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Hello Jim,
Did you try the replacement of the GPS module board as I suggested you on my previous posts?
I had exactly the same problem on my Voyager G2 during about 2 years. I solved it definitively 8 years ago by changing the GPS board. The new one was fitted with a new GPS module U BLOX 5 (or 6, not sure of the figure) much stronger against electromagnetic disturbances than the original U BLOX LEA 4A.
I purchased the new GPS board at MGL. Before the replacement, each flight was polluted by ‘GPS not available’ messages; since the replacement I never had the trouble anymore… I flew more than 600 hours without any problem.
Alain, can I ask what actually made you think it was the GPS/USB Board?
I spent two years checking everything on my aircraft, changing antenna, wirings etc… until the day Rainier posted the information about the new GPS board less sensitive to the electromagnetic disturbances. I immediately decided to test the new board, and it was done a few weeks later…
I explained all this with lots of posts in the previous forum
To answer your question, I have not look at the GPS module any further, but thanks for re-posting and reminding me. I have just txt our Australian MGL Dealer about this problem and asking about the up-graded GPS module.
I hope Rainier can still supply this up-graded GPS module for the G2 Voyager, as I will order one if I can.
As I have a little more time away from work, I am going to pull out the instrument panel, take Diamonds advice and check all the panel's wiring, connections and connectors.
I will also make up some D-9 extension cables so I can swap the DC power supply to each of my EFIS, to see if the GPS Satellite Fix dropouts follows the swapping of the DC power supply.
I am also thinking when making up these D-9 extensions, I should add some fly leads to the positive and negative pins, so I can easily attach an oscilloscope to monitor the DC power supply right as it enters the EFIS, during flight.
For those who followed this thread, my work has got in the way for many weeks, so I've had little time to look further into this GPS issue, "GPS not available, GPS available".
I was looking at getting the updated GPS Board that should be able to take a bit more interference, but then I was told I should try to find the root cause of the GPS drop outs and most likely it's going to be some type of electrical interference or voltage spiking.
So when I replaced the ribbons cables in both EFIS about 5 weeks ago, it gave me the chance to have a good look at the wiring on the back of the instrument panel to see what is wired to the 2 negative busbars on the back of the instrument panel.
I saw a couple of things I need to change, but at the time I wanted to get the plane back in the air. These 2 negative busbars are not insulated from the instrument panel and my EFIS's are not wired directly back to the negative of the battery as they should be, they are wired to these 2 negative busbars.
These 2 busbars have everything earthing to them, the Fuel Pump, Transponder, 2 VHF's, Landing /Wig Wag Lights, Strobes, Nav Lights, Beacon, Autopilot and the 2 EFIS's. The 2 busbars have a short cable running between them and then the same size cable that runs back to the standard negative post for a Jabiru on the firewall near the battery. This negative bus cable is around the right gauge size for the amount of load, but for sensitive electronics I don't think its a good design.
But for the moment, I connected all the high load and noisy electrical stuff onto the 2nd busbar so they were as far up the busbar system as I could get them from my EFIS connections, so any spiking could be travelling away from the EFIS connections if that makes sense.
Did this help?, well I think so as it seemed to change the way and the amount of time the issue is showing up.
Over the last few hours of flying I am yet to have a GPS drop out in the air. But on two occasions after I taxied back in and started to turn stuff off, I've heard those dread words "GPS not available, GPS available". I think changing the order of the connection on negative busbar has improved things, but getting the EFIS's wired right back to the battery may well be a better answer, we will see.
I was looking at getting the updated GPS Board that should be able to take a bit more interference, but then I was told I should try to find the root cause of the GPS drop outs and most likely it's going to be some type of electrical interference or voltage spiking.
MGL gave me exactly the same reply when I wanted to purchase the new board but I insisted and they finally agreed to send me one. I paid it less than 100 Euros and since the time I mounted that board (8 years ago), I never had any GPS trouble…
You should really insist.
