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). --Andrew -------------------------------- Andrew E. Kalman, Ph.D. On Sat, Apr 24, 2021 at 9:14 AM paul swed <[email protected]> wrote: > Andrew > Welcome to time-nuts. I really appreciate your detailed write up. I have > seriously considered a used gps emulator a few times. Really don't need > complex solutions. Its more for recovering and working on quite old GPS > receivers and down converters like Austron 2201s. 1990s stuff. > Whats great about the writeup is at least for this unit I can see the > requirements for operation that are far more complex then I would have > expected. I seem to recall there was a series of GPS emulators on ebay that > were priced about right for a hobbyist to consider. > Now at least if some unit shows up I will know what to look out for. Other > wise its a expensive box. > Thanks > Paul > WB8TSL > > On Sat, Apr 24, 2021 at 7:02 AM Andrew Kalman <[email protected]> wrote: > >> So, an update. I was graciously provided with the User Manual for the >> GSS4200 (thank you!). Having read through it and having played with my >> GSS4200, I conclude the following: >> >> - My unit is functionally working (well) -- 10MHz clock was not far >> off, >> output levels are correct, etc., it is generating a signal where one >> should >> be. >> - Most of the "commanded" behavior I had been observing (using the >> GSS6100 user manual as a guide, issuing commands over GPIB) was the >> behavior of the unit when operating in GSS6100 emulation mode (single >> channel, ability to change the SVID, maybe the ability to change the >> week, >> etc.). >> - This GSS4200 has (sadly) only one scenario loaded in its NVM memory >> -- >> "4200calibration" that is 10 minutes long. It basically outputs a >> single-channel signal on PRN 1, makes sense for calibration. >> - Based on my reading of the manual, at a minimum, if you have access >> to >> the utilities CD ROM, you can load scenario "libraries" (#sats, signal >> strengths, ground trajectories, etc.) and then run them (in a looping >> mode, >> if you want) on this unit. A combination of utilities (that work only >> over >> USB) load scenarios into the GSS4200. >> - Each scenario also includes the appropriate ephemeris and almanac >> info >> (provided by Spirent). >> - Scenarios must be under 5 minutes long.Dunno how the 4200calibration >> scenario is 600s long ... >> - The scenario and other file formats are not / not well documented. >> Spirent had a server that you would provide scenario requests to, and >> I'm >> guessing that it would generate the scenario file along with the >> accompanying ephemeris and almanac info, and crunch that all into a >> .scb >> scenario file. You can then use a provided utility to combine multiple >> scenarios into a scenario library that you can then load into the >> GSS4200. >> Note that there is no obvious way for a user to ** generate ** their >> own >> scenarios (or ephemeris or almanac). >> - GSS6100 emulation is "independent" of GSS4200 scenario operation. For >> example, the GSS4200 manual does not mention an explicit level command >> (that is part of the GSS6100's command set), yet the example scenarios >> alter the output level, so clearly the unit can do that. >> - So, the intended way to use this unit appears to be: >> - Obtain supplied/default scenarios (*.scb) or ones built for you >> via >> the Spirent web interface >> - Optionally combine them into libraries (*.scl) via the Scenario >> Selection Tool >> - Download them into the GSS4200 (max 512KB worth) using the Flash >> Loader Utility >> - Run the scenario via RUNS <x> for one run, or LOOP <x> for >> looping, >> where <x> is the scenario number. >> >> >> - So, I'm kinda stuck here. I want the GSS4200 available for a quick >> and >> consistent validation of the proper operation of GPS receivers. For >> that, >> at a minimum, I need some complete scenarios (the default ones supplied >> with the unit would be alright) that I can load into the unit to run in >> looping mode. There are 18 default scenarios, 3 each (different power >> levels, stationary vs. moving, etc.) for six cities: Boston, LA, Tokyo, >> Hanover, Seoul and Shanghai.They all run at various dates in 2003, >> suggesting that the GSS4200 was released around that time. >> - My unit only has the one calibration scenario (PRN 1 only, standard >> output level) loaded ... I'm not really clear on the usefulness of a >> single >> channel of GPS signal. >> - This unit differs from more modern units like Spectracom/Orolia GSG >> series units in that the newer units allow you to generate your own >> scenarios, and they pull ephemeris and almanac data directly from the >> internet. Plus more channels and constellations, more interference and >> other simulations, etc. >> >> So, I conclude that without the full GSS4200 utilities disk, I'm kinda >> stuck. :-( >> >> --Andrew >> >> -------------------------------- >> Andrew E. Kalman, Ph.D. >> >> >> On Fri, Apr 23, 2021 at 1:15 PM Andrew Kalman <[email protected]> wrote: >> >> > Hello. >> > >> > [SNIP] >> > >> > I am ** desperate ** for a User Manual for the Spirent GSS4200 GNSS >> > simulator (e.g., >> > https://www.testequipmentconnection.com/54837/Spirent_GSS4200.php). >> That >> > model is somewhat unique, in that it's one of only a very few that >> Spirent >> > released that can/will run without an external "control" program. Using >> the >> > manual from the GSS6100, I'm able to do a couple of things with the >> GSS4200 >> > over GPIB, but for the life of me I cannot figure out how to get the >> > GSS4200 into a mode other than single-channel (it supports 6 channels, >> and >> > has a single-channel mode). I suspect there is a command to do this, >> but I >> > have not been able to figure it out. >> > >> > I have spent 8+ hours searching sites and archives, to no avail. Spirent >> > has done a rather impressive job of locking down their support software >> and >> > docs behind a paywall (and I wonder if they even have the docs for the >> > GSS4200 any more). Any help is appreciated, I'm happy to give back if >> > someone wants to snag another GSS4200 (around $700 used) and use it as a >> > simulator. >> > >> > >> _______________________________________________ >> 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.
