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Radio Telephony
A radiotelephone (or radiophone), abbreviated RT, is a radio communication system for conducting a conversation; radiotelephony means telephony by radio. It is in contrast to ''radiotelegraphy'', which is radio transmission of telegrams (messages), or ''television'', transmission of moving pictures and sound. The term is related to radio broadcasting, which transmit audio one way to listeners. Radiotelephony refers specifically to two-way radio systems for bidirectional person-to-person voice communication between separated users, such as CB radio or marine radio. In spite of the name, radiotelephony systems are not necessarily connected to or have anything to do with the telephone network, and in some radio services, including GMRS, interconnection is prohibited. Design Mode of emission The word ''phone'' has a long precedent beginning with early US wired voice systems. The term means ''voice'' as opposed to telegraph or Morse code. This would include systems fitting into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ICOM IC-2E And Generetions Of Mobile Phones
ICOM may refer to: * International Council of Museums * Idaho College of Osteopathic Medicine, a medical school in the United States * Icom Incorporated, radio equipment manufacturer * Industrial Common Ownership Movement (ICOM), a co-operative federation that now forms part of Co-operatives UK Co-operatives UK is a British co-operative federation described as "the central membership organisation for co-operative enterprise throughout the UK". It was founded in 1870 as the Co-operative Central Board, changing its name to the Co-oper ... * Inputs, Controls, Outputs, and Mechanisms (ICOM), the conceptual parts of the IDEF0 function modeling methodology * ICOM Simulations, software company * ICOM Tele A/S, a Danish telecommunications operator {{disambig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Landline
A landline is a physical telephone connection that uses metal wires or optical fiber from the subscriber's premises to the network, allowing multiple phones to operate simultaneously on the same phone number. It is also referred to as plain old telephone service (POTS), twisted pair, telephone line, or public switched telephone network (PSTN). Landline services are traditionally provided via an analogue copper wire to a telephone exchange. ''Landline service'' is usually distinguished from more modern forms of telephone services which use Internet Protocol based services over optical fiber ( Fiber-to-the-x), or other broadband services ( VDSL/Cable) using Voice over IP. However, sometimes modern fixed phone services delivered over a fixed internet connection are referred to as a "landline" (i.e., non-cellular service). Characteristics Landline service is typically provided through the outside plant of a telephone company's central office, or wire center. The outside plant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airband
Airband or aircraft band is the name for a group of frequencies in the VHF radio spectrum allocated to radio communication in civil aviation, sometimes also referred to as ''VHF'', or phonetically as ''"Victor"''. Different sections of the band are used for radionavigational aids and air traffic control. In most countries a license to operate airband equipment is required and the operator is tested on competency in procedures, language and the use of the phonetic alphabet. Spectrum usage The VHF airband uses the frequencies between 108 and 137 MHz. The lowest 10 MHz of the band, from 108 to 117.95 MHz, is split into 200 narrow-band channels of 50 kHz. These are reserved for navigational aids such as VOR beacons, and precision approach systems such as ILS localizers. , most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118 to 136.975 MHz, in steps of 25 kHz. In Euro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spread Spectrum
In telecommunications, especially radio communication, spread spectrum are techniques by which a signal (electrical engineering), signal (e.g., an electrical, electromagnetic, or acoustic) generated with a particular Bandwidth (signal processing), bandwidth is deliberately spread in the frequency domain over a wider frequency band. Spread-spectrum techniques are used for the establishment of secure communications, increasing resistance to natural Interference (communication), interference, Noise (electronics), noise, and radio jamming, jamming, to prevent detection, to limit Spectral flux density, power flux density (e.g., in satellite downlinks), and to enable multiple-access communications. Telecommunications Spread spectrum generally makes use of a sequential noise-like signal structure to spread the normally narrowband information signal over a relatively wideband (radio) band of frequencies. The receiver correlates the received signals to retrieve the original information ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Modulation
Frequency modulation (FM) is a signal modulation technique used in electronic communication, originally for transmitting messages with a radio wave. In frequency modulation a carrier wave is varied in its instantaneous frequency in proportion to a property, primarily the instantaneous amplitude, of a message signal, such as an audio signal. The technology is used in telecommunications, radio broadcasting, signal processing, and Run-length limited#FM: .280.2C1.29 RLL, computing. In Analog signal, analog frequency modulation, such as radio broadcasting of voice and music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying (FSK), in which the instantaneous frequency of the carrier is shifted among a set of frequencies. The frequencies m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude Modulation
