GPS Time Signal Error

[westerlylad]

I've started getting an incorrect GPS time and date signal on my Lowrance HDS Gen 2 chartplotter. It was previously okay, but in the last month, the time and date being displayed has been showing as something like 00.00 hrs 2099.
This has the effect of removing the dynamic tides and currents icons from my display.
Anyone else had a similar problem?

 

[paulajayne]

Google found this. May help.

Settings
Network
Data Sources
GPS
All data global
Left arrow to next screen
Select Auto “your unit” IGPS

Scroll down to Time
Select Time
Select UTC Date this device
Select UTC Time this device.

As soon as you have a GPS lock, the time will be correct.

 

[westerlylad]

Thanks for your reply paulajayne, but i'm pretty sure I've tried that. At least, I've tried re-setting all the user selectable time parameters that I can find, including your suggestion, I think. Anyway, I'll try again when I'm next able to. The unit used to acquire satellites quite quickly, and the time and date came up correctly when it got it's two or more signals. It still acquires the satellites just the same, but now the time and date appear as described, i.e. some time in 2099. The GPS co-ords appear to be okay, but the dynamic tides and currents are now missing. I've tried a number of internet searches, but I appear to be the only person to have experienced this problem!

 

[andyp]

Not sure about Lowrance kit, but with the Classic Raymarine series chartplotters fed by a Raystar GPS unit, this was often a symptom of CMOS battery needing replacement.

The battery allowed the GPS unit to hold "ephemeral data" while the unit was switched off. Without the battery's contribution it was possible for the GPS unit to be fooled into locking on to a satellite constellation but with an incorrect time code.

Another good one to watch out for is GPS Week Number rollover - next due 6 April 2019.

Hope this helps...

 

[paulajayne]

Not sure about Lowrance kit, but with the Classic Raymarine series chartplotters fed by a Raystar GPS unit, this was often a symptom of CMOS battery needing replacement.

The battery allowed the GPS unit to hold "ephemeral data" while the unit was switched off. Without the battery's contribution it was possible for the GPS unit to be fooled into locking on to a satellite constellation but with an incorrect time code.

Another good one to watch out for is GPS Week Number rollover - next due 6 April 2019.

Hope this helps...

Some units have a capacitor to carry out the job of a battery.
Usually easy to spot a bad one as the cap will have bulged.

Easy to change.

 

[Buck Turgidson]

Thanks for your reply paulajayne, but i'm pretty sure I've tried that. At least, I've tried re-setting all the user selectable time parameters that I can find, including your suggestion, I think. Anyway, I'll try again when I'm next able to. The unit used to acquire satellites quite quickly, and the time and date came up correctly when it got it's two or more signals. It still acquires the satellites just the same, but now the time and date appear as described, i.e. some time in 2099. The GPS co-ords appear to be okay, but the dynamic tides and currents are now missing. I've tried a number of internet searches, but I appear to be the only person to have experienced this problem!

Funnily enough we have the same problem with our shinny new Bombardier (Airbus now) CSeries jets. We have a reset procedure which involves powering down the aircraft. Not bad for 60 million dollars a pop!!!

 

[lw395]

Google found this. May help.

Settings
Network
Data Sources
GPS
All data global
Left arrow to next screen
Select Auto “your unit” IGPS

Scroll down to Time
Select Time
Select UTC Date this device
Select UTC Time this device.

As soon as you have a GPS lock, the time will be correct.

So in principle what you are suggesting is that it's set to take its time from somewhere other than the GPS, and that other is absent, resulting in the time being zero or some other nonsense value?

I've seen something similar on (non-boaty) equipment where the time can be set to 'network time' instead of GPS time.
There could be a 'real time clock' in there which could indeed be stuffed due to a backup battery being dead.

 

[AndrewL]

Most (all?) GPS receivers will have an internal clock and will also store the lat/long from the most recent fix. At startup the time and location are used to lookup in the almanac the identity of the satellites that should currently be overhead. If the unit does not have this data then it would be much slower to acquire a fix. This is often referred to as a "cold start" and it can take a few minutes.

