The Scottish Triangle ...

[FullyFlapped]

A mystery for all you clever types out there ....

Yesterday (glorious Sunday!) my wife and I flew from Leeds for a day out in her ancestral home of Edinburgh (explains why the MIL looks like Mel Gibson in Braveheart, and is equally scary :D ) Fantastic trip, glorious weather, etc etc, and then ..... at about 55degs 39.45mins North, just above Galashiels, the GPS signal to some of the onboard systems disappeared ...

I have a GNS430, which continued to work beautifully : so obviously that was receiving GPS signals. I also carry (for VFR trips) a pocket PC (moving map) attached to a GPS unit. That lost the plot. And finally, because I'm experimenting with different gear, I had onboard a tablet PC, also attached to yet another standalone GPS. That also lost the signal. Wierd.

Now, a while ago, I was travelling up to Glasgow, when exactly the same thing happened, at roughly the same latitude, but further over towards the west coast.

It's a strange thing : kind of like the Midwich Cuckoo effect. The signal reappeared at exactly the same place flying back South.

So : two queries here. Firstly, is there some sort of Bermuda Triangle thing going on in the Scottish lowlands ? And secondly, why would portable GPS units lose signal when the wired up GNS430 kept going nicely ?

And finally, I guess this is a salutory lesson to all those who put absolute dependence on hand-held GPS units ... keep hold of those maps !

FF :ok:

[FNG]

That'll be a pink airspace violation, then? Some pretty weird stuff transmits from up there, so that may account for a disrupted signal. Either that, or the military are up to some conspiracy-tastic "Edge of Darkness" style naughtiness.

[FullyFlapped]

Errr ... a "pink airspace violation" ? What's that then, oh sagacious one ?

Is this yet another fact I should know but don't ? Cor, life's full of them ... :D

[david viewing]

FF

Can you be sure that the outage was related to your physical position over the ground? I have witnessed a similar simultaneous outage of completely independent GPS but am not convinced that it was caused by external factors.

Might there be a relationship with on-board equipment? A change of radio frequency, Nav aid, squawk? Or (surely not) mobile phone left on? Portable GPS are bound to have inferior signal/noise performance than installed equipment, and of course the antenna might actually be inside the cockpit.

Such a geographical outage would surely lead to much howling from everyone from boaters to haulage contractors. I believe there is published information on GPS outages (It's referred to in the recent CAA 'stick to reliable ADF' report) so perhaps someone can supply more information on the status on your date/time.

David

[FNG]

Just a weak jest, FF, referring to the ground location of the pink nuttiness that afflicted this forum for a while, but is now fading thankfully into memory and myth.

I wonder if any peculiarity of topography could account for the signal difficulties, but assume not, as the satellites are, derr, above the Earth. I know very little about how GPS really works, but quite a few people here know a lot about this stuff and may be along in a while to offer more informed suggestions.

[witchdoctor]

Maybe all your kit panicked due to the proximity of the only race on earth tighter than a Tyke!

Fly up there all the time doing survey work and the GPS has never showed a problem yet. At least I presume not. The gaffer uses it, not me, so it's barely visible from my position. I prefer the foldy up plastic picture thingy with all the pretty colours and patterns on it - it helps pass the time trying to match it to the bumps and squiggles on the ground.;)

[Flap40]

I fly a Jodel from Perth with a skyforce II and also have one of the PDA gps's also.
I have never had a problem with GPS coverage in Scotland but did loose both between Draycott Water and North Leach roundabout while going to the PFA rally last year and the same coming back.

[sunday driver]

Well, I'm not a GPS expert (when did that stop anyone ?) but -

Roof mounted antenna picks up loads of satellites - always gets a good fix.

Portable system can't see the satellites vertically above, and is relying on the absolute minimum quantity, one of which is just above the horizon. And then one of those damn Munro's gets in the way and blocks your last link with reality.

Any other offers ?

SD

[FunctionedSatis]

FF,

Sunday's hit the nail on the head, the GNS430 using the external fuse mounted antenna will be able to keep more sats in its sights, the small antennas on PDA and handhels GPS's aint man enough for the task, i belive that they may not be able to receive the same amount of sat's as the GNS430 can. ill need to look into that one.

Or maybe the Wobbble is back on????:D

Stu,

[mad_jock]

Unfortunatly it is quite common up North for the signal to drop out.

The GPS Guru's are proberly quite right its a combination of installation, Local wx effects, topography. Being a Sunday the Mil jamming won't be as high up the list as it would during a week day.

MJ