Sporadic E propagation on arvau

Wikipedia / Sporadic E propagation

SporadicE (abbreviated E or SpE) is an uncommon form of radio propagation using a low level of the Earth's ionosphere that normally does not refract radio waves above about 15MHz.

SporadicE propagation reflects signals off relatively small ionization patches in the lower E region located at altitudes of about . The more conventional forms of skywave propagation in the ionosphere's higher F region refract off layers of electrons that are knocked off gas atoms and molecules by intense UV light, which are renewed on a regular repeating daily cycle. In both cases, the electrons, when present, refract (or "bend") radio signals back toward the Earth's surface creating a "bent pipe" path for radio signals.

The E propagation often supports occasional long-distance communication during the approximately 6weeks centered on summer solstice at very high frequencies (VHF), which under normal conditions propagate mostly by line-of-sight.

Overview

As its name suggests, sporadicE is an unpredictable event that can happen at almost any time; it does, however, display strong seasonal and diurnal patterns. SporadicE activity peaks predictably near the solstices in both hemispheres. In the mid-latitude of the Northern Hemisphere, activity usually begins in mid-May, with the peak most noticeably beginning in early June. It begins trailing off after mid-July and becomes much less reliable by early August. A much smaller sporadic-E peak occurs during the winter solstice. For the mid-latitudes of the Southern Hemisphere, the timeframes are inversed; the highest activity occurring during their summer solstice.

Communication distances of can occur using a single E cloud. This variability in distance depends on a number of factors, including cloud height and density. The maximum usable frequency (MUF) also varies widely, but most commonly falls in the 25–150MHz range. This includes the bandII FM broadcast band (87.5–108MHz), bandI VHF television (former American analog TV channelsA2–A6, Russian channelsR1–R5, and former European analog channelsE2–E4), CB radio (27MHz), and the amateur radio 2 meter, 4 m, 6 m, and 10 m bands. On very rare occasions, a MUF of 225MHz can be attained.

No conclusive theory has yet been formulated as to the origin of sporadicE. One theory involves the presence of wind shear forming mid-latitude E from vertical shears in the horizontal neutral wind. Scholars also attribute other factors such as diurnal and semi-diurnal tides. Attempts to connect the incidence of sporadicE with the eleven-year Sunspot cycle have provided tentative correlations. There seems to be a positive correlation between sunspot maximum and E activity in Europe. Conversely, there seems to be a negative correlation between maximum sunspot activity and E activity in Australasia. Harrison implies that there is a correlation between the formation of sporadicE and iron/magnesium micrometeoroid ablation in the ablation zone, above the earth surface. Maruyama discusses this possibility further.

Characteristic distances

Television and FM signals received via sporadicE can be extremely strong and range in strength over a short period from just detectable to overloading. Although polarisation shift can occur, single-hop E signals tend to remain in the original transmitted polarization. Long single-hop () sporadicE television signals tend to be more stable and relatively free of multipath images.

Shorter-skip () signals tend to be reflected from more than one part of the sporadicE layer, resulting in multiple images and ghosting, with phase reversal at times. Picture degradation and signal-strength attenuation worsens with each subsequent sporadicE hop.

SporadicE usually affects the lower VHF bandI (TV channelsA2–A6, E2–E4, and R1–R5) and bandII (88–108MHz FM broadcast band). A 1945 FCC engineering study concluded that E caused interference issues 1% of the time for a station broadcasting at 42MHz, but only 0.01% for one at 84MHz.

The typical expected distances are about . However, under exceptional circumstances, a highly ionized E cloud can propagate bandI VHF signals down to approximately . When short-skip E reception occurs, i.e., under in bandI, there is a greater possibility that the ionized sporadicE cloud will be capable of reflecting a signal at a much higher frequency – i.e., a VHF band3 channel – since a sharp reflection angle (short skip) favours low frequencies, a shallower reflection angle from the same ionized cloud will favour a higher frequency. In this case even E DVB-T reception might be possible if a MUX uses VHF band3, preferably channelE5, especially if QPSK mode is used, due to its low signal requirements. In addition to that, band3 signals are more affected by tropospheric propagation which may indirectly increase the actual MUF because the signals only need to be refracted to low enough elevations that they get refracted towards the ground by the troposphere.

Equatorial sporadic E

Equatorial sporadicE is a regular daytime occurrence over the equatorial regions. For stations located within ±10° of the geomagnetic equator, equatorial E-skip can be expected on most days throughout the year, peaking around midday local time.

