![OTVbelweder-front](https://upload.wikimedia.org/wikipedia/commons/f/f6/OTVbelweder-front.jpg)
Analog television is the original
television
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
technology that uses
analog signal
An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies c ...
s to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
,
phase and frequency of an analog signal.
Analog signals vary over a continuous range of possible values which means that
electronic noise
In electronics, noise is an unwanted disturbance in an electrical signal.
Noise generated by electronic devices varies greatly as it is produced by several different effects.
In particular, noise is inherent in physics, and central to the ...
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
Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advanc ...
(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
Terrestrial television or over-the-air television (OTA) is a type of television broadcasting in which the signal transmission occurs via radio waves from the terrestrial (Earth-based) transmitter of a TV station to a TV receiver having an ant ...
and
satellite television
Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location. The signals are received via an outdoor parabolic antenna comm ...
) or can be distributed over a cable network as
cable television
Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with broa ...
.
All
broadcast television system
Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
Analog television systems were standardized by ...
s used analog signals before the arrival of DTV. Motivated by the lower bandwidth requirements of
compressed digital signals, beginning in the 2000s, a
digital television transition is proceeding in most countries of the world, with different deadlines for the cessation of analog broadcasts.
Development
The earliest systems of analog television were
mechanical television
Mechanical television or mechanical scan television is a television system that relies on a mechanical scanning device, such as a rotating disk with holes in it or a rotating mirror drum, to scan the scene and generate the video signal, and a si ...
systems that used spinning disks with patterns of holes punched into the disc to scan an image. A similar disk reconstructed the image at the receiver. Synchronization of the receiver disc rotation was handled through sync pulses broadcast with the image information. Camera systems used similar spinning discs and required intensely bright illumination of the subject for the light detector to work. The reproduced images from these mechanical systems were dim, very low resolution and flickered severely.
Analog television did not really begin as an industry until the development of the
cathode-ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictur ...
(CRT), which uses a focused electron beam to trace lines across a
phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...
coated surface. The electron beam could be swept across the screen much faster than any mechanical disc system, allowing for more closely spaced scan lines and much higher image resolution. Also, far less maintenance was required of an all-electronic system compared to a mechanical spinning disc system. All-electronic systems became popular with households after
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
.
Standards
Broadcasters of analog television encode their signal using different systems. The official systems of transmission were defined by the
ITU
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
in 1961 as: A, B, C, D, E, F, G, H, I, K, K1, L, M and N. These systems determine the number of scan lines, frame rate, channel width, video bandwidth, video-audio separation, and so on. A color encoding scheme (
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
,
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
, or
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
) could be added to the base monochrome signal. Using
RF modulation
An RF modulator (or radio frequency modulator) is an electronic device whose input is a baseband signal which is used to modulate a radio frequency source.
RF modulators are used to convert signals from devices such as media players, VCRs a ...
the signal is then modulated onto a
very high frequency
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF ...
(VHF) or
ultra high frequency
Ultra high frequency (UHF) is the ITU designation for radio frequency, radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one ten ...
(UHF)
carrier wave
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a ...
. Each frame of a television image is composed of
scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernible ...
s drawn on the screen. The lines are of varying brightness; the whole set of lines is drawn quickly enough that the human eye perceives it as one image. The process repeats and next sequential frame is displayed, allowing the depiction of motion. The analog television signal contains timing and synchronization information so that the receiver can reconstruct a two-dimensional moving image from a one-dimensional time-varying signal.
The first
commercial television
Commercial broadcasting (also called private broadcasting) is the broadcasting of television programs and radio programming by privately owned corporate media, as opposed to state sponsorship. It was the United States′ first model of radio (an ...
systems were
black-and-white
Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey.
Media
The history of various visual media began with black and white, and as technology improved, altered to color. ...
; the beginning of
color television
Color television or Colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white t ...
was in the 1950s.
A practical television system needs to take
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
,
chrominance
Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying luma signal (or Y' for short). Chrominance is usually represente ...
(in a color system), synchronization (horizontal and vertical), and
audio signal
An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals, or a series of binary numbers for digital signals. Audio signals have frequencies in the audio frequency range of r ...
s, and broadcast them over a radio transmission. The transmission system must include a means of
television channel
A television channel is a terrestrial frequency or virtual number over which a television station or television network is distributed. For example, in North America, "channel 2" refers to the terrestrial or cable band of 54 to 60 MHz, with ...
selection.
