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Selcall
Selcall (selective calling) is a type of squelch protocol used in radio communications systems, in which transmissions include a brief burst of sequential audio tones. Receivers that are set to respond to the transmitted tone sequence will open their squelch, while others will remain muted. Selcall is a radio signalling protocol mainly in use in Europe, Asia, Australia and New Zealand, and continues to be incorporated in radio equipment marketed in those areas. Details The transmission of a selcall code involves the generation and sequencing of a series of predefined, audible tones. Both the tone frequencies, and sometimes the tone periods, must be known in advance by both the transmitter and the receiver. Each predefined tone represents a single digit. A series of tones therefore represents a series of digits that represents a number. The number encoded in a selcall burst is used to address one or more receivers. If the receiver is programmed to recognise a certain number, then ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selective Calling
In a conventional, analog two-way radio system, a standard radio has ''noise squelch'' or ''carrier squelch'', which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel (co-channel users), selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—''individual calling'' and ''group calling''. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios. Selective calling is akin to the use of a lock on a door. A radio with carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct "key", in this case a specific digital code. Selective calling systems can overlap; a radio may have (group call) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CCIR (selcall)
There are many types and formats of CCIR Selcall. For exampleCCIR 493-4is a standard format for HSelcallfor Land Mobile applications. CCIR (Consultative Committee on International Radio) functions have largely been taken over by ITU-R. One common type of CCIR selcall used in VHF and UHF FM two-way radio communications, is a 5-tone selective calling system mainly found in some European countries and used by the Swedish Police and the Turkish Police. The tone duration of a 5 tone CCIR selcall is 100 millisecond A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be called ...s (± 10 ms) and the tones are transmitted sequentially. References * {{refend Radio technology Telephony signals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selective Calling
In a conventional, analog two-way radio system, a standard radio has ''noise squelch'' or ''carrier squelch'', which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel (co-channel users), selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—''individual calling'' and ''group calling''. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios. Selective calling is akin to the use of a lock on a door. A radio with carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct "key", in this case a specific digital code. Selective calling systems can overlap; a radio may have (group call) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Squelch
In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a strong input signal. Essentially, squelch is a specialized type of noise gate designed to suppress weak signals. Squelch is used in two-way radios and VHF/UHF radio scanners to eliminate the sound of noise when the radio is not receiving a desired transmission. Carrier squelch A carrier squelch or noise squelch is the most simple variant of all. It operates strictly on the signal strength, such as when a television mutes the audio or blanks the video on "empty" channels, or when a walkie-talkie mutes the audio when no signal is present. In some designs, the squelch threshold is preset. For example, television squelch settings are usually preset. Receivers in base stations, or repeaters at remote mountain top sites, are usually not adjustable remotely from the control point. In two-way radios (also known as radiotelephones), the received si ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexadecimal
In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexadecimal uses 16 distinct symbols, most often the symbols "0"–"9" to represent values 0 to 9, and "A"–"F" (or alternatively "a"–"f") to represent values from 10 to 15. Software developers and system designers widely use hexadecimal numbers because they provide a human-friendly representation of binary-coded values. Each hexadecimal digit represents four bits (binary digits), also known as a nibble (or nybble). For example, an 8-bit byte can have values ranging from 00000000 to 11111111 in binary form, which can be conveniently represented as 00 to FF in hexadecimal. In mathematics, a subscript is typically used to specify the base. For example, the decimal value would be expressed in hexadecimal as . In programming, a number of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Milliseconds
A millisecond (from ''milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be called a centisecond, and one of 100 milliseconds a decisecond, but these names are rarely used. To help compare orders of magnitude of different times, this page lists times between 10−3 seconds and 100 seconds (1 millisecond and one second). ''See also'' times of other orders of magnitude. Examples The Apollo Guidance Computer used metric units internally, with centiseconds used for time calculation and measurement. *1 millisecond (1 ms) – cycle time for frequency 1 kHz; duration of light for typical photo flash strobe; time taken for sound wave to travel about 34 cm; repetition interval of GPS C/A PN code *1 millisecond - time taken for light to travel 204.19 km in a single mode fiber optic cable for a wavelength of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ericsson
(lit. "Telephone Stock Company of LM Ericsson"), commonly known as Ericsson, is a Swedish multinational networking and telecommunications company headquartered in Stockholm. The company sells infrastructure, software, and services in information and communications technology for telecommunications service providers and enterprises, including, among others, 3G, 4G, and 5G equipment, and Internet Protocol (IP) and optical transport systems. The company employs around 100,000 people and operates in more than 180 countries. Ericsson has over 57,000 granted patents. Ericsson has been a major contributor to the development of the telecommunications industry and is one of the leaders in 5G. The company was founded in 1876 by Lars Magnus Ericsson and is jointly controlled by the Wallenberg family through its holding company Investor AB, and the universal bank Handelsbanken through its investment company Industrivärden. The Wallenbergs and the Handelsbanken sphere acquired their v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dirty Pretty Things (film)
''Dirty Pretty Things'' is a 2002 British social thriller film directed by Stephen Frears and written by Steven Knight. Following the lives of two immigrants in London, it was filmed in a documentary style and was produced by BBC Films and Celador Films, and distributed by Buena Vista International through Miramax Films. Plot Okwe, a doctor in his home country (not initially named) who was forced to flee after being falsely accused of murdering his wife, lives in the United Kingdom as an undocumented immigrant. He drives a cab in London during the day and works at the front desk of a hotel at night, which is staffed by other immigrants, both documented and undocumented. He is pressed into giving medical treatment to other poor immigrants, including fellow cab drivers with venereal diseases. He is supplied with antibiotics by his friend Guo Yi, an employee at a hospital mortuary. Juliette, a sex worker who regularly conducts her business at the hotel, informs Okwe about a blocked ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
