[TG] [TG11] No GPS Info on MFD GPS Status Page

[magic8]

Thanks for reply Tom
On post dated 09-30-19 you can see 2 pictures IMG 4618 and IMG 4622.
These were taken whilst tied up to my jetty. The first shows the GPS position at the end of the trip after showing me sailing over land.
Whilst tied up to the jetty I then reset the GPS using the E80 and it then showed the correct position on the jetty. Is there any chance this could be to do with DGPS? I will switch this off next trip as you suggest.
Does the RS150 treat the DGPS differently to the RS 125 as I had no issues before I changed the GPS antenna due to the other one failing.
After moving the antenna for testing I still got that momentary False GPS position and then the boat would get back on track and would be ok then.
As you could see from the instantaneous dog legs.
From your information the recorded track information is then ok and not a problem.
Thanks again for your input

[magic8]

Further to the last message to try and find problem, the error seems to equate to 450 metres most times that I am able to calculate it
Thanks again

[Tom - Raymarine - Moderator]

Hello magic8,

Quote:Does the RS150 treat the DGPS differently to the RS 125 as I had no issues before I changed the GPS antenna due to the other one failing.

The RS125 wasn't sensitive enough to pick up these differential systems on the horizon, so we never saw a problem. We've only started seeing problems like this with eS-series, Axiom, Axiom Pro, RS150, AR200.

Quote:Whilst tied up to the jetty I then reset the GPS using the E80 and it then showed the correct position on the jetty.

Resetting the GPS will force it to reacquire a fix, which would initially be non-differential. This may explain the higher accuracy. I do not normally resetting a GPS as this involves starting from scratch with the fix and usually makes things worse rather than better.

Quote:the error seems to equate to 450 metres most times that I am able to calculate it

450m is a big error. Is it really that far, and if so, is it consistent (in both distance and direction)? If it's consistent, are you absolutely sure that there's no other source of GPS data in the system? Position toggling between two locations is the kind of thing I would expect if there were more than one source.
The other factor is Datum: if there's a consistent position offset, that's usually an incorrect datum. You might get this if, for example, your MFD were receiving a Datum instruction (e.g. NMEA0183 DTM message) from another device that was periodically overriding its own setting.
Standard GPS position errors can be large but would not be expected to be consistent in distance or direction, they should be essentially random.

What else is the E80 connected to? Any NMEA0183 or third-party devices?

Regards,
Tom

[magic8]

Thanks again
Here are some of the coordinates during the errors

With error
S 16.48.152 E 145.42.474

After GPS reset and known correct position.
S 16.48.294 E 145.42.271

450M error I think

S16.48.070 E145.43.190
APPROX S16.47.950 E 145.42.460

1.3 KM ERROR!!!!

S16.47.901 E 145.42.885
APPROX S16.47.996 E145.42.996

260 METRES ERROR

The only NMEA I have as far as I know is a GPS output to the VHF radio to give it a position.
I do have a HF radio and that may also have the same but the that radio has not been used for a long time during coastal cruising.
I will put all the wiring back to normal and switch DGPS off but those dogleg errors were there with only the E80 connected to the GPS antenna via the converter and the rest of the seatalk network was isolated and powered seperately.
Hope this helps and will report further when I can get out for a sail after I have done as above.
Thanks again

[Tom - Raymarine - Moderator]

Ok.

Unfortunately the ST1-STNG convertor doesn't pass satellite status information through to ST1 so we won't be able to see the satellites in view and signal levels on the E-series. If you were able to beg/borrow/steal a more modern STNG-compatible chartplotter than can show the satellite status that would give us a lot more options for diagnosis.

Since I posted my original reply to you I've written this FAQ to collate potential problems I know of and troubleshooting info. I'd suggest having a read through this. I am 100% confident in the RS150, where it has:
1. a low-noise environment
2. a clear view of the sky
Any GPS position errors I've ever seen on one of these GPS receivers has been down to one or other of the above, or something like another (poorer) GPS receiver in the system taking precedence.

