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# E Region - HF radio signals are reflected here back towards the Earth # E Region - HF radio signals are reflected here back towards the Earth and sometimes higher frequencies# F Region - Also reflects HF signals# F Region - Most forms of skywave propagation use the normal and cyclic ionization properties of this layerSporadic E or Es can allow VHF signals (30-300 MHz) to propagate over long distances via a reflection from the E layer. Sporadic E is generally classified into three types by, Mid-latitude, Equatorial and Auroral. Sporadic E propagation bounces signals off smaller "clouds" of unusually ionized atmospheric gas in the lower E region.Sporadic E activity peaks predictably in the summertime in both hemispheres. In North America, the peak is most noticeable in mid-to-late June, trailing off through July and into August. For a signal to propagate via Es a cloud of sufficient ionization must exist at the mid-path point. Just like the F layer, a sporadic E cloud will support a maximum frequency, above this frequency signals will not be reflected to earth. Because of the limited size of the cloud the areas where propagation occurs are also limited.