VHF splitters for AIS or separate aerial ?

[tom52]

Do vhf splitters really work ? Even with a splitter is the reception strength degraded so your radio is compromised ?
Would a rail mounted separate aerial for the AIS be a better choice ? OK, much reduced range compared to masthead, but radio uncompromised and you have an extra vhf aerial for an emergency and it is only half the price of a splitter.
What do you think.

 

[Blue5]

rail mounted separate aerial

 

[Salty John]

This comes up regularly and the overwhelming view is get a separate antenna.

A rail mounted AIS antenna works because it is communicating with large vessels on which the antenna is mounted very high up, so the combination of antenna heights is still conducive to reasonable distances. A receiver height of only 10' and a transmitter height of 40' gives 12 nm range.

 

[[2574]]

I had the rig down so got the rigger to add a separate aerial for the AIS at the masthead - just because I didn't want to compromise the VHF which is, after all, no. 1 piece of safety kit. With the mathead AIS aerial I can see shipping mid channel on the AIS when I'm in Plymouth Sound.

rob

 

[Amulet]

I have a rail-mounted separate aerial. It gets ships up to 15 miles away (at least), was cheap, and works pretty well with my main VHF which could be useful if my mast went over the side.

 

[mixmaster]

I just had an easysplit installed and works great. One aerial up the mast used for both vhf and a class B transceiver. On the other hand I had a cheap splitter with an ais receiver before that and the reception was very poor.
My conclusion is the splitter you use matters and the easysplit product works very well.

 

[boatmike]

If you have the opportunity a second antenna is certainly better as there is less to go wrong and it does not matter if it is low down. Splitters work OK though. I have just added a Standard Horizon DSC radio, SH 500 plotter with easyAIS and I got an easy splitter thrown in with the package deal.
I have fitted the new VHF with a new masthead antenna without splitter (and it is superb) The old Kelvin Hughes fixed VHF still works OK so I fitted the splitter between that and the AIS on an antenna on my rear arch. The AIS works very well and it does not seem to have degraded the signal to the KH much either so I have back up if anything were to fail on my DSC.
The lesson I think is that AIS does not need a high antenna, but splitters don't make too much difference to the signal if you need to use one. The important issue I think is work on the kiss principle with your VHF. If the splitter were to go wrong you dont want to lose your main distress calling radio.

 

[whipper_snapper]

This does keep coming up and of course there is no right or wrong. But my analysis led me to go for a pushpit mounted 2nd antenna:

splitter------------------------------- 2nd ant on pushpit
------------------------------------------------------------
more expensive----------------------less expensive
some signal loss to VHF-------------no signal loss to VHF
minimum of 4 RF connections------minimum of 2 RF connections
additional point of failure-----------no extra POF
no back-up for VHF ant-------------backup for VHF ant
easy installation ---------------------less easy installation
Increased range for AIS-------------marginally reduced AIS range
shiny gizmo with flashing LEDs-----no shiny gizmo /forums/images/graemlins/frown.gif

I would not put 2 ants at the masthead either as I would worry about interference and overload, and it provides no backup if the rig comes down. The marginal AIS range increase from a masthead mount does not seem very useful.

 

[Channel Ribs]

Another vote for a second vhf antenna here.

 

[fireball]

all you who have put a second antenna at the mast head - have you managed to achieve a min 1m separation between antennas?

 

[RestlessL]

[ QUOTE ]
all you who have put a second antenna at the mast head - have you managed to achieve a min 1m separation between antennas?

[/ QUOTE ]

I thought long and hard about this, and this was, in the end, the main reason why I did not mount the AIS aerial at the mast head.

My main VHF stands off to the side of the masthead, and I did consider mounting a short stub vhf aerial in line with the main aerial, inverted and below it. This would minimise interference between the two aerials. I also considered mounting the stub aerial on the spreaders.

In the end, I retained the pushpit mounted aerial. This is currently a 5ft fibre-glass job, but I may replace it with the short stub, which is less likely to be pulled off by accident.

