Sporadic E propagation

As a sporadic E layer ( Sporadic - E, Eb ) are called cloud-like regions of high ionization in the ionosphere in the amount of the E layer. The sporadic E layer occurs irregularly and not predictable on, but preferably in the months of May to July ( in the northern hemisphere) and during the day, so at times of generally relatively high ionization. The exact origin of the sporadic E layer is still unclear.

The impact on the short-wave radio communications are as follows:

  • At high frequencies, where no (or only weak) signals can be heard under normal conditions, suddenly from distances of several hundred km to 2300 km (first hop ) are getting very strong signals, preferably,
  • At medium frequencies Sporadic -E leads to a reduction or disappearance of the so -called dead zone ( unreachable area between ground and sky wave).

An increase in the ionization by Sporadic -E means that at high frequencies on shortwave transmitters can also be received at a lesser distance. This reduction of the dead zone is equivalent to an increase of the maximum usable frequency (MUF ). The frequency bands above 30 MHz then one speaks of overreach. The higher the frequency, the less likely it is however useful to propagation conditions. A few times a year, for example, the FM broadcast band at 100 MHz, or the 2 -meter amateur radio band at 144 MHz, affected.

While Sporadic -E brings a welcome increase in range with for the amateur radio at 50 MHz and 144 MHz, it is from the perspective of professional services, along with the broadcasters a disturbing phenomenon. The generally sized to a fixed coverage area wireless networks interfere with each other upon the occurrence of sporadic -E.

Do not confuse this with tropospheric propagation mode overreach when temperature inversions in the range above 50 MHz.