The world outside America (if it exists ) uses +ve shift. I have no knowledge of why Futaba/Hitec chose to do something different on 72MHz.

The cynical among us might think that the US is a big enough market for them to want to lock people into their kit i.e. prevent people from easily switching or mixing brands. But I couldn't say. Certainly there are no technical benefits to either shift.

As for PPM/PCM, if you're going to refer to just the PCM coding method and not mention that's it's transmitted over FM I'd suggest that it's a lot more logical to refer to PPM (the coding method). Talking about an FM Tx when you mean PPM, knowing full well that PCM is also FM is just technically wrong. Still I can tell I'm swimming against the tide with this one. It won't be the first time...or the last .

Steve