Regards,
Tom

[magic8]

Thanks for reply
All wiring and GPS antenna back as original
Will be off mid January on a big sail to Brisbane so will monitor what is being used should the defect come back.
Will also have DGPS turned off.
Thanks again and have a great Christmas and New Year

[Tom - Raymarine - Moderator]

Thanks, I hope the trip goes very well.

Tom

[magic8]

Just prior to leaving jetty on way down south noticed that there was NO GPS !!!!!!
Tried restiing GPS and it came back momentarily then lost again with red light on antenna.I contacted Raymarine and a local dealer and it was decided that we needed to swap out some parts starting with the antenna.
All appeared well ater fitting new antenna and off we went.
All good for a couple of days but i still get the occasional large XTE and suddenly showing the boat off the original track.Also at almost the same time time and sometimed on its own the SOG goes from the correct speed
to something like 14 or 20kts!!!!
This is what happened with the old antenna so can you let me know what you think.
I would have though that SOG woud have been calculated in the GPS antenna
I will try and take some pictures next time it happens
Thanks

[Tom - Raymarine - Moderator]

Do you know what pattern of flashes was showing on the RS150 when you saw the red LED? That pattern gives useful diagnostic information. The LED sequence for 'no GPS fix' is a single quick red flash every 3 seconds: is this what you were seeing?

Usually, red LEDs on RS150s indicate a supply voltage problem, either marginal low voltage or, more commonly, an unstable or high voltage from a misbehaving charging source. I can't remember the last time I saw an actually faulty RS150 except where they've been mounted incorrectly and had the breather on the bottom sitting in its own private puddle.

Yes, SOG is calculated inside the antenna and comes from a measurement of distance between recent position fix locations. All of the things you're describing except possibly the red LED (depending on what LED sequence you saw) come from poor GPS position fix quality. Unfortunately photos of the chart or an incorrect COG, SOG or position don't tell us anything about the cause of the poor fix.

Causes of poor GPS fix essentially boil down to:

1. a faulty antenna. Since replacing the antenna has not fixed the issue - as I say, RS150s pretty much never fail - then we can rule this one out in your case.
2. a poor view of the sky
3. some source of radio frequency (RF) interference which is drowning out the very weak radio signals from the GPS satellites (when I say weak signals, picture trying to see a 25W incandescent light bulb from 30,000km away.)
   

Assuming the RS150 is mounted out in the open where it has a clear view of the sky all around (is this the case? Please send photos of the mounting location), the problem is probably RF interference. There is more information about this on the FAQ that I linked to before. RF interference can come from all sorts of devices, not just those that are intended to transmit radio.

Unfortunately it's not easy to prove this is the case with the equipment you have on board. Seeing what satellites are in view over time with what signal levels can give good clues, but you've already said that you aren't seeing this in your system (in Menu > GPS Status) because it isn't passed through by the convertor. You would need a more recent, STNG-compatible MFD to be connected for this, which is something your dealer could usefully have done. Alternatively, a specialist technical dealer would need to visit the boat with a spectrum analyser that can scan the GPS frequencies at around 1.5GHz for RF noise. Not many dealers have the tools and expertise for this unfortunately, but if you can let me know where you are I can see who locally might be able to help.

Alternatively, you could turn the vessel battery isolators and all on-board systems off and temporarily power the E80 and RS150 via a completely independent battery and see how the GPS fix is then. Still, without GPS fix status it will be hard to clearly see the impact of this.

Regards,
Tom

[magic8]

Thanks for information
We have just left Hamilton island on our way south
Will lose phone coverage for a couple of days
GPS has been good and defect only happens every couple of days
As for power supply I was asked to check and the voltage was checked at 13.4 v with only a 2 foot cable feeding directly into the converter
The red light was flashing as you said and immediately fitting the new GPS antenna we had a good fix and solid green
I have noticed on this antenna that occasionally the green light does go out but all ops good is that normal
Thanks