|
Digital Selective Calling
Digital selective calling or DSC is a standard for transmitting predefined digital messages via the medium-frequency (MF), high-frequency (HF) and very-high-frequency (VHF) maritime radio systems. It is a core part of the Global Maritime Distress Safety System (GMDSS).Bréhaut (2009): 35 Workings DSC was developed to replace a voice call in older procedures. Because a DSC signal uses a stable signal with a narrow bandwidth and the receiver has no squelch, it has a slightly longer range than analog signals, with up to twenty-five percent longer range and significantly faster. DSC senders are programmed with the ship's Maritime Mobile Service Identity (MMSI) and may be connected to the ship's Global Positioning System (GPS), which allows the apparatus to know who it is, what time it is and where it is. This allows a distress signal to be sent very quickly. Often, ships use separate VHF DSC and MF/HF DSC controllers. For VHF, DSC has its own dedicated receiver for monitoring Ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
VHF Canal 70
Very high frequency (VHF) is the International Telecommunication Union, 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 propagation, line-of-sight, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the horizon, 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, Terrestrial television, television broadcasting, two-way radio, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geographic Coordinate System
The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system, the geographic coordinate system is not cartesian because the measurements are angles and are not on a planar surface. A full GCS specification, such as those listed in the EPSG and ISO 19111 standards, also includes a choice of geodetic datum (including an Earth ellipsoid), as different datums will yield different latitude and longitude values for the same location. History The invention of a geographic coordinate system is generally credited to Eratosthenes of Cyrene, who composed his now-lost ''Geography'' at the Library of Alexandria in the 3rd century&n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Telecommunications
International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * ''International'' (Kevin Michael album), 2011 * ''International'' (New Order album), 2002 * ''International'' (The Three Degrees album), 1975 *''International'', 2018 album by L'Algérino Songs * The Internationale, the left-wing anthem * "International" (Chase & Status song), 2014 * "International", by Adventures in Stereo from ''Monomania'', 2000 * "International", by Brass Construction from ''Renegades'', 1984 * "International", by Thomas Leer from ''The Scale of Ten'', 1985 * "International", by Kevin Michael from ''International'' (Kevin Michael album), 2011 * "International", by McGuinness Flint from ''McGuinness Flint'', 1970 * "International", by Orchestral Manoeuvres in the Dark from '' Dazzle Ships'', 1983 * "International (Serious)", by Estelle from '' All of Me'', 2012 Politics * Political international, any transnational organization o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Baud
In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulation rate in symbols per second or pulses per second. It is the number of distinct symbol changes (signalling events) made to the transmission medium per second in a digitally modulated signal or a bd rate line code. Baud is related to ''gross bit rate'', which can be expressed in bits per second. If there are precisely two symbols in the system (typically 0 and 1), then baud and bit per second (bit/s) are equivalent. Naming The baud unit is named after Émile Baudot, the inventor of the Baudot code for telegraphy, and is represented according to the rules for SI units. That is, the first letter of its symbol is uppercase (Bd), but when the unit is spelled out, it should be written in lowercase (baud) except when it begins a senten ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency-shift Keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the 1 is called the mark frequency and the 0 is called the space frequency. Modulating and demodulating Reference implementations of FSK modems exist and are documented in detail. The demodulation of a binary FSK signal can be done using the Goertzel algorithm very efficiently, even on low-power microcontrollers. Variations Multiple frequency-shift keying Continuous-phase frequency-shift keying In principle FSK can be implemented by using completely independent free-running ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Error Detecting Code
In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communication channels. Many communication channels are subject to channel noise, and thus errors may be introduced during transmission from the source to a receiver. Error detection techniques allow detecting such errors, while error correction enables reconstruction of the original data in many cases. Definitions ''Error detection'' is the detection of errors caused by noise or other impairments during transmission from the transmitter to the receiver. ''Error correction'' is the detection of errors and reconstruction of the original, error-free data. History In classical antiquity, copyists of the Hebrew Bible were paid for their work according to the number of stichs (lines of verse). As the prose books of the Bible were hardly ever ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Telecommunication Union
