For all those keen on upgrading your Solo to RTK capacity. Here are some lessons learned. Although I have a Drotek XXL RTK Base and NEO M8P GPS installed within my Solo. This is not yet sufficient for RTK capacity. I have learned that firmware Arducopter 3.5.* needs to be updated, However: Given Arducopter 3.5.0 is not safe with the original Solo stock cube, it has been strongly advised to install the new Green Cube (Pixhawk 2.1..etc). Only once the Green Cube is installed & Arducopter 3.5.0 firmware updated, will the Drotek Base and onboard GPS function with RTK capacity. Reference Document Read: 3DR Solo - ArduCopter Master Upgrade — Copter documentation Green Cube (Pixhawk 2.1) can be obtained from Jesters drones Jesters Drones Store At present I have not yet installed the Green Cube with Arducopter 3.5.0 firmware update. However fpvsteve has experience with this topic, and bet he will provide some assistance. Information on this post learned from fpvsteve, pulsar110 & Mr. Google.