  A simple relativistic analysis is presented which shows that near-field
superluminal longitudinal electric signals generated by an electric dipole
cannot be used to violate Einstein causality by using the relativistic "sync
shift" effect. The analysis shows that because a signal has some time extent
(i.e. after a signal is initiated one must waitat least one period for the
frequency and amplitude information to be determined), an electric dipole can
be used to transmit a signal backward in time, but not before the same signal
was initiated, thereby prohibiting a user from changing the signal that was
transmitted. The result is also shown to apply to the superluminal near-field
gravitational fields generated by an oscillating mass.
