GPS

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TonyBuckley

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I was driving down the A34 from the M4 to the M3 this afternoon when my built in car SatNav (Audi A6) went crazy with no signal.

I put on my iPhone Navigon app and that too was not good but was better.

For about an hour both did not know where they were.

I use SatNav pretty much every day in the car and routinely have on in the boat, but this is the first time I have seen such a failure after many years of use.

What could cause this; it did all eventually come back.

And no.... I don't rely on a SatNav position on the boat (except once when fog came from nowhere and I learnt some lessons) but today was strange and another good lesson. It wasn't kit failure.
 
Strong electrical signals apparently can cause this. It happened to us in the Bay of Naples, two sets were unable to pick up a signal. I researched it later and found this to be a well known problem in the area, close by a USA naval base that may be the source of the interference.
 
I believe the A34 goes past a number of MOD installations to say nothing of the research establishments, so you may well have been in the middle of a jamming exercise. We lost signal twice on a charter in Greece, both times a NATO plane was flying low overhead... Sometimes they announce that they're going to f about with the system and sometimes they don't - and it's not even their system!

Rob.
 
Happened to a mate of mine for no apparent reason when GPSs were fairly young. Ever since he told me the story (which was not that dramatic and ended up with him being late for the water taxi to get him to the pub) I write down lat and long every half an hour so ded reckoning can still be dusted off if needed. I don't go sailing with others that often so don't know if this is standard procedure, I would guess it must be? Not much help on the A34 though.
 
GPS is easily disrupted by competing signals; others have noted various likely man-made sources of interference.

GPS can also be disrupted by solar activity. Unlikely to be the case in this instance, but in regions close to the poles (and for this purpose, northern parts of the Uk are in the polar regions), this can be a significant cause of loss of signal. It is less of a problem now than it was in the early days, before the constellation was complete, but I would never discount the possibility of getting bad fixes from natural causes.
 
Could have been all sorts of explanations, any or all of the above, solar radiation also knocks out GPS if strong enough - GPS Jammers in use publicly, are becoming more and more prevalent, for mainly illegal or legal-but-dubious purposes, but as usual "Legal to sell, we advise they shouldn't be used for 'xxx' " is the defence...
 
TonyBuckley said:
I was driving down the A34 from the M4 to the M3 this afternoon when my built in car SatNav (Audi A6) went crazy with no signal.
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Were you lost? When did you take your last fix? How quickly did you find yourself? Is there a sextant in the car?
 
Swanrad2 said:
I write down lat and long every half an hour so ded reckoning can still be dusted off if needed. I don't go sailing with others that often so don't know if this is standard procedure, I would guess it must be?
Click to expand...

It's certainly considered good practice to plot a fix at least every hour in places where you can't easily get a visual fix whenever needed (out of sight of land, or land is a featureless brown line, or there's a possibility of fog, etc). Though I'm sure there are plenty of people who don't...

Pete
 
My plotter program on the PC records the position every 6 minutes, so I would have some vague idea of where I was - and unless you're out of sight of land, you should be able to work out where you are without too much trouble.
 
Joker said:
My plotter program on the PC records the position every 6 minutes, so I would have some vague idea of where I was - and unless you're out of sight of land, you should be able to work out where you are without too much trouble.
Click to expand...
Assuming the hard disk on your PC doesn't fall over at an in-opportune moment...
 
Camelia said:
Were you lost? When did you take your last fix? How quickly did you find yourself? Is there a sextant in the car?
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No I wasn't lost. It is a common route for me, but I use it for the traffic info.

It went crazy at the M4/A34 junction and had me stuck there until I was one mile from Portsmouth so that's 7 miles of the M3 and 20 miles of the M27 too.

I was curious as never seen an outage like that and certainly not for so long. The iPhone was a bit shaky but far better than the in car unit.

It was pissing down and a bit foggy.

Why would individuals jam GPS if say it was in a car or truck?

As I say, first time seen such a thing after many years of use.
 
