My GPS went wacky

[Ken Palmer]

I have owned my Magellan Meridian Receiver for many years, and it has always worked well. Yesterday while sailing I turned it on to feed lat-long data to my DSC VHF radio. I then noticed that even though I was sailing at about 5 knots, the GPS started to read over 11 knots. I had been heading north, and the GPS started indicating a west heading.

After turning it off and on (reboot), it worked for a couple minutes and started to go wacky again. The lat-long wasn't displaying properly on the radio either. I disconnected GPS from the radio and tried it with internal batteries only, and the same thing happened.

I tried to call customer service at Magellan, but they have discontinued telephone help for "legacy" marine gear. I then sent them an e-mail, with no response yet.

One other thing, I tried it in the car, and it appeared to work OK. I can think of nothing that was running on the boat that could have interfered with the signal, which was nice and strong.

Any ideas from you GPS geeks?

 

[tsmwebb]

...
Any ideas from you GPS geeks?

Localized interference and or multipath issues would be my first guess.

--Tom.

 

[sailingdog]

Recently, a few new GPS satellites when on-line, and some of the older receivers don't know how to deal with them. I doubt that Magellan made an updated firmware to allow your unit to deal with them.

I have owned my Magellan Meridian Receiver for many years, and it has always worked well. Yesterday while sailing I turned it on to feed lat-long data to my DSC VHF radio. I then noticed that even though I was sailing at about 5 knots, the GPS started to read over 11 knots. I had been heading north, and the GPS started indicating a west heading.

After turning it off and on (reboot), it worked for a couple minutes and started to go wacky again. The lat-long wasn't displaying properly on the radio either. I disconnected GPS from the radio and tried it with internal batteries only, and the same thing happened.

I tried to call customer service at Magellan, but they have discontinued telephone help for "legacy" marine gear. I then sent them an e-mail, with no response yet.

One other thing, I tried it in the car, and it appeared to work OK. I can think of nothing that was running on the boat that could have interfered with the signal, which was nice and strong.

Any ideas from you GPS geeks?

 

[Hermit Scott]

I wasn't real happy with magellan customer service. I won't buy another one.

 

[cat38skip]

Most GPS units have a separate internal battery to retain the memory when the unit is powered off. When this battery (usually a wafer type) finally fails, the GPS can return all kinds of fun readings. When mine died it said I was 9,999.99 miles from my next waypoint and that I was on course and would arrive in about 45 days. I had a new battery installed and all was well again.

 

[Ken Palmer]

Thanks all for the ideas. I am waiting for a break in the weather to go out again. Forecast is for more rain today, so may have to hold off another day.

In answer to some of the posts:
I went to the Magellan website. There is one update to that vintage GPS receiver, but it affects only the ability to use over-the-road maps in a different way then the marine way. I don't know what the heck they are talking about and will not blindly install it.

Localized interference or multipath. I doubt interference since it did it 5 miles off-shore. Multipath. I don't know about multipath on receiving satellite signals. What would cause multipath at those frequencies? Keep in mind that the unit was working fine a week ago on a 20 mile trip and back. Only a second test will prove this one.

A new satellite. Again, it worked fine a week ago. I think that satellite was launched some time ago.

Internal battery. There is nothing in the manual to indicate there is an internal battery. Besides, all the waypoints and initial settings are still there.

Magellan service. In the past, they have been very helpful, as are most marine product suppliers or companies. Perhaps the new in-car GPS receivers have overwhelmed their service department. I am still waiting for a reply to my e-mail to them. That is why I would rather talk to a tech on the phone instead of checking my in-box all day long.

I have high hopes that this was an abnormality as they call it in the biz.

 

[zeehag]

exderienced gps depthsounding failure in storms outside mobile bay---turned out to be only a connection defect---check your connections before blaming magellan--i was impressed with this gps--and i was a raytheon fan.....

 

[sailingdog]

Thanks all for the ideas. I am waiting for a break in the weather to go out again. Forecast is for more rain today, so may have to hold off another day.

In answer to some of the posts:
I went to the Magellan website. There is one update to that vintage GPS receiver, but it affects only the ability to use over-the-road maps in a different way then the marine way. I don't know what the heck they are talking about and will not blindly install it.

Localized interference or multipath. I doubt interference since it did it 5 miles off-shore. Multipath. I don't know about multipath on receiving satellite signals. What would cause multipath at those frequencies? Keep in mind that the unit was working fine a week ago on a 20 mile trip and back. Only a second test will prove this one.

A new satellite. Again, it worked fine a week ago. I think that satellite was launched some time ago.

Yes, but it isn't always visible to the GPS, since it moves around the earth... and when it isn't visible to your GPS, the GPS will work just fine...so that isn't an indicator of that being the issue or not.

Internal battery. There is nothing in the manual to indicate there is an internal battery. Besides, all the waypoints and initial settings are still there.

Magellan service. In the past, they have been very helpful, as are most marine product suppliers or companies. Perhaps the new in-car GPS receivers have overwhelmed their service department. I am still waiting for a reply to my e-mail to them. That is why I would rather talk to a tech on the phone instead of checking my in-box all day long.

