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Loss of Satellite Lock

 
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LostMike
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Joined: Jan 17, 2008
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Location: Monmouthshire

PostPosted: Sun Dec 11, 2011 12:12 pm    Post subject: Loss of Satellite Lock Reply with quote

I have had my A10 for years and am very pleased with the device. It has proved a very useful and reliable tool. However, twice in the past when out walking in open conditions the device has evidently lost satellite lock. The first time on a fine day, on a rise, with no large trees around it ran about 60 yds off my track for a few minutes. The second time, with a cloudless sky on a hill top near the coast the device suddenly decided I was in fact about 12 miles off shore! This probably lasted for less than a minute, the device concluding that I had returned to shore at close to the speed of sound! I never got to the bottom of either event but they were just two isolated and now distant events.

Then on Friday I went for a walk on a fairly fine day with little cloud cover. The device seemed to have a good lock and followed me well for most of the 8 miles but on 2 occasions it concluded that I had gone off at high speed. The first time it believed that I had gone off at about 90 mph and the other at 600 mph. On both occasions the device appears to have lost lock I was not under tree cover, there were no buildings or power lines near and the cloud cover was light. The location was just to the north of Newport in South Wales so I have no reason to assume that the MOD were involved in signal jamming in the area. I always carry the device clipped to my right shoulder.

Has anyone else had similar experiences? Has anyone any suggestions as to what may be causing it or how to stop it? I have considered sending the unit in for a service but apart from these two blips the device seems fine.

I am a little surprised that the software does not flag up such odd high speed jumps. As it does not I would like to suggest that in any future upgrade SatMap consider allowing the walker or cyclist to set a maximum speed they expect to achieve so that the device can double check before reporting such ridiculous jumps.
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LostMike
Satmap A10. Platform 21
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rkm_hm
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Joined: Nov 28, 2004
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Location: Warwick, UK

PostPosted: Mon Dec 12, 2011 12:17 am    Post subject: Re: Loss of Satellite Lock Reply with quote

LostMike wrote:
Has anyone else had similar experiences? Has anyone any suggestions as to what may be causing it or how to stop it? I have considered sending the unit in for a service but apart from these two blips the device seems fine.


I've had at least one oddity - not as bad as yours though.
I was about to go walking in an open area in the New Forest, and had parked in a car-park alongside a minor road. I turned the A10 on, and left it to get a fix while putting my boots etc. on. When it did get a fix, it said that I was in the middle of a field about 200 metres to the west of my actual position. A few minutes later, as I was setting off on the walk, it suddenly snapped to the correct position. No idea what caused that - but it was a bit worrying.
[BTW, I was NOT in Planning Mode, in case anyone asks!]
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nonoftheabove
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Joined: Oct 27, 2007
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PostPosted: Mon Dec 12, 2011 11:14 am    Post subject: Reply with quote

rkm_hm wrote
I've had at least one oddity - not as bad as yours though.
I was about to go walking in an open area in the New Forest, and had parked in a car-park alongside a minor road. I turned the A10 on, and left it to get a fix while putting my boots etc. on. When it did get a fix, it said that I was in the middle of a field about 200 metres to the west of my actual position. A few minutes later, as I was setting off on the walk, it suddenly snapped to the correct position. No idea what caused that - but it was a bit worrying.
[BTW, I was NOT in Planning Mode, in case anyone asks!]

I have had that happen several times and so long as the error when starting the walk or after a shortish time interval it is in the acceptable range (10s of metres) think nothing more about it.
Probably to do with the number and position of satellites that the device gets a fix from. The greater the positional separation and number the greater the accuracy maybe
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WalkerDan
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Joined: Feb 04, 2010
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PostPosted: Mon Dec 12, 2011 3:55 pm    Post subject: Reply with quote

Can only remember this happening once in 2 years of fairly heavy useage. Staying at Blackpool had a walk along the front and back for 5 miles or so but at one point when I checked the route it showed us about 5 miles out to sea before coming back to the right position. So no satellite obstruction and as I can't swim Embarassed it was just as well it wasn't right.
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rkm_hm
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PostPosted: Mon Dec 12, 2011 5:29 pm    Post subject: Reply with quote

nonoftheabove wrote:
I have had that happen several times and so long as the error when starting the walk or after a shortish time interval it is in the acceptable range (10s of metres) think nothing more about it.
Probably to do with the number and position of satellites that the device gets a fix from. The greater the positional separation and number the greater the accuracy maybe


In my case, it was more than tens of metres. If it happened in the middle of a walk, it would put me on completely the wrong path!