I currently have receive-only AIS. Class B set is way down on my list of priorities. I did consider the effects of using a pushpit mounted aerial for transmitting, but am assured that there is no significant safety issue.

I also have a receive-only FM-VHF splitter so that the pushpit aerial also drives the FM radio. This is mounted just below the VHF set, and the mast-top and pushpit aerial leads can be swapped over if required so I could extend the rande of the AIS, at the expense of VHF range if I wanted to.

The pushpit aerial lead passes through the deck via a plug/socket (all my other feed throughs are glands). I also have ready-made lead and adapters to connect the handheld (Entel), allowing me to connect the h/h from the cockpit to the masthead aerial should my main VHF set fail.

John

 

[hubert]

I'm all for a second antenna for the ais. IMHO there should be as few as possible connections between the vhf and antenna.
Inserting a splitter needs a joint between the centre of the coax to the plug...the plug to the socket...socket to pcb...pcb to other socket... socket to plug....plug to cable.
The screen has the same number of connections.
That adds 12 extra joints in the vhf cable. When things fail it's usually at a joint!!!

 

[PCUK]

Splitters degrade VHF transission.
Stub aerial at roof level is fine.

 

[pielago]

Hello,

Very good news regarding this topic. There has been recently launched a AIS VHF splitter that works with AIS class B transponder. You can share the same antenna both for AIS transmission and VHF radio.

http://digg.com/hardware/Boating_electronics_First_splitter_for_AIS_transponder

and you can purchase it from this site:

http://www.atlantic-source.com/class-b-ais-splitter


-------

good wind and miles for every sailor!

pielago

 

[tom52]

Ignacio, what are you the owner of atlantic-source or just an employee ?

Very good news my ar$e !

My rail mounted stubby works fine and was cheaper than a splitter, does not compromise my radio reception and provides an emergency radio aerial. All for £40.

If you intend to do anymore sales pitches on here then at least credit us with some intelligence and do us the courtesy of some subtlety.

 

[samwestwood]

I did allot of work for charter companies and have always found that VHF aerials and splitters are a big no no as most degrade quickly becuse of the power going through them when the arial is in TX.

 

[tudorsailor]

What make & model is your stubby aerial???

TudorSailor

 

[markdj]

Very interesting post and one I was thinking of asking to so many thanks for starting the post.

All of the splitters just so happen to leave out the fact of reduced VHF sensitivity and for VHF this is a very important issue.

If you are 50 miles from the CG transmitter you want to make sure you are going to be able to hear the transmissions and that you are getting the maximum clean signal transmitted.

For FM and general radio I have found a handrail the best for an aerial so that keeps any reduction in using another splitter.

We will probably be fitting a class B digital yacht AIS as they sell them with a seperate GPS and VHF aerial included - I haven't found a better deal anywhere.

The stubby aerial with it is probably not that great but at least it's better than a splitter and height is the key.

I think an SWR meter is invaluable here for testing your antennae. I've seen a 1/1.1 antenna that looks likes it's gone through a war yet the connections were spotless, the length of the wire was never cut and it used tinned cable so it worked great for long distance.

 

[richardm47]

Is it technically feasible to make a VHF/DSC radio that also does AIS? All in one box. Connections from radio to only one aerial. No separate AIS box, and no separate splitter box.

After all AIS is using vhf transmissions, so is DSC, so why couldn't one box do all those jobs? But I've only seen separate dedicated AIS boxes. Would be great to cut down on the number of boxes on board, wouldn't it?

Anyone got the technical knowledge to comment? Maybe it is commercially better to wait until everyone has bought separate boxes before they bring out a combined one and sell them all over again? (Or maybe they are already available and I've missed them.)

 

[alan]

Yes, technically it is possible and probably quite easy. The way to go would be to use DSP (Digital Signal processing) and do everything with software including filtering e.t.c. I don't know what this would cost but if one company did it ahead of the others and grabbed what is a potentially a huge market still waiting to upgrade to DSC Radio then the number of potential sales should be quite attractive.

Alan.