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Sporadic E
Sporadic E (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 15 MHz. Sporadic E 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 knocked off of gas atoms and molecules by intense UV light, which are renewed on a regular repeating daily cycle. In both cases, the electrons, when present, refracts (or "bends") 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 6 weeks centered on summer solstice at very high frequencies (VHF), which under normal conditions can usually propagate mostly by line-of-sight. Overview As its na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
4-metre Band
The 4-metre (70 MHz) band is an amateur radio band within the lower part of the very high frequency (VHF) band. As only a few countries within and outside of Europe have allocated the band for amateur radio access, the availability of dedicated commercially manufactured equipment is limited. Most radio amateurs active on the band are interested in home construction or the modification of private mobile radio (PMR) equipment. As a result, communication on the 4-metre band tends to focus on technical topics, with long 'rag chews' being the norm as long as there is some local activity. History Historical Overview The 4-meter band, occupying the 70 MHz frequency range, has been historically significant for various regional radio services. Post-World War II, the United Kingdom allocated a segment of the band, specifically 56-68 MHz, to British community radio stations, a provision that lasted until 1949. This allocation was subsequently reassigned for television broadcas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ATSC 3
ATSC 3.0 is a major version of the ATSC standards for terrestrial television broadcasting created by the Advanced Television Systems Committee (ATSC). The standards are designed to offer support for newer technologies, including High Efficiency Video Coding (HEVC) for video channels of up to 4K resolution (2160p) at 120 frames per second, wide color gamut, high dynamic range, Dolby AC-4 and MPEG-H 3D Audio, datacasting capabilities, and more robust mobile television support. The capabilities have also been foreseen as a way to enable finer public alerting and targeted advertising. The first major deployment of ATSC 3.0 occurred in South Korea in May 2017, in preparation for the 2018 Winter Olympics. In November 2017, the FCC passed rules allowing American broadcast stations to voluntarily adopt ATSC 3.0 ("Next Gen TV"), provided that full-power stations preserve the availability of their programming in their city of license via legacy ATSC signals; adoption is being steer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumference, halfway between the North Pole, North and South Pole, South poles. The term can also be used for any other celestial body that is roughly spherical. In three-dimensional space, spatial (3D) geometry, as applied in astronomy, the equator of a rotating spheroid (such as a planet) is the parallel (circle of latitude) at which latitude is defined to be 0°. It is an imaginary line on the spheroid, equidistant from its geographical pole, poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the plane (geometry), plane perpendicular to its axis of rotation and midway between its geographical poles. On and near the equator (on Earth), noontime sunlight appears almost directly o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tropospheric Propagation
Tropospheric propagation describes electromagnetic propagation in relation to the troposphere. The service area from a VHF or UHF radio transmitter extends to just beyond the optical horizon, at which point signals start to rapidly reduce in strength. Viewers living in such a "deep fringe" reception area will notice that during certain conditions, weak signals normally masked by noise increase in signal strength to allow quality reception. Such conditions are related to the current state of the troposphere. Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (8 km). Such signals are thus directly affected by weather conditions extending over some hundreds of miles. During very settled, warm anticyclonic weather (i.e., high pressure), usually weak signals from distant transmitters improve in strength. Another symptom during such conditions may be interference to the local transmitter resulting in co-channe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
QPSK
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal such a system is termed coherent (and referr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DVB-T
DVB-T, short for Digital Video Broadcasting – Terrestrial, is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in Singapore in February 1998. This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation. It is also the format widely used worldwide (including North America) for Electronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point. It is also used in the US by amateur television operators. Basics Rather than carrying one data carrier on a single radio frequency (RF) channel, COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulates a set of closely spaced adjacent sub-carrier frequencies. In the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Broadcasting (magazine)
''Broadcasting & Cable'' (''B&C'', or ''Broadcasting+Cable'') was a telecommunications industry monthly trade magazine and, later, news website published by Future US. Founded in 1931 as ''Broadcasting'', subsequent mergers, acquisitions and industry evolution saw a series of name changes, including ''Broadcasting and Broadcast Advertising'', and ''Broadcasting-Telecasting'', before adopting its current name in 1993. ''B&C'', which was published biweekly until January 1941, and weekly thereafter, covers the business of television in the U.S.—programming, advertising, regulation, technology, finance, and news. In addition to the newsweekly, ''B&C'' operates a comprehensive website which offered a forum for industry debate and criticism. On August 6, 2024, Future announced that the magazine would cease publication after its September 2024 issue, and switch to a digital-only format as part of sister website ''Next TV''. However, ''Next TV'' as a whole ceased publishing new cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase (waves)
In physics and mathematics, the phase (symbol φ or ϕ) of a wave or other periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is expressed in such a scale that it varies by one full turn as the variable t goes through each period (and F(t) goes through each complete cycle). It may be measured in any angular unit such as degrees or radians, thus increasing by 360° or 2\pi as the variable t completes a full period. This convention is especially appropriate for a sinusoidal function, since its value at any argument t then can be expressed as \varphi(t), the sine of the phase, multiplied by some factor (the amplitude of the sinusoid). (The cosine may be used instead of sine, depending on where one considers each period to start.) Usually, whole turns are ignored when expressing the phase; so that \varphi(t) is also a periodic function, with the same period as F, that repeatedly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polarization (waves)
, or , is a property of transverse waves which specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. One example of a polarized transverse wave is vibrations traveling along a taut string, for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves ( shear waves) in solids. An electromagnetic wave such as light consists of a coupled oscillating el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Australasia
Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecologically, where the term covers several slightly different but related regions. Derivation and definitions Charles de Brosses coined the term (as French ''Australasie'') in ''Histoire des navigations aux terres australes'' (1756). He derived it from the Latin for "south of Asia" and differentiated the area from Polynesia (to the east) and the southeast Pacific ( Magellanica). In the late 19th century, the term Australasia was used in reference to the "Australasian colonies". In this sense it related specifically to the British colonies south of Asia: New South Wales, Queensland, South Australia, Tasmania, Western Australia, Victoria (i.e., the Australian colon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
