The Modified Range Time Intensity Technique for studying the height variation of the backscatter power of VHF radar echoes at Jicamarca has been used to show that the growth time of E-region irregularities is less than 1 min. Further, these irregularities disappear or reappear precisely at the time when delta-H at an equatorial minus delta-H at a non-equatorial station is close to zero irrespective of absolute H over the dip equator. This is consistent with the idea that E-region irregularities over the dip equator scattering the HF or VHF radio waves are due to gradient drift instability and supports the double-current hypothesis for the equatorial electrojet.