AIS greatly reduced range

[continuouswave]

Also in regard to Class-B, the recently authorized Class-B SOTDMA devices are permitted 5-Watts of power. This puts them at only a -4 dB disadvantage compared to the 12.5-Watt Class-A transmitters.

Further, the Class-B SOTDMA devices are permitted to transmit their data as often as every five seconds, while Class-B CSTDMA can only transmit at most at 30 second intervals. This gives the "SO" devices a six-fold greater rate of transmission in some instances.

[dlclark]

Practical Sailor's latest edition (February 2019) has a great article on this very issue. There are a lot of possible factors in the transmission and reception of your AIS/VHF signal.

1. VHF cable connections, typically use PL259 connectors, which do not seal very well unless you use dielectric grease on the contacts and self-amalgamating tape.

2. The Antenna could be damaged and most marine Antennas still use PL259 connectors - at the mast head.

3. If you have a mast head antenna, you should make sure it is only 3db antenna; as the high gain (6db) antennas for example have a radiation pattern that is oblong rather than omni directional. Which can also cause this.

4. I always carry an antenna SWR tester on board to check the standing wave ratio, this can tell you if you have too much loss in the cable and connections.

If you find you have high loss, you could try taking the PL259's apart and check them (at the radio, at the mast step, at the antenna). You may find you need to run new COAX up the mast to solve!

You could also have a radio problem!

Here is an example of a SWR tester: https://www.westmarine.com/buy/shake...iABEgI3efD_BwE

Daryl()

[stormalong]

Originally Posted by dlclark

Practical Sailor's latest edition (February 2019) has a great article on this very issue. There are a lot of possible factors in the transmission and reception of your AIS/VHF signal.

1. VHF cable connections, typically use PL259 connectors, which do not seal very well unless you use dielectric grease on the contacts and self-amalgamating tape.

2. The Antenna could be damaged and most marine Antennas still use PL259 connectors - at the mast head.

3. If you have a mast head antenna, you should make sure it is only 3db antenna; as the high gain (6db) antennas for example have a radiation pattern that is oblong rather than omni directional. Which can also cause this.

4. I always carry an antenna SWR tester on board to check the standing wave ratio, this can tell you if you have too much loss in the cable and connections.

If you find you have high loss, you could try taking the PL259's apart and check them (at the radio, at the mast step, at the antenna). You may find you need to run new COAX up the mast to solve!

You could also have a radio problem!

Here is an example of a SWR tester: https://www.westmarine.com/buy/shake...iABEgI3efD_BwE

Daryl()

I would not trust that device.

Here is a real SWR tester.

MFJ Enterprises Inc.

Find a local Ham radio operator with one of these or a similar antenna analyzer. Offer to buy him lunch if he/she comes and tests your antenna. Far cheaper and more reliable than Shakespeare.

[Jim Cate]

3. If you have a mast head antenna, you should make sure it is only 3db antenna; as the high gain (6db) antennas for example have a radiation pattern that is oblong rather than omni directional. Which can also cause this.

Not so: the horizontal radiation pattern is still omnidirectional with the higher gain masthead antennae. The issue is that the vertical radiation pattern is compressed towards the horizon when the mast and antenna are vertical. When the boat heels, the athwartships radiation pattern is skyward on one side and into the water on the other, fore and aft are not bothered very much, with intermediate angles affected appropriately.

The higher the gain, the more pronounced the effect.

Jim

[continuouswave]

Originally Posted by dlclark

Practical Sailor's latest edition (February 2019) has a great article on this very issue. ...

None of the elements you cite as being mentioned in the article are applicable to any difference between a Class-A and a Class-B device. Those concerns are all external to the devices.

[ramblinrod]

Most VHF/AIS antenna problems (where the antenna is less than 20 years and there are no signs of lightning strike) are due to improper connector installation.

Either the screen or centre conductor connections are high Z or moisture has gotten into the connection.