Cheers
Alain
Hmm, I hate selling things that may turn out to be a waste of money.
The "GPS no available" followed immediately by "GPS available" is a big hint that the GPS signal is not getting to the GPS receiver module in a clean way or it is weak or the antenna is partly shielded and does not have an unobstructed view of the sky.
One of the items to check - the antennas are designed to be mounted on a metal surface. This is actually important - the surface acts as a ground plane and brings the antenna into tune - significantly enhancing the received signal strength (you can see the effect of this if you use the GPS status screen - note the height of the bars changing - the higher you get them the better).
The antenna needs a clear view of the sky without any metals in the way - that includes metals that are in line relatively close to the horizon. Sometimes you need the satellites that are closer to the horizon to get a fix as there happens to be not much overhead. Again the GPS status can give a hint - the sky view shows you where the satellites are - the center of the circle is straight up. The inner ring represents a 45 degree angle between horizon and sky. You need 4 satellites with green bars for a 2D fix. 5 for a 3D fix.
If there are no satellites at all visible in the signal strength bar but the satellite ID numbers are changing every few seconds - there is likely no power on the GPS antenna output - it requires 3.3V to power the antenna. There is an internal fuse that will trip but automatically reset after a while if current is exceeded for whatever reason.
Do not underestimate the effect of any digital equipment onboard the aircraft - that stuff likes to radiate and harmonics can go easily to 1.5Ghz, the frequency band the GPS operates on - the signals received are really weak, they are easily interfered with.
As time progressed we always upgrade to the latest GPS modules - but only after a short while so we can get an idea how they perform. Over time they have become more sensitive (able to receive weaker signals) while at the same time more robust to all sorts of interference. Anti-jamming, once state of the art, is now an everyday thing.
It is very possible that installing a later model GPS board makes things work much better - that is only to be expected. But that should not really be needed - even our very first GPS chip sets were pretty good - the Antaris in the ublox 4 at the time. But I can attest to it getting nailed by engine ignition systems - that happened to me in one of my older aircraft that was fitted with the Enigma prototype - the antenna was simply stuck on the dash close to the windscreen (no ground plane either, just a piece of fiberglass). Only once I moved this to a better location (far away from the engine) did things work well. The effect was that it would only become intermittent once in a while - of course it depended on the current satellite constellation - most of the time there were lots visible and in a good position - just sometimes things were a little less than good and the GPS struggled hearing the satellites over the engine noise...
Hmm, I hate selling things that may turn out to be a waste of money.
Hello Rainier,
at the time I experienced this GPS problem, I spent more than 2 years rewiring everything, changing antenna mounting, antenna location, antenna, even testing another Voyager EFIS loaned to me by the MGL French dealer, two years during which every flight was polluted the "GPS not available" "GPS available" massages.
I agree with you that there is certainly something noisy in my aircraft around the 1.5GHz frequency, but what and how to fix this? How many wasted time would be necessary to find a hypothetic solution?
To me the risk of wasting a few money in comparison with the waste of time was nothing... and with the new GPS board, all is perfect.
It's just my experience, I'm very happy with it now, and I'm quite sure it should be the solution for Jim.
Regards
Alain
Thank you both for your comments Alain and Rainier about this GPS issue, I really do appreciate your comments.
Alain, I've had some of your frustration, I hear how long you spent in trying to fix the same issue. I also agree if spending some money will fix the issue without question, it's a good way to go in not having that frustration.
I also understand what Rainier is saying, as I work in the world of event P.A. systems with wireless microphone systems. These microphones transmit with only 20mw and all these microphone system are limited to this by law.
So it's a dark art you need to lean when setting up wireless microphone every other weekend. Sometimes you can just move power cables cm's away from antenna cables and this can be the difference in having a weak and flakey signal or getting strong signal.
But at events at other times even adding an antenna gain booster still leaves you with a weak and flakey signal. But moving the wireless RX antenna position by 15cm can make the microphone signal go from being weak and flakey to rock solid, even without the need for the antenna booster.