Analog
broadcast television systems
Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
Analog television systems were standardized by ...
come in a variety of frame rates and resolutions. Further differences exist in the frequency and modulation of the audio carrier. The monochrome combinations still existing in the 1950s were standardized by the
International Telecommunication Union
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
(ITU) as capital letters A through N. When color television was introduced, the chrominance information was added to the monochrome signals in a way that black and white televisions ignore. In this way
backward compatibility
Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...
was achieved.
There are three standards for the way the additional color information can be encoded and transmitted. The first was the American
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
system. The European and Australian
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
and the French and former Soviet Union
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
standards were developed later and attempt to cure certain defects of the NTSC system. PAL's color encoding is similar to the NTSC systems. SECAM, though, uses a different modulation approach than PAL or NTSC. PAL had a late evolution called
PALplus
PALplus (or ''PAL+'') is an analogue television broadcasting system aimed to improve and enhance the PAL format by allowing 16:9 (or 1.77:1) aspect ratio broadcasts, while remaining compatible with existing television receivers, defined by Internat ...
, allowing widescreen broadcasts while remaining fully compatible with existing PAL equipment.
In principle, all three color encoding systems can be used with any scan line/frame rate combination. Therefore, in order to describe a given signal completely, it's necessary to quote the color system and the broadcast standard as a capital letter. For example, the United States, Canada, Mexico and South Korea use
NTSC-M
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
, Japan uses
NTSC-J
NTSC-J is the informal designation for the analogue television standard used in Japan. The system is based on the US NTSC (NTSC-M) standard with minor differences. While NTSC-M is an official CCIR and FCCNational Television System Committee (1 ...
, the UK uses
PAL-I, France uses
SECAM-L, much of Western Europe and Australia use
PAL-B/
G, most of Eastern Europe uses
SECAM-D/
K or PAL-D/K and so on.
However, not all of these possible combinations actually exist. NTSC is currently only used with system M, even though there were experiments with
NTSC-A (
405 line) in the UK and
NTSC-N (625 line) in part of South America. PAL is used with a variety of 625-line standards (B, G, D, K, I, N) but also with the North American 525-line standard, accordingly named
PAL-M
PAL-M is the analogue TV system used in Brazil since 19 February 1972. At that time, Brazil was the first South American country to broadcast in colour. Colour TV broadcast began on 19 February 1972, when the TV networks Globo and Bandeirantes t ...
. Likewise, SECAM is used with a variety of 625-line standards.
For this reason, many people refer to any 625/25 type signal as ''PAL'' and to any 525/30 signal as ''NTSC'', even when referring to digital signals; for example, on
DVD-Video
DVD-Video is a consumer video format used to store digital video on DVD discs. DVD-Video was the dominant consumer home video format in Asia, North America, Europe, and Australia in the 2000s until it was supplanted by the high-definition Blu-r ...
, which does not contain any analog color encoding, and thus no PAL or NTSC signals at all.
Although a number of different broadcast television systems were in use worldwide, the same principles of operation apply.
Displaying an image
![Raster-scan](https://upload.wikimedia.org/wikipedia/commons/7/72/Raster-scan.svg)
A
cathode-ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictur ...
(CRT) television displays an image by scanning a beam of
electrons
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
across the screen in a pattern of horizontal lines known as a
raster
Raster may refer to:
* Raster graphics, graphical techniques using arrays of pixel values
* Raster graphics editor, a computer program
* Raster scan, the pattern of image readout, transmission, storage, and reconstruction in television and compu ...
. At the end of each line, the beam returns to the start of the next line; at the end of the last line, the beam returns to the beginning of the first line at the top of the screen. As it passes each point, the intensity of the beam is varied, varying the
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
of that point. A
color television
Color television or Colour television is a television transmission technology that includes color information for the picture, so the video image can be displayed in color on the television set. It improves on the monochrome or black-and-white t ...
system is similar except there are three beams that scan together and an additional signal known as chrominance controls the color of the spot.
