Hoolie
Well-Known Member
I'm thinking of installing a second antenna at the masthead for an AIS transponder. Is there likely to be any mutual interference with the VHF antenna about 50 cm away?
Masthead VHF antennas
- Thread starter Hoolie
- Start date
lw395
Well-Known Member
Yes.
pvb
Well-Known Member
The usual guidance is that VHF antennae need to be at least 2 metres apart, so the masthead is out as a potential location. You could mount an antenna on the spreaders, but it would probably be easiest to put one on a stern rail - the slight loss of range won't be a major problem for AIS use.
Hoolie
Well-Known Member
Thanks! We already have an AIS antenna on the stern rail but it's receive only. It's OK for up to about 12nm so I was hoping for something better on the mast when we upgrade to a transponder.
pvb
Well-Known Member
What sort of range were you hoping for? It's AIS after all, not life-or-death communications.
johnalison
Well-Known Member
My AIS works with a splitter and I regularly pick up ships from 40 miles from my masthead VHF aerial.
Hoolie
Well-Known Member
I must admit a splitter is a possibility but we have the mast off now and an additional antenna could be a low cost option.
pvb
Well-Known Member
Stick it on the stern rail and you can use it as an emergency VHF antenna if you ever get dismasted.
Mrnotming
Well-Known Member
A splitter seems a good idea, especially if you retain the Pulpit mount or make a pole mount aft.
Best of both worlds, and covered in case of a dismasting!
Glad to hear that a splitter allows reception up to 40nm.
Wondering what the maker name of that kit is?
Best of both worlds, and covered in case of a dismasting!
Glad to hear that a splitter allows reception up to 40nm.
Wondering what the maker name of that kit is?
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paddywackcocker
Well-Known Member
Just done this me self, slight on the tilt so it doesn't catch the wind pointy on the VHF aerial thing and even then it was a, well if the winds that strong they'll bend at the same rate. Ended up I reckon about 0.5mtr closest.
As interference goes, even sheilded the coax runs down the mast an awfull long way side by side and don't seem to have any probs, I think much better than a splitter and at the end of the day as mentioned, if contact made and your under presure then your probably relying on the Radio and your loundry requirements more than the ais so you could always switch it off. In my case when really needing clean communication on the radio, it's the fridge compressor that gets me rattled, that goes straight off.
As interference goes, even sheilded the coax runs down the mast an awfull long way side by side and don't seem to have any probs, I think much better than a splitter and at the end of the day as mentioned, if contact made and your under presure then your probably relying on the Radio and your loundry requirements more than the ais so you could always switch it off. In my case when really needing clean communication on the radio, it's the fridge compressor that gets me rattled, that goes straight off.
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pvb
Well-Known Member
I can't see the logic of putting an AIS transceiver antenna at the masthead. The thing only transmits at 2W, so you'll be lucky to get much more than 7 or 8 miles range, and you'll get nearly that with an antenna on the stern rail.
paddywackcocker
Well-Known Member
Mast was down, I was renewing cables and coax so I thought, "what the heck"
Good job, there was a horrible chafe on the VHF coax ware in exited top of mast that would have created problems later.
And I like to look at boats 20 miles away that I'm not going to hit
Good job, there was a horrible chafe on the VHF coax ware in exited top of mast that would have created problems later.
And I like to look at boats 20 miles away that I'm not going to hit
pvb
Well-Known Member
IanR
Well-Known Member
My understanding for receivers is that an aerial splitter is ok
For transponders it is a NO unless the ais transceiver is electronically combined I.e. Well aware of the other unit and synchronised as it is not a good thing for both to transmit simultaneously
For transponders it is a NO unless the ais transceiver is electronically combined I.e. Well aware of the other unit and synchronised as it is not a good thing for both to transmit simultaneously
RichardS
N/A
Having the AIS antenna at the mast head with an active splitter obviously gives a much greater reception range than 7 or 8 miles - from 50 miles to ten times that on my unit - but I've never bothered to monitor how far the furthest away Class B transmitter is. Of course, it's primarily the Class A boats that I'm concerned about but the Class B reception range is an interesting point. I'll check out the Class B range when I'm next on the boat.
Richard
RichardS
N/A
Any active splitter will ensure that both AIS and VHF cannot transmit at the same time. In addition, if power is lost, most/all will also ensure that the VHF remains connected to the antenna.
Richard
pvb
Well-Known Member
You'll find it's not very far. Only 2W output.
And, of course, most plotters only display a finite number of AIS targets, and generally prioritise those nearest.
RichardS
N/A
Just checked on several random locations on Marine Traffic and there are plenty of Class B targets which are 30km offshore and must be being picked up by shorebased receivers, I guess.
Richard
pvb
Well-Known Member
Marine Traffic also shows data from satellite receivers and vessel-based receivers.
PaulRainbow
Well-Known Member
Fitting the antenna on the mast will give a greater range purely because of the greater horizon.
Some of the figures being quotes on here are a bit suspect. The typical horizon between two sailing yachts with masthead mounted antennas is about 18 miles. If another vessel is being picked up at 40-50 nm then someone has an extremely high antenna.
Some of the figures being quotes on here are a bit suspect. The typical horizon between two sailing yachts with masthead mounted antennas is about 18 miles. If another vessel is being picked up at 40-50 nm then someone has an extremely high antenna.
