Sporadic E propagation

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Sporadic E propagation

Sporadic E or E_s is an unusual form of radio propagation

Radio propagation

Radio propagation is a term used to explain how radio waves behave when they are transmitted, or are wave propagation from one point on the Earth to another....
utilizing characteristics of the earth's ionosphere

Ionosphere

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Sporadic E or E_s is an unusual form of radio propagation

Radio propagation

Ionosphere

The ionosphere is the uppermost part of the Earth's atmosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere....
. Whereas most forms of skywave propagation use the normal and cyclic ionization properties of the ionosphere's F region to refract (or "bend") radio signals back toward the earth's surface, sporadic E propagation bounces signals off of smaller "clouds" of unusually ionized atmospheric gas in the lower E region (located at altitudes of approx. 90 to 160 km). This occasionally allows for long-distance communication at VHF and UHF frequencies not usually well-suited to such communication.

Communication distances of 800–2200 km can occur utilizing a single E_s cloud. This variability in distance depends on a number of factors, including cloud height and density. MUF

Maximum usable frequency

Maximum usable frequency describes, in radio transmission , using Reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time, independent of transmitter power....
also varies widely, but most commonly falls in the 27–110 MHz range, which includes the FM broadcast band

FM broadcast band

In most of the world, the FM broadcast band, used for broadcasting FM radio stations, goes from 87.5 to 108.0 Megahertz. In Japan the FM broadcast band is 76–90 MHz, unlike any other country in the world....
(87.5–108 MHz), and the amateur radio

Amateur radio

Amateur radio, often called Etymology of ham radio, is both a hobby and a service in which participants, called "hams," use various types of radio communications equipment to communicate with other radio amateurs for Public services, recreation and self-training....
10- and 6-meter bands. Strong events have allowed propagation at frequencies as high as 250 MHz.

As its name suggests, sporadic E can happen at almost any time, but it does display seasonal patterns. Sporadic E activity peaks predictably in the summertime in both hemispheres. In North America, the peak is most noticeable in mid-to-late June, trailing off though July and into August. Interestingly, a much smaller peak is seen around the winter solstice. Activity usually begins in mid-December in the northern hemisphere, with the days immediately after Christmas being the most active period.

Sporadic E propagation

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