Manuals, Timing, Ham Radio, Test Equipment

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GPS week rollover of July 30, 2017 and Thunderbolt Monitor

The GPS system has few flaws. The week rollover is one of them. From the Trimble Thunderbolt manual:

This field represents the current GPS week number. GPS week number 0
started on January 6, 1980. Unfortunately, the GPS system has allotted only 10-bits of
information to carry the GPS week number and therefore it rolls-over to 0 in just 1024
weeks (19.6 years,) and there is no mechanism built into GPS to tell the user to which
1024 week epoch the week number refers. The first week number roll-over will occur as
August 21, 1999 (GPS) transitions to August 22, 1999 (GPS). The ThunderBolt adjusts for
this week rollover by adding 1024 to any week number reported by GPS which is less that
week number 936 which began on December 14, 1997. With this technique, the
ThunderBolt will provide an accurate translation of GPS week number and TOW to time
and date until July 30, 2017.

There is no fool proof way to automatically correct the wrongful information, unless you have another independent source of accurate timing. Since that is usually not the case for a small system like the TB Monitor kit, we have to come up with a manual patch.

The TB Monitor firmware version 4.0.0 and up will be upgraded by providing a new menu entry allowing you to select the epoch number applied to correct the date coming from the Thunderbolt. By default, this correction will only apply to the time displayed on the LCD display. If you are using the WiFi option, the data stream from the Thunderbolt will be unaffected. The reason being that the GPS data stream simply has no provision for the extra epoch information. The good news is that any software that will use the WiFi data (like Lady Heather), most likely will already have a correction routine since this software has access to the current approximate date/time through the operating system. 

After the rollover of July 30, 2017, you will have to flash the new firmware in your kit and use the menu to select the appropriate epoch. Detailled instructions will be available here.

A new firmware version will be released shortly after July 30, 2017 (so that I can test it) and will be available to all TB Monitor kit customers. Information about how to upgrade your kit will be available in this page at that time. Of course, new kits will be loaded with the new software after that date.

Please note that the firmware upgrade only applies to the kits with firmware version 4.0.0 and up. I am not planning an upgrade for the older kits.