I have high hopes that this was an abnormality as they call it in the biz.

 

[Ron20324]

Most GPS units have a separate internal battery to retain the memory when the unit is powered off. When this battery (usually a wafer type) finally fails, the GPS can return all kinds of fun readings. When mine died it said I was 9,999.99 miles from my next waypoint and that I was on course and would arrive in about 45 days. I had a new battery installed and all was well again.

Friends have stored their GPS over the winter by removing the AA batteries. They found out the hard way if the internal battery fails without the AAs installed, the memory will dump the waypoints. If you love your waypoints, replace the internal before it dies- maybe every few years?

 

[Ken Palmer]

I normally take out batteries when storing electronics over the winter. Batteries have too often leaked and corroded the connectors. Don't ask how I know that.

On the GPS, I have left batteries in because I use the GPS for Geocaching when not sailing. My waypoints are still there, and if I do lose them, I just download them from the computer. However... One change is that I now have the GPS connected to the boat DC system and have taken the batteries out. The DC is only on when I go for a sail. However... I tried it on internal batteries when this was happening and the symptom was the same. I did not have a waypoint selected, was just watching the speed and heading.

I will have to research this new GPS satellite. Any links come to mind?

 

[tsmwebb]

...
Localized interference or multipath. I doubt interference since it did it 5 miles off-shore. Multipath. I don't know about multipath on receiving satellite signals. What would cause multipath at those frequencies? Keep in mind that the unit was working fine a week ago on a 20 mile trip and back. Only a second test will prove this one....

I'm very much keeping in mind that the unit worked fine both before and after the incident. That's why I'm suggesting this type of error. Keep in mind the kind of interference I'm suggesting is essentially random so a second test may or may not prove anything.

I saw periodic GPS interference off New Caledonia caused (I think) by Navy comms. Multip-path is common enough -- VHF will bounce off lots of things. I've heard VHF voice stations > 200 miles away offshore, all of those signals are bouncing. BUT, like I said, it's just a guess.

It isn't clear to me from your description if you were only looking at the display on the DSC or if you were getting direct readings from the GPS. If the former then a noisy serial cable is a very likely problem. And, there are lots of other plausible culprits. Given a scanty report about a single error what are you hoping for by way of answers?

Here are some common systemic GPS issues: http://www.trimble.com/gps/howgps-error2.shtml

--Tom.

 

[TimCup]

Sailing Dog- has the technology changed?

"Yes, but it isn't always visible to the GPS, since it moves around the earth... and when it isn't visible to your GPS, the GPS will work just fine...so that isn't an indicator of that being the issue or not."

I used to be in the satellite tv business, and the sats were geo-synchronous: they were in a fixed position, so all we had to do was aim at the bird, and we received the signal. Are you saying that new sats operate differently? No disrespect intended, I really have no idea!!

cup

 

[tsmwebb]

...
I used to be in the satellite tv business, and the sats were geo-synchronous: they were in a fixed position, so all we had to do was aim at the bird, and we received the signal. Are you saying that new sats operate differently? No disrespect intended, I really have no idea!!

GPS sats are in a low Earth orbit and so are not geosynchronous. The constellation from the POV of a receiver is constantly changing.

--Tom.

 

[TimCup]

Thanks, Tom.

Now I have to figure out how they stay up there...

cup

 

[zeehag]

magic....

 

[tsmwebb]

Now I have to figure out how they stay up there...

They're trying their best to fall into the Earth but it keeps running out of the way.

--Tom.

 

[Skipper]

Owned for many years

"Owned for many years" and "legacy" are words synonomous with "chip degradation, corrosion, solder failure"

Time to go shopping.

 

[Ken Palmer]

It isn't clear to me from your description if you were only looking at the display on the DSC or if you were getting direct readings from the GPS. If the former then a noisy serial cable is a very likely problem. And, there are lots of other plausible culprits. Given a scanty report about a single error what are you hoping for by way of answers?
--Tom.

Two things... When I noticed on the GPS display that the speed was over double and the heading was off 45 degrees (compared to knotmeter and compass), I went below to check the radio display, which is getting the GPS data from a data cable to the same GPS Receiver. The radio had garble in place of the coordinates. That lead me to believe that the GPS was sending wrong data to the radio as well as to it's own display.

What I was hoping for on the original post was if anybody has experienced any similar behavior from a GPS Receiver.

I am very anxious to give this another try tomorrow. We just had a heck of a thunderstorm here in Rochester.

 

[tsmwebb]

...
I am very anxious to give this another try tomorrow.

Any excuse to go sailing !

--Tom.

 

[dvideohd]

Different GPS's may have different chip sets - and antennas...

So the "smallest" versions - might not have as good of an antenna as a "larger" version. There is SURE a difference in chip sets as well....

when you see two very different GPSs going on the "fritz" at the same time...... it could be the source satellites or the conditions between..... its RF, after all...

I look for sensitivity, antenna type (can you use an external antenna?) and such... You can also - if you are of a mind - find a cheap (but good) USB to GPS interface for a PC.

It is just another reason to always have backup...

--jr