[time-nuts] Re: 20210423: Introduction and Request for Spirent GSS4200 User Manual / Help

Sat Apr 24 17:31:29 UTC 2021

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 <paulswedb at gmail.com> 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 <aekalman at gmail.com> 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 <aek at pumpkininc.com> 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.
>> >
>> >
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