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union, making it the oldest UN agency. The ITU was initially aimed at helping connect telegraphic networks between countries, with its mandate consistently broadening with the advent of new communications technologies; it adopted its current name in 1932 to reflect its expanded responsibilities over radio and the telephone. On 15 November 1947, the ITU entered into an agreement with the newly created United Nations to become a specialized agency within the UN system, which formally entered into force on 1 January 1949. The ITU promotes the shared global use of the radio spectrum, facilitates international cooperation in assigning satellite orbits, assists in developing and coordinating worldwide technical standards, and works to improve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
International Distress Frequency
An international distress frequency is a radio frequency that is designated for emergency communication by international agreement. History For much of the 20th century, 500 kHz was the primary international distress frequency. Its use has been phased out in favor of the Global Maritime Distress Safety System. Use of some distress frequencies is permitted for calling other stations to establish contact, whereupon the stations move to another frequency. Such channels are known as ''distress, safety and calling frequencies''. Satellite processing from all 121.5 or 243 MHz locators has been discontinued. Since February 1, 2009, the U.S. Coast Guard only monitors distress signals from emergency position indicating radio beacons ( EPIRBs) that broadcast using digital 406 MHz signals. Digital 406 MHz models became the only ones approved for use in both commercial and recreational watercraft worldwide on January 1, 2007. Maritime Mobile Service frequencies Internat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Man Overboard
"Man overboard!" is an exclamation given aboard a vessel to indicate that a member of the crew or a passenger has fallen off of the ship into the water and is in need of immediate rescue. Whoever sees the person's fall is to shout, "Man overboard!" and the call is then to be reported once by every crewman within earshot, even if they have not seen the victim fall, until everyone on deck has heard and given the same call. This ensures that all other crewmen have been alerted to the situation and notifies the officers of the need to act immediately to save the victim. Pointing continuously at the victim may aid the helmsman in approaching the victim. Causes A person may fall overboard for any number of reasons: they might have been struck by one of the ship's booms, they may have lost their footing on a slippery deck or while climbing the ship's ratlines, they may have deliberately jumped overboard in a suicide attempt, or any number of other reasons. Falling overboard is one of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ship Collision
Ship collision is the structural impact between two ships or one ship and a floating or still object such as an iceberg. Ship collisions are of particular importance in marine accidents. Some reasons for the latter are: * The loss of human life. * The environmental impact of oil spills, especially where large tanker ships are involved. * Financial consequences to local communities close to the accident. * The financial consequences to shipowners, due to ship loss or penalties. * Damage to coastal or off-shore infrastructure, for example collision with bridges. As sea lanes are getting more congested and ship speeds higher, there is a good possibility that a ship may experience an important accident during her lifetime. Higher speeds may cause larger operational loads, like slamming, or excessively severe loads, for example during a collision. Denser sea routes increase the probability of an accident—in particular a collision—involving ships or ships and shore or offshore s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna (radio)
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver (radio), receiver. In Transmission (telecommunications), transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic radiation, electromagnetic waves (radio waves). In Receiver (radio), reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be Amplifier, amplified. Antennas are essential components of all radio equipment. An antenna is an array of conductor (material), conductors (Driven element, elements), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna Tuner
An antenna tuner (and any of the names in the list below) is a device that is inserted between a transmitter, radio transmitter and its antenna (radio), antenna; when placed close by the antenna and properly adjusted (tuned) it optimizes power transfer by Impedance matching, matching the Electrical impedance, impedance of the radio to the impedance of the end of the feedline connecting the antenna to the transmitter. Various alternate names are used for this device: antenna matching unit, Impedance matching, impedance matching unit, matchbox, matching network, transmatch, antenna match, antenna tuning unit (ATU), antenna coupler, feedline coupler. English language technical jargon makes no distinction between the terms. Antenna tuners are particularly important for use with transmitters. Transmitters are typically designed to feed power into a reactance (electronics), reactance-free, resistive load pull, load of a specific value: Radio transmitters built after the 1950s are alm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
