recognising a constant envelope in modulation

[yefj]

Hello,In the article bellow they say that we use clas AB amplifiers for constant envelope.
how can i see that the modulation has a constant envelope?
Why Class Ab is suitable for it?
Thanks.

 

[FvM]

they say that we use class AB amplifiers for constant envelope.

Not particularly, rather the opposite. Of course class AB can be used for FM, but class C is preferred for higher efficiency.

how can i see that the modulation has a constant envelope?

Empirically by looking at the envelope. Or theoretically by applying elementary knowledge about modulation methods.

 

[G4BCH]

A complication of written english.
The 'it' in the second sentence refers to the Class C PA, not the Class AB PA.

 

[vfone]

You can use Class AB to amplify both, constant or non-constant envelope modulations, but Class C can be used only for constant envelope modulations.

An easy way to identify the envelope type of a signal is to use a simple diode AM detector, which (faithfully) would demodulate only the AM envelope.