1. An apparatus for calculating a predistortion function from characteristics of a power amplifier, comprising: a predistortion module responsive to a predistortion function and an input signal by generating a predistorted signal; the amplifier responsive to said predistorted signal by generating an output signal; and a predistortion function calculating module responsive to said amplifier characteristics by generating said predistortion function, said predistortion function calculating module using a magnitude of said input signal at a given time to estimate said predistorted signal at said given time to calculate said predistortion function.