AIS range issue...

[Salty John]

AIS works on VHF, just as the radio does. The antenna doesn't increase the power of the signal, it directs it. It's location will determine how efficiently it does it's job but it doesn't influence the output power of the signal - that's done by the transmitter.
The AIS engine is designed to receive VHF signals from the AIS transmitter on a ship at whatever power they are transmitted. In fact, you can use the same antenna to receive and transmit your radio signal as well as your AIS signal - but I would prefer to have separate antennas rather than use a splitter.
There is no such thing as an 'AIS antenna', it's a vhf antenna.

 

[lenseman]

HEY!! /forums/images/graemlins/shocked.gif Let's slow down to a fast gallop!

You state that the connectors are 75 Ohm? This connector has a far thinner centre pin than the 50 Ohm BNC connector that is required. The 75 Ohm male centre conductor is more like a needle compared to a 50 Ohm centre pin.

In a 50 Ohm connector, the centre pin is about 30% fatter and more rounded at the end and without a noticeable 'shoulder' visible half way down the centre pin like the 75 Ohm connectors.

It might not even be making a connection with the AIS receiver at all and the poor AIS receiver might be really struggling to obtain any incoming data from the antenna? If this is the case then 2nM would be brilliant.

Change to 50 Ohm cabling and 50 Ohm connectors and re-test before you try and return the unit to the manufacturers.

 

[Graham_Wright]

[ QUOTE ]
AIS works on VHF, just as the radio does. The antenna doesn't increase the power of the signal, it directs it. It's location will determine how efficiently it does it's job but it doesn't influence the output power of the signal - that's done by the transmitter.
The AIS engine is designed to receive VHF signals from the AIS transmitter on a ship at whatever power they are transmitted. In fact, you can use the same antenna to receive and transmit your radio signal as well as your AIS signal - but I would prefer to have separate antennas rather than use a splitter.
There is no such thing as an 'AIS antenna', it's a vhf antenna.

[/ QUOTE ]

Right;- I'll try again!
Accepted you can share an antenna between VHF/DSC and AIS functions with suitable switching BUT if you have separate aerials and they are at the same height, e.g. the masthead, when you transmit on your VHF, you are irradiating the antenna used for the reception of AIS info with 25 watts. Someone called "Salty John" advised against that!

 

[Salty John]

Ah, the scales have fallen from my eyes! I understood you to mean that if you used the 'wrong' antenna then the extra power of the incoming radio transmission would fry the AIS engine and I was, therefore, trying to point out that they are all simply vhf radio waves.
You are, of course, right to be concerned at transmitting from one antenna into another at a few cm's distance. A horizontal separation of at least a meter is recommended. Sorry!

 

[Talbot]

[ QUOTE ]
This is a valid point for a limited number/frequency of potential threats. I agree that the ideal would be 20nm reception and let the software manage a filtering process based on proximity and CPA.

However, from the experiences of ranges in this thread, this implies a masthead antenna with VHF radio/AIS splitter complications. I agree this is probably the ideal way to go but my present setup has been so useful and effective over the past three years I am unlikely to change it anytime soon, or until I next have the mast down.But it also means that Mobos will always have a distance limitation .....

[/ QUOTE ]

My ranges are based on a 1.1m stailess whip from JGTech mounted on the top of my davits.

Distance from the VxTronix at the masthead was nearly double that.

 

[pongoglo]

OK. Last weekend (interesting weather!) I swopped the 75 ohm cable and connectors for 50 ohm RG 58 RF cable and 50 ohm BNC screw on type connectors from Maplin. We made a short but windy passage from Haslar to Chichester and back, mainly under engine due to wind direction and wave state. Much to my disappointment (and annoyance) I found that there was no improvement in detection range,despite there being a lot of big targets around (including Pride of Biboa..), all making much easier passage than us! On return I tested the cable and connectors with a £9.99 network cable tester also from Maplins. Great bit of kit http://www.maplin.co.uk/Module.aspx?Modu...=%5B%5BID%5D%5D . This showed instantly that one of the connectors was 'short circuiting'. Presumably the inner coming into contact with the outer. I re-did the connection, and all indicator lights show good. I used the screw on type BNC because they are much easier to use and provide a firm grip, but with hindsight the clamp on type are probably easier to check visualy. Anyhow, I suspect John Baldock is right, and the fault lies with the connections not the antenna or unit. All that remains to do is to test the connection at the base of the Glomex, and I suspect this might also show a 'short' . Hay ho - next weekend.....

 

[Massey]

Slightly different tack (!) and I hope fairly straight forward - I have a new VHF aerial at masthead and am planning to mount my old one on the pushpit for AIS (receive only). Which one should I use for AM/FM. Many thanks

 

[fireball]

Your Pushpit one - leave your masthead antenna connections and cable to the VHF as simple as possible ... the one thing that can be relied on is that technology will fail at the worst point possible ...