AIS greatly reduced range

[double u]

circuit is completely open across the plug that comes from the antenna & goes into the splitter. Just tried an emergency vhf antenna directly to the ais - slight improvement of the range: from 5 to 7 miles (lots of ships here in & around Colon/Panama)

[DefinitelyMe]

Originally Posted by double u

circuit is completely open across the plug that comes from the antenna & goes into the splitter. Just tried an emergency vhf antenna directly to the ais - slight improvement of the range: from 5 to 7 miles (lots of ships here in & around Colon/Panama)

OK that could mean all sorts of things. Definitely a problem somewhere though if you’re getting better range with an emergency antenna. What kind of antenna do you have? Do you know what the resistance characteristics should be? Based on post #29 it seems my methods might no longer be appropriate, but if you know what model you have perhaps you could look it up online or email the manufacturer without too much trouble (and without needing any fancy equipment)?

[double u]

today we're going to buy new antenna & cable, still have to hunt for connectors here in Panama. hopefully pulling the cable into the conduit in the mast will work ok...
thank youall for the contributions

[DefinitelyMe]

No worries. You know, you could always try the thing with some aluminium foil and a multimeter to test the cable. That test at least should be definitive. It would be a shame to go through all that work and throw out a perfectly good cable for nothing. In my experience it’s usually the antennas that fail or one of the connectors that becomes corroded. Rarely the cable.

[wsmurdoch]

Originally Posted by DefinitelyMe

You can get an idea of whether your antenna/cable might be at fault using a multi-meter. Set it to ‘resistance’ (measured in ohms). Unplug the cable from the splitter and measure the resistance of the cable-antenna assembly between the inside and outside conductors (the central pin and the outside body of the connector). Most (but not all) VHF antennas show zero ohms resistance if they are working properly and all the connections are good. The Shakespeare masthead whip aerials that are the most common in the US fall into this category. Pacific aerials, which are common among New Zealand and Oz boats, don’t (they show an open circuit). Assuming your aerial falls into the former category:

You should, if all is well, see a very low number when you measure the resistance like this. Somewhere between zero and ten ohms max. If you see this then your cable-antenna assembly is probably not the problem.

If you see an open circuit (infinite resistance) then you either have a break in the circuit somewhere or a very damaged antenna.

If you see a number between, say, twenty ohms and several thousand ohms then you have a poor connection somewhere or an antenna that is starting to fail.

This method won’t give a definitive diagnosis of a problem, but it might give you an idea of whether or not a problem is likely to exist and where that problem might be. If you see an unacceptable resistance the next step is to climb the mast, unplug the aerial, stuff a bit of aluminium foil in the connector to short between the conductors and then measure resistance from the other end. That will tell you whether the resistance you are seeing is coming from the cable, the aerial or a combination of the two.

According to the tech sheet that came with my Shakespeare 4200 antenna, it should test "open circuit".


Bill

[double u]

new Shakespeare 5215, new RG58CU, new connectors - are seeing ships up to 56.3 nm out!
thank you everybody for contributing!

[deadliest catch]

Congrats on solving the problem Double U. Can you share which connectors you used? Solder or solderless?

Cheers

Mike

[double u]

PL259 connectors, not new but from a short length of cable another Austrian cruiser gave us, the type that is screwed onto the folded-back screen & the center is soldered. I unsoldered & reused them.
No better cable available & no connectors at all (at least in Colon & as far as I could see)

[smac999]

58 up a mast is tiny. You should replace again if you find something bigger in the future. Rg8x /240 at min. Your tx will suffer.

Surprised the emg antenna didn't do much better if it was a cable / ant issue.

[double u]

the range-improvement with the emergency antenne was only just enough to convince me it was an antenna/cable issue.
changing cable to RG213 will have to wait for a while, but I thought 50nm plus range wasn't so bad. Maybe having the cable run uninterrupted from antenna to splitter - no connectors at maststep - helps too

[crewtv]

Originally Posted by double u

suddenly our AIS (Matsutec) is showing only targets at greatly reduced range, nothing further out than say 9nm, often only 4-5nm before an approaching target is shown/a passed one is lost, when before 24nm was no rarity. I suspect the VHF antenna-installation, cable or connectors (the Matsutec is only 1/2 year old & otherwise working perfectly)
the question now is: what sort of test can be done to see how much power comes out of the VHF masthead antenna (the AIS shares the antenna with the VHF via a coupler).
any other suggestions? (of course I could "just" change the mast cable & the aerial at the masthead as "regular maintenance"...but if I can be sure of the fault before going that way...)
btw: it's not the coupler/splitter, directly connecting the antenna cable made no difference

I had that happen in a fog sailing from Talin, Estonia to Finland. I had 30 meters of visibility and was crossing a busy shipping lane and scared to death. I had nearby ships give me radar and AIS info. I had less than a mile of AIS contact and heard huge ships buzzing all around me. The nearby ships saved my boat and crew with their help. When I got to Helsinki I went up the mast and discovered the antenna was loose and just replaced it and it worked fine and had 45+ sea miles of visibility. Easy fix. Good luck. Scott Charter a sailboat in Stockholm | Sailing Sweden

[sarita]

Originally Posted by smac999

Buy one of these , tempory stick it in the deck and plug it in. and see if the range comes back. You should be carrying one anyone's incase you ever break the antenna or mast.

If it does. Time to replace ant and or cable.

5911 Classic Emergency VHF Antenna | Shakespeare Marine Antennas

Or make one yourself from some coax cable as shown here and haul it up the mast on a halyard to see what range you get :- https://pocketmariner.com/aisaerial/.

[stormalong]

Originally Posted by sarita

Or make one yourself from some coax cable as shown here and haul it up the mast on a halyard to see what range you get :- https://pocketmariner.com/aisaerial/.

Something happened to that article - it cannot be found on pocket mariner. Is there some other way to read it?

[sarita]

Originally Posted by stormalong

Something happened to that article - it cannot be found on pocket mariner. Is there some other way to read it?

How about this link?

https://pocketmariner.com/simple-3db...l-co-ax-cable/

[nilespf]

Double U


I have a Matsutec as well. Try using a dedicated antenna and make sure it is being marketed to accommodate the AIS channels. Yes a standard VHF whip will work but pay a bit more and get one specifically tested/spec'd for the upper band. A marine VHF whip usually has a gain pattern that has begun to fall by the time it reaches the AIS frequency. My system usually displays AIS targets (Ray E80) much farther away than detectable by radar. On rare occasions, some radar targets initially show w/o a corresponding AIS detection. Rather than sharing, I mounted the AIS antenna on the Bimini. A shared antenna using a coupler will reduce operating sensitivity of the receiver and reduce effective transmit power of the transmitter.


PN