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Old 15-02-2012, 15:52   #1
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GPS Signal Drop Out

On Monday, the 13th of Feb,2012, I took a couple of visiting friends out for a three hour cruise. On the ICW, near the Ponce lighthouse, I experienced a GPS signal loss. No boat icon, no time display or position. After about a minute, I got a GPS failure alarm on my chartplotter. Nothing I could do to fix it, except shutting the unit down and restarting it, which would then acquire normally. This happened five times in about ten/ fifteen minutes. Finally, it stopped doing this, and the rest of the cruise followed normalcy, including the return trip through the same area about an hour and a half later.
The Chartplotter is relatively new, a Standard Horizon CPV350 with the VHF built in. No other parts of the unit were affected, just the GPS signal. I have had no issues with this unit and it has been tested by all day, multi day use in the past, so I don't suspect it is a unit issue.
The puck antenna came with the unit, and has also seen a heap of use with no issues. It was a clear day, and the puck is located in open air to the sky.
It just keeps niggling at my brain as to what was going on, and if anyone has had this sort of thing occur to them, so I am throwing this out there in hopes of some enlightenment on what the cause may have been.
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Old 15-02-2012, 16:21   #2
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Re: GPS signal drop out

A sure way to find out if it is your unit or the GPS system is to have a handheld cheapy or another GPS of some sort and turn it on to see what you get. In my experience, if one GPS unit isn't working it is usually the unit, not the signal, but there has been some testing going on in the southeast and it may have impacted the signals. The area of concern was further north than where you were, but still I wonder. I have witnessed the GPS signal go very wildly off kilter for a period of a few minutes back in the days of Selective Availability, but not since.
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Old 15-02-2012, 16:36   #3
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I had the same issue once and after much trying and testing the equipment we that one of the passangers was sitting on the GPS antenna!
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Old 15-02-2012, 16:49   #4
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Re: GPS signal drop out

By the way, us old farts will remember all the fun we had back in the day with LORAN when it seemed you would always lose the signal or the fix when you most needed it. At the extreme range of LORAN in the Bahamas I was able to get a fix several times by crossing a LORAN line with a sextant shot of the sun. Other times I crossed a LORAN line with an RDF signal.
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Old 15-02-2012, 17:14   #5
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Re: GPS signal drop out

I had something similar happen a few years ago. In the middle of a gale, off the west coast of Vancouver Island, I lost GPS signal (at a time when it would have been a comfort to know my exact position in relation to the coast). GPS became intermittent and then stopped altogether. After things calmed down enough for me to check things out, I found the fault to be in the cable between the external GPS antenna and the unit.
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Old 15-02-2012, 17:17   #6
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Re: GPS signal drop out

during my sailing of the gulf o fmeico we had some of that happen occasionally--- usually in mid gulf.... came back in short order.
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Old 15-02-2012, 17:55   #7
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Re: GPS signal drop out

With the VHF built it, I suspect the puck contains the GPS chipset and antenna to prevent interference. For example my handheld VHV starts a clicking noise if it gets within a couple of feet from my small Garmin plotter with internal antenna.

May be a good idea to carefully inspect the cable to the puck, looking for chafing of even a kink in the cable that could indicate stress has broken a data wire inside the cable. Also where the cable enters the puck itself should be examine carefully.

If the cable was moved around during the outage could be a clue something is wrong in the cable, as moving it may have resolved an intermittent connection.

As Kettlewell mentioned, another handheld GPS (or smart phone w/gps) on board would be the fast track to knowing if the SH unit has a problem, assuming it happens again of course.
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Old 15-02-2012, 18:08   #8
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Re: GPS signal drop out

I,read some where the US Navy or some offical branch of the Goverment was going to be takng GPS down for short periods along the east coast.Forget wher I,saw it maybe AC.
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Old 15-02-2012, 18:23   #9
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Re: GPS signal drop out

Here you want to start a conspiracy?


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Old 17-02-2012, 07:57   #10
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Re: GPS Signal Drop Out

Thanks for all your thoughts on this.
I agree on the checking against one of my other gps units if it happens again. Next time we go out I intend to have one up and running in the cockpit with us. Unfortunately, I wasn't able to leave the helm where we were at and go below to retrieve it this time. Also, the puck/antenna issue is probably not an issue here. The puck antenna cable goes down one side of the guard, and is mounted aft, while the vhf antenna cable runs down the other tube of the guard and is up the mast. We wrapped both with double shrink wrap where they exited the instrument housing and otherwise came into contact with areas where chafe might become an issue in the future. After spending almost two weeks installing the new pedestal, instruments,housings and running all the wires, cables and the like, we wanted to be VERY sure we didn't ever have to repeat the process in the future LOL!
I was thinking that perhaps the recent GA. "tests" may have bled over to my area, but I am not convinced that is in play here either. I didn't know if there has been any experiences of "anomalous" areas where others have had intermittent dropout. Looks like Zee may have seen this out in the Gulf, so there may be certain areas or reasons (either man-created or atmospheric, magnetic...who knows) where this rarely happens.
It wasn't like when one has a chart interruption, where the chart disappears for a moment before the next datum starts showing up. And oddly, the speed and computer course displays stayed up, while the time, Lat/Lon, and boat icon disappeared.
I just hope I don't have any further occurrences, I was in home waters, so it was not a problem, just ...odd.
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Old 17-02-2012, 10:19   #11
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Re: GPS Signal Drop Out

Quote:
Originally Posted by Pma View Post
I had the same issue once and after much trying and testing the equipment we that one of the passangers was sitting on the GPS antenna!
Did the chartplotter show a pic of their butt?
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Old 17-02-2012, 12:15   #12
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Re: GPS Signal Drop Out

My favorite is when the signal adjusts and shows me to be on dry land. That always inspires me. But the GPS is just a tool- its not like your trying to land an aircraft or anything with it...
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