GPS Jamming over most of UK 7/8 JUL
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Ah good old JMC!
great fun!
Its prob covering their backs - my past comms experience would bring me to think that think there would be little backscatter at GPS freqs but I bet they would want to make sure there was not blame if something did happen!
As GPS was orig a MIL system I don't think its protected in any way - someone may enighten us otherwise
great fun!
Its prob covering their backs - my past comms experience would bring me to think that think there would be little backscatter at GPS freqs but I bet they would want to make sure there was not blame if something did happen!
As GPS was orig a MIL system I don't think its protected in any way - someone may enighten us otherwise
PPruNaholic!
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I agree that its unlikely to affect us a long way away, say London area, unless at great height / line of sight - e.g. 30,000'
All that would required to block / jam GPS is a signal on a similar frequency capable of swamping the receiver front-end. Given the low signal strength at microwave frequencies involved in reception of signals from satellites, this isn't too hard in itself if you can put a jamming source close to the receiver you are trying to jam.
But its hard to imagine how you do this effectively over a very wide area? Maybe instead of relying on very strong blocking signals they are instead transmitting bogus, but similar, signals to confuse receivers and cause intentional errors?
But I have no idea whether this is what they do in practice and agree with previous post that the NOTAM is probably a "CMA" effort! I'd be very surprised if we notice it in practice. Still, we just don't know - and we'd better play safe and heed the NOTAM warning I suppose!
All that would required to block / jam GPS is a signal on a similar frequency capable of swamping the receiver front-end. Given the low signal strength at microwave frequencies involved in reception of signals from satellites, this isn't too hard in itself if you can put a jamming source close to the receiver you are trying to jam.
But its hard to imagine how you do this effectively over a very wide area? Maybe instead of relying on very strong blocking signals they are instead transmitting bogus, but similar, signals to confuse receivers and cause intentional errors?
But I have no idea whether this is what they do in practice and agree with previous post that the NOTAM is probably a "CMA" effort! I'd be very surprised if we notice it in practice. Still, we just don't know - and we'd better play safe and heed the NOTAM warning I suppose!
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Dunno why they feel the need to jam GPS...its already possible to disable GPS in certain areas, while keeping it active elsewhere, and I'm sure if Tony was to have a word with his buddy George W, then they'd turn it off wherever we asked 
The best GPS jammer I've seen is a GPS receiver with a dodgey antenna, causing it to re-radiate. Knocked out all GPS's within a 2 mile radius...(and took us f@@king days to find, as no one though a GPS 'receiver' could re-radiate)
Cheers
EA
The best GPS jammer I've seen is a GPS receiver with a dodgey antenna, causing it to re-radiate. Knocked out all GPS's within a 2 mile radius...(and took us f@@king days to find, as no one though a GPS 'receiver' could re-radiate)
Cheers
EA
GPS is dead easy to jam - it's such a low power transmitter, any signal on the same frequency will mess with it. If the duration of the jamming signal is more than 25 seconds (the length of one complete cycle of the pseudo random code, a receiver will have great problems working out it's postion. The Russians have developed a GPS jammer, and it's commercially available 
You can bet the Serbians had a few during the Kosovo war!
Also bear in mind that it's Uncle Sam's toy and he can do with it what he pleases. Although SA (Selective Availability - the system where accuracy is downgraded) is currently switched off, it can be switched on again at any time and the level of downgrading increased - even locally. The only way to avoid this SA is to have a receiver that picks up the military GPS frequencies and have the current encryption de-codes. A civilian aint going to get those!
You can bet the Serbians had a few during the Kosovo war!Also bear in mind that it's Uncle Sam's toy and he can do with it what he pleases. Although SA (Selective Availability - the system where accuracy is downgraded) is currently switched off, it can be switched on again at any time and the level of downgrading increased - even locally. The only way to avoid this SA is to have a receiver that picks up the military GPS frequencies and have the current encryption de-codes. A civilian aint going to get those!
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The other way to get around SA is to use a differential GPS receiver. This receives another signal from a ground station also with a GPS receiver. The ground station knows exactly where it is it can work out the SA error. This is then transmitted to your differential GPS giving a very accurate position.
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One problem , if your GPS receiver is jammed, the differential GPS receiver which must be in close proximuity will also be jammed.
Each GPS transmitter is on average 16 times more powerful than a Satellite TV transmitter and spread over a wide frequency spectrum. To jam it for even 25 seconds, over a mediocre range, will require an enormous ammount of RF energy bearing in mind the bandwidth and that the RF field reduces in accordance with the inverse square law.
Each GPS transmitter is on average 16 times more powerful than a Satellite TV transmitter and spread over a wide frequency spectrum. To jam it for even 25 seconds, over a mediocre range, will require an enormous ammount of RF energy bearing in mind the bandwidth and that the RF field reduces in accordance with the inverse square law.
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The error signal from DGPS could be on a totally seperate frequency from the GPS signal and it could be spread over any number of frequencies. Bit difficult to jam. I work in engineering where the industry uses DGPS regularly for survey work. Very accurate. Ordnance Survey operate an 'active network' of error transmitters.
All that said, the fixed station has to be reasonably close, within a couple of miles, to reduce the errors by enough.
All that said, the fixed station has to be reasonably close, within a couple of miles, to reduce the errors by enough.
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But its not the error signal that would be jammed, its the GPS input to the reference receiver which is likely to be in close proximity to the working receiver (2 miles you state). If one goes the other goes and the reference signal won't exist.
DGPS only takes out propogation and position errors it doesn't increase immunity to jamming.
DGPS only takes out propogation and position errors it doesn't increase immunity to jamming.
still saving the money for it.
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bcfc
No, I didn't notice anything this time, but I am a bit distant from the action.
DGPS is not the answer, as a number of correspondents have already pointed out. If the diff station is receiving corrupt data from the satellites, it will only compound the error.
GPS jamming is however good for the ego - I once got an indicated 630 kts
out of a Diesel Astra on the Quiraing road between Staffin and Uig.
The JMC finished last night - as soon as we can be sure the Septics
are out of Scottish waters, it'll be safe to come out...
http://news.bbc.co.uk/hi/english/uk/...00/2122687.stm
Happy days!
Rattus
No, I didn't notice anything this time, but I am a bit distant from the action.
DGPS is not the answer, as a number of correspondents have already pointed out. If the diff station is receiving corrupt data from the satellites, it will only compound the error.
GPS jamming is however good for the ego - I once got an indicated 630 kts
out of a Diesel Astra on the Quiraing road between Staffin and Uig.The JMC finished last night - as soon as we can be sure the Septics
are out of Scottish waters, it'll be safe to come out...http://news.bbc.co.uk/hi/english/uk/...00/2122687.stm
Happy days!
Rattus
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On Tuesday a British frigate fired a shell into a loch eight miles off target and just one mile from the village of Durness.
I flew from London to Yorkshire on the 7th, having picked up the notam from notamplot. (Endorse AA's comments about how useful it is - why did AAIS not launch the product themselves?)
Did not notice a thing. But a good job that there was reasonable VMC throughout. The cu's over Lincolnshire provided one of those aerial playgrounds that come along rarely....
Skua
Did not notice a thing. But a good job that there was reasonable VMC throughout. The cu's over Lincolnshire provided one of those aerial playgrounds that come along rarely....
Skua
