old 19-08-2019, 18:06   #13
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Re: VHS/AIS Limited Range

Thanks
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Old 19-08-2019, 18:07   #14
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Re: VHS/AIS Limited Range

OK. Thanks
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Old 19-08-2019, 21:44   #15
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Re: VHS/AIS Limited Range

first thing you need to do is stick a SWR meter on the line. and see what reading you get.

next stick a spare antenna outside on the deck connected to the radio to see if it's any better. every sail boat should have a spare antenna. to use if the top one breaks off, or mast breaks off.

both of those before you go up a mast.
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