|
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] |
Amateur Radio
Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency, emergency communications. The term ''"radio amateur"'' is used to specify ''"a duly authorized person interested in radioelectric practice with a purely personal aim and without wikt:pecuniary, pecuniary interest"'' (either direct monetary or other similar reward); and to differentiate it from commercial broadcasting, public safety (police and fire), or two-way radio professional services (maritime, aviation, taxis, etc.). The amateur radio service (''amateur service'' and ''amateur-satellite service'') is established by the International Telecommunication Union (ITU) through their recommended radio regulations. National governments regulate technical and operational characteristics of transmissions and issue individual station li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sine Wave
A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic function, periodic wave whose waveform (shape) is the trigonometric function, trigonometric sine, sine function. In mechanics, as a linear motion over time, this is ''simple harmonic motion''; as rotation, it corresponds to ''uniform circular motion''. Sine waves occur often in physics, including wind waves, sound waves, and light waves, such as monochromatic radiation. In engineering, signal processing, and mathematics, Fourier analysis decomposes general functions into a sum of sine waves of various frequencies, relative phases, and magnitudes. When any two sine waves of the same frequency (but arbitrary phase (waves), phase) are linear combination, linearly combined, the result is another sine wave of the same frequency; this property is unique among periodic waves. Conversely, if some phase is chosen as a zero reference, a sine wave of arbitrary phase can be written as the linear combination of two sine wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Demodulation
Demodulation is the process of extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave. There are many types of modulation, and there are many types of demodulators. The signal output from a demodulator may represent sound (an analog audio signal), images (an analog video signal) or binary data (a digital signal). These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. For example, in a modem, which is a contraction of the terms modulator/demodulator, a demodulator is used to extract a serial digital data stream from a carrier signal which is used to carry it through a telephone line, coaxial cable, or optical fiber. History Demodulation was first used in radio receivers. In the wireless telegraphy radio systems us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Video Signal
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) systems, which, in turn, were replaced by flat-panel displays of several types. 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 broadcasts, magnetic tape, optical discs, computer files, and network streaming. Etymology The word ''video'' comes from the Latin verb ''video,'' meaning to see or ''videre''. And as a noun, "that which is displayed on a (television) screen," History Analog video Video developed from facsimile systems developed in the mid-19th century. Early mechanical video scanners, such as the Nipkow disk, were patented as early as 1884, however, it took sev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carrier Signal
In telecommunications, a carrier wave, carrier signal, or just carrier, is a periodic waveform (usually sinusoidal) that conveys information through a process called ''modulation''. One or more of the wave's properties, such as amplitude or frequency, are modified by an information bearing signal, called the ''message signal'' or ''modulation signal''. The carrier frequency is usually much higher than the message signal frequency; this is because it is usually impractical to transmit signals with low frequencies over long distances (due to attenuation). The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as in a cable television system). The term originated in radio communication, where the carrier wave creates the waves which carry the information (modul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Continuous Wave
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle accelerator having a continuous output, as opposed to a pulsed output. By extension, the term ''continuous wave'' also refers to an early method of radio transmission in which a sinusoidal carrier wave is switched on and off. This is more precisely called interrupted continuous wave (ICW). Information is carried in the varying duration of the on and off periods of the signal, for example by Morse code in early radio. In early wireless telegraphy radio transmission, CW waves were also known as "undamped waves", to distinguish this method from damped wave signals produced by earlier ''spark gap'' type transmitters. Radio Transmissions before CW Very early radio transmitters used a spark gap to produce radio-frequency oscillations i ... [...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] |
Telecommunications
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of transmission may be divided into communication channels for multiplexing, allowing for a single medium to transmit several concurrent Session (computer science), communication sessions. Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the electrical telegraph, telegraph, telephone, television, and radio. Early telecommunication networks used metal wires as the medium for transmitting signals. These networks were used for telegraphy and telephony for many decades. In the first decade of the 20th century, a revolution in wireless communication began with breakthroughs including those made in radio communications by Guglielmo Marconi, who won the 1909 Nobel Prize in Physics. Othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronics
Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield of physics and electrical engineering which uses Passivity (engineering), active devices such as transistors, diodes, and integrated circuits to control and amplify the flow of electric current and to convert it from one form to another, such as from alternating current (AC) to direct current (DC) or from analog signal, analog signals to digital signal, digital signals. Electronic devices have significantly influenced the development of many aspects of modern society, such as telecommunications, entertainment, education, health care, industry, and security. The main driving force behind the advancement of electronics is the semiconductor industry, which continually produces ever-more sophisticated electronic devices and circuits in respo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
Modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was established by François Bayrou to succeed the Union for French Democracy (UDF) and contest the 2007 legislative election, after his strong showing in the 2007 presidential election. Initially named the Democratic Party (''Parti démocrate''), the party was renamed "Democratic Movement", because there was already a small Democratic Party in France. MoDem secured an agreement with La République En Marche! (LRM) — later Renaissance (RE) — in the 2017 legislative election after Bayrou had endorsed the candidacy of Emmanuel Macron in February. The two parties have since been in alliance, as of late named Ensemble. The party's founder and leader Bayrou has served as Prime Minister of France since December 2024. History Background MoDem tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
