Flipping stupid AIS aerial - what am I doing wrong?

[Heckler]

Sorry to hijack CWs useful thread but I too have an AIS issue....
Vesper XB8000 (the wifi one) fed through a Vesper splitter using a new patch lead and the original masthead vhf coax. Vesper supply an app which shows system status and a relative vswr meter. The app says the system is fully operational with a goodish vswr reading, yet I never show on Marinetraffic, only briefly on Vessel finder, and only at short range - 1 mile or so on friends boats receivers. I only receive from up to 2 or 3 miles away. VHF radio works fine yet very poor output and receive on the AIS.
With my limited knowledge and reading this thread it would seem I need to replace my Hawk aerial with something tuned for both Radio VHF and AIS VHF??
So Bru, give me a call/pm next time you are near Ipswich and there could be some beer tokens in it for you and make me feel better at spending lots of hard earned on a small plastic box.

My mate here in Gib with his expensive Vesper and Vesper splitter is having exactly the same prob! We are fiddling with it while we wait for Vesper to come back!
Stu

 

[Habebty]

My mate here in Gib with his expensive Vesper and Vesper splitter is having exactly the same prob! We are fiddling with it while we wait for Vesper to come back!
Stu

Be good to hear what they say, as they told me it was likely to be a poor aerial or connections?

 

[david_bagshaw]

As per Salty John's post

Plus ... if you're in a marina, you''re surrounded by lots of big metal things sticking up all over the place and, most likely, in a hole in the ground. With an antenna mounted low down your AIS reception is likely to be fairly pants. Once you get out into open water, it should be perfectly adequate

You can run a transceiver through a splitter but it needs to be an active splitter which is considerably more expensive than a passive splitter (an active splitter switches the antenna between two transmitters thus avoiding the receive side of the inactive transceiver from being blasted to hell and gone by the active transceiver)

A final thought ... I'm beginning to seriously wonder if there isn't a downside to having an AIS transceiver antenna mounted high up. Obviously, given my line of work, I play around with quite a lot of kit on quite a lot of boats and I have a growing suspicion that the downside of masthead AIS antennas is reduced frequency of transmission especially when there's a lot of targets being picked up

My theory, and it's very much speculation at this stage, is that given that there are a limited number of transmission time slots available, a transceiver which is seeing targets at long range (> 10 to 15 miles, and mine merrily picks up shipping at 30 to 50 miles consistently and sometimes out beyond 100 miles if the conditions are right) sometimes struggles to find a "free" time slot whereas with a lower mounted antenna with reduced range the transceiver sees more "free" time slots

I'm not sure at this stage whether it's a significant issue (my feeling is that it isn't) but at some point in busy waters I'm going to switch around between my mizzen mast AIS antenna and (when I get the thing fitted) my pushpit rail mounted backup rubber duck and see what happens

interesting thought. I believe the system can cope with 8000 ships at once. had no problem with transmitting in Rotterdam when i had 750 ships showing on my system.

 

[Bru]

interesting thought. I believe the system can cope with 8000 ships at once. had no problem with transmitting in Rotterdam when i had 750 ships showing on my system.

It was a passing thought and having looked deeper into the workings of AIS it can probably stay passed!

There are in fact 4,500 time slots a minute for transmissions and the system can cope with significant levels of overload without too much degradation and prioritises vessels within 8 to 10 miles of each other

 

[BrianH]

Below are two track reports of my day sail yesterday, the first reported by MarineTraffic, the second by VesselFinder. Note the straight lines where no report was received from my transmitter and the track line joins from the last received to the next.

MarineTraffic offers receiver location and operability data and this track was supplied by data from Koper, Slovenia, ca. 20nm distant from the position area. VesselFinder is very coy about where its contributing receiver stations are, nevertheless, its coverage is usually more extensive.

Wind was from the south at ca. 15 knots and once clear of the lagoon at the Lignano entrance I was under full sail alone. As both straight lines of no reception for MarineTraffic and few by VesselFinder, were when on starboard tack with the port side of the boat down, the AIS antenna is mounted on the aft rail on the port side so I am presuming it is pressed down too low or shielded (perhaps by the wind generator mast ahead of it) on that point of sailing. And, of course when heeled, the half-wave dipole is no longer vertical with the most effective horizontal propagation.

So perhaps for a sailing vessel the angle of heel is also as important as height of antenna ......

 

[BrianH]

Below are two 'Last Track' reports of my afternoon day sail yesterday, the first reported by MarineTraffic, the second by VesselFinder. Note the straight lines where no report was received from my transmitter and the track line joins from the last received to the next.

MarineTraffic offers receiver location and operability data and this track was supplied by data from Koper, Slovenia, ca. 20nm distant from the nearest report position area. VesselFinder is very coy about where its contributing receiver stations are, nevertheless, its coverage is usually more extensive.

Wind was from the south at 15 knots and once clear of the lagoon at the Lignano entrance and its 1nm seaward channel, I was under full sail alone. As both straight lines of no reception for MarineTraffic and few by VesselFinder, were when on starboard tack with the port side of the boat down, the AIS antenna is mounted on the aft rail on the port side so I am presuming it is pressed down too low (basically almost to sea level) or shielded (perhaps by the wind generator mast ahead of it) on that point of sailing. And, of course when heeled, the half-wave antenna is no longer vertical with the most effective horizontal-plane radiation pattern.

So perhaps for a sailing vessel the angle of heel is also as important as height of antenna ...... Or a gimbled antenna, anyone?

​

 

[ex-Gladys]

That's a common factor with Marine Traffic, but is because they do have to have a volunteer with an AIS receiver plugged into their network to receive the signal... You won't see many leisure tracks mid channel between Devon/Cornwall and France for example

 

[Habebty]

That's a common factor with Marine Traffic, but is because they do have to have a volunteer with an AIS receiver plugged into their network to receive the signal... You won't see many leisure tracks mid channel between Devon/Cornwall and France for example

True, but it is a bit disappointing to look at Marine Traffic on ones phone and see the yacht next to you but not ones own signal

 

[Heckler]

Be good to hear what they say, as they told me it was likely to be a poor aerial or connections?

They came back making noises about antennas but did offer to send the unit back to NZ for checking! I put my SWR meter on the cable direct from the radio to the antenna up the mast. It read 3 plus even though the software on the Vesper said the SWR through the Vesper splitter and the antenna was one! I am of the opinion that the software could be crap, giving a wring reading. I checked the connection under the mast, it looked like a cheap tv connector and was all verdigreed. We put a proper 259 connector on and it got a touch better BUT the mast cable was a solid wire core piece of poo! I got the bins on the mast head antenna, it looked like a Metz. I told him he needs to get some decent coax up to the Metz and then we can recheck it.
Stu

 

[RIBW]

.... I put my SWR meter on the cable direct from the radio to the antenna up the mast. It read 3 plus ....Stu

FYI: On my boat, using a typical cable loss figure and the mast height, a VSWR of 3 at the base of the mast equates to total reflection of the RF at the top of the mast i.e. no RF power into the antenna. In practice, I could get an occasional DSC 'ping'.

Cheers
Bob

 

[Rivers & creeks]

I did my first ever decent bit of soldering on the plug, well nice it was. Had no effect on the signal