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Radiotelephone
A RADIOTELEPHONE (or RADIOPHONE) is a communications system for transmission of speech over radio . Radiotelephone systems are not necessarily interconnected with the public "land line" telephone network. "Radiotelephony" means transmission of sound (audio ) by radio, in contrast to radiotelegraphy (transmission of telegraph signals) or video transmission. Where a two-way radio system is arranged for speaking and listening at a mobile station, and where it can be interconnected to the public switched telephone system, the system can provide mobile telephone service. CONTENTS* 1 Design * 1.1 Mode of emission * 1.2 Modes of operation * 2 Features * 2.1 Privacy and selective calling * 3 Uses * 3.1 Conventional telephone use * 3.2 Marine use * 4 Regulations * 5 See also * 6 Notes * 7 References * 8 External links DESIGNMODE OF EMISSIONThe word phone has a long precedent beginning with early US wireless voice systems
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Video
VIDEO is an electronic medium for the recording, copying , playback, broadcasting , and display of moving visual media . Video
Video
was first developed for mechanical television systems, which were quickly replaced by cathode ray tube (CRT) systems which were later replaced by flat panel displays of several types. Video
Video
systems vary in display resolution , aspect ratio , refresh rate , color capabilities and other qualities. Analog and digital variants exist and can be carried on a variety of media, including radio broadcast , magnetic tape , optical discs , computer files , and network streaming
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Electronic Circuit
An ELECTRONIC CIRCUIT is composed of individual electronic components , such as resistors , transistors , capacitors , inductors and diodes , connected by conductive wires or traces through which electric current can flow. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another. Circuits can be constructed of discrete components connected by individual pieces of wire, but today it is much more common to create interconnections by photolithographic techniques on a laminated substrate (a printed circuit board or PCB) and solder the components to these interconnections to create a finished circuit. In an integrated circuit or IC, the components and interconnections are formed on the same substrate, typically a semiconductor such as silicon or (less commonly) gallium arsenide
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Transponder
In telecommunication , a TRANSPONDER can be one of two types of devices. In air navigation or radio frequency identification, a flight transponder is an automated transceiver in an aircraft that emits a coded identifying signal in response to an interrogating received signal. In a communications satellite , a satellite transponder receives signals over a range of uplink frequencies usually from a satellite ground station , amplifies them, and re-transmits them on a different set of downlink frequencies to receivers on Earth, often without changing the content of the received signal or signals. The term is a portmanteau for TRANSmitter-resPONDER. It is variously abbreviated as XPDR, XPNDR, TPDR or TP
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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. CONTENTS* 1 Details * 1.1 Tone Sets * 1.2 Tone Periods * 1.3 Repeat Tone * 2 Implementations * 2.1 Automatic Number Identification * 2.2 Status Gap * 3 Proprietary Implementations * 3.1 As push-to-talk identifier * 4 Trivia * 5 External links DETAILSThe transmission of a selcall code involves the generation and sequencing of a series of predefined, audible tones
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Megahertz
The HERTZ (symbol: Hz) is the derived unit of frequency in the International System of Units
International System of Units
(SI) and is defined as one cycle per second . It is named for Heinrich Rudolf Hertz
Hertz
, the first person to provide conclusive proof of the existence of electromagnetic waves . Hertz
Hertz
are commonly expressed in multiples : kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Some of the unit's most common uses are in the description of sine waves and musical tones , particularly those used in radio - and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven
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CTCSS
In telecommunications , CONTINUOUS TONE-CODED SQUELCH SYSTEM or CTCSS is a circuit that is used to reduce the annoyance of listening to other users on a shared two-way radio communications channel. It is sometimes referred to as TONE SQUELCH or SUB-CHANNEL since it has the effect of creating multiple virtual channels which are all using the same radio frequency . It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency (called co-channel users), CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS. The CTCSS feature does not offer any security. A receiver with just a carrier or noise squelch unmutes for any sufficiently strong signal; in CTCSS mode it unmutes only when the signal also carries the correct sub-audible audio tone
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Bandwidth (signal Processing)
