Trouble with AIS transmitter

Jan 5, 2017
143
Hunter 356 SF Bay / Delta
I'm struggling with the AIS transmitter on my vessel. She is a 2003 Hunter 356. The masthead antenna whip was recently replaced and is a GAM SS-2. The cabling is original as far as I know.

I hooked the AIS unit to a laptop and ran ProAIS2. After two transmits it throws a VSWR fault, with values seemingly all over the place but all very high. Some were around 6:1, some were 12:1, and a few were even higher (one read 47:1 and one result even showed 1635:1.)

There is a splitter in place, but bypassing it didn't noticeably change VSWR numbers.

Thoughts on where to start?
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Since AIS is used on marine VHF (ch. 87B/88B - 161.975MHz/162.025MHz), you can use a regular VHF antenna. I would not recommend using a homebrewed antenna, but a real VHF antenna. Put the antenna on the rail and run a short length of RG58 to the antenna. Then run your test again. This will help rule out the AIS transmitter.

Next I would use a length of coax that equals the length to top of the mast. Same test to the antenna on the rail. See if there is an appreciable amount of loss.

Your next test would be to run the cable up to the top of the mast and connect to the current antenna. It could be the internal cable has gain moisture or the antenna is faulty. The results will tell you which.

The simplistic version is either the cable is bad, or the connectors need to be re-soldered.

I know, lots of work. But it is better if you follow a straight path and not jump around from part to part.

Added - If you want you can use your regular marine VHF antenna for testing.
 
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Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Give someone your handheld, send them downrange about 10 miles, tune one of the recreational channels (NOT Ch.16) and see if they can receive your radio check. I’m guessing you have an antenna/co-ax/connector problem.
 
Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Thanks guys. I found someone with an emergency VHF antenna and cable for testing, but I believe I already found the culprit -- there is a nasty split in the coax cable between the deck and mast.

Going to try a splice here until next time I drop the stick and can run a new wire. I assume factory cable is RG-213?
 

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Could be, or it might be LMR-400. Either way, you will insert a SWR that will not be 1.x:1, but it should be consistent. Change out that bad cable as soon as possible.
 
Mar 20, 2004
1,729
Hunter 356 and 216 Portland, ME
Look closely at the coax- -my factory original 2002 356 had RG-8x, Not marine cable, and the connector at the mast base wasn't even soldered on! The cable was really corroded.
 
Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Chuck, do you know if there's room at the top of the mast to feed in a new cable with the connector already attached? If I do climb the mast, I'd like to avoid making multiple trips.
 
Mar 20, 2004
1,729
Hunter 356 and 216 Portland, ME
no, there isn't - the base connector has to be installed after the wire is fished thru the mast. the entry hole is small at the mast head, and the thick cable is really stiff. I plan to cut off the masthead connector, cut away a couple of inches of the shield, dielectric, and cover on the old and new cables and securely twist together the center conductor. normally I'd solder them, but the old cable is probably too corroded to solder. I then cover the splice with a thin layer of gaffer tape (like duct tape, but much stronger, used in theaters) and pull the cable thru. I think it would be really hard with the mast up. In any case, it wouldn't hurt to have the mast pulled for a thorough inspection. I found 2 damaged D2 stays that the yard missed in the mast in inspection I paid for every year
 
Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Just to follow up on this... After crimping a new connector at the bottom of the mast I'm now seeing a VSWR of 3.5:1. There did appear to be corrosion in the cable because of the cut that I suspect isn't helping. It dropped to 1.9:1 when I replaced the connection at the mast with a portable antenna.

This will at least get me by until I can replace the entire cable in the mast.
 
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Mar 20, 2004
1,729
Hunter 356 and 216 Portland, ME
Yes - I'm doing the same thing. You want the VSWR to be below 2. NOt an immediate issue because I run 2 radios with separate antennas. I plan to do the replacement this winter after the mast comes out. It's stored inside.
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Just to follow up on this... After crimping a new connector at the bottom of the mast I'm now seeing a VSWR of 3.5:1. There did appear to be corrosion in the cable because of the cut that I suspect isn't helping. It dropped to 1.9:1 when I replaced the connection at the mast with a portable antenna.

This will at least get me by until I can replace the entire cable in the mast.
Thanks for the update. It bugs me to no end (and I do it too) when there is no closure for a problem. I currently am having outboard issues (when don't I ever have outboard issues) and as soon as I have a solution I will close that thread.