GPS fix problems.

[tsekul]

Hi There,

We have recently acquired a boat with a standard horizion gps chart plotter.. It can take hours for it to acquire its position which makes it fairly useless for anything but long passages. What things can I check to see where the problem lies ? it is attached to a standard horizon vhf linked for dsc.

I will start by checking the cabling but not sure where to go from there

The antenna is located on the transom clear of all obstructions, we do have another gps, older Garmin which is located in the cabin which works fine.

thanks
T

 

[AngusMcDoon]

Check connections. It's nearly always the connections. Scrape pins with a screwdriver.

 

[johnjfrake]

Go to your local branch of Maplins and buy some contact/switch cleaner. get some coarse cloth and an old tooth brush. Use contact cleaner generously with old tooth brush on pins and sockets, wipe with cloth firmly but don't wrench at anything. You won't be able to get to the bottom of the sockets but you may be able to penetrate far enough without doing any physical damage.The gold plating should be nice and shiny. Be careful when scraping with anything sharp you can remove the plating after which its all down hill unless the plugs and sockets are very well sealed in which case why corrosion to begin with? Good luck

 

[lw395]

Is the cable to the antenna co-ax or multi core?
If It is coaxial, you probably have a typical active antenna, that is an antenna with a low-level amplifier built in.
In that case, I would try substituting another active antenna, you can get them on eBay for a few pounds, the trick is getting the right connector or finding an adaptor. Most require a metal ground plane to work properly, they are intended to mag-mount on a car roof. A piece of metal about a foot square will do.
This test will tell you if your old antenna is dead, quite common for them to fill with water or just corrode.

If it's multicore, the antenna has a receiver built in and passes data to the display box. If it's not a simple wiring problem you need a similar unit to test with.

Do you leave the GPS on for long periods? It is a good thing to do, many of the receivers correct their internal frequency, which will drift over time, but will only make corrections after a long period of being switched on.
Old GPS's which used to acquire in a minute or so commonly take many minutes to acquire because they have drifted, even if they are not faulty.
I have an old Magellan which I rarely use, it will take 15 minutes or so to acquire if it's not been on for a year. When it acquires, it will be fine, and will hold lock as well as most things.
In many units there is a software option to tweak the internal settings.

 

[ostell]

If the Plotter has an internal aerial, and many SH have, then it could be shielded by it's surroundings so that it takes a long time to acquire. Check that there are no areas of metal in the area of the plotter, especially above. Can you move the plotter into clear air (in the cockpit)? If matters improve then you know what the problem is.

 

[tsekul]

Thanks for all the tips. will give it a go and see where we get to. Being a silversmith I should be able to get things clean and shiny.

Tim

 

[MASH]

I think he said the antenna is on the transom...

In which case the most likely cause is the cable connector at one end or the other, or possibly dud cable or antenna, so check them first. If no joy substitute another antenna and see what happens. They're cheap enough on ebay/amazon/maplin.

 

[bitbaltic]

Just because there is an antenna on the rail doesn't mean it's connected to the standard horizon... Previous owners often do silly things! The Garmin works fine and if it's an old school one then it needs an external antenna which probably means the one on the rail is working fine. My first thought is that said antenna is connected only to the garmin and not to the standard horizon, which is struggling with an internal antenna. First thing I'd do is chase down the external wire to eliminate this possibility.

 

[ithet]

If it is a SH180 or 300 with external aerial it will be an active aerial. This sends out NMEA0183 data to the plotter. You can see the data that is being recieved at the plotter using one of the menu settings. If this data is not available then I would check the electrical connections as recommended. The cable is a multi core type, but not all cores are used. (If the cable is co-ax then contrary to earlier post it suggests it is not an active - NMEA aerial).

If you confirm that you have one of these types of plotter I can give more info.

 

[noelex]

I think it will be an active antennae (an external GPS unit). Checking and cleaning all the connections is the first step, but its likely the antennae unit is defective.
A slow fix can be caused by an internal battery problem and replacing this battery in the antennae would be worthwhile.
If this does not fix the problem its a new active antennae, but any model with NMEA 0183 output should be OK. The Evermore units have a reasonable reputation at low cost.