hi,I see the your video PX4 with M8P
And, I don't understand , why the CD under the antenna???
Can you tell me?
It's a metallic ground plane for the GPS receiver. It's purpose is to ensure no GPS signals on multipaths reflected from below are received by the receiver. This improves GPS positioning accuracy. The ground plane in this video is on the large side.
Would copper foil underneath the GPS work as a ground plane?
Yes. The thickness of the metal is not that critical. You can use copper foil or tinfoil.