[time-nuts] GPS week rollover

[Mark Sims]

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.