Wednesday, 2 May 2012

Navstar B&G GPS and the curse of the year 2000

I have some old GPS units, even a Walker 412 satnav, that will never work as the satelites were turned off many years ago but what of a quality unit like the B&G they sold and named Navstar GPS? it was also named the XR4-G GPS receiver and the B&G 4000 GPS.

The manual, very well put together and easy to follow each step.

The start of the matter, explained as an amplifier antenna, the co-ax is said to be quite special and only available from Navstar themselves.

This was the Rolls Royce of GPS once, so what happened to it?  hooked up to the original B&G stick GPS antenna and a 12 volt power source, the functions still work fine.

The set has a lable on it, who it was supplied by and the year, its dated 1980 and thats the problem.

The sets position was entered manually by me, so was the time, the height of the antenna but its the date thats the issue? It takes the date in three groups of two numbers, so this is what I entered  01.05.12  but the almanac is thinking its the year 1912 and knows nothing at all about the year 2012!

How sad is that.

The set is functional excepting it can not find a satelite, its doing all the searches, the sets program runs a test on the computer, antenna, it just can not work due to the date?


An hour or so later, I have left the set switched on and the searches across the sky are continuing, the antenna is under a cement tile roof, that will not help the situation?

(incorrect position entry)

 The set has found a satelite! not only that but the angles to others are now being shown to me.

The set is finding the satelites and I assume storing the information in what will be a very dead memory, I guess the answer is to leave it on 24 hours and see what happens?

Each satelite is checked, even if slowly, it is working things out?

The next day I ran the stick antenna outside and in clear air, the result was similar, it would find satelite signals but the set just does not work, end of May Day holiday idea!


Will Your GPS Work In the Year 2000?

by Charlie Courtney

Published in the December, 1996, GOFC Newsletter

Some GPS receivers may no longer operate correctly after 21 August, 1999 unless returned to the factory for an upgrade. Affected units will think that 22 August 1999 is actually 6 January, 1980. Since GPS receivers use the current date and time to calculate their position, accuracy of the affected units will be destroyed.

This has nothing to do with the infamous "year 2000 problem" looming over the computer industry, although the situation is similar. Many business-related computer programs, especially those written years ago for big mainframe computers, cannot deal with dates later than 31 December, 1999. These programs think that the next day is 1 January, 1900 because the leading "19" in the year is understood to be present, and the computer only stores the last two digits of the year. As a result, a mortgage payment received and posted on 31 December, 1999, one day ahead of a due date of 1 January, 2000, is viewed by affected programs as arriving 100 years too late -- the computer thinks the payment was due on 1 January, 1900!

The GPS problem occurs because, among other things, GPS satellites broadcast the current date and time to your GPS receiver. Your receiver then uses this information to calculate its position from the location of the satellites it can "see." Unfortunately, the date information broadcasted by a GPS satellite is given as the number of weeks elapsed since 6 January, 1980 -- the official "birthday" of the GPS system -- and the amount of computer space allocated in the GPS system for storing the week number only can hold 1023 weeks. (It's a 10-bit value for all you computer nerds that may be interested.)

On 22 August, 1999, the GPS week number will reset to zero, since the previous week was GPS week number 1023. Some older GPS units were not programmed to handle rollover of the GPS week back to zero. An affected unit will become totally lost on 22 August, 1999. It will not "see" the location of GPS satellites correctly, because it will look for them where they were supposed to be on 6 January, 1980, instead of 22 August, 1999.

Garmin, manufacturer of the best selling marine GPS units, has stated that all its units will handle the rollover correctly. Most likely recent units from other reputable manufacturers will do so as well. However, those of you with older, non-Garmin units should check with the manufacturer. Also, be sure to check for this problem before buying a used GPS unit or a bargain-priced new unit from a no-name manufacturer.

This page last updated 3 November, 1996

Charles H. Courtney (

My thanks to Charles on the words in his artical.