When analog television was developed, no affordable technology for storing video signals existed; the luminance signal had to be generated and transmitted at the same time at which it is displayed on the CRT. It was therefore essential to keep the raster scanning in the camera (or other device for producing the signal) in exact
synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
with the scanning in the television.
The physics of the CRT require that a finite time interval be allowed for the spot to move back to the start of the next line (''horizontal retrace'') or the start of the screen (''vertical retrace''). The timing of the luminance signal must allow for this.
The human eye has a characteristic called
phi phenomenon
The term phi phenomenon is used in a narrow sense for an apparent motion that is observed if two nearby optical stimuli are presented in alternation with a relatively high frequency. In contrast to beta movement, seen at lower frequencies, the st ...
. Quickly displaying successive scan images creates the illusion of smooth motion. Flickering of the image can be partially solved using a long persistence phosphor coating on the CRT so that successive images fade slowly. However, slow phosphor has the negative side-effect of causing image smearing and blurring when there is rapid on-screen motion occurring.
The maximum
frame rate
Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images (frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be ca ...
depends on the
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
of the electronics and the transmission system, and the number of horizontal scan lines in the image. A frame rate of 25 or 30
hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
is a satisfactory compromise, while the process of
interlacing two
video field
In video, a field is one of the many still images which are displayed sequentially to create the impression of motion on the screen. Two fields comprise one video frame. When the fields are displayed on a video monitor they are "interlaced" so th ...
s of the picture per
frame
A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent.
Frame and FRAME may also refer to:
Physical objects
In building construction
*Framing (con ...
is used to build the image. This process doubles the apparent number of video frames per second and further reduces flicker and other defects in transmission.
Receiving signals
The television system for each country will specify a number of television channels within the UHF or VHF frequency ranges. A channel actually consists of two signals: the picture information is transmitted using
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 ...
on one carrier frequency, and the sound is transmitted with
frequency modulation
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 Run-length limited#FM: .280. ...
at a frequency at a fixed offset (typically 4.5 to 6 MHz) from the picture signal.
The channel frequencies chosen represent a compromise between allowing enough
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
for video (and hence satisfactory picture resolution), and allowing enough channels to be packed into the available frequency band. In practice a technique called
vestigial sideband
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 m ...
is used to reduce the channel spacing, which would be nearly twice the video bandwidth if pure AM was used.
Signal reception is invariably done via a
superheterodyne receiver
A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carr ...
: the first stage is a ''tuner'' which selects a television channel and frequency-shifts it to a fixed
intermediate frequency
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sign ...
(IF). The signal
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost the v ...
performs amplification to the IF stages from the microvolt range to fractions of a volt.
Extracting the sound
At this point the IF signal consists of a video
carrier signal
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a ...
at one frequency and the sound carrier at a fixed offset in frequency. A
demodulator
Demodulation is 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 ...
recovers the video signal. Also at the output of the same demodulator is a new frequency modulated sound carrier at the offset frequency. In some sets made before 1948, this was filtered out, and the sound IF of about 22 MHz was sent to an FM demodulator to recover the basic sound signal. In newer sets, this new carrier at the offset frequency was allowed to remain as ''intercarrier sound'', and it was sent to an FM demodulator to recover the basic sound signal. One particular advantage of intercarrier sound is that when the front panel fine tuning knob is adjusted, the sound
carrier frequency
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a m ...
does not change with the tuning, but stays at the above-mentioned offset frequency. Consequently, it is easier to tune the picture without losing the sound.
So the FM sound carrier is then demodulated, amplified, and used to drive a loudspeaker. Until the advent of the
NICAM
Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.Croll, M.G., Osborne, D.W. and Spi ...
and
MTS systems, television sound transmissions were monophonic.
Structure of a video signal
The video carrier is demodulated to give a
composite video
Composite video is an analog video signal format that carries standard-definition video (typically at 525 lines or 625 lines) as a single channel. Video information is encoded on one channel, unlike the higher-quality S-Video (two channels) a ...
signal containing luminance, chrominance and synchronization signals. The result is identical to the composite video format used by analog video devices such as
VCRs
A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recordin ...
or
CCTV cameras
A closed-circuit television camera can produce images or recordings for surveillance or other private purposes. Cameras can be either video cameras, or digital stills cameras. Walter Bruch was the inventor of the CCTV camera. The main purpose ...
