Originally Posted by
Marvin Hagler
come on yes or no?, can you with a 25$ product from ********.com find that a vhf tracked car that has the tracker armed for example its been reported stolen works ? thus meaning the asian gentleman who told me this was infact correct
you dont understand gps very well...
the civilian available frequencys are currently based on 2 seperate frequency groups with a third in development. the early civilian GPS used whats known as the L1 frequency band.
In simple terms the early civvy GPS network uses a message that contains 3 core bits of info, satellite time/date info, emphemeris data (wherethat satellite is in orbit NOW), and almanac data (rough positions of all satellites).On top of that is a coarse/aquisation code which in essence helps you calculate the "offset". Then the computer once its locked onto 3 satellites (2d fix) and 4 or more satellites (3d fix) it uses the data to calculate a position.
it is more complicated than that in reality as its all the signals are modulated onto a carrier wave so have to be demodulated and broken down, errors calculated etc etc etc before you even get to the point of calculating a position.... but google if you want to know more
now the good old US has upgraded the civvy GPS to use the L2 frequency which does not use a CA code but uses two data streams to do ranging and hence offsets. so works slightly different as well as being on a different frequency.
most new GPS recievers use a combination of both frequencys and methods to get better positional accuracy and faster fixs.
most newer GPS recievers have anti-jam capabilities and sufficient redundancy to get past most basic GPS jammers.
Almost all jammers are focused on the L1 frequency. Especially anything you and I (and more importantly criminal scum) can afford. Anything sub £200 (including the ebay jammers) arfe simple continous wave jammers operating on the L1 frequency.
most modern GPS units can filter out continous wave jamming on the L1 frequency unless the signal is very strong or directly in line of sight of satellites.
the better jammers that cost several hundreds use noise generation on the L1 frequency and hence are much more effective.
Even so their range is very limited due to the very low power of these types of devices. It doesnt help that most are based on cigarette power supplies so low down in car, and its 50/50 whether the aerial is high up or low down. It will be minimally effective on a high up GPS aerial. But they can be quite effective on low down GPS units such as cheap/older units or the magnetic undercar trackers (which is what they were designed for countering really).
all this wont effect L2 frequencies so the GPS will still get a fix in quick order due to stored C/A data and alamanac data. Such jammers would only slow down a fix on L2 frequency for a cold start on a GPS unit thats got no data whatsoever in it.
of course none of this effects the precise positioning systems or the p-code military systems.
GPS tracking and electronic warfare against both jammers and GPS is a very interesting subject... some of the latest kit uses either electronically or physically steerable phased array aerials that can remove all ground interference for advanced anti-jamming meaning youd need an aircraft with a jammer to stand a chance at all of jamming such modern devices. However thats a bit beyond the scope of car usage and generally reserved for top level civvy and mostly military usage.
oh and most people dont realise that one of the other uses of the GPS satellites is to detect nuclear missile launches and detonations as part of the US defence network. Thats a small part of how in the nuclear war films NORAD can see where all the missiles come from and detonate
cool or what???
Originally Posted by
Phil2002
No they won't stop VHF tracking which is why i would only have a VHF and gps tracker. The blockers i have seen do NOT BLOCK GPS they only block the gsm signal the gps will work the tracker will be able to see where it is but will have no way of communicating with the operating center as it will have no gsm(mobile phone network) coverage the reason they use this is because it works theses products were designed for use in hospitals libarys and doctors surgerys etc.
Blocking the GSM network is much much easier.
however similar limitations apply to the units used. GSM jammers sited inside a car will have little/no effect on an underbody tracker and limited impact on a higher up GSM aerial or a GSM aerial sited outside the main cabin.
So jamming GSM and GPS isnt as simple as a £20 chinese piece of crap off ebay as people think. Its hit and miss both for us the car owner and them the thief. Thats why its common for them to dump the car or try and find the tracker as they know they cant defeat them all.
the best defence as phil says is a layered defence of a tracker that uses GPS, GSM AND VHF as even if the maniacs have dual GSM and GPS jammers they still will never stop the VHF.