This paper considers the effect of changes of the waveform parameters over the distance. The objective is to show the near field effects on transient radiation and how near the equipment under test can be located to an antenna without significant changes of the width or rise time of the field pulse. It is shown that the well known frequency domain estimation models fail because the dimension of antenna systems and the wave propagation lead to a special kind of dispersion. The importance of this near field dispersion for practical applications is demonstrated by both theoretical considerations and measurements with a half impulse radiation antenna.