Hi Put a $35 eBay rubidium on board and you would have to be sure the time solution stayed correct as the take over was implemented.
I know strange to tie timing into a discussion like this :)…. Bob On Dec 15, 2011, at 8:20 PM, Jim Lux wrote: > On 12/15/11 2:24 PM, Azelio Boriani wrote: >> There are GPS simulators for lab use (never seen live or in a picture), I >> suppose they have one connector to feed the GPS receiver antenna. >> Generating in one equipment all the signals you don't need many but only >> one precise timing source. >> >> > > Not quite (there's a discussion of this on the list about a year or so ago)... > > It's harder than you think to generate realistic fake signals for a moving > target. > > At work (JPL) we have a fancy Spirent GPS simulator. And sure enough, it can > generate all the signals your receiver would see given a particular path you > expect your receiver to follow. > > But, in order to use that to provide a spoofing signal, you'd need to know > (fairly precisely) > > a) the position and velocity of the victim > b) the position and velocity(zero) of the jamming station > > You calculate what the expected time,code phase, and doppler of the GPS > signals would be at the victim. Then, you subtract out the time from jammer > to victim and the doppler from jammer to victim, and use that generate your > spoofing signal. > > Then, the trajectory of the spoofed position has to be something that is > internally consistent (i.e. the acceleration, velocity, and position all have > to agree in the Kalman filter), and you have to continously update your > jamming signal with continuously updated position and velocity of the victim. > > > Spoofing GPS is very hard.It was designed to be so, both for its original > military purposes and because you want internal consistency checks to make > sure you aren't displaying false information to a user. > > Jamming GPS to deny it is relatively easy. A high power swept tone does it > very nicely on inexpensive receivers. There are more sophisticated > approaches. You can buy them for $20 on the internet that plug into a car > cigarette lighter. You get one of these jammers, put it on an airplane with > a big power amplifier and fly above your sovereign territory and you can deny > GPS to pretty much everyone underneath you. There are receiver designs that > can tolerate tone or swept or barrage jammers, but they are more expensive, > heavier, etc, and I suspect they wouldn't bother on a UAV. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