If you unit is getting a fix in the usual amount of time then the internal clock must be working.

GPS is really a very accurate time distribution system. Each satellite is transmitting the time from its onboard atomic clock. To solve the GPS equations to obtain the position, the receiver unit must use the signal from several satellites to determine the exact time. Each signal takes a different amount of time to arrive, because the distance between each satellite and the receiver will be different. The receiver can only calculate its distance from each satellite once it has determined, very precisely, the time.

Basically, for your receiver to calculate a position it will have derived the time to within a few nanoseconds. However, the time it displays might be garbage, perhaps due to a software bug.

 

[lw395]

Most (all?) GPS receivers will have an internal clock and will also store the lat/long from the most recent fix. At startup the time and location are used to lookup in the almanac the identity of the satellites that should currently be overhead. If the unit does not have this data then it would be much slower to acquire a fix. This is often referred to as a "cold start" and it can take a few minutes.

If you unit is getting a fix in the usual amount of time then the internal clock must be working.

GPS is really a very accurate time distribution system. Each satellite is transmitting the time from its onboard atomic clock. To solve the GPS equations to obtain the position, the receiver unit must use the signal from several satellites to determine the exact time. Each signal takes a different amount of time to arrive, because the distance between each satellite and the receiver will be different. The receiver can only calculate its distance from each satellite once it has determined, very precisely, the time.

Basically, for your receiver to calculate a position it will have derived the time to within a few nanoseconds. However, the time it displays might be garbage, perhaps due to a software bug.

These days, GPS is seen in some contexts as a moderately accurate, moderately reliable time distribution system. Many systems want better, so have the option of, or default to, other clocks.
If you're running an inertial navigation system in case GPS goes titsup, you are not going to be using GPS as your favoured clock. When it comes to fine detail, the GPS time is not that great, I've worked on systems that have needed and internal Rubidium clock for instance. If you're thinking of survivng a jamming war, you will want a real-time clock to be able to over-ride the GPS clock.

 

[westerlylad]

Thanks to all who have replied. I have tried all suggestions and re-set and re-configured the unit several times now, but still getting the date on the satellites screen coming up as 2099. I had thought there may be a general problem with the actual satellites, but I guess it's simply a software fault with my Lowrance HDS Gen 2 unit. Ouch!

 

[Hoolie]

It's a problem widely reported on Cruisers Forum. It appears to be due to a software error in the GPS modules used across the Navico range of plotters, including Lowrance. I gather Navico are aware and are actively trying to develop a work-around. Keep your device up-to-date with updates from Navico!

 

[Hoolie]

An update on this issue from Billknny on Cruisers Forum:-

A little update on this ongoing GPS issue.

It started on October 22, 2018 when the "week code" cycled from 999 to 1000. This code is broadcast as a 10 digit binary number, but the calculations to turn it into a human readable date are done in decimal. Apparently the manufacturer of the GPSengine did not allocate enough memory to handle a week number of >999.

This affects several different makers of instruments, none of whom make their own GPS chips. I haven't seen the name of the offending party yet. If you are a clever lawyer looking for a class action lawsuit this might be an opportunity for you!

In my case, the malfunctioning device is a B&G Zeus Touch, T12.

I was able to partially fix the issue by installing a ZG100 standalone GPS on my NMEA2000 network and set the "GPS Source" to that device.

Unfortunately, the T12 still insists on sending out what it thinks is the correct time on the network. Today (Dec 4, 2018) it is broadcasting the date as April 21, 99. Some devices on the network interpret this as "1999," some as "2099," and others recognize it as invalid and ignore it. Depending in what the device is this varies from a minor annoyance, to incapacitating. For example, I use software on my computer to log sailing data, and it relies on the network time stamp to sort the data. When it rejects the time as invalid, it can not longer time stamp the data.

I did call Navico Tech Support today. As I expected, "Engineering is working on it." But what I really wanted to do was find a way to turn off the GPS engine inside the T12 so it would stop contaminating the network with invalid dates. Unfortunately, that can not be done.

