Sporadic E (Es) propagation can affect signals on the 6m, 4m and 2m VHF amateur bands. The cause(s) of Sporadic E are the subject of much debate, but essentially an area or areas of the E layer of the earths atmosphere (some 100 to 120km high) contain ionised atoms which reflect radio signals back to earth. The height varies with time, and the location of the ionised areas moves over the surface of the earth. In addition the extent and energy of the ionised area varies rapidly.
All this variability means that “Sporadic” E really lives up to its name, and signals can appear and fade with remarkable rapidity, or they may be nearly constant for a period of time. The ionised area or “cloud” is often a very good reflector, and it can lead to signals from 1500km away being as strong as a station just down the road. Frustratingly, some ionised areas are very small as well as being intense and this can provide you with spectacular signals from the DX, while your near neighbour will hear nothing, or hear a completely different station.
The distance favoured by Sporadic E covers from around 1400 to 1900km in a single hop. Much rarer events can include a second hop, which can almost double the distance.
Es propagation is largely a daytime occurrence in the summer months of May to August, and the hours of the day with the most probability of Es are between 0800 and 1000, 1200 and 1400, and 1600 to 2000 in Europe. But never stop listening and tuning – remember – it’s Sporadic !
When you do hook some DX – please keep it brief.