Lost GPS fix

[Aquavit]

Hi everyone - we are new to the forum and wonder if anyone can offer any advice.
Do you ever lose GPS fix in the Solent? On a regular basis travelling east from Yarmouth to Southampton Waters we lose GPS fix in the area of Beaulieu River entrance (mid Solent) and this continues until Calshot Spit. If we stop the boat when the fix is lost and turn through 180 degrees, ie heading west, the fix returns. The number of satellites in use increases and decreases (all to zero/2 before losing fix) as the boat is turned through 360 degrees. The problem only occurs travelling 'east' and in about the same location each time. We do not get the same problem anywhere else. Today we lost fix whilst anchoring in Thorness Bay and have had the same problem outside Newtown Creek, but this only happens when the bow is in a 60 degree or so segment heading E/NE. We are using a new Raymarine plotter/radar with overlay and very up to date Raystar GPS receiver (not the faulty 120). The installation and positioning of GPS has been carefully checked and all seems OK - Raymarine are involved and are equally puzzled by the problem but have had similar reports. We have the same problem when using a Garmin GPS and can mirror the problem using a handheld Garmin GPS. One possibility presented to us is interference from a land based radar. Does anyone else get the same problem or have any ideas?



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[powerskipper]

Hi and welcome, /forums/images/icons/wink.gif

Was on a boat coming down the river from the folly’s on Cowes today and lost the gps fix, had to reset machine and when she reset came up with fix then, will keep an eye open for it occurring when out in future.





<hr width=100% size=1><A target="_blank" HREF=http://powerskipper.mysite.freeserve.com/>http://powerskipper.mysite.freeserve.com/</A>
Julie

 

[studgies]

been to most of the places you mention a few times recently and never had a problem but will look more closely in future!

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[BrendanS]

I regularly go to all those places. Not reliant on GPS as I know the area to navigate by mark one eyeball, but always have the GPS on, if only as a trip meter for mileage for the day. Using Garmin 172C and previously Garmin III, have never suffered any outage.


<hr width=100% size=1>Catapultam habeo. Nisi pecuniam omnem mihi dabris, ad caput tuum saxum immane mittam.

 

[plombier]

Have lost contact a couple of times near the navy ships in Pompy - leaves a big gap in the trace. They are, no doubt, putting out some blocking rays. Could be the Calshot radar tower but that would affect others I would have thought.

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[Sunnyseeker]

In my experience its boats buildings and electrical noise, the signal is very small compared to the ammount of radio noise around in busy areas. In harbour often we cant get weather fax from SSB receiver, but 5 miles out to sea and its perfect, I'm sure some of this radio noise must effect reception, as well as satelites close to horizon (30-40degrees elevation) will not be seen through boats and even a bunch of masts, and definately not buildings, as you get motoring down the rivers..
GPS's aren't for close up Navigation, weve found ours have failed quite often, two hand held Garmins just gave up, and the fixed decided not to play at the same time. Garmins response was well sell you a new one!

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[Sunnyseeker]

In my experience its boats buildings and electrical noise, the signal is very small compared to the ammount of radio noise around in busy areas. In harbour often we cant get weather fax from SSB receiver, but 5 miles out to sea and its perfect, I'm sure some of this radio noise must effect reception, as well as satelites close to horizon (30-40degrees elevation) will not be seen through boats and even a bunch of masts, and definately not buildings, as you get motoring down the rivers..
GPS's aren't for close up Navigation, weve found ours have failed quite often, two hand held Garmins just gave up, and the fixed decided not to play at the same time. Garmins response was... we'll sell you a new one!

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[ianainge]

Good to see your using the forum, spoke to you yesterday about having the same problem in the Beaulie river, bit know where else. hopefully someone one hear may have the answer, see you at the weekend.

Ian

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[jon_bailey]

A couple of weekends ago we returned from Bucklers Hard to the Itchen. After downloading track that evening there was a large gap between mouth of Beaulieu River and Calshot, i.e. heading East. The rest of the track was fine including outbound.

So is there a problem heading East from Beaulieu River?

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[Oldhand]

Have no such problems in the areas you mention with a Raynav 300 GPS installation. Looks like it must be something to do with your installation and/or interfering sources. Just as an example, the ICS Nav6 Navtex display puts out enough radiated EMC to wipe out GPS reception form a receiver antenna in its proximity.

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[gonfishing]

Hi
A friend of mine seems to be suffering from something similar with the latest, updated Raymarine software, possible cause is a command line missing within the software programme, causing all sorts of nasty antics especially with the auto pilot!!! havn't seen him today to see is it was resolved this week so I will ask him tomorrow. might be worth following a similar line off enquiry??

rgds
Julian

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[Aquavit]

Thanks to all those who offered a information or a solution to our GPS fix loss problem. Had a day out on boat with Raymarine yesterday and we finally tracked down the problem. The culprit was our radar arch mounted TV antenna/booster being left switched on during voyage (in fact left switched on all of the time). We travelled to the 'black hole, around West Lepe buoy in the Solent). When the TV antenna was turned on and we travelled NE, sure enough the GPS lost fix. The fix could be gained and then lost by turing the boat through 360 degrees. It happened in the same area each time, but fix was lost (and GPS signals lost completely) only when travelling approx NE. No problems in any other direction or in any other place. When the antenna was turned off no GPS fix loss was encoutered. An interesting phenomenon - it appears that a TV signal booster (?) on the Isle of Wight (possbly one of the hill top aerials we see from the water) and the antenna on the boat combine effect at that particular position/alignment and knocks out the GPS. Anyway - problem solved - we just have to remember to make sure that the TV aerial/booster is turned off before we set out.
Massive thanks to Raymarine - they have been just great about trying to sort out this problem (thanks especially to Charlie, Scott). This is not just a Raymarine GPS problem, a secondary Garmin GPS on board also had the same problem and was mirrored by a Garmin handheld too.
Watch out for those RF signals!!


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[MainlySteam]

There is a known problem with active TV antennas (has been known for quite some years) and a number are listed on the USCG internet site here <A target="_blank" HREF=http://www.uscg.mil/hq/gm/moa/docs/11-02.htm>http://www.uscg.mil/hq/gm/moa/docs/11-02.htm</A>. In the case of the Shakespeare ones, which are well regarded, they are just batches of a particular model that displayed interference - those older and newer of the same model are ok.

There are undoubtedly many active antennas which have not been tested and I personally would be very wary of using any not intended for marine use (eg the caravan shop type ones). We use a Shakespeare one on our own boat and have also specified them for commercial vessels with no problems experienced.

Generally loss or error in GPS position is due to a problem on the boat suffering the loss or error and not on active external influences. Your forthrightness in your post (commendable /forums/images/icons/smile.gif) may help make that clear.

John

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