[aprssig] GPS Epoch Rollover Findings

Brian Webster info at wirelessmapping.com
Thu Apr 25 13:01:17 EDT 2019

I just found this thread and used the program they linked to updated my date and time on my Garmin GPS III (not plus). It took me two tries but I got it to work. The unit shows the proper date and time now. For the record I had replaced the internal battery a couple of years ago. If you have had a unit sitting in storage with no working batteries in it for a long period of time your internal battery may be dead. I believe the GPSII+ has a rechargeable internal battery that should recharge after being hooked up to power for a day or so.




Brian N2KGC



From: aprssig [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Stephen H. Smith via aprssig
Sent: Wednesday, April 24, 2019 12:51 PM
To: TAPR APRS Mailing List
Subject: [aprssig] GPS Epoch Rollover Findings


GPS expresses the current time and date with a?? series of binary counters.?? This included a 10-bit binary counter for the current week, meaning that it could only count 1024 (decimal) weeks (just under 20 years) before rolling over from 1111111111 to 0000000000, and starting over.?? This 1024-week cycle is known as an "epoch".?? The previous epoch ended on April 6th of this year.?? As of April 6th, a 16-bit counter for weeks replaced the 10-bit one.?? This change will put off the NEXT epoch rollover for 65,535 weeks - about 1200 years. 

Some older GPS hardware (actually firmware) couldn't handle either the rollover from 1023 back to 0000, or couldn't handle the new longer 16-bit counter format.?? Such devices quit working on April 6th of this year.?? 


Now that the GPS equivalent of "Y2K" (April 6th) has come and gone, here are my findings testing a bunch of older GPS hardware.


-???? Radio Shack "DigiTraveller" (a faceless serial puck-type device that looked like a flying saucer) -?? DIED

-???? Holux GM-200?? USB-connected faceless mouse-type device - DIED

-???? Rand McNally serial mouse-type device - DIED

-???? 2nd-gen Delorme Earthmate small yellow unit with interchangeable serial and USB cables (not the original large Earthmate) - DIED

The Holux and Rand-McNally are visible in this pic on my website:
????????  <http://WA8LMF.net/aprs/GPS-Antenna-Farm.htm> <http://WA8LMF.net/aprs/GPS-Antenna-Farm.htm>

-???? Tri-M "Super Skymaster"?? white hard-mount combo antenna/receiver (shown in the inset photo of the above pic) survived and WORKS.?? This is especially amazing, given that it was the oldest of all these units.

- ?? Globalsat BC-337 compact flash/PCMCIA unit - DIED?? 

-???? Garmin Foretrex 201 wrist-wearable that is actually a repackaged version of the classic yellow Etrex - WORKS

-???? Globalsat BU-353 (USB) and BU-355 (serial) mini-pucks available for USD $30 on Amazon - WORK

-???? Various unbranded generic units based on uBLox G7 chipset - WORK 

-???? Internal GPS of Kenwood TH-D72 APRS handheld - WORKS


\Stephen H. Smith?????? wa8lmf (at) aol.com 

Skype:?????????????? WA8LMF
EchoLink: ?? Node #?? 14400?? [Think bottom of the 2-meter band]
Home Page:?????????????????? http://wa8lmf.net

Live Off-The-Air APRS Activity Maps
????  <http://wa8lmf.net/map> <http://wa8lmf.net/map>

Long-Range APRS on 30 Meters HF 
????  <http://wa8lmf.net/aprs/HF_APRS_Notes.htm> <http://wa8lmf.net/aprs/HF_APRS_Notes.htm>





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