AIS aerial vs AIS/VHF splitter

Champagne Murphy

Champagne Murphy

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I have both a splitter for the mast head antenna and a push pit antenna on short pole. Currently, the AIS is on the splitter/mast head, as it gets much better range up there. The AIS worked on the pushpit antenna but the range was about 16 nm. I tried a stubby rubber antenna on my old NASA AIS "radar" receiver. It worked but the range was about 10 nm.
 
Where does your DSC radio get its GPS signal from ?
If its not built into the radio then be aware that this could affect your decision if the baud rate of the radio and plotter are incompatible.
I ended up buying a separate GPS aerial for my radio
 
I have heard stories of problems with VHF+ splitters but mine at the masthead works fine. I can perceive no difference in the radio from before, and I get AIS from ships at something over 40m in average conditions. My splitter is installed with a Raymarine AIS, but I don't hink it is from them. I suspect that the specification and quality of the splitter are important, as with so many things.
 
Halo said:
Where does your DSC radio get its GPS signal from ?
If its not built into the radio then be aware that this could affect your decision if the baud rate of the radio and plotter are incompatible.
I ended up buying a separate GPS aerial for my radio
Click to expand...

The thread is about a VHF/AIS antenna, not GPS.

Do try and keep up :)
 
My preference is for a separate antenna at the pushpit. I prefer to keep AIS and VHF separate and having the antenna at the pushpit give you an almost ready you use emergency VHF antenna.

Make a cable up with a PL259 at one end, taped next to the VHF antenna socket and a connector at the other end for the AIS antenna cable, taped near the AIS.

or

Fit the AIS close to the VHF and fit a PL259 to the AIS antenna cable, use an adapter to connect it to the AIS box.
 
A single antenna for more than one frequency (that includes sending the whole VHF band up one twig) is a compromise. You usually select the antenna to suit the most important (most used) channel and accept that performance for other frequencies is reduced.
So, if there are no other considerations then one twig for VHF and one for AIS is best.
But (and theres always a but) there is usually more to consider...
Antenna real estate for one, how many can you fit where you want them?
Installation, its way easier to use a splitter than run another coax up the mast.
Appearance, do you want to sail a hedgehog?
 
Champagne Murphy said:
Does anyone have any experience of these alternatives?
I've been using a VHF aerial on the pushpin rail but twice it has proven to be vulnerable and I'm fed up with the cost of replacement. Glomex produce a rubber 'stubby'

https://seamarknunn.com/cgi-bin/sh0...ais-marine-antenna-ra111ais-5040.html#SID=553

which might be good but how does it compare against a splitter like this?

http://www.force4.co.uk/glomex-vhf-...gclid=CKft3pi6uNQCFcS37QodoZUODw#.WT6cvTOZNjQ
Click to expand...

I have a splitter on my AIS transceiver and it works very well and was easy to wire up.

You need to consider whether you might ugrade from an AIS receiver to and AIS transmitter/receiver because the Force 4 on will not work with AIS transmissions. If you might upgrade it might be more cost effective to buy a suitable splitter at this stage.

Richard
 
I had mine on a pushpit aerial, and the range wasn't great. I recently put a Glomex splitter in and it's WAY better.

Worth the £60.
 
Dougal Tolan said:
A single antenna for more than one frequency (that includes sending the whole VHF band up one twig) is a compromise. You usually select the antenna to suit the most important (most used) channel and accept that performance for other frequencies is reduced.
So, if there are no other considerations then one twig for VHF and one for AIS is best.
But (and theres always a but) there is usually more to consider...
Antenna real estate for one, how many can you fit where you want them?
Installation, its way easier to use a splitter than run another coax up the mast.
Appearance, do you want to sail a hedgehog?
Click to expand...

But AIS is VHF, and is part of the marine band segment of the VHF part of the spectrum.

VHF is a bit imprecise in this discussion, though commonly used. (VHF = 30 to 300 MHz)
So technically any antenna is best on only a single frequency, the standard marine VHF antenna is also a compromise, being used on a range of frequencies (channels), and AIS is within that range.
 
