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Wideband HF channel probe measurements were used to study the structure, time development, and reflection mechanism involved in mid-latitude sporadic E. A system bandwidth of 125 kHz was used for evaluating the sporadic E reflection coefficient, while a bandwidth of 1 MHz was used to describe the structure and time variation of the reflecting layer. Evidence linking the maximum observed frequency for sporadic E, ƒtEs, to total reflection from discrete, overdense electron density patches is presented. This observation appears to be true independently of blanketing conditions and time of day or night. Evidence is also presented showing the presence of scatter type signals at levels of the order of 30 dB below the maximum level of the reflected signal. The scatter signals frequently influence the observed value of ƒtEs. Finally, evidence is presented purporting to show sporadic E returns from rapidly rising and descending layers. Some of the vertically moving layers appear to originate within the E layer and could be an indication of physical processes contributing to the time variability of the layer.