So I am thinking what Rainier is telling us, going out and just buying the newer GPS chip module Board may not solve the problem if you have really bad EMI and you have not tried reducing that first.
It interesting I did not have this issue in my plane for some 35 hour I had flown it, during this time I had removed my instrument panel on a number of occasion. I then recently pulled out the instrument panel and after putting it back into my plane, the GPS problem started. I have no idea what I changed or moved to bring this issue on, but it only effects the pilot side Voyager EFIS, even when swapping over the two EFIS's.
I still have a few thing I am going to try and one easy thing to do is slave the pilot side EFIS to the co-pilot EFIS's GPS, just to make sure the issue is really just on the Pilot side GPS set up.
But I did recently change the placement of how thing were wired to my 2 instrument panel negative buses and this seem to change the occurrence of the GPS issue.
Just a quick note, as weeks are slipping away and I am guessing others may be reading this thread hoping to solve their own GPS issues.
I did not have this GPS problem for the first 40 hours of flying this plane, then the GPS problems started, so after bench testing my EFIS's hardware and getting all that sorted, I still found I had this GPS issue.
The next step, this could be some type of electrical interference and or electrical discharge causing my GPS dropouts. So I thought, what could I have changed to bring about this GPS issue.
I realized I had changed the order of how my electrical equipment was wired to the instrument panel's negative bus bar. One or two of the wires were a little tight, so I swapped them around on the bus bar.
I pulled the panel and changed the wiring order on the negative bus bar back to what I thought it was previously. Well on the first flight, there seemed to be a difference in my GPS problems, I had no GPS dropouts.
Now having a few more flight hours up, the EFIS continues to operate without any GPS dropouts in the air. I've had the odd time where I got "GPS not available" and a quick "GPS available" when taxing back up near my hanger. But as yet, I have not been watching the GPS signal page to see if I am losing signals due to the closeness of the hanger.
I have not fixed the cause of the problem, but maybe I have moved the interference far enough away so that it does not cause the same level of interference to the GPS.
Time will tell, but hey this is a really dodgy fix and I need to find and stop the cause of the electrical interference and or electrical discharge.
Something has lessened the occurrence of my GPS issues since I pulled the instrument panel and changed the order of the connections on my instrument panel's negative bus bar. So now, only on odd occurrence this GPS issue is happening, the problem has moved from my pilot EFIS to my passenger EFIS.
So I went flying to watch my passenger EFIS and I could see it had slightly weaker satellite signals and its satellite numbers seemed to be more random compared to the Pilot EFIS. Those that have followed my posts may remember that both my EFIS GPS signals have been around the same in the past.
I am guessing a possible cause could be that the passenger GPS antennas may have a voltage drop in the cabling or at the antenna and this is causing the antenna to lose gain structure and so maybe allowing any EMI in my plane to have more of an effect over this GPS with its weaker satellite signals.
So I am thinking replacing my GPS antennas would not hurt and then I should go hunting for any EMI, RFI or ground loops that may be in my planes electrical system.
I am no expert with an oscilloscope, but I am thinking some really cheap sniffer probes would be a good way to help sniff out where any EMI problems might be hanging out in my electrical system.
If anyone has had any experience using these sniffer probes, please do head me in the right direction with any hints how to use them.
Cheers
JimJab
Last edited by JimJab on Tue Dec 28, 2021 3:49 pm, edited 1 time in total.
Just a follow up, I have flown a number of hours since my last post on this problem.
I did say in the previous post the issue had moved from the pilot Voyager to the Passenger Voyager and this issue has certainly been reduce by at least 95% after changing around my electrical earth connections on my negative bus bar behind my instrument panel.
I realize this is not very scientific, but currently that' where I am at, I will replace the GPS antenna to that passenger Voyager as time permits and will get some cheap sniffer probes if the problem flairs back up.