Doppler effect from a transmitter in translational motion

The effect of motion on the signal received from a source in translation is investigated. The Courier spectrum of the signal is evaluated by the method of steepest descent. The spectrum associated with a monochromatic source turns out to be bandlimited, and to have two infinite peaks. These peaks disappear when the receiver is activated during part of the time only. Finally, the spectrum of the signal received from a sinusoidal transmitter modulated by a Gaussian pulse is discussed. There, again, the infinite peaks disappear.