Why do shortwave stations change frequencies so often?
First of all, some shortwave stations don’t change frequencies. Some stations use only one frequency, all day and all year long. This means that their coverage area will vary throughout the day and throughout the year, since the ionosphere is affected by daily and seasonal conditions on the sun. (Yes, the sun really affects shortwave “propagation,” as we call it.) To make the best of these changing propagation conditions, many shortwave stations change frequencies throughout the day (and during different seasons of the year), in order to maintain the best possible coverage of a particular target area. They use sophisticated computer programs and on-the-scene listener monitor reports to determine which is the best frequency range to use at a particular time of the day to reach a particular target area. And this frequency range will often vary according to the different seasons of the year. All of this is designed to give the listener the best possible reception of the station, although
