Primarily for general aviation discussion, but other aviation topics are also welcome.
By 100poundburger
#1796156
Hello everyone, i'm asking this in 'general aviation' as i'm not sure what category it belongs..
can anyone explain what is the purpose of these jamming trials ...and who carries them out ?
Obviously it must be 'legal' to jam GPS signals ....how does this work ?
Many thanks.
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By Iceman
#1796198
GPS signals are very weak (typically sub noise) by the time that they reach a receiver, hence it is very easy to jam a GPS receiver, either deliberately or inadvertently. These trials are not GPS jamming trials per se, more anti-GPS jamming trials in which various companies evaluate their anti-jamming kit. In order to do this, jammers have to be used in order to evaluate the AJ performance, these jammers emitting power in the GPS bands with various frequency spectrums. The trials are typically orchestrated by a government defence research agency, but many AJ vendors, both civil and military oriented will be evaluating their kit.

It is illegal to jam GPS deliberately so these trials are the only opportunity that AJ vendors get to evaluate performance. Jammer power levels are well controlled in order to limit the affected area.

Iceman 8)
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By Red
#1796218
Funny you mention this today, were they jamming today from Sennybridge? , I found no Notam regarding this but did get repeated dropouts. on 2 seperate recievers
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By matthew_w100
#1796220
I remember reading electronics mags as GPS was being developed. Pages and pages were devoted to explaining the spread-spectrum techniques that would render it unjammable.
By jacekowski
#1796233
matthew_w100 wrote:I remember reading electronics mags as GPS was being developed. Pages and pages were devoted to explaining the spread-spectrum techniques that would render it unjammable.


GPS can be very easily jammed and spoofed (as in, do it at home for £200), at least as far as civilian code is concerned, P(Y) and M codes are encrypted which prevents spoofing but can still be jammed (and are still susceptible to replay attacks (as in record code from another location and then re-transmit it somewhere else - making the receiver think it is at the time and location where recording happened).
Both of those attacks are reasons why devices like this https://www.microsemi.com/product-direc ... s-firewall exist (it measures things that are not part of GPS standard (bit like during WW2 enemy could tell who was the specific person transmitting encrypted morse code message), and also can have atomic clock added to it to be able to defend against longer attacks).
By ChrisRowland
#1796242
I can understand jamming, the signal is very weak, but spoofing? The receiver is getting data from multiple satellites and all of them would need to be replicated by the spoof signal - woudn't they? I've seen it done on NCIS but that's not reality.
I'm not denying what you are saying but a little surprised. Could you really do this for a random passing aircraft or do you need to be really close so that you can be confident that all the signals come from the spoofer?
By riverrock
#1796251
The signals aren't encrypted, antenna aren't directional, the signals are very weak (I read 0.1 fWatts (so 15 zeros after the decimal point) so spoofing just involves timing and a stronggr signal. Should be doable fairly easily.
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By jacekowski
#1796252
ChrisRowland wrote:I can understand jamming, the signal is very weak, but spoofing? The receiver is getting data from multiple satellites and all of them would need to be replicated by the spoof signal - woudn't they? I've seen it done on NCIS but that's not reality.
I'm not denying what you are saying but a little surprised. Could you really do this for a random passing aircraft or do you need to be really close so that you can be confident that all the signals come from the spoofer?


To do it to any random passing aircraft you would need transmitter powerful enough to be stronger than GPS signal (not that much power is actually needed as you would be significantly closer) or directional antenna and point it at the aircraft.

All you need is https://www.amazon.co.uk/Great-Scott-Ga ... 01COVX464/ and a PC - this will cover ~200-300m (assuming line of sight).

Then if you want better range a 2nd hand RF power amplifier will run you into few 100's + decent antenna (pretty cheap).

Both images below were taken ~10 minutes apart (time it took me to find my old sat nav as additional device to test against). 1st one shows somewhere in scotland, 2nd one somewhere in china.
I have also tested it against IFR GPS, which to make it worse, was perfectly happy to go into approach mode and provide LNAV approach (and with some work SBAS signals can also be simulated so LPV should also be possible)

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By Hangar16
#1796254
Red wrote:Funny you mention this today, were they jamming today from Sennybridge? , I found no Notam regarding this but did get repeated dropouts. on 2 seperate recievers


I was flying over mid Wales at 6000 ft yesterday and the Garmin G3X lost its GPS signal. My pilot aware wasn’t affected. As far as I can find out the only warnings for GPS jamming yesterday were at Luce Bay with a range of 60 miles. Mid Wales is 160 miles away, but I did wonder.

Dan