AIS

[Graham_Wright]

I have had a suspicion that my Mtsutec AIS was not transmitting as Marine Traffic et al showed only intermittent records.
Son, monitoring from afar, reported the same.
I currently have problems marrying all the electronicals but the flashing lights indicated A & B reception and transmission.
Eventually got round to diagnosing. The SWR meter declared one antenna good the other not so good.
Tracing the cables from the nav station to the mast base, I discovered the AIS output coax mysteriously changed colour from black to white during its passage behind the head lining.
That was not true. I had used the wrong cable mixing it up with the NASA "Radar".
Connecting properly, the ship is now visible to all.
However.
The above head lining cable is roughly three metres in length, dangling freely and obviously not terminated. Despite that, it was apparently receiving information quite happily and occasionally transmitting.
Fascinating!

 

[Refueler]

Good you found the problem ...

Headlinings are lovely - till you need to sort wiring.

Note : SWR meters and VHF Radio Diagnostic Menu are useless if you use a splitter on the antenna ... the splitter will not allow SWR meter to function ... and the radio diagnostics will report error antenna ...

 

[Graham_Wright]

Good you found the problem ...

Headlinings are lovely - till you need to sort wiring.

Note : SWR meters and VHF Radio Diagnostic Menu are useless if you use a splitter on the antenna ... the splitter will not allow SWR meter to function ... and the radio diagnostics will report error antenna ...

I have two masthead antennae separated by the required 1 metre. Looks over the top but works!
I would still like another antenna for emergency use (e.g. when the mast goes over the side) but hate embellishing the pushpit.

 

[johnphilip]

I have two masthead antennae separated by the required 1 metre. Looks over the top but works!
I would still like another antenna for emergency use (e.g. when the mast goes over the side) but hate embellishing the pushpit.

When I upgraded to class B from receive only I found the Garmin 800 had a built in splitter so that was an easy choice without introducing more hardware or aerials. So the old AIS aerial on a pole on the pushpit is now my spare and the AIS gets better reception. (that may also be because the Garmin is rather better than the old NASA. Yes it was not the cheapest but it saved other expense and faf.

 

[Refueler]

I have two masthead antennae separated by the required 1 metre. Looks over the top but works!
I would still like another antenna for emergency use (e.g. when the mast goes over the side) but hate embellishing the pushpit.

Quote from AIS Data site :

The minimum recommended separation distance between VHF and AIS antennas is generally 2 meters (approximately 6.5 feet) horizontally and 1 meter (approximately 3.3 feet) vertically. This separation helps minimize interference between the antennas and ensures optimal performance for both.

 

[lustyd]

We’ve had numerous issues on MarineTraffic which I’ve spent hours trying to diagnose.
Turns out when you sail far enough you hit the black spots that have no uplinks the Skerries is one example and north of Campbeltown another.

 

[st599]

Where did 1m come from between antennas (everything in electronic engineering is pluralised with an s for simplicity)?

I'm calculating about 1.9m minimum to prevent them interacting and changing the radiation pattern.

 

[Graham_Wright]

Quote from AIS Data site :

The minimum recommended separation distance between VHF and AIS antennas is generally 2 meters (approximately 6.5 feet) horizontally and 1 meter (approximately 3.3 feet) vertically. This separation helps minimize interference between the antennas and ensures optimal performance for both.

My 1 metre came from numerous sources and seems to be effective. 2 metres at the masthead would be very considerate towards pigeons and seagulls I suppose.

 

[st599]

My 1 metre came from numerous sources and seems to be effective. 2 metres at the masthead would be very considerate towards pigeons and seagulls I suppose.

It's not correct then. Less than 2 and you'll alter the radiation pattern of both antennas. There's also a significant likelihood you'll overload the AIS receiver every time the VHF is keyed.

 

[Refueler]

My 1 metre came from numerous sources and seems to be effective. 2 metres at the masthead would be very considerate towards pigeons and seagulls I suppose.

All online advice I find says 2m separation ...

I have an ex RF Engineer works for me ... he says 2m is MINIMUM !!

