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.
The article says that a "constant envelope" occurs with an FM transmission that has a constant carrier output level (envelope). Therefore a class-C RF amplifier can be used.
AM modulation needs the low distortion produced by a class-AB RF amplifier because the sounds are produced by the envelope fluctuations..
Class-AB is linear and is symmetrical push-pull.. It has 2 transistors that are never turned off so they get hot with wasted power.
Class-C uses a pulse each carrier cycle. Since its transistor is turned off during a fairly larger part of the cycle then it is efficient.
It's not potential, it's actual.
As AG noted, a Class C stage is on for only part of the sinewave cycle, so cannot generate a low-distortion amplitude-modulated signal.
The sinewave of a Class C stage is generated by an LC tank circuit.
The transistor just periodically pulses the tank to keep it oscillating.