Sporadic E - When the air suddenly becomes electric!

Have you ever been surprised to find that your car radio or so-called kitchen radio plays a multilingual babble of music and voices in the FM range instead of the usual local radio, which almost pushes your favorite station that's otherwise always easy to receive to one side? Then it could be that this is due to overreach by Sporadic E.

Fascinating phenomenon of radio communication

In the summer months from May to July/August, it can occasionally be observed that stations from all over Germany and the surrounding European countries can suddenly be received in the FM broadcasting band from 87.5 to 108 MHz. These rare propagation conditions usually occur during the day in the late morning, afternoon or early evening. The 6 m, 4 m and 2 m amateur radio bands are then often also affected by this particular type of overreach. Even on shortwave from 25 MHz upwards, this phenomenon occurs when stations from the dead zone are suddenly heard. Here, however, these unusual propagation conditions attract less attention. In the VHF range, where such long-range connections are not normally possible, the anomaly of propagation conditions known as Sporadic E is used by VHF amateurs for a welcome DX. From the point of view of professional radio services and broadcasters, it is merely a disturbing natural phenomenon that impairs undisturbed reception in defined coverage areas and frequency grids. Sporadic-E should not be confused with the overreach caused by occasional inversion weather conditions and troposcatter, which provides a more or less available, normal DX propagation path in the VHF range at all times. However, Sporadic E is not an operating mode, but merely stands for a special form of propagation conditions, via which basically any operating mode is possible. The usual operating mode is SSB, FM and CW are used less frequently.

Mysterious layers in the sky: the phenomenon of Sporadic E

H. J. Pietsch, DJ6HP, once defined these interrelated terms succinctly in his amateur radio lexicon[1]: The E-layer (Kenelly Heaviside layer) has its maximum electron concentration between 110 and 140 km altitude. In this range, the so-called sporadic E-layer (Es-layer) occasionally occurs, a deviation from the usual state of the E-layer. In a narrow altitude range of the E-layer, there is a multiple increase in the electron concentration compared to the normal state. The expansion ranges locally from a few kilometers to an expansion of several hundred kilometers. The Es layer can occur suddenly, especially during the day and in summer. This leads to irregularities in HF and VHF propagation, so that ionospheric reflections are possible at the Es layer, from the upper shortwave to the VHF range." Rothammel's Antenna Book[2] defines Sporadic E as follows: "Sporadic E (abbreviated to Es) refers to reflection layers at altitudes of around 100 km that have a very high ion concentration and reflect electromagnetic waves. With particularly high ionization, frequencies of 50 to 220 MHz are reflected. The extent of such clouds can be up to 5 km vertically and between 10 and 100 km horizontally. As the occurrence of these "electronic" clouds is unpredictable, i.e. more or less random - i.e. sporadic - this propagation is called Sporadic E. It is a typical summer dispersion mode.

The secrets of the sunspot cycle: On the trail of Sporadic E phenomena

Obviously, there is a clear connection between the sunspot cycle and the frequency of sporadic E. During periods in which the magnetic polarity of the sun and the earth coincide, Es activity is particularly frequent. Furthermore, there is currently no solid explanation for the formation of Es clouds. Various theories are discussed in the literature. Possible causes include solar activity, the introduction of metals through meteor showers or isolated meteorites, high-altitude winds or the influence of thunderstorms[3].

Maximum range with minimum effort: strategies, equipment and operating technology

From an exposed location, you can sometimes even use a handheld radio. Sufficient station equipment for the 2 m band consists of a VHF transceiver with 10 W output power and an omnidirectional antenna or, even better, a 6-element Yagi. Any additional equipment, transmitting power and antenna effort naturally increases the chances of success. You will find these and other helpful tips on these and the following aspects in [4]. The following applies to operating technology: Keep it short! It is not possible to predict how long the connection will be maintained. The opening time can last from a few seconds to several hours. The signals of long-lasting connections often have a strong QSB. As a rule, however, most openings are only quite short. If possible, you should not call CQ at all, at most only very briefly. You should only answer if the DX station can be heard loud and clear. A quick change of calling frequency saves a lot of QRM for everyone involved. The pile-up generated by the DX stations is problematic. It usually makes more sense to rotate across the band and search for other DX stations where there is less pile-up. A good operating technique adapted to Sporadic E is important: listening, taking notes and observing the cluster are essential. Callsign, RST and locator, if necessary the name, lengthy explanations of further details are not usual. You should always bear in mind that propagation paths and reception zones are usually very limited locally. This means that conditions can be completely different a few tens of kilometers away. This means that the DX station cannot be heard there - or can only be heard there. Furthermore, the location of an Es cloud does not remain stationary. Due to the earth's rotation, it always moves in a westerly direction in the northern hemisphere. The maximum distances are between 1,200 and 2,200 km. Rare double jumps can enable sporadic E connections of up to 3,500 km. The field strengths range from "briefly as strong as a local station" to "almost unrecordable".

Recognition of Sporadic E and practical tips for radio amateurs

There is no long-term prediction for the occurrence of this particular propagation path, as it is a sporadic phenomenon. Observation of the cluster is essential to detect the occurrence of sporadic E conditions. Monitoring the VHF broadcast bands is also an important indicator of the occurrence of sporadic E. Now two more tips for the ambitious Sporadic E hunter: With the help of the DX-Robot[5] from the Netherlands, you can also have a 144 MHz Sporadic E alarm sent to your cell phone as a text message. You can also find information on installing a Sporadic E DX monitor with automatic notification at [6].

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