  The Whittaker period formula on metaplectic $SL(2)$ was previously
established only when the base field $F$ is totally real. We present a new
simple proof that works for all base number fields. Our local argument is
uniform at every local place of $F$, based on the isometry property of
quadratic Fourier transform and the estimates of matrix coefficients and
Whittaker functions imposed by the unitariness of the local representations.
