Sporadic E is very unpredictable form of radio wave propagation as a result of highly ionized patches or clouds that occasionally form in the E region of the ionosphere at altitudes between approximately 80 and 150 kilometres.
Wavecom W-CODE, Do not wind chokes on red toroids!, How does an antenna tuner work ?, Fundamentals of Radio Waves Propagation, 160 meter antenna problems and solutions, Kenwood TS890S Mods, Gordon West W5YI Ham Instructor Program., TY0RU Benin DX Pedition, TY0RU Log Online