AIS Fault Message

[DeepFrz]

Those VSWR readings really suggest that the radio sees no antenna. Perhaps a visual inspection of the coax output connector on the radio itself will reveal a problem. It is possible that the output connector was damaged when replacing the coax/antenna. Just a guess. Good luck.

[Emerald Sea]

Originally Posted by Neptune's Gear

IMO the coax quality is insufficient for the low power output of a class B AIS, at the lead length you have (22m)

From the previous thread, the RG213 provides less 'loss' than my original RG58. -2.3db/100ft (or approx 1.65db for 22m) compared to -6.5db/100ft for RG58. There are no intermediate joints. Is it really the case that the RG213 quality is insufficient compared to the RG58 for the low AIS output power?

Im discussing also with Raymarine but no solutions yet. Also no answers from the Raymarine forum, yet.

PS: thanks for this support!

[Abgreenbank]

I have 2 cables and 2 antenna , one is a metz ais antenna the other I can't remember but a metal whip style. The co ax cables, one is rg213u and the other rg8, if I plug them in to my raymarine AIS650 I get the following results.
the rg213 and ordinary whip Antenna VSWR from pro AIS 2 software is 1:1.1 and I can tx/rx with the nearest base station on the top of a 300m hill around 30 km away.
with the rg8 and metz ais antenna VSWR is 1:2 and does not get the repeated targets from Ais base station, and targets max about 3nm, antennas co located on the mast.
all I can conclude is the 27 meter run from nav station to the top of the mast is a little too far for rg8.
the maximum distance I have seen an AIS target without a base station repeater is over 80km, however it was a SAR chopper!
I have purchased raymarine splitter and still get 1:1.1 and both my VHF and AIS have good range, the rg8 cable is just a spare and will be replaced as and when.

Regards

Ab

Ab


Sent from my iPad using Cruisers Sailing Forum

[btrayfors]

Emerald Sea:

You don't need an SWR meter. What you need is an antenna analyzer, e.g., the MFJ-259B. This will work at AIS frequencies 162mHz and will tell you the SWR at those frequencies.

I found that my "AIS antenna" was giving a high SWR and that was the reason for transmit failures (though I could receive very well). This usually happened to me when it rained.

Solution was simple: trim the antenna itself (a s/s whip which was a bit too long in my case) so that SWR at the AIS unit was low. I did that two years ago, and mine has been perfect ever since...even in the rain!

The coax cable "too long to work" argument doesn't make sense. And, I hate all splitters, no matter their published specs. Avoid them if you can.

Disclosure: I work on this stuff professionally.

Bill
WA6CCA

[Paul L]

Originally Posted by Emerald Sea

Paul, DeepFrz, quite right, I redid the 2nd test (coax, antenna direct into the AIS650; isolating the Splitter) and let it sit for a longer period and received an improved VSWR readings from ProAIS between 14.3:1 to 16.8:1 (see attached). However the readings don't tell me much as Im not a electech. Note also that with the coax/antenna directly connected I still get the VSWR alarm sounding off.

Attachment 128875

Paul, I don't quite understand what you are asking "Can you try test #2 with a longer coax and the antenna mounted in a normal position?". My coax is approx 22m long, runs up the mast and plugged into the 3db antenna. This is a 'normal' position - at least to me.

So far, by switching the antenna between the AIS650 and Splitter100 and having no desired improvement, it seems the fault would lie with the 22m coax or the new antenna. Since I just changed the antenna last week from a 6db to a 3db, with no change, then the coax seems to be the final area of fault. I did change this out earlier this year from a RG58 to RG213 and did continuity checks.

If I do change out the coax again, should I go back to a RG58?

I misread your description of the test and thought you had the antenna cabled directly into the unit, not at the mast head. If you take the antenna down and do some more direct testing you still need some coax between the antenna an the AIS.

[Emerald Sea]

Originally Posted by btrayfors

You don't need an SWR meter. What you need is an antenna analyzer, e.g., the MFJ-259B. This will work at AIS frequencies 162mHz and will tell you the SWR at those frequencies. WA6CCA

I can get access to a Antenna/Radio Tester ART-3 (Antenna/Radio Tester ART-3) but its frequency range is 155-158 MHz. So Im guessing it won't work for 162MHz AIS frequency? I'll ask around to see if I can find a MFJ-259B or equivalent.

Despite the VSWR alarm, we get excellent tx/rx with both from the VHF and AIS i.e. 30mi out when at sea.

Bill, well its a lovely new Shakespeare 36" 5215 AIS-VHF 3db s/s whip (http://shakespeare-ce.com/marine/pro...-body-antenna/). It would be a 'difficult' cut! How much did you trim it back by?

