Sure, he designed it, but I don't think those nice printed PCBs are "homemade". I'd be more impressed if it were through-hole construction. Still, it's pretty cool.
Homemade GPS Receiver
11–20 of 67 posts
Re: Homemade GPS Receiver
#12Sure, he designed it, but I don't think those nice printed PCBs are "homemade". I'd be more impressed if it were through-hole construction. Still, it's pretty cool.
Doubtful you can get an FPGA of that class in a thru-hole package. The dude was smart to shop out the PCB instead of spending weeks trying screen and drill his own.
Re: Homemade GPS Receiver
#13Hmm. I don't see any mention of whether this design complies with the COCOM Limits, an agreement that GPS devices should disable themselves when at an altitude above 60,000 feet and a speed faster than 1,000 knots.
Probably not Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data In practice, not sure how this is achieved, but for speed this may even be a limitation of the circuit (for example, if you can't compensate for the doppler effect at that speed or has to add some other processing - still, the doppler effect should be small) 1000 knots is still +/- 1.5 Mach (at sea…
> Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data
Actually, no. All military aircraft have inertial navigation packages that, among other values, provide altitude above the elipsoid, position, and velocity vector. When available, these systems are fixed periodically to GPS-based measurements.
Re: Homemade GPS Receiver
#14Sure, he designed it, but I don't think those nice printed PCBs are "homemade". I'd be more impressed if it were through-hole construction. Still, it's pretty cool.
Doubtful you can get an FPGA of that class in a thru-hole package. The dude was smart to shop out the PCB instead of spending weeks trying screen and drill his own.
Good point. Any idea what ballpark speed one would need?
Re: Homemade GPS Receiver
#15Earlier quoted context omitted.
Probably not Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data In practice, not sure how this is achieved, but for speed this may even be a limitation of the circuit (for example, if you can't compensate for the doppler effect at that speed or has to add some other processing - still, the doppler effect should be small) 1000 knots is still +/- 1.5 Mach (at sea…
> Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data Actually, no. All military aircraft have inertial navigation packages that, among other values, provide altitude above the elipsoid, position, and velocity vector. When available, these systems are fixed periodically to GPS-based measurements.
Yes, but GPS modules can't expect to have this information input into them. See http://en.wikipedia.org/wiki/CoCom
You're right from the point of view of the aircraft/missile, where several pieces of information are put together (GPS, barometric, inertial, etc) for navigation purposes.
Re: Homemade GPS Receiver
#16Earlier quoted context omitted.
> Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data Actually, no. All military aircraft have inertial navigation packages that, among other values, provide altitude above the elipsoid, position, and velocity vector. When available, these systems are fixed periodically to GPS-based measurements.
Yes, but GPS modules can't expect to have this information input into them. See http://en.wikipedia.org/wiki/CoCom You're right from the point of view of the aircraft/missile, where several pieces of information are put together (GPS, barometric, inertial, etc) for navigation purposes.
Right, minor brain fart. I was thinking at the systems level, but the requirement is for the module to cut itself out, not have an external system do it.
Re: Homemade GPS Receiver
#17Hmm. I don't see any mention of whether this design complies with the COCOM Limits, an agreement that GPS devices should disable themselves when at an altitude above 60,000 feet and a speed faster than 1,000 knots.
Probably not Which is funny, because to know you're higher/faster than allowed you need to calculate that from GPS data In practice, not sure how this is achieved, but for speed this may even be a limitation of the circuit (for example, if you can't compensate for the doppler effect at that speed or has to add some other processing - still, the doppler effect should be small) 1000 knots is still +/- 1.5 Mach (at sea…
I don't think there's a requirement to completely shut down, only a requirement to cut off your data output. You can keep calculating your speed and position, you just stop telling the outside world.
Re: Homemade GPS Receiver
#18It blows my mind that all that complexity is baked into your smartphone
Re: Homemade GPS Receiver
#19Earlier quoted context omitted.
Doubtful you can get an FPGA of that class in a thru-hole package. The dude was smart to shop out the PCB instead of spending weeks trying screen and drill his own.
Good point. Any idea what ballpark speed one would need?
Speed of the FPGA? FPGAs are given speed grades, but the actual design dictates the max speed. Different logic sections, depending on pipelining, size, which pins they are connected to can run at different speeds. You might have an overall max speed/critical path of say 50mhz, but you might be able to safely run a small section of the design at 200mhz.
Re: Homemade GPS Receiver
#20I have to join in to say that this page (which exists since some time, only has recently be updated) is really impressive, and a very good educational material for everyone wanting to really understand the workings of GPS. Nevertheless it's not the only attempt, bug a very good one, at "open source GPS" projects. There's at least http://www.gnss-sdr.org/ which is a more software-centric approach being able to work wi…
Many standalone recievers are just that- completely standalone. They just spit out a string of coordinates and other information on configurable intervals.