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TV DX and FM DX are two terms, customarily grouped together, that mean "distant reception" of TV and FM stations, respectively. These terms refer to the search for faraway radio or television stations that can be received during unusual tropospheric conditions, or E-skip. An FM or TV tuner or receiver must be used to pick up stations.
Main article: Tropospheric ducting
Virtually all DX reception of digital television occurs by tropospheric ducting (due to most, but not all, DTV stations broadcasting in the UHF band). Signals have a slow cycle of fading and will produce signals strong enough for noise-free stereo reception on FM or clear TV pictures, sometimes in full color.
E-skip, also called Sporadic E, is the phenomenon of irregularly scattered patches of relatively dense ionization that develop seasonally within the E region of the ionosphere and reflect and scatter TV and FM frequencies, generally up to about 150 MHz. When frequencies reflect off multiple patches, it is referred to as multi-hop skip. E-skip allows radio waves to travel many miles beyond their intended area of reception. E-skip is unrelated to tropospheric ducting.
E-skip usually affects the lower VHF channels (channels 2-6 and the FM band), and usually enhances stations from beyond 600 miles; however, under exceptional circumstances, a highly ionized cloud can propagate E-skip receptions over a distance as little as 450 miles, and can even go up to channel 10.
Another form of E-skip, called skywave, occurs every night in the mediumwave and lower shortwave bands, allowing broadcast stations and amateur radio operators on those frequencies to be heard from across the continent.
E-skip is a regular daytime occurrence over the equatorial regions and is common in the temperate latitudes in late spring, early summer and, to a lesser degree, in early winter.
At high, i.e. polar, latitudes, E-skip can accompany auroras and associated disturbed magnetic conditions.
E-skip can sometimes support reflections for distances of up to 2,400 km at frequencies up to 150 MHz or, on rare occasions, even higher.
Source: Federal Standard 1037C
F2 propagation is related to the sunspot cycle and occurs in the F2 layer of the ionosphere, peaking every 11 years when the MUF, or Maximum Usable Frequency, is high enough to propagate TV signals. F2 tends to affect signals below 40 MHz, though it does get as high as 60 MHz. Signals have been known to travel very far through this method of propagation. Pictures propagated through F2 tend to be very smeared, unlike pictures through Es and tropo.
On January 31, 1981, Todd Emslie received audio transmitted from London, England by the BBC's television service in Sydney, Australia, 10,560 miles away. (At the time, the BBC were still using VHF frequencies to broadcast television.)
Meteor scatter occurs when a signal reflects off a meteor. The signals come out as sporadic bursts.
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