lost GPS fix

[Dockhead]

For whatever it may be worth, my GPS fix on my 10 year old Raymarine system became intermittent a year ago. After powering it up, it takes 10 - 20 minutes to start putting out position data. Which it -- knock on wood -- always does. One day it will just go dead, I guess -- hopefully after I replace the whole system . . .

[cas206]

Consider the Light Squared fiasco. Reading between the lines seems to imply that GPS signals are very susceptable to unintentional jamming either from onboard systems or from external sources.

Intentional? Try a google on GPS Jamming. Note the problems South Korea are claiming from North Korea jamming. The localized effect of car thief devices are by design not technical limitations. A large area affect device would get the attention of multiple government authorities (FAA, Air Force, Trucking networks, etc).

Of course you wouldn't expect an external interference source in the middle of nowhere. But ...

(put on your tin foil hat!)

[ZenithOcean]

When you only have on GPS it's obviously difficult for you determine whether its a hardware issue or an issue with the signal.
Admitedly GPS jamming is becoming more prevailant by the military in different countries, although is often announced on the navtex/hydrolant/hydropacs/navarea warnings. Other possibilities are obstructions in a cove, reducing the amount of satellites visible and finally atmospheric issues and solar activity interference.
I agree with the above comments that it's more likely to be hardware issues. Do you have a feature on your GPS to monitor how many satellites you are receiving and the signal strength? It may be worth monitoring this whenever you are out, to see how the GPS is performing.
Connections, breakages in the coaxial cable and issues with the antenna are all the most likely issues.

[noelex 77]

The Raymarine gps units like the OP's are all active. The gps electronics are built in and they output a NMEA or seatalk position.
Most of the older units like the Garmin -32 have an antennae thats just that, it connects via coaxial cable to the display? It is the display that has all the electronics and does the processing. With this latter type if you suspect a problem you can try another antennae, you can even build one quite easily from a few bent bits of wire,
With the active units you have to replace the whole unit, or have a go at repairing the electronics. Replacing the battery is worth trying, especially if the unit is working some of the time, and is slow to get a position fix.

[Wotname]

Originally Posted by Dockhead

For whatever it may be worth, my GPS fix on my 10 year old Raymarine system became intermittent a year ago. After powering it up, it takes 10 - 20 minutes to start putting out position data. Which it -- knock on wood -- always does. One day it will just go dead, I guess -- hopefully after I replace the whole system . . .

Suspect internal memory battery is flat; without the memory backup, the GPS receiver does not hold previous data and has to download an almanac and ephemeris each time it is turned on - typically 15 minutes on older units.

[Pete7]

Originally Posted by Wotname

Suspect internal memory battery is flat; without the memory backup, the GPS receiver does not hold previous data and has to download an almanac and ephemeris each time it is turned on - typically 15 minutes on older units.

Don, it's the two watch batteries inside the antenna, a $5 fix and 10 minutes of your time. Have a read of this thread, sadly they are all getting to an age when they need new batteries now.

http://www.cruisersforum.com/forums/...c80-52914.html

Pete

[sailorboy1]

Originally Posted by Pete7

Don, it's the two watch batteries inside the antenna, a $5 fix and 10 minutes of your time. Have a read of this thread, sadly they are all getting to an age when they need new batteries now.

http://www.cruisersforum.com/forums/...c80-52914.html

Pete

Didn't even know the antennas had a battery and will check into, thanks.

[s/v Beth]

Don I just have to know what you did- Did you (gasp) go down and find a paper chart and a hockey puck compass and shoot a fix??? Or look down into the water to see if you could see the reef???
Inquiring minds just gotta know

[sailorboy1]

Originally Posted by s/v Beth

Don I just have to know what you did- Did you (gasp) go down and find a paper chart and a hockey puck compass and shoot a fix??? Or look down into the water to see if you could see the reef???
Inquiring minds just gotta know

No didn't look at the paper chart, which I have on board and had out earlier that day showing my crew where we were going. And I didn't really worry about about not having the chartplotter as I knew where I was, the direction I needed to go to get home, how to read my compass, and how to follow the bouys.

I've had problems in the past with my other boat's chartplotter it didn't stop me from going out to sail. I can sail without it!

At the same time the next morning the autopilot wasn't working and I was more pissed about that that the chartplotter. It turns out there is a display on the autopilot when the chartplotter is on because of the Seatalk, but the autopliot was off. It helps to shut the AP breaker when you want it work (only took 30 seconds to "fix" that one).

PS - just because I didn't have a fix the chartplotter still works, only it is just a small chart that can be read from the helm and is still useful overall.

[gjordan]

I have a hand held aviation GPS that I use in a light plane. I was learning to use it last year on a flight to an airport about 5 miles inland from the coast. It was a crystal clear day and I could see the airport from 10 miles out, which my new GPS was indicating. I was loving my new toy and changed to the 7.5 mile scale as I got close. The display was great. I started paying more attention to traffic and ignored the GPS for a while. I happen to look down when I was abeam of the runway and the GPS showed that I was out over the ocean. After I landed it showed me right in the middle of the runway. Why it showed me 6 or 7 miles off when I was over the airport I have no idea. I have used it since with no problems, but it made me very leary of having blind faith in GPS. Would I sail in a boat with all electronic , interfaced nav devices, without paper charts. HELL NO! I like modern electronics but I dont bow to the gods of electronic wizardry. ____my 2 cents worth.___Grant.

[s/v Beth]

I know, I know- I was just giving Don grief cause he is the electronic marvel. That he has a paper chart on board- and I bet a handheld compass?? Well he will do just fine in a lighting strike. Just don't clutch your chartplotter to your chest when it happens Don!.

[sailorboy1]

Originally Posted by s/v Beth

I know, I know- I was just giving Don grief cause he is the electronic marvel. .

electronic marvel, that's funny!

I hate it when I have to get out "The Book"! No matter what language I try I don't understand it!

[ZenithOcean]

Originally Posted by gjordan

. Would I sail in a boat with all electronic , interfaced nav devices, without paper charts. HELL NO! I like modern electronics but I dont bow to the gods of electronic wizardry. ____my 2 cents worth.___Grant.

It's important to be aware of the limitations of GPS, and have a rough understanding of how the system works. Most GPS units have hardware/software that will alert the user when the positions is suspected to be inaccurate.
Many large yachts (i.e 60m+) and cruise ships are designed to be paperless, although generally use paper charts when near coastal.

The ability to fix your position by alternative means is incredibly important, no matter what size vessel you are operating.

[sailorboy1]

When into that cove again this weekend and didn't lose my signal. I read though the little antenna manual and there hidden in the specs is a battery with a 10 year life, so this look like the most likely cause of the problem even though it hasn't done it again. But was tired when I got back from sailing and forgot to see if I can take the antenna apart to get to it.

[noelex 77]

If its the battery, leaving the gps permantly powered up gives less drain on battery so that may keep it going till fixed, but I would not count on it.
Be suspicios of the data it's giving untill is fixed or replaced.