Sporadic E

Sometimes, most often during summer and when the sunspot number is high, at about 100 km of altitude the ionosphere can produce a very efficient reflective layer, giving the possibility of radio contacts by space wave. All bands are interested, not only the HF, but also VHF and even UHF. However, the low altitude of the reflective layer limits the maximum reachable distance at about 3,000/4,000 Km.