What causes the sudden loss of GPS?

[phantomnoobpilot]

Had an "oh-crap-i'm-gonna-crash" moment today.

I did the usual pre-flight checks, compass calibration, and the wait for the green slow flashing lights before taking off at this beach area where I've flown before some time back.

The last time, I took off at the usual spot and had zero issues, no GPS loss, whatsoever.

But THIS TIME, I got 11 satellites locked prior to take-off, took off and hovered around the sea to check if it's stable and maintaining its position, but something odd happened when I attempted to turn back.

When I turned the quad to face me, all of a sudden my quad started drifting away from me really quickly. then I realized that the green flashing had disappeared and changed to yellow. thank god I regained control of it. Then turned the quad
away from me, with its back facing me and all of a sudden i got back my 11-12 satellites. Okay, I thought maybe it's just a one off thing. But when I turned the quad back to its front facing me again, my satellite count went to zero wtf?

Had to fight the wind to bring it back to land. this is incredible puzzling. It's a freaking beach, an open area. Furthermore the last time I flew there, I never had this mysterious GPS lock disappearance.

I decided to take off from a different spot this time, somewhat 200 meters away and this time it flew flawlessly with a solid 13 satellites locked and never had any drops.

Anyone can explain what's going on?

I'm guessing this sudden loss of GPS is the reason for all flyaways caused. Thankfully I was alert or else mine could be the next one to experience this dreaded flyaway.

 

[N017RW]

There's been a lot of talk regarding loose GPS to PCB connector issues. That MIGHT explain it for you. You'll need to open up the quad to inspect and remedy.

But this does not cause flyaways per se. The loss of GPS automatic 'position holding' that occurs with loss of reception or when in Atti. mode can be combined with winds aloft to cause the quad to ride-away with the wind. Sometimes the pilot, I mean Operator, doesn't realize this loss of GPS and then cannot recover in time, etc. So it's not a fly away but operator error of sorts.

 

[phantomnoobpilot]

There's been a lot of talk regarding loose GPS to PCB connector issues. That MIGHT explain it for you. You'll need to open up the quad to inspect and remedy.

But this does not cause flyaways per se. The loss of GPS automatic 'position holding' that occurs with loss of reception or when in Atti. mode can be combined with winds aloft to cause the quad to ride-away with the wind. Sometimes the pilot, I mean Operator, doesn't realize this loss of GPS and then cannot recover in time, etc. So it's not a fly away but operator error of sorts.

But why didn't the sudden loss of GPS loss happen again when I flew off again about 200 meters away from that "jinxed" spot?

 

[msinger]

phantomnoobpilot, check out this thread:
viewtopic.php?f=27&t=30912

If this is your issue, then it really has nothing to do with the location of the Phantom. The plug could become loose at any time during flight.

 

[RichWest]

As far fetched as this may sound, but you could have a sunken treasure beneath the sand....

It does seem strange you lose GPS signal in one orientation and then it returns to normal when re-oriented. It's possible there is a metallic object unseen, but still doesn't make sense why one direction and not the other... Don't fly there anymore...

 

[N017RW]

There's been a lot of talk regarding loose GPS to PCB connector issues. That MIGHT explain it for you. You'll need to open up the quad to inspect and remedy.

But this does not cause flyaways per se. The loss of GPS automatic 'position holding' that occurs with loss of reception or when in Atti. mode can be combined with winds aloft to cause the quad to ride-away with the wind. Sometimes the pilot, I mean Operator, doesn't realize this loss of GPS and then cannot recover in time, etc. So it's not a fly away but operator error of sorts.

But why didn't the sudden loss of GPS loss happen again when I flew off again about 200 meters away from that "jinxed" spot?

No one knows for sure what caused YOUR issues.

Your observations may be inaccurate or missing something else you didn't notice or consider. Eyewitness accounts are very unreliable. Video helps others see and theorize.
We're just telling you about what has happened to others and Rich has brought up something I don't understand so I can't help with that either.

 

[CapnBob]

The GPS antenna is pointed straight up and has roughly hemispherical coverage. It is a simple patch antenna, and horizontal rotation should have absolutely
no effect whatsoever, unless rotation is disturbing the connector, making it intermittent. I would be suspicious of compass cal, especially if you calibrated it at that particular spot. If there is any substantial ferrous metal around, it will hose the cal. Buried pipes are a prime offender.

 

[N017RW]

Bob, you seem knowledgeable in this area.

Why the concern over the compass cal regarding a GPS loss upon a/c rotation (assuming that's all we're dealing with here)?

 

[RichWest]

Bob, you seem knowledgeable in this area.

Why the concern over the compass cal regarding a GPS loss upon a/c rotation (assuming that's all we're dealing with here)?

Bob was correcting (nicely) my insertion into the conversation, which my reply was incorrect for GPS - I would be suspicious of compass cal, especially if you calibrated it at that particular spot. If there is any substantial ferrous metal around, it will hose the cal. Buried pipes are a prime offender.

Since Bob mentioned Pipelines... Were I'm at, pipelines do emit interference for some reason, at least to radios. Can't find any data on the issue, but I know they apply DC voltage/signal for cathodic protection. It would be interesting, as a side note, whether there was any pipeline ROW at that location of the beach. Pipeline posted signs (here in the USA) would be what I would look for...

 

[N017RW]

Bob, you seem knowledgeable in this area.

Why the concern over the compass cal regarding a GPS loss upon a/c rotation (assuming that's all we're dealing with here)?

Bob was correcting (nicely) my insertion into the conversation, which my reply was incorrect for GPS - I would be suspicious of compass cal, especially if you calibrated it at that particular spot. If there is any substantial ferrous metal around, it will hose the cal. Buried pipes are a prime offender.

Since Bob mentioned Pipelines... Were I'm at, pipelines do emit interference for some reason, at least to radios. Can't find any data on the issue, but I know they apply DC voltage/signal for cathodic protection. It would be interesting, as a side note, whether there was any pipeline ROW at that location of the beach. Pipeline posted signs (here in the USA) would be what I would look for...

Thanks Rich.
I kinda misread it I guess as I now see what he seemed to mean.