Auroral sporadic E

At polar latitudes, sporadicE can accompany auroras and associated disturbed magnetic conditions and is called auroralE.

Unlike equatorial or mid-latitude E, sporadicE propagation over high latitude paths is rare, and supports unexpected contacts between locations surrounding the Arctic, even during periods of low solar activity.

Occasional "bonanza" events

On 12June 2009, sporadicE allowed some television viewers in the eastern United States to see VHF analogTV stations from other states at great distances, in places and on TV channels where local stations had already done their permanent analog shutdown on the final day of the DTV transition in the United States. This was possible because VHF has been mostly avoided by digital TV stations, leaving the analog stations the last ones on the band.

As of April2010, it was possible for many in the U.S. to see Canadian and Mexican analog in this manner during sporadicE events; this should continue until all parts of those countries complete their own analog TV shutdowns over the succeeding few years.

In some cases it is even possible to get DTV E receptions from well over , since even for DTV, some U.S. stations still use band1. These signals are characterized for being either extremely clear, or extremely blocky. They are also much easier to identify. Furthermore, ATSC 3.0 could make sporadicE DTV reception easier, due to its usual modulation scheme being more resistant to multipath propagation, as well as impulse noise encountered on those frequencies.

Notable sporadic E DX reception events

The Medford Mail Tribune in Medford, Oregon reported on June 1, 1953, that KGNC-TV, channelA4 in Amarillo, and KFEL-TV, channelA2 from Denver had been received on the Trowbridge and Flynn Electric Company's television set at their Court Street warehouse, and with a pre-amplifier, a New York station's test pattern was reportedly picked up.
The June 4, 1953 issue of the Brimfield News in Brimfield, Illinois reported that area residents " 'saw' Salt Lake City Monday (via television)". It reported that a local farm family witnessed interference to WHBF-TV, channelA4 of Rock Island, Illinois by KDYL-TV in Salt Lake City, which "blocked out all their favorite programs."
In June1981, Rijn Muntjewerff, in the Netherlands, received 55.25MHz TV-2 Guaiba, Porto Alegre, Brazil, via a combination of sporadicE and afternoon TEP at a distance of .
On May 30, 2003, Girard Westerberg, in Lexington, Kentucky, made the first known reception of digital television by sporadicE when he decoded the PSIP identification of KOTA-DT, broadcasting on channelA2 from Rapid City, South Dakota, away.
On June 26, 2003, Paul Logan, in Lisnaskea, Ireland, was the first DXer to receive transatlantic sporadicE at frequencies above 88MHz. Stations received included 88.5MHz WHCF Bangor, Maine (), and 97.5MHz WFRY Watertown, New York (). David Hamilton from Cumnock in Ayrshire, Scotland, received CBTB-FM from Baie Verte, Newfoundland and Labrador, Canada, on 97.1MHz on this day also.
On July 20, 2003, Jozsef Nemeth, in Győr, Hungary, received TR3 Radio Miras on OIRT FM 70.61MHz from Uly Balkan, Türkmenistan, transmitter away.
On July 6, 2004, an intense high MUF Sporadic-E opening allowed Mike Bugaj of Enfield, Connecticut, to receive KATV A7 from Little Rock, Arkansas.
On June 15, 2005, Danny Oglethorpe in Shreveport, Louisiana, received a KBEJ-TV test signal on channelA2, from Fredericksburg, Texas, by sporadicE, at a very short distance for this propagation mode: .
On June 26, 2009, Paul Logan, in Lisnaskea, Ireland, had transatlantic sporadicE reception on the FM band from eight US States and one Canadian Province. The most distant signal received was that of 90.7WVAS radio in Montgomery, Alabama, at . This reception was recorded and later confirmed by WVAS newsreader Marcus Hyles.
On May 31, 2010, Mike Fallon, in East Sussex, United Kingdom, received a transatlantic signal from the religious station La Voz de la Luz, in Salvaleón de Higüey, a radio station in the Dominican Republic on 88.7MHz from 12:48 UTC for approximately 20 minutes at a distance of via multihop Sporadic-E. This reception was confirmed via an email from the station.
On November 24, 2016, many radio listeners from Australia and New Zealand were able to listen to radio stations from other states of Australia, overlapping many radio signals. Many people complained about this, saying that many of their favorite radio stations got replaced by different radio stations from other states. Later, the ACMA confirmed that this was caused by sporadicE.