I wrap all antenna connections with self-amalgamating tape, from about 2" up the cable, over the connector, and onto 2" of the adjoining cable.

[ramblinrod]

Originally Posted by smac999

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

Line of sight transmission.

If the emergency antenna was at deck level, 5 miles is about as far as it can see to the horizon.

[continuouswave]

Originally Posted by Jim Cate

...When the boat heels, the athwartships radiation pattern is skyward on one side and into the water on the other, fore and aft are not bothered very much, with intermediate angles affected appropriately.

In actual operation, a tilted vertical antenna does not have its radiation pattern tilted electrically by the exact same amount as the mechanical tilt, unless the antenna is in free space. Predicting exactly what the vertical radiation pattern of a real antenna will be when the radiating element is inclined from 90-degrees to the imperfect ground plane of the sea would require some careful analysis and modeling.

If you look at the radiation patterns for well-designed 3-dB and 6-dB vertical antenna arrays, you see that a 6-dB gain antenna still has better gain at 10-degrees off the horizon than the lower gain antenna. You have to get to about 20-degrees off horizon before the 6-dB gain antenna begins to have less gain than a 3-dB gain antenna.

Even if we could assume that the radiation pattern would match the mechanical tilt, you'd have to be tilted 20-degrees before any harm would occur from using a 6-dB gain antenna, and, again, that is ignoring that in actuality we really don't know how the pattern will be affected for a real antenna mounted some unknown height above a less than perfect ground plane of the sea.


If you are always sailing about with 20-degree of heel, then perhaps you should think about a lower gain antenna, but otherwise I wouldn't take as gospel the notion that a 6-dB antenna will always result in lower signals.

The first deep null in a 6-dB gain antenna occurs about 30-degrees off horizon. If your boat is heeled or rolling 30-degrees, then a lower gain antenna might be more useful.

[ka4wja]

Hello to all,

I came to this discussion a bit late, as the original poster had gotten a solution already....and then I steered clear of the "argument part"....but..

1) There is some very good, and fairly easy-to-understand, information on VHF / AIS radio range and VHF/AIS Radiowave Propagation right here on Cruiser's Forum....(and some info about coax losses, cable connectors, etc...and even AIS "splitters"....all with factual results to show..)

Please have a look...

http://www.cruisersforum.com/forums/...ge-149499.html

http://www.cruisersforum.com/forums/...ld-130803.html



2) And, when I read what Rod wrote here, I just had to chime in with praise!!!
Rod, hit the nail on the head regarding "most" VHF/AIS antenna problems!!!
Kudos to you!!

Originally Posted by ramblinrod

Most VHF/AIS antenna problems (where the antenna is less than 20 years and there are no signs of lightning strike) are due to improper connector installation.

Either the screen or centre conductor connections are high Z or moisture has gotten into the connection.

I wrap all antenna connections with self-amalgamating tape, from about 2" up the cable, over the connector, and onto 2" of the adjoining cable.

In my ~ 45 years in electronics (and > 50 years on the water, sailing, etc.) I can say with much certainty that it is the installation, wiring, commissioning, programming, and weather-proofing, of the electronics systems that make or break the system / performance!!

And, when it comes to antenna systems, the cable / cable connectors, are almost always the first thing to fail!! And, of course that is especially true when dealing with poorly weather-proofed marine antenna installs!!

So, again...big thanks to Rod!!

{Yes, I'm aware that this does not directly figure into the AIS "Class A" vs. "Class B" part of the discussion....but...
But, in my experience, many "Class B" installs are poorly done (actually some DIY installs are better than some of the "pro" installs that I've seen)...where most Class A installs are pretty good...
So...
So, this does, in a "round-about-way" bear onto the issue at hand...at least in my opinion....
So, again....a big thank you to Rod!!}



I hope this helps some...

BTW, I'm not going to ramble on and on here....'cuz the original poster got a solution, and all the info that you all could probably need about VHF/AIS range, radiowave propagation, coax, etc., is right here on Cruiser's Forum already.....have a look at the threads referenced above...


