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E-skip
Sporadic E (usually abbreviated E) is an unusual form of radio propagation using a low level of the Earth's ionosphere that normally does not refract radio waves. Sporadic E propagation reflects signals off relatively small "clouds" in the lower E region located at altitudes of about 95~150 km (50~100 miles). These "clouds" are composed of ionized metals ablated off micrometeoroids. Whereas E layer propagation depends on the temporary abundance of metallic meteor dust, the more conventional forms of skywave propagation in the ionosphere's higher F region refract off layers of electrons knocked off of gasses by intense UV light, which are renewed on a fairly regular daily cycle. In both cases, the ionized material, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skywave
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands. As a result of skywave propagation, a signal from a distant AM broadcasting station, a shortwave station, or – during sporadic E propagation conditions (principally during the summer months in both hemispheres) a distant VHF FM or TV station – can sometimes be received as clearly as local stations. Most long-distance shortwave (high frequency) radio communication – between 3 and 30 MHz – is a result of skywave propagation. Since the early 1920s amateur radio operators (or "hams"), limited to lower transmitter power than broadcast stations, have ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2-meter Band
The 2-meter amateur radio band is a portion of the VHF radio spectrum that comprises frequencies stretching from 144 MHz to 148 MHz in International Telecommunication Union region (ITU) Regions 2 (North and South America plus Hawaii) and 3 (Asia and Oceania) and from 144 MHz to 146 MHz in ITU Region 1 (Europe, Africa, and Russia). The license privileges of amateur radio operators include the use of frequencies within this band for telecommunication, usually conducted locally with a line-of-sight range of about . Operation Because it is local and reliable, and because the licensing requirements to transmit on the 2-meter band are easy to meet in many parts of the world, this band is one of the most popular non- HF ham bands. This popularity, the compact size of needed radios and antennas, and this band's ability to provide easy reliable local communications also means that it is also the most used band for local emergency communications efforts, such as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maximum Usable Frequency
In radio transmission maximum usable frequency (MUF) is the highest radio frequency that can be used for transmission between two points via reflection from the ionosphere (skywave or "skip" propagation) at a specified time, independent of transmitter power. This index is especially useful in regard to shortwave transmissions. In shortwave radio communication, a major mode of long distance propagation is for the radio waves to reflect off the ionized layers of the atmosphere and return diagonally back to Earth. In this way radio waves can travel beyond the horizon, around the curve of the Earth. However the refractive index of the ionosphere decreases with increasing frequency, so there is an upper limit to the frequency which can be used. Above this frequency the radio waves are not reflected by the ionosphere but are transmitted through it into space. The ionization of the atmosphere varies with time of day and season as well as with solar conditions, so the upper frequenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
6-meter Band
The 6-meter band is the lowest portion of the very high frequency (VHF) radio spectrum internationally allocated to amateur radio use. The term refers to the average signal wavelength of 6 meters. Although located in the lower portion of the VHF band, it nonetheless occasionally displays propagation mechanisms characteristic of the high frequency (HF) bands. This normally occurs close to sunspot maximum, when solar activity increases ionization levels in the upper atmosphere. During the sunspot peak of 2005, worldwide 6 meter propagation occurred making 6 meter communications as good as or in some instances and locations, better than HF frequencies. The prevalence of HF characteristics on this VHF band has inspired amateur operators to dub it the "magic band". In the northern hemisphere, activity peaks from May through early August, when regular sporadic E propagation enables long-distance contacts spanning up to for single-hop propagation. Multiple-hop sporadi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ATSC 3
ATSC 3.0 is a major version of the ATSC standards for television broadcasting created by the Advanced Television Systems Committee (ATSC). The standards are designed to offer support for newer technologies, including HEVC for video channels of up to 4K resolution, 2160p 4K resolution at High frame rate, 120 frames per second, wide color gamut, High-dynamic-range video, 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 Emergency population warning, public alerting and targeted advertising. The first major deployments of ATSC 3.0 occurred in South Korea in May 2017, in preparation for the 2018 Winter Olympics. In November 2017, the Federal Communications Commission, FCC approved the voluntary use of ATSC 3.0 (also referred to as Next Gen TV) for television broadcasting in the United States; there will not be a mandatory transition as there was Digi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equator
The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also be used for any other celestial body that is roughly spherical. In 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 poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the 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 overhead (no more than about 23° from the zenith) every day, year-round. Consequently, the equator has a rather stable daytime temperature throu ... [...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 7.5 km. Such signals are thus directly affected by weather conditions extending over hundreds of kilometres. 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-channel inte ... [...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 reference signal (the 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 ter ... [...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'' (or ''Broadcasting+Cable'') is a weekly telecommunications industry trade magazine published by Future US. Previous names included ''Broadcasting-Telecasting'', ''Broadcasting and Broadcast Advertising'', and ''Broadcasting''. ''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 that provides a roadmap for readers in an industry that is in constant flux due to shifts in technology, culture and legislation, and offers a forum for industry debate and criticism. History ''Broadcasting'' was founded in Washington, D.C., by Martin Codel, Sol Taishoff, and former National Association of Broadcasters president Harry Shaw, and the first issue was published on October 15, 1931. Originally, Shaw was publisher, Codel editor, and Taishoff managing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very High Frequency
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF). VHF radio waves propagate mainly by line-of-sight, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting, two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR and ILS ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase (waves)
In physics and mathematics, the phase of a 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 denoted \phi(t) and 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 \phi(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 \phi(t) is also a periodic function, with the same period as F, that repeatedly scans the same range ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
