A Strange Thing Yesterday

1.1k · January 13, 2005

Yesterday lunchtime (12 Jan 05), I switched on my yellow etrex, and it took ages to get a lock.

By ages, I mean over 10 minutes. I was standing still with it in the middle of a wide open area on top of a hill, and the advanced skyview was just blank.

I had moved 70 miles since last switching it off 24 hours before, but it doesn't usually take that long to initialise.

I was beginning to fear that the US military had decided that I was a threat to their national security and had withdrawn the signal from my location as a precaution.

Has anyone ever experienced anything like this before?

2.9k · January 13, 2005

Yep batteries.

Moved a long way.

GPS to close to body or leaning over it.

January 13, 2005

I have a gps mouse mounted on the dash of my car (for in car navigation with my PDA) , it's been there for over a year and been faultless usually locking after 20-30 seconds, but last Sunday after half a hour it still hadn't locked, I stopped the car and turned on my yellow e-trex and got a lock straight away, so then thinking the mouse gps had died I just carried on driving, then after around 10 Mins It locked!! and has worked perfectly since.

So why it took so long on that one occasion I don't know, good job I knew where I was going and wasn't relying on it.

Richard

January 13, 2005

Myself and Davieradio (and his good lady) ran into each other on a cache near Kilmarnock and both our GPSr's were having an unsual hard time getting a lock <_<

However, after a coffee in the park tearoom which took a little more than ten minutes, we both locked on at the same moment.

We put it down to just the position of the satelites in the sky at that precise moment in time and of course local conditions.

2.5k · January 13, 2005

On Saturday I used my GPS in Tring (herts). It's a green ETrex Venture. I found my cache (yay!!) and switched it off.

The next day, Sunday, I turned it on again. It took AGES to get a lock and then when I searched for neaest caches my GPS decided that it was in Northumberland and listed the caches I had done up there over New Year. Turned it off and on again, same thing. Threw it onto passenger seat of car and drove to cache location, no signal at parking spot, but as soon as I walked up onto the hillside it recovered and decided that it was, in fact, in hertfordshire.

Weirdness! <_<

January 13, 2005

I believe that there is a reasonable explanation for this, but at present I'm still trying verify it.

The explanation (if correct) will be disappointingly technical and boring... :rolleyes:

January 13, 2005

At the Bristol Meet just before Christmas, my Magellan Meridian was having a terrible time hanging on to the signal, though everyone else's receivers seemed to be fine.

Fortunately, I knew the way home, and the GPS has now recovered...

Must have been just "one of those things"!

Bob Aldridge

January 14, 2005

Moving around, well from Bedford to Cumbria, noticed the same problem.

Two seperate GPSs, had the same problem, a sudden loss of GPSr.

Have a Garmin 76S and an older E-Map, both of them had a sudden loss of GPSr while in an "open sky" area. GPSr came back after some minutes and got 8 to 10 satellites!!! Have windscreen antennas for both.

Working at RAF Spadeadam currently and did mention it in passing and was told " Yes, we saw that as well, perhaps the USAF were doing something?"

Nick

January 14, 2005

OK. It appears that some things have been going on "up there" which could account for the effects reported "down here".

A couple of satellites are in maintenance or test mode which means they are unavailable. These shenanigans seem to have started around the 6th/7th Jan and are ongoing. Also: a new one (PRN02) was launched late last year and is in the process of being commissioned. (I don't know what its exact status is at the time of writing this.)

Such changes affect the almanac tables which your GPSr stores for repeat use. It could be that a given GPS unit (which has been off for a certain period) decides that it now needs to download the whole table again, before starting to use the signals.

The effect is to give what looks like a longer-than-usual acquisition time - similar to that seen when a brand new unit is fired up for the first time.

This may happen again around the 18th of this month.

Or, it may not... :rolleyes:

[Edited just for the hell of it]

Edited January 14, 2005 by wildlifewriter

1.1k · January 14, 2005

I believe that there is a reasonable explanation for this, but at present I'm still trying verify it.

The explanation (if correct) will be disappointingly technical and boring...

Technical explanations are fine by me, but then, it has been said that I should get out more.

1.4k · January 14, 2005

a new one (PRN02) was launched late last year and is in the process of being commissioned. (I don't know what its exact status is at the time of writing this.)

She was launched on the 6th of November and commissioned into the constellation on the 22nd.

She was offline from Sunday the 26th of December at 23:05 until 22:32 on the 7th of January.

She is currently showing a health status flag of "healthy".

WildLifeWriter's conjecture that a particular model of GPS may reject its own internally held almanac is an interesting idea. If true, it sounds like there's a bad algorithm in the firmware. Each of the satellites transmits not only its own almanac, but also those of all the other sats.