 

[Fr J Hackett]

For the life of me other than mounting an aerial on a long bracket attached to the mast head how does one get 2M? and my envisaged solution seems horrible

 

[lustyd]

For the life of me other than mounting an aerial on a long bracket attached to the mast head how does one get 2M? and my envisaged solution seems horrible

Agree, I’ve never seen anyone with 3m of stick and antenna on their mast so it’s irrelevant. Either install at spreaders/push pit or use a splitter. Even if one were to use a big stick, the antenna cable would be inside it right next to the other antenna!

 

[Refueler]

For the life of me other than mounting an aerial on a long bracket attached to the mast head how does one get 2M? and my envisaged solution seems horrible

Totally agree ... and is a good part of the reason splitters are there .... they are not only based on having one antenna doing the two jobs ... but also to avoid the 2m problem.

 

[dunedin]

For the life of me other than mounting an aerial on a long bracket attached to the mast head how does one get 2M? and my envisaged solution seems horrible

You don't get 2m separation. Hence why generally use a splitter for AIS

 

[pandos]

I see many boats with two antennas at mast head with only a foot between them. I have a stubby Ais and a Metz vhf on my masthead. Before I did this I spoke to several guys who have had the same setup for years and all reported no issues.

Lots of trawlers have masses of antennas close together..

I have never used my vhf to transmit but it receives very well and my AIS receives and transmits perfectly.

I wonder if this is a theoretical degradation or is it an actual real life issue...is an icom AIS so delicate that 25w of vhf transmitted a foot away via a aerial, which is different in style and shape, will fry it?

 

[st599]

I wonder if this is a theoretical degradation or is it an actual real life issue...is an icom AIS so delicate that 25w of vhf transmitted a foot away via a aerial, which is different in style and shape, will fry it?

It's not theoretical. No one's saying it will fry it. Having metal close to an antenna changes the radiation pattern. If you've got a second antenna at 1m, instead of a donut radiation pattern, you'll have a figure of 8 with nulls - meaning you can't transmit or receive well in those directions. A bad idea for both AIS and VHF.

 

[lustyd]

I wonder if this is a theoretical degradation or is it an actual real life issue

It’s certainly more a real life issue than the imagined problems with splitters, that’s for sure.

 

[AntarcticPilot]

It's not theoretical. No one's saying it will fry it. Having metal close to an antenna changes the radiation pattern. If you've got a second antenna at 1m, instead of a donut radiation pattern, you'll have a figure of 8 with nulls - meaning you can't transmit or receive well in those directions. A bad idea for both AIS and VHF.

Basically, directional antennae such as Yagis have extra "directors" parallel to the transmitting dipole. Remember the old "H" style TV antennae? If you put two antennae close together, that's what you'll be getting - a directional antenna, with nulls perpendicular to the line between the two and somewhat enhanced transmission/reception along the line joining them.

Splitters rule, unless you don't mind the reduced range of a pulpit mounted antenna.

Some AIS devices incorporate a built in splitter.

 

[pandos]

It's not theoretical. No one's saying it will fry it. Having metal close to an antenna changes the radiation pattern. If you've got a second antenna at 1m, instead of a donut radiation pattern, you'll have a figure of 8 with nulls - meaning you can't transmit or receive well in those directions. A bad idea for both AIS and VHF.

yes but is the loss in those directions not mitigated by the additional height of using the masthead? Also if the two antennas are substantially different in size ( One is a stubby) surely that won't cut off transmitting and receiving totally in some directions..)

Many mast head lights have some vertical metal elements in them do these not cause the same issue..

 

[pandos]

Basically, directional antennae such as Yagis have extra "directors" parallel to the transmitting dipole. Remember the old "H" style TV antennae? If you put two antennae close together, that's what you'll be getting - a directional antenna, with nulls perpendicular to the line between the two and somewhat enhanced transmission/reception along the line joining them.

Splitters rule, unless you don't mind the reduced range of a pulpit mounted antenna.

Some AIS devices incorporate a built in splitter.

As a teenager I used to build directional antennas for my CB...my memory was that the elements had to be precisely cut to length and carefully positioned to have any positive effect.