. To ensure good linearity and thus fidelity, consistent with affordable manufacturing costs of transmitters and receivers, the video carrier is never modulated to the extent that it is shut off altogether. When intercarrier sound was introduced later in 1948, not completely shutting off the carrier had the side effect of allowing intercarrier sound to be economically implemented.
![An interlaced PAL frame with 20ms duration](https://upload.wikimedia.org/wikipedia/commons/6/6e/An_interlaced_PAL_frame_with_20ms_duration.jpg)
Each line of the displayed image is transmitted using a signal as shown above. The same basic format (with minor differences mainly related to timing and the encoding of color) is used for PAL,
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
, and SECAM television systems. A monochrome signal is identical to a color one, with the exception that the elements shown in color in the diagram (the
colorburst
Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porc ...
, and the chrominance signal) are not present.
![Videosignal porch](https://upload.wikimedia.org/wikipedia/commons/3/32/Videosignal_porch.jpg)
The ''front porch'' is a brief (about 1.5
microsecond
A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available.
A microsecond is equal to 1000 n ...
) period inserted between the end of each transmitted line of picture and the leading edge of the next line's
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 s ...
. Its purpose was to allow
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
levels to stabilise in older televisions, preventing interference between picture lines. The ''front porch'' is the first component of the
horizontal blanking interval
Horizontal blanking interval refers to a part of the process of displaying images on a computer monitor or television screen via raster scanning. CRT screens display images by moving beams of electrons very quickly across the screen. Once the be ...
which also contains the horizontal sync pulse and the ''back porch''.
The ''back porch'' is the portion of each scan line between the end (rising edge) of the horizontal sync pulse and the start of active video. It is used to restore the black level (300 mV) reference in analog video. In signal processing terms, it compensates for the
fall time
In electronics, fall time (pulse decay time) t_f is the time taken for the amplitude of a pulse to decrease (fall) from a specified value (usually 90% of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10 ...
and
settling time
In control theory the settling time of a dynamical system such as an amplifier or other output device is the time elapsed from the application of an ideal instantaneous step input to the time at which the amplifier output has entered and remained ...
following the sync pulse.
In color television systems such as PAL and NTSC, this period also includes the
colorburst
Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porc ...
signal. In the SECAM system, it contains the reference subcarrier for each consecutive color difference signal in order to set the zero-color reference.
In some professional systems, particularly
satellite link
Satellite link is – according to ''article 1.113'' of the International Telecommunication Union's (ITU) ITU Radio Regulations (RR)ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.113, definition: ''satellite link'' ...
s between locations, the digital audio is embedded within the line sync pulses of the video signal, to save the cost of renting a second channel. The name for this proprietary system is
Sound-in-Syncs
Sound-in-Syncs is a method of multiplexing sound and video signals into a channel designed to carry video, in which data representing the sound is inserted into the line synchronising pulse of an analogue television waveform. This is used on point ...
.
Monochrome video signal extraction
The luminance component of a composite video signal varies between 0 V and approximately 0.7 V above the ''black'' level. In the NTSC system, there is a ''blanking'' signal level used during the front porch and back porch, and a ''black'' signal level 75 mV above it; in PAL and SECAM these are identical.
In a monochrome receiver, the luminance signal is amplified to drive the
control grid
The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consists ...
in the
electron gun
An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode-ray tubes (CRTs), used in nearly ...
of the CRT. This changes the intensity of the electron beam and therefore the brightness of the spot being scanned. Brightness and contrast controls determine the DC shift and amplification, respectively.
Color video signal extraction
![Burnt-in timecode](https://upload.wikimedia.org/wikipedia/commons/f/f4/Burnt-in_timecode.jpg)
U and V signals
A color signal conveys picture information for each of the
red, green, and blue components of an image. However, these are not simply transmitted as three separate signals, because: such a signal would not be compatible with monochrome receivers, an important consideration when color broadcasting was first introduced. It would also occupy three times the bandwidth of existing television, requiring a decrease in the number of television channels available.
