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2 Meters
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] |
Amateur Radio
Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency, emergency communications. The term ''"radio amateur"'' is used to specify ''"a duly authorized person interested in radioelectric practice with a purely personal aim and without wikt:pecuniary, pecuniary interest"'' (either direct monetary or other similar reward); and to differentiate it from commercial broadcasting, public safety (police and fire), or two-way radio professional services (maritime, aviation, taxis, etc.). The amateur radio service (''amateur service'' and ''amateur-satellite service'') is established by the International Telecommunication Union (ITU) through their recommended radio regulations. National governments regulate technical and operational characteristics of transmissions and issue individual station li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Whip Antenna
A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. A whip antenna is a form of monopole antenna. The antenna is designed to be flexible so that it does not break easily, and the name is derived from the whip-like motion that it exhibits when disturbed. Whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer whips, made for mounting on vehicles and structures, are made of a flexible fiberglass rod around a wire core and can be up to long. The length of a whip antenna is determined by the wavelength of the radio waves it is used with. Their length varies from compact electrically short antennas wavelength long, up to wavelength to improve directivity. The most common type is the ''quarter-wave whip'', which is approximately long. Whips are the most common type o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Low Earth Orbit
A low Earth orbit (LEO) is an geocentric orbit, orbit around Earth with a orbital period, period of 128 minutes or less (making at least 11.25 orbits per day) and an orbital eccentricity, eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around , while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 km, about one-third of the Earth radius, radius of Earth and near the beginning of the Van Allen radiation belt#Inner belt, inner Van Allen radiation belt. The term ''LEO region'' is used for the area of space below an altitude of (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital spaceflight, sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites. No human spaceflights other than the lunar missions of the Apollo program (1968-1972) have gone beyond L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amateur Radio Satellite
An amateur radio satellite is an artificial satellite built and used by amateur radio operators. It forms part of the Amateur-satellite service. These satellites use amateur radio frequency allocations to facilitate communication between amateur radio stations. Many amateur satellites receive an OSCAR designation, which is an acronym for Orbiting Satellite Carrying Amateur Radio. The designation is assigned by AMSAT, an organization which promotes the development and launch of amateur radio satellites. Because of the prevalence of this designation, amateur radio satellites are often referred to as OSCARs. These satellites can be used free of charge by licensed amateur radio operators for voice ( FM, SSB) and data ( AX.25, packet radio, APRS) communications. Currently, over 18 fully operational amateur radio satellites are in orbit. They may be designed to act as repeaters, as linear transponders, and as store and forward digital relays. Amateur radio satellites have helpe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
10-meter Band
The 10-meter band is a portion of the shortwave radio spectrum internationally allocated to amateur radio and amateur satellite use on a primary basis. The band consists of frequencies stretching from 28.000 to 29.700 MHz. History The 10-meter band was allocated on a worldwide basis by the International Radiotelegraph Conference in Washington, DC, on 4 October 1927. Its frequency allocation was then 28-30 MHz. A 300 kHz segment, from 29.700–30.000 MHz, was removed from the amateur radio allocation in 1947 by the International Radio Conference of Atlantic City. In the late 1970s, the impending ban by the FCC of the sale of older 23 channel CB equipment that did not meet more stringent restrictions on newer, 40 channel units, meant that a surplus of 23 channel CB gear was on the market. This was a windfall for amateur radio enthusiasts, allowing access to fairly inexpensive radios which could easily be modified for use in the 10&nbs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
70-centimeter Band
The 70-centimeter or 440 MHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio and amateur satellite use. The ITU amateur radio allocation is from 430 to 440 MHz; however, some countries, such as the United States, allocate hams 420 to 450 MHz. Depending on the country the band is shared with other radio services (in United States with government radar systems such as PAVE PAWS). 70 centimeters is a popular ham band due to the ready availability of equipment in both new and used markets. Most amateurs operating on 70 cm use either equipment purpose-built for ham radio, or commercial equipment designed for nearby land mobile frequencies. Amateurs usually use the band for FM or digital voice communications through repeaters (useful for emergency communications), as well narrow band modes (analog and digital) for long-distance communications (called "DX", including Moon bounce). The band is also popular for Amateur Satel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper limit of audio frequencies that humans can hear (though these are not electromagnetic) and the lower limit of infrared frequencies, and also encompasses the microwave range. These are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves, so they are used in radio technology, among other uses. Different sources specify different upper and lower bounds for the frequency range. Electric current Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or lower audio frequency alternating current, such as the 50 or 60 Hz current used in electrical power distribution. * Energy from RF currents in conduct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on Earth. Travel through this layer also impacts GPS signals, resulting in effects such as deflection in their path and delay in the arrival of the signal. History of discovery As early as 1839, the German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field. Sixty years later, Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland (now in Canada) usin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sporadic E Propagation
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 name ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maidenhead Locator System
The Maidenhead Locator System (a.k.a. QTH Locator and IARU Locator) is a geocode system A geocode is a code that represents a geographic entity (location or Geographical feature, object). It is a unique identifier of the entity, to distinguish it from others in a finite set of geographic entities. In general the ''geocode'' is a ... used by amateur radio operators to succinctly describe their geographic coordinate system, geographic coordinates, which replaced the deprecated QRA locator, which was limited to European Contact (amateur radio), contacts. Its purpose is to be concise, accurate, and robust in the face of Interference (communication), interference and other adverse transmission conditions. The ''Maidenhead Locator System'' can describe locations anywhere in the world. Maidenhead locators are also commonly referred to as ''QTH locators'', ''grid locators'' or ''grid squares'', although the "squares" are distorted on any non-equirectangular projection, equirectangu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tropospheric Ducting
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-chann ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Troposphere
The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the planetary surface of the Earth, the average height of the troposphere is in the tropics; in the middle latitudes; and in the high latitudes of the polar regions in winter; thus the average height of the troposphere is . The term ''troposphere'' derives from the Greek words ''tropos'' (rotating) and ''sphere, sphaira'' (sphere) indicating that rotational turbulence mixes the layers of air and so determines the structure and the phenomena of the troposphere. The rotational friction of the troposphere against the planetary surface affects the flow of the air, and so forms the planetary boundary layer (PBL) that varies in height from hundreds of meters up to . The measures of the PBL vary according to the latitude, the landform, and the t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
