A receiving station on the ground is receiving a signal of frequency 5 MHz from the receiver. Then the signal can come via

For ground wave propagation, the maximum range is

${\mathrm{d}}_{\max }=\sqrt{2\mathrm{Rh}}$

where h is the height of antenna.

The maximum frequency which can be propagated via sky wave is

$v_{\max }=9MHz$

Hence a 5 MHz signal can be propagated via sky waves and ground waves (depending on the height of antenna).