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 (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 0–300mV level is reserved for auxiliary signals and 300–1000mV is reserved for video information. In monochrome TV, 300mV (or sometimes 350mV) corresponds to black and 1000mV corresponds to white.( In color TV depending on the system used, superimposed color subcarrier may have slightly higher values.)
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 level and when there is a modulating video frequency (VF) signal the level of IF is lower. Since the level when transmitting a black scene is lower than the white level, the level of carrier when transmitting black is higher than the level of carrier when transmitting white.
Carrier modulated by 1 Volt VF. (1 volt corresponds to white.) In this illustration, the carrier frequency is much lower than would practically be used, relative to the video signal frequency.
The modulators are set[1] to yield 10% or 12.5% of carrier level when modulated by 1V signal (which corresponds to white scene) This percentage is known as residual carrier.
An example of the modulated carrier is shown in the accompanying figure. In this figure, the level of the modulating VF signal is 1 volt (white level). 1V yields residual carrier (10%). Short duration full carrier (100%) is the sync pulse and the 73% is so called back porch (black level). The duration of the signal is approximately 100 μs.
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 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.
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.
Chrominance is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal. Chrominance is usually represented as two color-difference components: U = B′ − Y′ (blue − luma) and V = R′ − Y′ (red − luma). Each of these difference components may have scale factors and offsets applied to it, as specified by the applicable video standard.
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation 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. The carrier is higher in frequency than the modulation signal. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is demodulated to extract the information bearing modulation signal.
The National Television System Committee (NTSC) developed the analog television format encoding system that was introduced in North America in 1954 and stayed in use until digital conversion. It is one of three major analog format television standards, the others being PAL and SECAM. All the countries using NTSC are currently in the process of conversion, or have already converted to the ATSC standard, or to DVB, ISDB or DTMB.
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver.
Pulse-amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal. Demodulation is performed by detecting the amplitude level of the carrier at every single period.
Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). A laser operated in this way is sometimes referred to as a femtosecond laser, for example, in modern refractive surgery. The basis of the technique is to induce a fixed phase relationship between the longitudinal modes of the laser's resonant cavity. Constructive interference between these modes can cause the laser light to be produced as a train of pulses. The laser is then said to be "phase-locked" or "mode-locked".
Video modulation is a strategy of transmitting video signal in the field of radio modulation and television technology. This strategy enables the video signal to be transmitted more efficiently through long distances. In general, video modulation means that a higher frequency carrier wave is modified according to the original video signal. In this way, carrier wave contains the information in the video signal. Then, the carrier will "carry" the information in the form of radio frequency (RF) signal. When carrier reaches its destination, the video signal is extracted from the carrier by decoding. In other words, the video signal is first combined with a higher frequency carrier wave so that carrier wave contains the information in video signal. The combined signal is called radio-frequency signal. At the end of this transmitting system, the RF signals stream from a light sensor and hence, the receivers can obtain the initial data in the original video signal.
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 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.
In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or "symbols per second". In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in "bits per second".
A Nyquist filter is an electronic filter used in TV receivers to equalize the video characteristics. The filter is named after the Swedish–US engineer Harry Nyquist (1889–1976).
A white clipper is a circuit in professional video products that limits the maximum amplitude of the luminance part of the analogue video signal to 1 volt. It is essential for both analogue recording and transmission of video material.
The following outline is provided as an overview of and topical guide to television broadcasting:
Differential phase is a kind of linearity distortion which affects the color hue in TV broadcasting.
The output power of a TV transmitter is the electric power applied to antenna system. There are two definitions: nominal 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.
Zero reference pulse or Zero pulse is an artificially produced pulse in a professional television receiver imitating no radio frequency case for modulation index measurements in analogue TV transmitters.
A digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog signal, which represents continuous values; at any given time it represents a real number within a continuous range of values.
CCIR System A was the 405-line analog broadcast television system adopted in the UK and Ireland. System A service started in 1936 and was discontinued in 1985.
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