There is another one of these vulnerabilities to poor coding coming up in April 2019 when the 10 digit binary code for the date goes from 1024 to 0000. That one actually is more widely anticipated, so MAYBE has been better addressed...

We were lucky--this time. The software error did not affect the reported position--only the date output. Another kind of mistake could easily be waiting for us that will disable some, most or all of our GPS devices.

If you are one of those who thinks that paper charts and traditional navigation skills are archaic and irrelevant, maybe you should think again.

Even though you may not have an affected Navico instrument it's a sobering thought that these technical oversights can affect us all ...

 

[sarabande]

Ha ! exactly the same problem that gave beneficial employment to thousands of Y2K contractors and consultants in the late 1990s

 

[westerlylad]

Thanks again all who replied. I've now received the following from Navico technical support :
"We are aware of this problem in some of our legacy products which used GPS chips from a particular manufacturer. It is possible to correct the time with an offset but not the date so yes, any tidal data pulled from the card won't be correct. I can assure you our R&D team are working on this as a top priority and any updates required will be made available on our website as and when they are available."

 

[Leighb]

Would this also affect Simrad plotters? I believe they are the same "family"?

 

[Hoolie]

The main Navico brands are B&G, Simrad and Lowrance (plus C-Map)

 

[Fenders]

I also have the same problem with a Lowrance chartplotter.
After exhaustively checking settings etc I gave up and emailed Lowrance support.
Quick response from them:


“Unfortunately this is a known problem that began a couple of weeks ago.
It is due to some satellite maintenance / servicing that has been conducted within the GPS constellation.

We have spoken to the chip set manufacturer to see if there is anything that can be done internally with the machine but we are advised there is nothing to do until the GPS servicing is completed.

The local time can be adjusted if required but nothing can be done to alter the UTC date which is received from satellite.

We are still waiting for a solution, which will probably come through a software updated.

The software update should come out in the next few weeks.”

Navico UK Service Team


It would have been helpful if the manufacturers of affected devices had posted details of the issue on their websites.

Fenders

 

[BabySharkDooDooDooDooDoo]

I remember this problem from the first time around which IIRC was some time in 1999 (at the time we had a Phillips AP navigator), so rather concerning that this seems to come as a surprise to GPS designers.

My current boat has a Zeus 2 providing the GPS for the rest of the electronics so a just little bit concerned that things might not be in order when I next switch them on.

 

[Leighb]

Went on the boat today to check on the plotter, Simrad Evo type. When I first switched on the time came up as 0100, but pretty soon it updated to the correct time and date. It had not been switched on for a couple of months so this may be normal?

 

[continuouswave]

There is not an "error" in the GPS time signal.

The most likely reason that various GPS receivers began to have problems with the date and time in mid-October 2018 is the rollover of the GPS Week Epoch to 1000 from 999. This occurred around October 21, 2018.

Some background: GPS date is kept in weeks since the beginning of a GPS Week Epoch. The week begins at zero and counts up to 1023 (which is 2 to the 10th power, as the data is limited to a ten-digit binary number).

There is nothing new about this occurring in GPS time keeping. GPS time is nearing the end of its second epoch. The first rollover in GPS Week Epoch occurred on August 21, 1999.

It is likely that the GPS receivers which are affected by the GPS Week Epoch reaching 1000 were probably made after August 21, 1999, and they are experiencing this for the first time. The likely reason for the problem occurring is those GPS receivers may have only allocated a three-digit decimal representation for the week. When the value for the week changed to 1000 from 999, those receivers became confused.

The next GPS Week rollover to zero will occur on April 6, 2019. At that point, the GPS receivers that were affected by the change to a four-digit decimal value for GPS Week, may begin to work correctly again.

Not all NAVICO or LOWRANCE devices are affected. I have an HDS-8 first generation device, and its GPS receiver is working properly. It correctly shows the year as 2018.

For a more detailed discussion, see

http://continuouswave.com/forum/viewtopic.php?f=12&t=4072