ftomteen4cat said on a related thread:

As far as I know, PPM encoding just varies the pulse width from 1 to 2us. To me, that is a pretty good description of PWM. (pulse width modulation) Pulse Position Modulation would use frame pulses or a sync pulse and move the pulse in time, relative to the frame or sync, but oh well I didn't name it.
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Maybe you should contact Futaba corp or Japan Radio and discuss this oversight on their part.
I read somewhere that PPM pulses are 400 us long and that the time between them varies between 1ms and 2ms.. PWM refers to one signal, one channel.
Pulse position Modulation refers to each individual channels position in the serial frame in relation to the sync. All our radios are multichannel so PPM is the correct useage.
The term PPM is used to describe all channels as a result of multiplexing them serially into one coherent signal. Is this true??