`(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 ?

Explanation

`(i)` This mode is called Sky wave propagation.
`(ii)` There is an upper limit because for frequencies above `30 MHz` radio waves penetrate through ionsphere and escape.