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500 KHz
From early in the 20th century, the radio frequency of 500 kilohertz (500 kHz) was an international calling and distress frequency for Morse code maritime communication. For much of its early history, this frequency was referred to by its equivalent wavelength, 600 meters, or, using the earlier frequency unit name, 500 kilocycles (per second) or 500 kc. Maritime authorities of many nations, including the Maritime and Coastguard Agency and the United States Coast Guard, once maintained 24 hour watches on this frequency, staffed by skilled radio operators. Many SOS calls and medical emergencies at sea were handled via this frequency. However, as the use of Morse code over radio is now obsolete in commercial shipping, 500 kHz is obsolete as a Morse distress frequency. Beginning in the late 1990s, most nations ended monitoring of transmissions on 500 kHz and emergency traffic on 500 kHz has been replaced by the Global Maritime Dist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
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 and Safety System (GMDSS). 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
SS Jeremiah O'Brien LF Radio
The ''Schutzstaffel'' (; ; SS; also stylised with SS runes as ''ᛋᛋ'') was a major paramilitary organisation under Adolf Hitler and the Nazi Party in Nazi Germany, and later throughout German-occupied Europe during World War II. It began with a small guard unit known as the ''Saal-Schutz'' ("Hall Security") made up of party volunteers to provide security for party meetings in Munich. In 1925, Heinrich Himmler joined the unit, which had by then been reformed and given its final name. Under his direction (1929–1945) it grew from a small paramilitary formation during the Weimar Republic to one of the most powerful organisations in Nazi Germany. From the time of the Nazi Party's rise to power until the regime's collapse in 1945, the SS was the foremost agency of security, mass surveillance, and state terrorism within Germany and German-occupied Europe. The two main constituent groups were the ''Allgemeine SS'' (General SS) and ''Waffen-SS'' (Armed SS). The ''Allgemeine SS' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Distress Signal
A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sound audible from a distance. A distress signal indicates that a person or group of people, watercraft, aircraft, or other vehicle is threatened by a serious or imminent danger and requires immediate assistance.Aeronautical Information Manual U.S. Federal Aviation Administration, 2016 Use of distress signals in other circumstances may be against local or . An [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Aircraft Emergency Frequency
The aircraft emergency frequency (also known in the USA as Guard) is a frequency used on the aircraft band reserved for emergency communications for aircraft in distress. The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD), International Aeronautical Emergency Frequency, or VHF Guard, and 243.0 MHz—the second harmonic of VHF guard—for military use, also known as Military Air Distress (MAD), NATO Combined Distress and Emergency Frequency, or UHF Guard. Earlier emergency locator transmitters (ELTs / EPIRBs) used the guard frequencies to transmit. As of February 1, 2009 satellite monitoring of the 121.5 and 243 MHz ELT (EPIRB) frequencies ceased, whereas an additional band from 406.0 to 406.1 MHz is now used exclusively by modern emergency locator transmitters (EPIRB). History The choice of 121.5 MHz was made by ICAO in conjunction with ARINC and the ITU. Monitoring In the United States, the emergency frequency ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
International Telecommunication Union
The International Telecommunication Union (ITU)In the other common languages of the ITU: * * is a list of specialized agencies of the United Nations, specialized agency of the United Nations responsible for many matters related to information and communications technology, information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union, the first formal and permanent international organization. The organization significantly predates the UN, making it the oldest UN agency. Doreen Bogdan-Martin is the Secretary-General of ITU, the first woman to serve as its head. The ITU was initially aimed at helping connect Telegraphy, 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 cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Electronic Chart Display And Information System
An electronic navigational chart (ENC) is an official database created by a national hydrographic office for use with an Electronic Chart Display and Information System (ECDIS). ECDIS and ENCs are the primary means of electronic navigation on cargo ships. Charts can be used in navigation to provide an indication of location once a position is fixed and the charted depths can be used in under keel clearance calculations to ensure the ship is navigating in safe water. Inland Electronic Chart Display and Information System are similar systems used for navigation of inland water. ENC An Electronic Navigational Chart (ENC) is a digital representation of a real-world geographical area for the purpose of Marine navigation. Real-world objects and areas of navigational significance, or to a lesser degree - informational significance, are portrayed through Raster facsimiles of traditional paper charts; or more commonly through vector images, which are able to scale their relative p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
SITOR
SITOR (SImplex Teletype Over Radio) is a system for transmitting text messages. It was developed in the 1960s by Koninklijke TNT Post as an improvement over radioteletype (RTTY). Although it uses the same frequency-shift keying (FSK) modulation used by regular RTTY, SITOR uses error detection, redundancy, and/or retransmission to improve reliability. There are two SITOR modes: * SITOR-A is used for point to point links. SITOR-A uses automatic repeat request (ARQ) to gain reliability. If the receiver detects an error, it requests a retransmission. * SITOR-B is used for broadcast links. SITOR-B transmits each character in a message twice to gain reliability. If the receiver detects an error in the first character, it uses the copy. If both characters are garbled, the receiver won't know what was sent. * SITOR-B by definition uses forward error correction (FEC), versus ARQ for SITOR-A. SITOR sends 7-bit characters as a bit stream at 100 baud (which, in this case, is 100 bits per se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Quadrature Amplitude Modulation
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signals, or two digital bit streams, by changing (''modulating'') the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves are of the same frequency and are out of phase with each other by 90°, a condition known as orthogonality or Quadrature phase, quadrature. The transmitted signal is created by adding the two carrier waves together. At the receiver, the two waves can be coherently separated (demodulated) because of their orthogonality. Another key property is that the modulations are low-frequency/low-bandwidth waveforms compared to the carrier frequency, which is known as the In-phase and quadrature components#Narrowband ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
NAVTEX
NAVTEX (NAVigational TEleX), sometimes styled Navtex or NavTex, is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety information (MSI) to ships. NAVTEX was developed in the late 1970s in northwestern Europe to provide a low-cost, simple, and automated means of receiving this information aboard ships at sea within approximately off-shore. There are no user fees associated with receiving NAVTEX broadcasts, as the transmissions are typically transmitted from the National Weather Authority (Italy) or Navy or Coast Guard (as in the US) or national navigation authority (Canada). Where the messages contain weather forecasts, an abbreviated format very similar to the shipping forecast is used. NAVTEX is a component of the International Maritime Organization/International Hydrographic Organization Worldwide Navigation Warning Service (WWNWS). NAVTEX is also a m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
World Radiocommunication Conference
The World Radiocommunication Conference (WRC) is a conference organized by the ITU to review and, as necessary, revise the Radio Regulations, the international treaty governing the use of the radio-frequency spectrum as well as geostationary and non-geostationary satellite orbits. It is held every three to four years. Prior to 1993, it was called the World Administrative Radio Conference (WARC); in 1992, at an ''Additional Plenipotentiary Conference'' in Geneva, the ITU was restructured, and later conferences became the WRC. At the 2015 conference (WRC-15), the ITU deferred their decision on whether to abolish the leap second to 2023. The most recent World Radio Communication Conference (WRC-23) took place from 20 November to 15 December 2023 in Dubai Dubai (Help:IPA/English, /duːˈbaɪ/ Help:Pronunciation respelling key, ''doo-BYE''; Modern Standard Arabic, Modern Standard Arabic: ; Emirati Arabic, Emirati Arabic: , Romanization of Arabic, romanized: Help:IPA/English, / ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