My old Garmin GPS12 monitors up to 12 satellites, but can get a fix on 3 or 4. But the A10 seems to need to be receiving from a lot of satellites before getting a fix. This provides a lot of redundancy - and I don't know how it decides which ones to believe if it gets conflicting information. Perhaps this is the problem?
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LostMike
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PostPosted: Sat Dec 17, 2011 1:13 pm    Post subject: Reply with quote

An update. No solution in sight yet..

On Monday on another walk, again with clear skies etc. a similar problem occurred. On Tuesday in valleys with wet trees and thick (snow) clouds, there was no problem!

I have subsequently studied the RAW files and note that instead of the usual string of "trkpt" (track-point?) data there are a few "trkseg" (track-segments?) entries. These trkseg entries seem to relate to the anomalies and sometimes be associated with apparent gaps in the time log.

I have made a couple of attempts to recreate them by very briefly removing a battery (to simulate a loose connection) but that just shut the machine down, and stopping and then restarting the log but that did not seem show in the RAW data at all.

Anyone with any bright ideas?
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Bosun
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Joined: May 02, 2005
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Location: Wakefield,West Riding of Yorkshire

PostPosted: Sat Dec 17, 2011 5:10 pm    Post subject: Reply with quote

I think probably the best course of action would be to ask Satmap,they make and program it so presumably they might know the answer,other people may have complained/commented on it to them.

Ian
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LostMike
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PostPosted: Sat Dec 17, 2011 5:19 pm    Post subject: Reply with quote

I'm sure you are right Bosun. Its just that we are now in the run up to Christmas/New Year and I can't reasonably expect to get anything from them until next year.

So I just wondered if any of the knowledgeable members of this forum might have had any bright ideas. Not that I expect you to be able to solve what appears to be a quite tricky problem, but I always live in hope.... ;-)
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LostMike
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Gibbo10
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PostPosted: Sat Dec 17, 2011 10:14 pm    Post subject: Reply with quote

I have had this problem on a couple of occasions and on both times it was when I had the A10 in the pro-shield and in my coat pocket. It seemed like the receiver wasn't powerful enough when inside the pro-shield and kept loosing the satellite lock. When I studied the gpx I too found that the route had been broken into segments, presumably at the points when satellite lock was lost then re-established. Since then I've not used the pro-shield it hasn't re-occurred! I now put some thin black plastic tape / electrical insulating tape around my A10 so it covers the gap between the A10 and the plastic cover and that totally stops water getting underneath and between the plastic shield and the glass screen.
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GPSwalker
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Joined: Nov 29, 2009
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Location: Yorkshire

PostPosted: Sun Dec 18, 2011 9:33 am    Post subject: Reply with quote

Soon after I started using my ProShield the sat lock would occasionally become lost. I suspected the signal would be weaker with the extra barrier of this heavy duty case and removed it, since which time the problem has not recurred under similar circumstances. Because I must have a water proof cover for my Active 10 I decided to get an Aquapac submersible Whanganui case. It is lightweight and tested to IP68, a higher rating than the ProShield. It is a useful piece of kit in my opinion but on the down side would not protect against impact like my ProShield. However, the Aquapac came with a lanyard and I always use it round my neck in rain. I am a long distance walker and suspect this solution is not so useful to bikers. If I had thought of the insulating tape method it could have saved me the 20 for Aquapac I suppose.
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LostMike
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PostPosted: Sun Dec 18, 2011 9:41 am    Post subject: Reply with quote

Thanks for your comments Gibbo10 and GPSwalker.

I don't use the pro shield, and to stop the problems with water getting under the screen cover I long ago removed the screen cover! I carry the A10 in its original carrying case on my right shoulder (when I'm not reading it). Now the standard carrying case may cut down the signal a bit but on these recent occasions it was dry and everything else pointed to a good signal. So I remain puzzled.

Nice to know that others got the segmentation issue and that it is not just me.
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LostMike
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GPSwalker
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PostPosted: Sun Dec 18, 2011 10:34 am    Post subject: Reply with quote

I have just recalled a one off incident when the A10 sat lock was lost. Out on the fells on a dull day everything was logging fine until an aircraft went overhead. It was above the low cloud layer so I could not see it, but the sound of the engines was like a military transporter plane, slow and powerful. The active ten did a wobbly and after the aircraft had gone into the distance I was able to get a lock with no problem. The only explanation I can think of was that some form of GPS jamming signal came from the aircraft?

BTW Mike, in dry weather I always carry my A10 in the standard case and lanyard it came with and have had no other problems with sat lock I can remember.
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