Sky waves can cover a very long distance and even can cover the earth. It extends from height of 65 km to about 400 km above the earths surface. Season Rollover Why Do Shortwave Frequencies Have To Change Encompass Marketing The oscillating electric field of electromagnetic wave changes the velocity of the electrons in the ionosphere which changes the effective dielectric constant and hence. . You may not hear anything unless you are listening at the right time or you may hear another language or you. The ionosphere is so called because of the presence of a large number of ions. Sky wave propagation is used by short wave broadcast services having a frequency range from few M Hz up to 30 to 40 M Hz Long-distance communication can be achieved by ionosphere reflection of radio waves back towards the earth as shown in Fig. The mode of propagation used by short wave broadcast services having frquency range from a few MHz upto 3