It is extremely common for one or two sats to transmit a health status of something other than healthy, either because of a self-identified fault or because the ground controllers are doing some work on the sraellite such as adjust its orbit, but there are around 30 birds in the flock at present, so there oughtn't be a problem with getting a good warm start fix.

In any working weekday, during business hours at Schreiver AFB or Cheyenne Mountain, you can expect at leat one of the sats to either be taken offline for maintenance work or to be being worked on to resolve some glitch or other.

A robust GPSr really ought to be able to simply reject an unhealthy sat without having to read the entire nav message to download the whole nine yards of almanacs every time it is switched on a hundred miles from where it was a week ago.

It shouldn't matter if its been two or three weeks since the machine was last switched on because the weekly drift rate in angles of elevation of azimuth of the NavStar birds is substantially less than a degree per week, so if the new actual position is within a couple of hundred miles of where it was last switched off in the past month or so, it should 'know' which sats to 'look' for first.

Of course, if the batteries have been removed from the GPSr for more than a few minutes or hours since it was last getting good fixes, then all bets are off on the warm-start race!

Cheers, The Forester

2.5k · January 14, 2005

...so no reply for my mysterious translocation to Northumberland then? I had used the GPS several times locally bewteen my Northumbrian rambling and my strangeness on Sunday. I will put it down to boggarts and gremlins then :huh:

1.4k · January 14, 2005

...so no reply for my mysterious translocation to Northumberland then?

Nope. I've never heard a comprehensible explanation of why anyone or anything goes there, though perhaps that's because the explainers have always been Geordies.

Haway the lads!

Cheers, The Forester

January 14, 2005

Horror stories :huh:

This is not good. I go geocaching mostly in the dark and often rely on my GPS to get me out of the woods. I would go mad if it decided not to work when I wanted to leave.

Luckily Like most GPS users I know how to read a map and compass, however that does not help much if you have no idea where you are. 1 Day I may have to spend the night in the woods. :huh: :huh:

January 14, 2005

Nope. I've never heard a comprehensible explanation of why anyone or anything goes there, though perhaps that's because the explainers have always been Geordies.

(Pedant mode = ON)

Geordies come from Tyneside, not Northumberland

(Pedant mode = OFF)

January 14, 2005

At the Bristol Meet just before Christmas, my Magellan Meridian was having a terrible time hanging on to the signal, though everyone else's receivers seemed to be fine.

I reckon Ozzy, Stuey's dog must have had something to do with it

January 14, 2005

I've had my magellan sportrak do similar things - normally when i'm about 100' from the cache OR when entering a town that I have never been to before and then *poof* no birdies

January 14, 2005

We were caching on 12 Jan around midday in Stafford area and after switching the device off it then took ages and ages to 'find' a set of sats. Thanks for the explanation.

By the way does the level of the batteries make any difference to the operaton of the GPS or does it continue as usual until there is insuffiecient power and then close down?

Peter

January 14, 2005

(snip) WildLifeWriter's conjecture that a particular model of GPS may reject its own internally held almanac is an interesting idea. If true, it sounds like there's a bad algorithm in the firmware. (etc huge snip)

It is possible. My iQue3600 shows this behaviour after a hard reset, even though Garmin say it didn't ought'a.

1.4k · January 15, 2005

Moving around, well from Bedford to Cumbria, noticed the same problem.

Two seperate GPSs, had the same problem, a sudden loss of GPSr.

Have a Garmin 76S and an older E-Map, both of them had a sudden loss of GPSr while in an "open sky" area. GPSr came back after some minutes and got 8 to 10 satellites!!! Have windscreen antennas for both.

Working at RAF Spadeadam currently and did mention it in passing and was told " Yes, we saw that as well, perhaps the USAF were doing something?"

Nick

If that happened anywhere near Spadeadam, then I'd suspect that you passed through a local area which was being jammed.

A few years ago the MoD developed and tested several models of GPS jammer and they are now in service with both the Army and the Air Force. They can be used to blot out GPS use in either local or wide areas.

As you no doubt know, there are two huge military training and testing areas around Spade, so that's a very likely place for the jammers to be used.

There is also a civilian defence contractor which flies FalconJets which have underwing jamming pods which can zap the GPS frequencies very easily and very thoroughly. They often fly jamming missions in support of miltary exercises and those exercise take place regularly in dozens of declared danger areas .

My guess is that what you observed was the effect of jamming on a civilian GPSr.

January 17, 2005

We had similar problems in Nottinghamshire and Derbyshire yesterday - where we couldn't get a lock on any satallites for about 40 minutes Others have reported the same condition as well in their logs.