Amplitude modulation (AM) is a signal modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the instantaneous amplitude of the wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation, in which either the frequency of the carrier wave is varied, as in frequency modulation, or its Phase (waves), phase, as in phase modulation. AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with Roberto Landell de Moura and Reginald Fessenden's radiotelephone experiments in 1900. This original form of AM is sometimes called double-sideband amplitude modulation (DSBAM), because the standard method produces sidebands on either side of the carrier frequency. Single-sideband modulation uses bandpass filters to eliminate one of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information. The process encodes information in form of the modulation or message signal onto a carrier signal to be transmitted. For example, the message signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. This carrier wave usually has a much higher frequency than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, receiving a radio wave requires a radio antenna with a length that is one-fourth of the wavelength of the transmitted wave. For low frequency radio waves, wavelength is on the scale of kilometers and building such a large antenna is not practical. Another purpose of modulation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Citizens Band Radio
Citizens band radio (CB radio) is a land mobile radio system, a system allowing short-distance one-to-many bidirectional voice communication among individuals, using two-way radios operating near 27 MHz (or the 11-m wavelength) in the high frequency or shortwave band. Citizens band is distinct from other personal radio service allocations such as FRS, GMRS, MURS, UHF CB and the Amateur Radio Service ( "ham" radio). In many countries, CB operation does not require a license and may be used for business or personal communications. Like many other land mobile radio services, multiple radios in a local area share a single frequency channel, but only one can transmit at a time. The radio is normally in receive mode to receive transmissions of other radios on the channel; when users want to communicate they press a "push to talk" button on their radio, which turns on their transmitter. Users on a channel must take turns transmitting. In the US and Canada, and in the EU and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Megahertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base units is 1/s or sā1, meaning that one hertz is one per second or the reciprocal of one second. It is used only in the case of periodic events. It is named after Heinrich Rudolf Hertz (1857ā1894), the first person to provide conclusive proof of the existence of electromagnetic waves. For high frequencies, the unit is commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz). Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light. The interval of time between events is called the period. It is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times per minute (2 hertz), its period is one half of a second. Special definitions of frequency are used in certain contexts, such as the angular frequency in rotational or cyclical properties, when the rate of angular progress is measured. Spatial frequency is defined for properties that vary or cccur repeatedly in geometry or space. The unit of measurement of frequency in the International System of Units (SI) is the hertz, having the symbol Hz. Definitions and units For cyclical phenomena such as oscillations, waves, or for examp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Procedure Word
Procedure words (abbreviated to prowords) are words or phrases limited to radiotelephony procedure used to facilitate Telecommunication, communication by conveying information in a condensed standard verbal format. Prowords are voice versions of the much older prosigns for Morse code, procedural signs for Morse code which were first developed in the 1860s for Electrical telegraph, Morse telegraphy, and their meaning is identical. The NATO communications manual ACP-125 contains the most formal and perhaps earliest modern (post-World War II) glossary of prowords, but its definitions have been adopted by many other organizations, including the United Nations Development Programme, the U.S. Coast Guard, US Civil Air Patrol, US Military Auxiliary Radio System, and others. Prowords are one of several structured parts of radio voice procedures, including brevity codes and plain language radio checks. Examples According to the U.S. Marine Corps training document FMSO 108, "understandi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Improved Mobile Telephone Service
The Improved Mobile Telephone Service (IMTS) was a pre- cellular VHF/ UHF radio system which linked to the public telephone network. IMTS was the radiotelephone equivalent of land dial phone service. Introduced in 1964, it replaced Mobile Telephone Service (MTS) and improved on most MTS systems by offering direct-dial rather than connections through a live operator, and full-duplex operation so both parties could talk at the same time. Technical Information The original Bell System US and Canadian mobile telephone system includes three frequency bands, VHF Low (35-44 MHz, 9 channels), VHF High (152-158 MHz, 11 channels in the U.S., 13 channels in Canada), and UHF (454-460 MHz, 12 channels). Alternative names were "Low Band", "High band" and "UHF". In addition to the Bell system ( wireline incumbent) channels, another 7 channels at VHF, and 12 channels at UHF were granted to non-wireline companies designated as "RCCs" (Radio Common Carriers). These RCC channe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