[Paul Elliott]

Originally Posted by Emerald Sea

From the previous thread, the RG213 provides less 'loss' than my original RG58. -2.3db/100ft (or approx 1.65db for 22m) compared to -6.5db/100ft for RG58. There are no intermediate joints. Is it really the case that the RG213 quality is insufficient compared to the RG58 for the low AIS output power?

I think the RG213 will have a loss of about 2.0dB (162 MHz, 22 meters in length). Here's a calculator: Coax Calculator

This is an acceptable amount of loss in your application.

As we have discussed, more loss actually reduces the SWR you will be measuring, so your problem is not being caused by a lossy, but otherwise good, cable.

[btrayfors]

Originally Posted by Emerald Sea

I can get access to a Antenna/Radio Tester ART-3 (Antenna/Radio Tester ART-3) but its frequency range is 155-158 MHz. So Im guessing it won't work for 162MHz AIS frequency? I'll ask around to see if I can find a MFJ-259B or equivalent.

Despite the VSWR alarm, we get excellent tx/rx with both from the VHF and AIS i.e. 30mi out when at sea.

Bill, well its a lovely new Shakespeare 36" 5215 AIS-VHF 3db s/s whip (5215 Classic AIS Squatty Body® Antenna | Shakespeare Marine Antennas). It would be a 'difficult' cut! How much did you trim it back by?

Steve,

First you have to determine whether your antenna is too long or too short, so you've really gotta measure SWR at the desired frequency (162 mHz).

In my case, the antenna was too long, i.e., resonance was BELOW 162 mHz. So, it was a simple matter of clipping off an inch or so of antenna, measuring the new resonance frequency, and doing it in steps until the point of resonance was raised to 162 mHz.

As I recall, it required clipping more than the formula would suggest, and more than I had imagined. Several inches came off the s/s whip before it became resonant at 162 mHz.

Remember, we're talking SWR at the feedpoint of the AIS transmitter, not the antenna itself. SWR is affected by a host of factors, inter alia: coax type and length, connectors, splitters if you have one, proximity to other antennas or metal fixtures, etc. These really don't matter, because what we're trying to do is make the AIS transmitter happy by presenting it with a very low SWR.

Bill

[smac999]

plug the AIS into a PC with the AIS software. it gives you a digital SWR reading each time it transmits and will list the errors.

don't screw with antennas. a normal marine VHF ant still gives less then 2:1 SWR on an AIS and is fine (as seen right in the AIS software at AIS freq). if you are getting a high alarm you either have a bad ant, bad cable, or bad unit.

the unit doesn't alarm unless it's really high like 5:1, so you have a real problem if it's going off.

I have seen a ray AIS give a really high SWR reading on the PC (like 100:1) but a very low reading on a meter when cable moved to a VHF. it was probably a screwed AIS unit.

if your unit was left on when the old antenna was blown off and continued to try to trasmit for a while it's possible the unit was damaged. though it should shut itself off with a high alarm.

note when you are seeing the high SWR alarm, the AIS is probbaly not transmitting any more for safety reasons. something to keep in mind if you are using it.

[smac999]

Originally Posted by Emerald Sea

VSWR Ratio:7498.4:1
I receive and send good AIS target info.

Attachment 128867

There is a large difference in the (ProAIS) VSWR ratios between the two above. What would this indicate to you?


I was able to access a SWR tester (Daiwa 1.8 - 150MHz SWR & Power Meter) and we tested it only on the VHF radio with good results, however it didn't register any ratios for when the meter's cables were installed via the Splitter100 or AIS650. We were unsure this meter has the correct sensitivity for the AIS (?).

you can't test an AIS with a portable SWR meter. an AIS transmits every ~5 mins for a split sec and is lower wattage and digital. you can unplug the cable from the AIS and test it using the VHF. so you are testing the same cable and ant as the AIS but using the VHF.

I'm betting 7000:1 isn't even physicaly possible. and the unit is screwed.

get a new antenna and shorter peice of cable and connect it straight to the AIS and hold it in the air and see what happens on the PC SWR reading. you should have a spare emg antenna on the boat anyways if your main one is on the mast.

if this still shows high then it's probably time for a new AIS

[Flysocal]

Emerald Sea,

Consider this!

Everything you've described happened to me. An unpredictable AIS alarm that would go off... especially in the middle of the night as we sailed along. VERY nerve racking.

I replaced my antenna. I switched to my other antenna. I had the line measured and tested with various meters by helpful electronics gurus. I ran new power because there wasn’t much left to do.

The only difference between what you’ve described and my situation is the actual AIS unit.
I had an ACR class B transponder. But, I suspect that the internals of the ACR AIS and the Raymarine 650 unit might be the same… based on the NASA AIS maybe?