2.5k · January 17, 2005

one effect of my unscheduled virtual visit to Northumberland is that the max speed on my GPS is down as 354mph... presumably as I instananeously 'moved' from up there to down here!! Cool!

Edited January 17, 2005 by Alibags

1.1k · January 17, 2005

one effect of my unscheduled virtual visit to Northumberland is that the max speed on my GPS is down as 354mph... presumably as I instananeously 'moved' from up there to down here!! Cool!

Make sure the plod don't see that. They'll probably do you for speeding down the M1

January 18, 2005

one effect of my unscheduled virtual visit to Northumberland is that the max speed on my GPS is down as 354mph... presumably as I instananeously 'moved' from up there to down here!! Cool!

Make sure the plod don't see that. They'll probably do you for speeding down the M1

lol :rolleyes:

I've had that a few times. GPS showing I have gone over 300PMH. And another thing..... I have only had my GPS a few weeks and it thinks that I have travelled over 2000 miles. That’s wrong, as the week before I had done only 68 miles. So In 1 week I have travelled 1932 miles COOL... I wish I had. But it has messed things up because I cannot reset the overall distance on my yellow extrex.

1.1k · January 18, 2005

You should be able to re-set total distance (trip odometer) by going to the navigation page (the one with the compass) and clicking the enter button (bottom left) then select 'Reset Trip' and enter again. This will reset the odometer.

If that's not what you mean by overall distance, what do you mean, as I've never seen another overall distance on mine. If there's a 'total covered by unit since manufacture', I'd love to see how far mine's gone.

BTW, in your profile you say that you've been told the yellow fellow is rubbish. I'd disagree. It's basic, but it should be as accurate as more expensive units, it's very robust, and being yellow means it's easier to find under the bush you've just dropped it in.

January 18, 2005

Hi,

Yeah I mean total distance (odometer) not trip odometer. Select "odometer" from the "change fields" section on the nav page. This will show how far the unit has travelled (and been locked on) since manufacture.

I agree with you, the yellow garmin Etrex is great. My mate that has in car sat nav said that the etrex was rubbish and that it was not even a colour screen. He knows nothing about geocaching. He will find it hard to geocach with his car sat nav. The strange thing is, that mate of mine has placed a bid on ebay for the Etrex since we went geocaching last week. He is just 1 of those people that have always got to be better then everyone else. At the time I wrote my profile I know nothing about GPS so asked this mate for his opinion because he used in-car sat nav. Anything I get he seems to think is rubbish but then gets one himself. :rolleyes:

1.1k · January 18, 2005

I do apologise for this thread veering off topic a bit, but I've not come accross this total distance function.

I can't find reference to it in the manual. I've got an etrex euro running firmware version 2.20.

I can't see a 'change fields' section on the nav page.

January 18, 2005

I do apologise for this thread veering off topic a bit, but I've not come accross this total distance function.

I can't find reference to it in the manual. I've got an etrex euro running firmware version 2.20.

I can't see a 'change fields' section on the nav page.

On the yellow Germin etrex from the "sky view" (main page) press the page button 3 times. You should now see 5 small boxes which contain information about your location. For example speed, time of day, next eta..... Now press enter and a small menu will come up highlight "change fields" and press enter.... Now use the up & down arrows on the your etrex to highlight one of the boxes then press enter, a new box will appear with a list of options. Use the up & down arrows to highlight "odometer" and press enter. Now press the page button again.

You should now have the "odometer" as one of the fields on the Nav/info screen.

Sorry if I have got the nav and info screen mixed up.

Garmin do list this in the user manul for the etrex. There is also a list near the back that explains all the fields available to use.

3.9k · January 18, 2005

Garmin do list this in the user manul for the etrex. There is also a list near the back that explains all the fields available to use.

Manual? there's a manual? :rolleyes:

January 18, 2005

Edited January 18, 2005 by kevin308

January 18, 2005

Manual? there's a manual?

Try Here

January 19, 2005

I'm actually working in RAF Spadeadam so do know what they do "up here"

I spoke to the "RAF" and they had also seen these GPSr "dead sections".

Nick

3.8k · January 19, 2005

one effect of my unscheduled virtual visit to Northumberland is that the max speed on my GPS is down as 354mph... presumably as I instananeously 'moved' from up there to down here!! Cool!

I can beat that have a look at my track log from last June

5,175,822mph :huh: and I was walking

January 19, 2005

Blimey, at that speed did your knees melt Deego?

Nick

January 19, 2005

5,175,822mph and I was walking

no ! i don't believe you

you must of been running :huh:

A Strange Thing Yesterday

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