RTK for Fendt VarioGuide with a third-party base, how-to guide

Here is a bit of a mini-tutorial on configuring the current Fendt VarioGuide with RTK correction using either a portable or fixed UHF base (correction source) and the built-in UHF radio. Contrary to accepted wisdom, this will work with more than just a "Fendt" portable base. Its entirely possible to get an RTK correction with a third-party UHF base, so long as the UHF base is within a certain range of frequencies and has matching channel spacing (see more below).

I'll try and keep this...

RTK for Fendt VarioGuide with a third-party base, how-to guide