BANDWIDTH is the difference between the upper and lower frequencies in a continuous set of frequencies. It is typically measured in hertz , and may sometimes refer to passband bandwidth, sometimes to baseband bandwidth, depending on context. PASSBAND BANDWIDTH is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter , a communication channel , or a signal spectrum . In the case of a low-pass filter or baseband signal , the bandwidth is equal to its upper cutoff frequency. Bandwidth in hertz is a central concept in many fields, including electronics , information theory , digital communications , radio communications , signal processing , and spectroscopy and is one of the determinants of the capacity of a given communication channel. A key characteristic of bandwidth is that any band of a given width can carry the same amount of information , regardless of where that band is located in the frequency spectrum
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Audio Signal
An AUDIO SIGNAL is a representation of sound , typically as an electrical voltage . Audio signals have frequencies in the audio frequency range of roughly 20 to 20,000 Hz (the limits of human hearing ). Audio signals may be synthesized directly, or may originate at a transducer such as a microphone , musical instrument pickup , phonograph cartridge, or tape head . Loudspeakers or headphones convert an electrical audio signal into sound. Digital representations of audio signals exist in a variety of formats. An AUDIO CHANNEL or AUDIO TRACK is an audio signal communications channel in a storage device , used in operations such as multi-track recording and sound reinforcement . CONTENTS * 1 Signal flow * 2 Parameters * 3 Digital equivalent * 4 See also * 5 References * 6 External links SIGNAL FLOWSignal flow is the path an audio signal will take from source (microphone ) to the speaker or recording device
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Switch
In electrical engineering , a SWITCH is an electrical component that can "make" or "break" an electrical circuit , interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving object such as a door, or may be operated by some sensing element for pressure, temperature or flow
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Ionosphere
The IONOSPHERE (/aɪˈɒnəˌsfɪər/ ) is a region of Earth's upper atmosphere , from about 60 km (37 mi) to 1,000 km (620 mi) altitude, and includes the thermosphere and parts of the mesosphere and exosphere . It is ionized by solar radiation, plays an important part 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 the Earth
Earth

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Matchbox
A MATCHBOX is a box made of cardboard or thin wood and designed to hold matches . It usually has a coarse striking surface on one edge for lighting the matches contained inside. Sivakasi , a city located in South India supplies matchboxes throughout India and exports them to other countries
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Microphone
A MICROPHONE, colloquially nicknamed MIC or MIKE (/ˈmaɪk/ ), is a transducer that converts sound into an electrical signal . Microphones are used in many applications such as telephones , hearing aids , public address systems for concert halls and public events, motion picture production, live and recorded audio engineering , sound recording , two-way radios , megaphones , radio and television broadcasting, and in computers for recording voice, speech recognition , VoIP , and for non-acoustic purposes such as ultrasonic sensors or knock sensors . Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone , which uses a coil of wire suspended in a magnetic field; the condenser microphone , which uses the vibrating diaphragm as a capacitor plate, and the piezoelectric microphone , which uses a crystal of piezoelectric material
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Watt
The WATT (symbol: W) is a unit of power . In the International System of Units (SI) it is defined as a derived unit of 1 joule per second , and is used to quantify the rate of energy transfer . In dimensional analysis it is described by M L 2 T 3 {displaystyle {mathsf {ML}}^{2}{mathsf {T}}^{-3}} . CONTENTS * 1 Examples * 2 Origin and adoption as an SI unit * 3 Multiples * 3.1 Femtowatt * 3.2 Picowatt * 3.3 Nanowatt * 3.4 Microwatt * 3.5 Milliwatt * 3.6 Kilowatt * 3.7 Megawatt * 3.8 Gigawatt * 3.9 Terawatt * 3.10 Petawatt * 4 Conventions in the electric power industry * 5 Radio
Radio
transmission * 6 Distinction between watts and watt-hours * 7 See also * 8 Notes * 9 References * 10 External links EXAMPLESWhen an object's velocity is held constant at one meter per second against a constant opposing force of one newton , the rate at which work is done is 1 watt
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Frequency
FREQUENCY is the number of occurrences of a repeating event per unit of time . It is also referred to as TEMPORAL FREQUENCY, which emphasizes the contrast to spatial frequency and angular frequency . The PERIOD is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (that is, 60 seconds divided by 120 beats ). Frequency
Frequency
is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio (sound ) signals, radio waves , and light
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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 sufficiently strong desired input signal . Squelch is widely used in two-way radios and radio scanners to suppress the sound of channel noise when the radio is not receiving a transmission. Squelch can be 'opened', which allows all signals entering the receiver to be heard. This can be useful when trying to hear distant, or otherwise weak signals (also known as DXing ). CONTENTS * 1 Carrier squelch * 2 Tone squelch and selective calling * 2.1 CTCSS * 2.2 SelCall * 2.3 DCS * 2.4 XTCSS * 3 Uses * 4 See also * 5 Notes CARRIER SQUELCHA 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
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