1-63 AMPLITUDE(instantaneous voltage) of a coil is found by the formula: PHASEor PHASE ANGLEis the angle that exists between the starting position of a vector generating the sine wave and its position at a given instant. FREQUENCYis the rate at which the vector rotates. HETERODYNINGis the process of mixing two different frequencies across a nonlinear impedanceto give the ORIGINAL frequencies, a SUM frequency, and a DIFFERENCE frequency.