Which mode of propagation is used by short wave broadcast services?

(i) Which mode of propagation is used by shortwave broadcast services having frequency range from a few MHz upto MHz ? Explain diagrammatically how long distance communication can be achieved by this mode. (ii) Why is there an upper limit to frequency of waves used in this mode ?

The mode of propagation used by short wave broadcast services is

The mode of propagation used by short wave broadcast services is

The mode of propagation used by short wave broadcast services is

The mode of propagation used by short wave broadcast services is

The mode of propagation used by short wave broadcast service is

The mode of propagation used by short wave broadcast services having a frequency range from a few 3 MH_z "up to 30" MH_z is

The mode of propagation used by short wave broadcast services having a frequency range from a few 3 MH_z "up to 30" MH_z is