I saw this while I was Googling earlier - haven't really studied it, but it looks interesting... https://vk3atl.org/technical/Diplexer_1cc.pdf
Interesting, I thought it would involve multiple ICs for processing. Seems like a pretty analog way doing it.
By the way anyone have the specs / drawings on the NMO standards? I figured that building a motorized base myself might be the fastest way.