As for the surface vs air - as I recall the receiver I have might well have a telemetry function which is not supported by the air radios - or something, either way I have a Spektrum receiver here that does not talk to a DX6i - that much I am certain of, so I guess all I'm trying to say is be sure to read the small print before you buy (unlike me...
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Lol
! Sometimes I miss the small print too. I believe you when you say you had one that wouldn't bind to a DX6i. Based on Spektrum's propaganda, it seems that it might have been the exception and not the rule...just like how some AR6000s don't like to bind to DX5e's despite the fact that DSM is supposed to be backwards compatible to DSM2 txs
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