question_answer

Which mode of propagation is used by short wave broadcast services having frequency range from a few MHz up to 30 MHz? Explain diagrammatically how long distance communication can be achieved by this mode. Why is there an upper limit to frequency of waves used in this mode? Or What is sky wave communication? Why is this mode of propagation restricted to the frequencies only up to few MHz?                                         

Answer:

                Sky wave propagation can be used by short wave broadcast services having frequency range from a few MHz to\[\text{3}0\text{ MHz}\]. In sky wave propagation, a radiowave is directed towards the sky and is reflected by the ionosphere towards the desired location of the earth, as shown in Fig. In this way, radiowaves can travel very large distances and can even bend round the earth. Sky wave propagation is restricted to frequencies up to 30 MHz because ionosphere cannot reflect e.m. radiations having frequencies greater than\[\text{3}0\text{ MHz}\].