[time-nuts] GPS week rollover

[Michael Wouters]

A multichannel, L1 GPS-only simulator/recorder costs about US5k. We have
one of these that we used to test for rollover problems with some older
receivers that we use (none found). The software with this lower cost
device is not very sophisticated. As Bob hints though, a top of the line
simulator is very expensive, about us200k, the last time I asked.


On Sat, 30 Mar 2019 at 8:00 am, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> Obviously the real answer is going to be “that depends”.
>
> Back when I worked for a living, we had an HP generator that would “play
> back” a recorded ~ 30 minute
> set of GPS “full sky” observations. It was strictly a playback with no
> real way to tweak this or that. We also
> had a single channel device that could be set to do just about anything
> (but only a single channel / sat). The
> “full sky” gizmo is fine for things like sensitivity. The single channel
> device is of more use for poking at rollover
> issues.
>
> Indeed if you have the budget, you can get a setup that will let you run
> multiple sat systems with a dozen sats
> on each system at any simulated location,  time, signal level, errors …...
> Last time I priced one … .yikes ….. I don’t
> know of anybody doing timing with that sort of setup.
>
> Bob
>
> > On Mar 29, 2019, at 3:22 PM, John C. Westmoreland, P.E. <
> john at westmorelandengineering.com> wrote:
> >
> > To All:
> >
> > I have a related question; hope it's OK:
> >
> > What are these companies using for their "GPS Simulation/Simulators?".
> >
> > Is it actually simulating the RF downlink or is a direct data stream
> > injection into a tap into the receiver??
> >
> > Thanks In Advance,
> > John W.
> >
> >
> > On Fri, Mar 29, 2019 at 11:00 AM Michael Shields via time-nuts <
> > time-nuts at lists.febo.com> wrote:
> >
> >> Avidyne avionics are known to be affected by the rollover, causing the
> >> loss of some displayed data.
> >>
> >> https://www.avidyne.com/files/downloads/606-00182-019.pdf
> >>
> >>
> >> On Thu, Mar 28, 2019 at 3:04 PM Mark Sims <holrum at hotmail.com> wrote:
> >>>
> >>> I doubt that any GPS receivers will be newly affected on April 6.
>  Some
> >> very early receivers were hit on the first GPS rollover, but those made
> >> since then usually have a 1024 week compensation built in based upon the
> >> firmware creation date.  Those rollover 1024 weeks from that date and
> start
> >> sending incorrect dates at other places in the 1024 week cycle.  Some
> >> receivers even let you force the rollover week.
> >>>
> >>>> I have a Z3816A that’s showing a yellow “ro” next to the date in LH
> >> and is 18 seconds ahead of a Motorola 12 channel
> >>>
> >>> If Lady Heather sees a date earlier than a set year (currently 2017),
> it
> >> assumes the GPS device has rollover issues and adds 1024 weeks to
> correct
> >> the date and shows the "ro" flag.
> >>>
> >>> As far as the 18 second time difference, one of the devices is
> >> configured to show GPS time and the other is set for UTC time.  At the
> top
> >> right corner of the screen it should say either "UTC time OK" or "GPS
> time
> >> OK" (as long as the device has a valid time).  The TG and TU commands
> can
> >> switch between GPS and UTC time displays.  Some receivers have firmware
> >> commands to switch between the two.  For the others, Heather does the
> >> conversion in software using the "UTC offset" (i.e. leapsecond count)
> >> value.  Many receivers send this offset.   If it does not, the user can
> set
> >> the value.  And if no value is available Heather makes a best guess as
> to
> >> what the value might be (and shows it in RED).  The guessed value is
> rather
> >> prone to errors, but is better than nothing.
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