Hi The lowest cost “commercial” simulator that I know of is the Jackson Labs Claw:
http://www.jackson-labs.com/index.php/products/claw_gps_simulator <http://www.jackson-labs.com/index.php/products/claw_gps_simulator> Taking a look at the manual: http://www.jackson-labs.com/assets/uploads/main/CLAW-Simulator.pdf <http://www.jackson-labs.com/assets/uploads/main/CLAW-Simulator.pdf> It appears to be a fully documented interface. ( unlike the device that started this thread off). The support software is freeware so there is no lockdown there either. Time transfer is claimed to be in the 3 to 5 ns range. My guess is that you can trust that number :) :). As far as I can see, it will do pretty much everything you would want to do to check out a GPS device or to drive one off of some other source ( like your basement ensemble of Cs fountains …. ) It looks like a nice little box. Bob > On Apr 24, 2021, at 1:56 PM, Lux, Jim <[email protected]> wrote: > > On 4/24/21 10:31 AM, Andrew Kalman wrote: >> Hi Paul. >> >> Yes, I've been on this same journey. After I learned (somewhat unrelated) >> that one is supposed to have an FCC license to rebroadcast GNSS signals >> (e.g. via a repeater inside a lab, makes eminent sense), I started thinking >> more about GNSS simulators and how they might be added to my company's >> workflow. So I bid on a couple of units, got them for pennies on the >> dollar, and started messing with them in the hope of ending up with an >> ATE/rack-type setup that I can build into a nearly automatic test & >> validation suite. >> >> Let's say I was much more successful with the Spectracom/Orolia GSG-5 than >> with the Spirent GSS4200 ... In the case of the GSG-5, it's really just a >> question of how many options you can afford -- the rest is all there, you >> don't need a support contract, it's all easily accessible in the unit >> itself, and as long as the Internet exists the GSG-5 will probably keep >> working (it gets time, ephemeris and almanac data from servers -- it can >> simulate stuff NOW (wth the right options), not just in the past and >> future). The GSS4200 is about 10-15 years older, and it shows (in terms of >> ease-of-use), along with how Spirent chose to monetize their users / >> subscribers. Also, the GSG-5 adds things like interference to the signals >> (all for a price, of course). IOW, the newer units (at least, from >> Spectracom was XL Microwave is now Orolia) are a whole lot easier to use >> ... but they come at a price. It's an interesting business. >> >> I will say that the build quality of the Spirent is very good. I have not >> opened up the GSG-5, just did a calibration and it was very close. >> >> I'm a little bit surprised that there is not an open-source, SDR-based GNSS >> simulator (at least, one I could find). > > > > Not much demand, I suspect. I seem to recall a GNSS generator that was open > source about 5-10 years ago, but I can't find it now. > > The record/playback boxes are actually pretty simple - just a single bit in > many cases. After all, a lot of the receivers use a single bit input, because > the signal of interest is below the thermal noise floor. > > The real challenge isn't the SDR part (a USRP would work just fine as long as > you get a daughter card that supports L-band) - it's the "scenario building" > which requires simulating the orbits of the GNSS satellites, simulating the > track of the receiver, calculating the time delays (including iono and tropo > effects), and generating the PN codes appropriately. > > Each of those isn't too tough, but putting it all together is quite > challenging, and, apparently, it's not "dissertation topic" suitable (which > is where a lot of niche SDR stuff comes from). > > A *real* challenge is that to do it right, you need very good orbit > propagators - if you're looking to simulate nanosecond scale phenomenology, > you need to be able to generate orbit behavior on a few cm or better sort of > uncertainty. For some applications (differential GPS, RTK surveying) you > could probably get away with something that's not perfect, but doesn't have > problems for YOUR specific application. But it wouldn't be a generalized box. > > One strategy we've used at JPL is to have the fancy expensive box generate > the signals for a scenario, and record them with a much cheaper > record/playback box, then use the playback for testing. > > Right now, my project (SunRISE mission) is working on how to generate > realistic test signals for a space interferometer - Where we need to generate > signals that can be received, and the output of the receiver fed into GIPSY-X > for post processed precision orbit determination. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