PaulRainbow said:
My preference is for a separate antenna at the pushpit. I prefer to keep AIS and VHF separate and having the antenna at the pushpit give you an almost ready you use emergency VHF antenna.
Click to expand...
That is my philosophy too, my pushpit antenna - a very whippy, half-wave, shunt-fed Metz - performs well with an average reception of ca. 15nm. Presumably my 2W transmission coverage could be slightly less but well withing safety reporting range. No need to clutter the target list with unnecessary processing for distant ships I am unlikely to be within striking distance of in a day's sailing ... Let's not forget the fundamental functionality of why we install the technology.
 
Barnac1e said:
That is my philosophy too, my pushpit antenna - a very whippy, half-wave, shunt-fed Metz - performs well with an average reception of ca. 15nm. Presumably my 2W transmission coverage could be slightly less but well withing safety reporting range. No need to clutter the target list with unnecessary processing for distant ships I am unlikely to be within striking distance of in a day's sailing ... Let's not forget the fundamental functionality of why we install the technology.
Click to expand...

It is slightly amusing in AIS threads to read people saying "but i could only see targets 20nm away".
 
PaulRainbow said:
It is slightly amusing in AIS threads to read people saying "but i could only see targets 20nm away".
Click to expand...

I would be happy to spot the fast cats from Ireland coming into Holyhead from more than 20 miles out. It takes me over an hour or more to get from Carmel Head to South Stack or Port by which time they may be on me.

Consider also if you are using a transponder that its job is to alert other users as to your position and track.

I doubt in the sort of sea conditions that we meet in this area that my pushpit mounted ais gives them more than 10 miles AIS visibility. I will be fitting a splitter for our transponder to use the masthead VHF for improving our visibility to other faster and bigger water users. I would prefer they spotted us earlier rather than later!
 
For VHF communication range (radio and AIS) height above sea level is the most significant factor.
(Your radio horizon in nm is 1.4 x root of antenna height in feet above SL. Range is your radio horizon plus that of the antenna you're communicating with).
So, if you can put both antennas at the masthead with better than at least 0.5m horizontal separation, it's the way to go. Next best would be masthead with a good quality splitter. Many splitters only allow AIS reception, not transmission.

What the splitter doesn't give you is a back up system - in case you lose the mast, or if the masthead system is in some way faulty. A pushpit antenna provides back-up.

Also worth mentioning that an AIS antenna is, in many cases, a VHF radio antenna with a couple of inches lopped off the whip. This moves the tuning point from the centre of the frequency range up to 162 MHz, at the far right hand side of the band. Any improvement in performance over a standard VHF antenna is minimal, if detectable at all. Clearly, if you are using a splitter, you should use a full VHF range antenna so as not to compromise radio performance and the same applies if you want the pushpit AIS antenna to serve as the radio antenna in an emergency.

Commercial warning: I sell VHF antennas.
 
I don't have particularly strong feelings about splitters vs dedicated antenna and I mainly decided to use a splitter as it was much easier to install as the AIS transceiver is mounted "below decks" next to the VHF.

Thinking about what is more likely, being run down in the day or night by a larger vessel or getting into some other survival situation where the masthead antenna is down and I quickly need a backup VHF antenna, I'm a lot more concerned about the "big ship" scenario so anything which transmits my AIS signal are far as possible and allows me to see them coming from as far away as possible seems like a good side-benefit from using the simpler installation.

Richard
 
Splitters do work but they are a compromise. Some signal strength is lost, although this is more important transmitting than receiving because leisure boats are Class B which is reduced in power compared to Class A.

So yes, a splitter does work and makes installation easy.
But to get the best out of the AIS it is better to fit a separate aerial, although I would argue this is only necessary for transmitting. Receiving is not a problem.

Consider all the things Dougal mentioned in post #8, but also, if you want to be seen by friends and family on Marine Traffic as well as by other boats & ships, fit a separate aerial, the longer the better (taking into account post #8 above).

If being seen on the internet isn't important, you'll be fine with a splitter although ships won't see you from quite as far away.
 
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