pongoglo
regular
Reged: 28/09/2006
Posts: 28
Loc: Portsmouth
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I have a NASA AIS 2 connected to a Garmin 298C plotter/sounder. The AIS seems to interface fine with the Garmin but the detection range is very very poor. I am only picking up AIS targets at 1.5 miles or less? I believe the problem might lie with my antenna connection? Im using a pushpit mounted 2m Glomex antenna which should give me a detection range of 12 miles or more, however Im using a standard TV aerial extension cable between the Glomex lead and the AIS BNC fitting? Do I need a specific marine VHF cable, or do you think the problem might lie with the connectors? Any advice gratefully received!
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Saltyjohn
regular
Reged: 06/09/2004
Posts: 1974
Loc: UK
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You need a 50 ohm impedence coaxial cable, TV cable is 75 ohm.
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John
http://www.saltyjohn.co.uk
Uncommon cruising kit: Metz, Loos, Bandit, Clipper...
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R32Stbrigid
regular
Reged: 16/01/2004
Posts: 160
Loc: Solent
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I have a pushpit mounted aerial and regularely see AIS targets at 12+ miles, So I am sure SaltyJohn is correct .....
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Fireball
regular
Reged: 15/11/2004
Posts: 7849
Loc: Chichester
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Whilst my learned friends are pointing towards your antenna and cabling can I suggest that you test your engine using a mast head antenna.
With my masthead antenna I can receive ships from ~35Nm away, but this was after having the engine replaced by NASA following a range issue where I could only "see" ships less than 5Nm away ...
It would be really handy if you could test against another known good engine/display on your current set up - if your engine is still giving poor range then contact NASA as it is likely to be an engine fault - this appears not to be uncommon!!
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pongoglo
regular
Reged: 28/09/2006
Posts: 28
Loc: Portsmouth
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Thanks for that. any idea where I can source a 50 Ohm cable - (pref with connectors fitted!)?
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Barnac1e
regular
Reged: 31/01/2008
Posts: 153
Loc: Switzerland/Italy
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I have my antenna (supplied with the AIS receiver along with 5M of cable) mounted on an aft mast about 2m high and receive reports on average between 6nm to 10nm. The maximum I have seen has been 23nm.
Someone in the marina said I should mount it at the masthead as he had seen a demonstration where reports were being received from ships 50nm away. I answered that I wasn't interested in ships 50nm away - I only wanted to know about the ship on a collision course in my immediate vicinity. Why clutter your reporting list with irrelevant reports that you may never get close to?
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maxi77
regular
Reged: 11/11/2007
Posts: 858
Loc: Kingdom of Fife
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Try Maplin who I think do cut lenths and a wide range of connectors.
I there is a radio ham or CB radio store near you they will be able to supply as well.
Avoid marine electronics places as their prices make your eyes water.
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Peter
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pongoglo
regular
Reged: 28/09/2006
Posts: 28
Loc: Portsmouth
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Ok. Maplins do it. Ive also noted that my BNC connectors are 75 Ohm, so that might be causing the problem as well? If I dont get any joy with the 50 ohm cable, and replacement connectors I will take up Fireballs suggestion and return to NASA.
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pongoglo
regular
Reged: 28/09/2006
Posts: 28
Loc: Portsmouth
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I agree with Barnacle. Too great a range would be an impediment. Even with the 1.5 to 2 NM range Im getting at the mo Im finding I get sufficient warning at night to be useful, but 5 -12 NM would be nice! What I am finding is that a lot of contacts are comin up as 'unknowns', and the system can take up to 10 mins to identify the target by name. Has anyone else found this?
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Fireball
regular
Reged: 15/11/2004
Posts: 7849
Loc: Chichester
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No no no no no ... don't just return ... theyll send it back saying there is nothing wrong with it .... YOU have to test it first!! Based in Portsmouth there should be loads of others with similar setup, it doesn't take long to do, but will give you peace of mind that it is your cabling at fault and no the engine ... or vis versa!
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