Anyway… this problem plagued me for years but at first it wasn’t an issue because I didn’t have a chart plotter. The thing that I think clued me into the problem was when looking at the AIS messages in openCPN. Every now and then I would see… the same group of messages.

Essentially, it was a message that would appear as if the unit re-booted. It was the same 10 line or so message. Again… everything seemed to be working correctly with the AIS, and it would go right back to normal AIS messages.

That is until I got an e127 Raymarine Chart plotter. It has an alarm that went off erratically. It drove me CRAZY. It couldn’t be silenced because it wasn’t a proximity alarm. It was an alarm that said “External AIS Fault’ or ‘VSWR Fault’.

How did I fix it? I pulled the ACR unit and replaced it with a new Vesper XB-8000. I don't know what the old VSWR measured, but the Vesper unit says its at 1:1.

Knock on wood…. In the last couple of days I haven’t had an alarm. I really think its finally fixed.

I wish I could have figured out what caused the issue… but starting over seemed to be the answer.

Good luck.

Adam
s/v Volare
cruisingvolare.com

[Emerald Sea]

To close this discussion, after a lot of review, discussion with various 'experts', including Raymarine, testing with VSR testers, etc, the solution to this annoying problem has been to replacing the 6db antenna with a Shakespeare 5215 AIS/VHF 3dB antenna. Following two months with the new antenna, all seems back to normal.

Thanks to those above who have assisted in your support.

[ka4wja]

Steve,
Thank you for coming back here, and letting us all know your outcome!
That is especially nice!!!

Originally Posted by Emerald Sea

To close this discussion, after a lot of review, discussion with various 'experts', including Raymarine, testing with VSR testers, etc, the solution to this annoying problem has been to replacing the 6db antenna with a Shakespeare 5215 AIS/VHF 3dB antenna. Following two months with the new antenna, all seems back to normal.

Thanks to those above who have assisted in your support.

This backs up what Paul Elliot (and I) thought was the proximate cause, way back in February...

Originally Posted by ka4wja

3) But, big kudos to Paul for picking up on what I was going to write!
Higher-gain antennas, especially higher-gain collinear verticals, will exhibit a narrower operational bandwidth (both in gain and VSWR)....

Originally Posted by Paul Elliott
This sounds like the higher-gain style of antenna I was mentioning. I've only done the measurements on a few of these, but at least on mine the antenna tuning is much sharper than it is for the short VHF whips. I measure a good SWR on channel 16, and a pretty bad one (the number escapes me) on the AIS channels.



Originally Posted by ka4wja
Paul hit the nail on the head here!!!
Combine the high-VSWR at 162mhz of the typical "6db" [sic] marine VHF antenna, with the lower loss of new coax (and/or lower-loss coax), and you have a damn good guess of what's going on with Steve's set-up!!!

While a shorter VHF Marine Whip antenna (such as the typical 3' SS end-fed half-wave), should be able to have an acceptable VSWR across the entire 6mhz wide "VHF Marine Band", even some of these do not....and certainly most of the longer, higher-gain 8' / 6db[sic] do not....and the problem is worse for the larger antennas...
{note that some "new" versions may use a stagger-tuning, to allow a good VSWR near 156.8mhz and 162mhz (with a slight sacrifice in gain)....but most do not..}

I'm not being boastful here, rather using this positive outcome (changing to a regular 3' SS VHF whip antenna), as an example of what can happen when some well-meaning folks (marine electronics "experts", fellow cruisers, dock mates, etc.) misunderstand the technical minutia, and give/take recommendations based on false info/assumptions....


The basic lesson:
Don't mess with what works...

The specific lesson:
Higher gain antennas can cause more problems than most think...

The hard lesson:
Higher gain antennas on sailboats are to be avoided....they are totally unnecessary (see my other thread on VHF and AIS range and radiowave propagation), and cause problems...



Steve, thanks again for the conclusion!!
Fair winds...

John

[smac999]

Originally Posted by Emerald Sea

To close this discussion, after a lot of review, discussion with various 'experts', including Raymarine, testing with VSR testers, etc, the solution to this annoying problem has been to replacing the 6db antenna with a Shakespeare 5215 AIS/VHF 3dB antenna. Following two months with the new antenna, all seems back to normal.

Thanks to those above who have assisted in your support.

since this is split to your VHF and AIS you'll now have a higher SWR on your VHF and less performance there.... I would only use an AIS antenna as a dedicated AIS one.

a reg VHF antenna should be able to handle the AIS freq just fine without a SWR alarm. could have been a bad antenna or connection.