Fair winds.

John

[ramblinrod]

Originally Posted by continuouswave

In actual operation, a tilted vertical antenna does not have its radiation pattern tilted electrically by the exact same amount as the mechanical tilt, unless the antenna is in free space. Predicting exactly what the vertical radiation pattern of a real antenna will be when the radiating element is inclined from 90-degrees to the imperfect ground plane of the sea would require some careful analysis and modeling.

If you look at the radiation patterns for well-designed 3-dB and 6-dB vertical antenna arrays, you see that a 6-dB gain antenna still has better gain at 10-degrees off the horizon than the lower gain antenna. You have to get to about 20-degrees off horizon before the 6-dB gain antenna begins to have less gain than a 3-dB gain antenna.

Even if we could assume that the radiation pattern would match the mechanical tilt, you'd have to be tilted 20-degrees before any harm would occur from using a 6-dB gain antenna, and, again, that is ignoring that in actuality we really don't know how the pattern will be affected for a real antenna mounted some unknown height above a less than perfect ground plane of the sea.


If you are always sailing about with 20-degree of heel, then perhaps you should think about a lower gain antenna, but otherwise I wouldn't take as gospel the notion that a 6-dB antenna will always result in lower signals.

The first deep null in a 6-dB gain antenna occurs about 30-degrees off horizon. If your boat is heeled or rolling 30-degrees, then a lower gain antenna might be more useful.

Don't forget about antenna flexure atop the mast of a rockin and rollin sailboat. ;-)

[GTom]

Originally Posted by crewtv

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

Here you go, before throwing 2000$ out of the window on a Class A system or even 900$ on B+ and drilling your deck/cable conduits to cheese to fit an RG213...

I am renewing my VHF-comms and adding an AIS, but try to remain pragmatic. Thousands of boats do just fine on plain Class B, some even show up on satellite AIS: I highly doubt, that the herds of <50' fishing boats buy Class A (they're not even obliged to carry Class B in the UK)... This tells me to focus on proper, robust installation rather than following dream specs.

One thing I am considering: instead of a splitter, I want to add a second antenna for the AIS (see under "robust installation/redundancy"). However, got no clue ATM where to put it, but likely it'll go on the stern radar pole (in case the mast goes down, again "redundancy").

[CarinaPDX]

i mounted my AIS antenna above and behind the radar dome, on a radar mast at the transom. It seems to be working well enough. I personally prefer to keep AIS separate from the ship's VHF - no splitter for me. My AIS antenna is designed for that purpose; i.e. it is tuned for the two AIS channels, not channel 16 or in the middle of the band. It could be used as an emergency VHF antenna, just not optimally. Here in the U.S. a new Class B+ costs about half of what you are reporting; the last I checked it was about $100 more than the older designs, and for that I think it is worth it.

Greg

[GTom]

Originally Posted by CarinaPDX

i mounted my AIS antenna above and behind the radar dome, on a radar mast at the transom. It seems to be working well enough. I personally prefer to keep AIS separate from the ship's VHF - no splitter for me. My AIS antenna is designed for that purpose; i.e. it is tuned for the two AIS channels, not channel 16 or in the middle of the band. It could be used as an emergency VHF antenna, just not optimally. Here in the U.S. a new Class B+ costs about half of what you are reporting; the last I checked it was about $100 more than the older designs, and for that I think it is worth it.

Greg

This side of the pond a reduced price B+ unit costs £600+, standard B can be found below £400. Still not a show-stopper difference, but an amount I'd expect more than paying for a nicer paint on the box, i. e. some perceiveable advantage during my trips in my boat.

[alc]

I guess equipment does fail from time to time or maybe the OP is just making up the story.

[double u]

Originally Posted by alc

I guess equipment does fail from time to time or maybe the OP is just making up the story.

YOU are the expert there...