80-meter Band - Propagation

Propagation

As the maximum usable frequency for long distance communication seldom dips below 3.5 MHz anywhere on the planet, the main propagation barrier to long distance communication is heavy D-layer absorption during the daytime, ensuring that DX paths must be largely, although not entirely, in darkness. At times, there is pronounced dark-side gray-line propagation, which is most useful on polar routes, away from equatorial thunderstorm activity.

At higher latitudes, a noticeable skip zone sometimes appears on the band during darkness hours in midwinter, which can be as much as 300 miles/500 km, rendering communication with some nearby stations impossible. This is not generally a problem at middle or equatorial latitudes, or for large parts of the year anywhere, but it does occasionally limit local wintertime traffic on the band in areas such as Northern Europe, the northern tier of the United States and Canada.

During spring and summer (year-round in the tropics), lightning from distant storms creates significantly higher background noise levels, often becoming an insurmountable obstacle to maintaining normal communications. Nearby convective weather activity during the summer months can make the band completely unusable, even for local communications. In the winter months during the peak years of the sunspot cycle, auroral effects can also render the band useless for hours at a time.