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Output Power Of An Analog TV Transmitter
The output power of a TV transmitter is the electric power applied to antenna system. There are two definitions: nominal (or peak) and thermal. Analogue television systems put about 70% to 90% of the transmitters power into the sync pulses. The remainder of the transmitter's power goes into transmitting the video's higher frequencies and the FM audio carrier. Digital television modulation systems are about 30% more efficient than analogue modulation systems overall. Analogue vs digital Analogue * The large amount of energy that Sync Pulses use is largely independent of the measurement system and efficiency of the analogue TV transmitter (as most analogue transmitters have on average 75% efficiency). * The transmission of FM audio (including Stereo subcarriers) is only overall the 3rd largest consumer of TV transmitter power. * Power consumption (most to least) : Sync Pulses, High Frequency Video, FM Audio, Vestigial AM Digital * DVB like transmission systems, with their gro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TV Transmitter
A television transmitter is a transmitter that is used for terrestrial (over-the-air) television broadcasting. It is an electronic device that radiates radio waves that carry a video signal representing moving images, along with a synchronized audio channel, which is received by television receivers ('televisions' or 'TVs') belonging to a public audience, which display the image on a screen. A television transmitter, together with the broadcast studio which originates the content, is called a television station. Television transmitters must be licensed by governments, and are restricted to a certain frequency channel and power level. They transmit on frequency channels in the VHF and UHF bands. Since radio waves of these frequencies travel by line of sight, they are limited by the horizon to reception distances of 40–60 miles depending on the height of transmitter station. Television transmitters use one of two different technologies: ''analog'', in which the picture and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude Modulation
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) 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, 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 sidebands and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Television Technology
Large-screen television technology (colloquially big-screen TV) developed rapidly in the late 1990s and 2000s. Prior to the development of thin-screen technologies, rear-projection television was standard for larger displays, and jumbotron, a non-projection video display technology, was used at stadiums and concerts. Various thin-screen technologies are being developed, but only liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been publicly released. Recent technologies like organic light-emitting diode (OLED) as well as not-yet-released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are in development to replace earlier flat-screen technologies in picture quality. Large-screen technologies have almost completely displaced cathode-ray tubes (CRT) in television sales due to the necessary bulkiness of cathode-ray tubes. The diagonal screen size of a CRT television is limited to abou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CCIR System B
CCIR System B (originally known as the "Gerber Standard") was the 625-line VHF analog broadcast television system which at its peak was the system used in most countries. It's usually associated with CCIR System G for UHF broadcasts. It is mostly replaced across Western Europe, part of Asia and Africa by digital broadcasting. Specifications The system was developed for VHF (also known as VHF-3) band (part of RF band lower than 300 MHz.) Some of the most important specs are listed below. A frame is the total picture. The frame rate is the number of pictures displayed in one second. But each frame is actually scanned twice interleaving odd and even lines. Each scan is known as a field (odd and even fields.) So field rate is twice the frame rate. In each frame there are 625 lines (or 312.5 lines in a field.) So line rate (line frequency) is 625 times the frame frequency or 625•25=15625 Hz. The video bandwidth is 5.0 MHz. The video signal modulates the carrier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microwave Power Meter
A microwave power meter is an instrument which measures the electrical power at microwave frequencies typically in the range 100 MHz to 40 GHz. Usually a microwave power meter will consist of a measuring head which contains the actual power sensing element, connected via a cable to the meter proper, which displays the power reading. The head may be referred to as a power sensor or mount. Different power sensors can be used for different frequencies or power levels. Historically the means of operation in most power sensor and meter combinations was that the sensor would convert the microwave power into an analogue voltage which would be read by the meter and converted into a power reading. Several modern power sensor heads contain electronics to create a digital output and can be plugged via USB into a PC which acts as the power meter. Microwave power meters have a wide bandwidth—they are not frequency-selective. To measure the power of a specific frequency component i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Residual Carrier
In analogue TV technology, residual carrier is the ratio of carrier level which is modulated by the maximum video signal to the unmodulated carrier level. Video signal Video signal (VF) or more formally composite video signal (CVS) is the signal which carries the video information as well as some auxiliary signals for synchronizing. In all systems 0–300 mV level is reserved for auxiliary signals and 300–1000 mV is reserved for video information. In monochrome TV, 300 mV (or sometimes 350 mV) corresponds to black and 1000 mV corresponds to white.( In color TV depending on the system used, superimposed color subcarrier may have slightly higher values.) Modulation The signal modulates a carrier by vestigal sideband modulation (a version of amplitude modulation), where an increase in the video modulating signal produces a decrease in the carrier amplitude, called "negative modulation". When there is no modulating signal, the carrier has the full l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RF Signal
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies; these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range. Electric current Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or lower audio frequency alternating current, such as the 50 or 60 Hz current used in electrical power distribution. * Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). This is the basis of radio technology. * RF current does not penetrate deeply into electrical condu ... [...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 broadcast, magnetic tape, optical discs, computer files, and network streaming. History Analog video Video technology was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) television systems, but several new technologies for video display devices have since been invented. Video was originally exclusively a live technology. Charles Ginsburg led an Ampex research team developing one of the first practical video ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Constant
In physics and engineering, the time constant, usually denoted by the Greek letter (tau), is the parameter characterizing the response to a step input of a first-order, linear time-invariant (LTI) system.Concretely, a first-order LTI system is a system that can be modeled by a single first order differential equation in time. Examples include the simplest single-stage electrical RC circuits and RL circuits. The time constant is the main characteristic unit of a first-order LTI system. In the time domain, the usual choice to explore the time response is through the step response to a step input, or the impulse response to a Dirac delta function input. In the frequency domain (for example, looking at the Fourier transform of the step response, or using an input that is a simple sinusoidal function of time) the time constant also determines the bandwidth of a first-order time-invariant system, that is, the frequency at which the output signal power drops to half the value it has at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electric Power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively. A common misconception is that electric power is bought and sold, but actually electrical energy is bought and sold. For example, electricity is sold to consumers in kilowatt-hours (kilowatts multiplied by hours), because energy is power multiplied by time. Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes (as domestic mains electricity) by the electric power industry through an electrical grid. Electric power can be delivered over long distances by transmission lines and used for applications such as motion, light or heat with high efficiency. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Root Mean Square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the squares) of the set. The RMS is also known as the quadratic mean (denoted M_2) and is a particular case of the generalized mean. The RMS of a continuously varying function (denoted f_\mathrm) can be defined in terms of an integral of the squares of the instantaneous values during a cycle. For alternating electric current, RMS is equal to the value of the constant direct current that would produce the same power dissipation in a resistive load. In estimation theory, the root-mean-square deviation of an estimator is a measure of the imperfection of the fit of the estimator to the data. Definition The RMS value of a set of values (or a continuous-time waveform) is the square root of the arithmetic mean of the squares of the values, or th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sync Pulse
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal. Analog signals vary over a continuous range of possible values which means that electronic noise and interference may be introduced. Thus with analog, a moderately weak signal becomes snowy and subject to interference. In contrast, picture quality from a digital television (DTV) signal remains good until the signal level drops below a threshold where reception is no longer possible or becomes intermittent. Analog television may be wireless (terrestrial television and satellite television) or can be distributed over a cable network as cable television. All broadcast television systems used analog signals before the arrival of DTV. Motivated by the lower bandwidth requirements of compressed digital signals, beginning in the 2000 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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