Shortwave propagates differently during the day and at night. Its propagation is mainly due to bounding off layers of the ionosphere. Different layers absorb an

Shortwave propagates differently during the day and at night. Its propagation is mainly due to bounding off layers of the ionosphere. Different layers absorb and reflect different frequencies. During the day (relative to the broadcaster) frequencies above 12MHz propagate farther than lower frequencies. At night this effect is reversed.