3DR and Pixhawk GPS lost 3D lock queries

Last weekend I was helping a mate setup a new Quad in Sydney. After completing all the calibrations and tuning we had the Pixhawk controlled Quad hovering beautifully and holding position perfectly in a slight breeze in PosHold mode. All of a sudden the Pixhawk beeped and the telemetry reported we had lost GPS lock. I switched to Stab Mode as it started to Toilet Bowl badly as soon as the GPS 3D lock was lost. The flight continued OK in Stab mode but did not regain 3D GPS lock. The entire weekends flying was dogged with high HDOP. (EKF was enabled)

Yesterday, back in Brisbane, I was flying my new X8 in stabilize mode (EKF enabled) when the Pixhawk beeped and my telemetry informed me I had lost GPS 3D lock and had high HDOP, 8 Sat and a HDOP of 2.8. No probs as I was flying in Stab mode. After completing the flight I connected my 2nd Quad which also uses a Pixhawk and 3DR GPS module. It reported the same GPS status, 8 Sat and a HDOP of 2.8. I figured maybe sun spots or someone/something was tinkering with the satellites……conspiracy theory……

Neither Pixhawk’s would now arm due to the arming safety so my flying was over……

Out of curiosity though I fired up the GPS tracker software on my Samsung mobile phone…To my surprise, with my mobile phone positioned right next to the 3DR GPS units it measured 22 Sats and a HDOP of 1.0. Excellent numbers…………Both my 3DR GPS mast mounted modules have been calibrated against interference. On the ground though the motors aren’t running so minimal interference but they refused to get past the high HDOP or increase the number of Sat’s detected.

Reconnecting the Pixhawks I still only got 8 Sat and a HDOP of 2.8 so tail between legs packed up and returned home.

[b][i]Can anyone explain why there would be such a difference between the Pixhawks and mobile phone? Is this a 3DR GPS hardware issue or a software issue?

Will this improve / go away if I replace the 3DR ublox LEA-6H with ublox NEO-M8N or would it help if the original 3DR GPS was supplemented with the M8N, i.e. both GPS modules installed on my quads?[/i][/b]

Are there any other options to ensure a reliable GPS signal so flyers don’t run the risk of the HDOP suddenly increasing in flight causing GPS 3D lock issues?

I was watching a 3DR video last night with a guy demonstrating ‘Follow Me’. What surprised me was he left his transmitter on the ground whilst he paddled out across the water with his QUAD following him. If he had lost GPS lock he had no transmitter to switch back to stab mode to safely recover the flight… youtube.com/watch?v=RW1Vcyk0j2E