GPS signal disruption in NW Scotland

[ianfitz]

For planned NATO excercises...


http://www.bbc.co.uk/news/uk-scotland-h ... s-32252012

Take a map too folks

[ScotRoutes]

Never mind that, take water!!

http://www.bbc.co.uk/news/uk-scotland-h ... s-32247821

[Zippy]

Latest etrex uses glonass too ;-)

[fatbikephil]

Why do they have to jam the GPs signal just because they want to go and play soldiers?

[wfbroddy]

I was always under the impression that it wasn't so much they jammed it but went back to the old way of only making it roughly accurate to civilian GPS receivers were as the military ones had the full software that could process the signal correctly so making them more accurate. this is what used to happen many years ago before the USA decided to make the full signal available to all an sundry

after all its a satellite transmitting a timing signal so dont see how they could jam it as such, but I could see them changing the signal somehow so only the military ones picked up the full signal, all GPS satellites relies on super accurate clocks to send the timing signal with a marker which dictates what satellite you're picking the signal up from so I dont see them messing about with that.

[whitestone]

That's the SA (Selective Availability) signal, effectively it randomises the true location. It's not a true random signal as if you know the seed and how far in to the sequence you are then you can work out the real signal. GPS signals can be jammed, they are pretty low strength, but it's usually in very specific areas. If they turned the SA back on then it would affect the whole world not just the NW of Scotland, I think the US government/military have said that they don't intend doing so outside of a full military conflict. As far as I know it's a system wide setting you can't turn it on for one location or area - the satellites are all at slightly different altitudes and on different orbits so from one moment to the next you are receiving signals from an ever changing set of satellites.

I worked in the middle east on a seismic survey using differential GPS (basically a base station that knew exactly where it was and could transmit a correction signal), the other guys said that during the first Gulf War they'd know when an attack was imminent as they'd suddenly find that they were 5000 metres below sea level We were working to 5cm accuracy in all three axes.

[touch]

They dont need to do anything to the satellites to jam the signal. All you need to do to jam GPS is broadcast a stronger signal on the same frequency - just static noise would block it or you could even broadcast a different time and give receivers false readings. As the signal from the satellies is quite weak, it doesnt take much to create a stronger signal.

You can buy gps jammers which work on this principle. People often use them to stop gps trackers on their vehicles - fleet managers watching where their trucks are or insurance 'black boxes' monitoring how fast you drive. They are illegal to use though because you need a licence to broadcast on that frequency.

The GPS we use was developed by the american military and they allow the public to access it free-of-charge. I think it's fair enough that they interfere with it a couple of times a year.