Hi guys,
I need your advice...I currently own a Phantom 1 with zenmuse h2-3d and I'm planning to upgrade the gimbal to the zenmuse h4-3d.

is my Phantom 1 with an upgraded board compatible with new H4-3d gimbal?

If your answer is yes, which version should I purchase? GCU or without? Do I have to get the "anti interference board" as well?

Your advice will be highly appreciated.

Thanks!

A quick look at the documentation would indicate no.  "Phantom 2, A2, WKM, NAZA-M, NAZA-M V2 supported"

Actually with the upgraded control board it should be compatible.  The Phantom 1 uses the Naza Flight Controller and firmware and is compatible like any other Naxa M based product.  The GCU interface is the same as the H3-3D which others have used on Phantom 1 copters