TonyBuckley said:
No I wasn't lost. ..It was pissing down and a bit foggy.

Why would individuals jam GPS if say it was in a car or truck?

As I say, first time seen such a thing after many years of use.
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Somebody might have jammed GPS in a car or truck in the traffic near you.
Perhaps to fool the tracker as they have stolen it, or it is a firms car and the management monitors its position.
 
Yup, like LW says - Tachometers are now starting to use GPS technology, as are systems designed for companies to ensure that their vehicles are where the employees say they are.

Also, anti-theft devices use GPS, as do some insurance companies, if you carry a GPS to monitor your mileage and speed, you get a lower premium - So the less-than-white types look to get the benefit of the lower premium, then jam the GPS and drive how they want.

The benefits of using a GPS Jammer by crims stealing high-value cars is obvious!

GPS jammers create a "bubble" of jamming around the unit, so can affect devices that use GPS to function.
 
TonyBuckley said:
It was pissing down and a bit foggy.

.
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You answered your own question!!!!


Not unusual for thick cloud activity to interfere with the weak signals...Certainly have such problems up here from time to time but not usually for that length of time however some of the recent rain storms could have some overloaded load systems up there!!

Even Sky TV loses the battle to reach dishes sometimes!
 
Over such a long distance it was probably a signal jammer as others have said - the phone will back up to using the 3g signal to locate itself when it can find it so that would seem less problematic. GPS units actually pick up very very low power signals so in theory are quite easy to overwhelm with anything stronger on close frequencies. My boat GPS unit takes signals from the US GPS system and the Russian Glasnos satellites too which are on slightly different frequencies so in theory should be less vulnerable but a half hourly plot on the paper chart is something my instructor insisted upon and knowing what a techno reliant person I am still thinks to remind me about every now and then even now! Its also worth remembering the US Govt retain the right to turn off or alter the GPS signal at any time without notice. AFAIK they have not done so yet but in times of heightened tension it may well be an option they take in the future...
 
The GPS system was stable and fully operational on the 15th of December, with no advisory notes ('NANUs') issued. That means 31 operational satellites, which means full coverage, so we can rule out any issue with GPS itself.

The weather is very unlikely to be the cause unless your car system is broken (eg the connection to the antenna has high attenuation) as there's loads (20dB or so) excess signal when seen outside. A modern car system is designed to track position even in urban 'canyons' where signals are distorted and obscured, so rain and fog will not have been enough to stop the system working (unless, as I said your car's one is faulty). Planes land on augmented GPS systems all the time and they have to keep working in the worst of weather.

Jamming is possible but extremely implausible over such a long time and distance unless you were inadvertently tail-gating the vehicle with the jammer the whole way.

Much the most likely is a software bug! GPS sets are by no means immune (I have loads of data from testing our receivers and those of our competitors; inducing aberrant behavior was not difficult!). To compound the issue car makers are, and with good reason, averse to new and possibly unproven technology so the chips and associated firmware, including that of the GPS in the Audy, are likely to be several years behind the state-of-the-art (typically a chip is selected by a car manufacturer several years before the car goes into production, frequently to the extent of being phased out of new designs by that time!). Cars also have almost no workable procedure for distributing software fixes (as a data point, the GPS and nav software in my new-ish VW is way out of date and it does not recognise many roads opened 4 years ago despite being 'the latest release' according to the VW garage).

So a plausible explanation is that the almanack or clock of the GPS set got corrupted - possibly by interference or a jammer - but then the set took ages and ages to clear out the corrupted information due to some latent s/w bug long after the original problem went away. Had you been able to force a cold restart it should have re-acquired in a couple of minutes at most.

PS: The link margin for Satellite TV is much less than it is for GPS, the frequency is ~10GHz as opposed to ~1.5GHz for GPS, and the TV satellites are geo-stationary and hence over the equator, which means that they have very low elevation (esp in Scotland). These combined mean that TV is much more susceptible to rain than is GPS.
 
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