Instead, the RGB signals are converted into
YUV
YUV is a color model typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, compared to a "direct" RGB-representation. H ...
form, where the Y signal represents the
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
of the colors in the image. Because the rendering of colors in this way is the goal of both
monochrome
A monochrome or monochromatic image, object or palette is composed of one color (or values of one color). Images using only shades of grey are called grayscale (typically digital) or black-and-white (typically analog). In physics, monochrom ...
film and television systems, the Y signal is ideal for transmission as the luminance signal. This ensures a monochrome receiver will display a correct picture in black and white, where a given color is reproduced by a shade of gray that correctly reflects how light or dark the original color is.
The U and V signals are ''color difference'' signals. The U signal is the difference between the B signal and the Y signal, also known as B minus Y (B-Y), and the V signal is the difference between the R signal and the Y signal, also known as R minus Y (R-Y). The U signal then represents how purplish-blue or its complementary color, yellowish-green, the color is, and the V signal how purplish-red or it's complementary, greenish-cyan, it is. The advantage of this scheme is that the U and V signals are zero when the picture has no color content. Since the human eye is more sensitive to detail in luminance than in color, the U and V signals can be transmitted with reduced bandwidth with acceptable results.
In the receiver, a single demodulator can extract an additive combination of U plus V. An example is the X demodulator used in the X/Z demodulation system. In that same system, a second demodulator, the Z demodulator, also extracts an additive combination of U plus V, but in a different ratio. The X and Z color difference signals are further matrixed into three color difference signals, (R-Y), (B-Y), and (G-Y). The combinations of usually two, but sometimes three demodulators were:
In the end, further matrixing of the above color-difference signals c through f yielded the three color-difference signals, (R-Y), (B-Y), and (G-Y).
The R, G, and B signals in the receiver needed for the display device (CRT, Plasma display, or LCD display) are electronically derived by matrixing as follows: R is the additive combination of (R-Y) with Y, G is the additive combination of (G-Y) with Y, and B is the additive combination of (B-Y) with Y. All of this is accomplished electronically. It can be seen that in the combining process, the low-resolution portion of the Y signals cancel out, leaving R, G, and B signals able to render a low-resolution image in full color. However, the higher resolution portions of the Y signals do not cancel out, and so are equally present in R, G, and B, producing the higher-resolution image detail in monochrome, although it appears to the human eye as a full-color and full-resolution picture.
NTSC and PAL systems
![Waveform monitor](https://upload.wikimedia.org/wikipedia/commons/f/fa/Waveform_monitor.jpg)
In the NTSC and PAL color systems, U and V are transmitted by using
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 signal ...
of a subcarrier. This kind of modulation applies two independent signals to one subcarrier, with the idea that both signals will be recovered independently at the receiving end. For NTSC, the subcarrier is at 3.58 MHz. For the PAL system it is at 4.43 MHz. The subcarrier itself is not included in the modulated signal (
suppressed carrier), it is the subcarrier sidebands that carry the U and V information. The usual reason for using suppressed carrier is that it saves on transmitter power. In this application a more important advantage is that the color signal disappears entirely in black and white scenes. The subcarrier is within the bandwidth of the main luminance signal and consequently can cause undesirable artifacts on the picture, all the more noticeable in black and white receivers.
A small sample of the subcarrier, the
colorburst
Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porc ...
, is included in the horizontal blanking portion, which is not visible on the screen. This is necessary to give the receiver a phase reference for the modulated signal. Under quadrature amplitude modulation the modulated chrominance signal changes phase as compared to its subcarrier and also changes amplitude. The chrominance amplitude (when considered together with the Y signal) represents the approximate saturation of a color, and the chrominance phase against the subcarrier reference approximately represents the hue of the color. For particular test colors found in the test color bar pattern, exact amplitudes and phases are sometimes defined for test and troubleshooting purposes only.
Due to the nature of the quadrature amplitude modulation process that created the chrominance signal, at certain times, the signal represents only the U signal, and 70 nanoseconds (NTSC) later, it represents only the V signal. About 70 nanoseconds later still, -U, and another 70 nanoseconds, -V. So to extract U, a synchronous demodulator is utilized, which uses the subcarrier to briefly gate the chroma every 280 nanoseconds, so that the output is only a train of discrete pulses, each having an amplitude that is the same as the original U signal at the corresponding time. In effect, these pulses are discrete-time analog samples of the U signal. The pulses are then low-pass filtered so that the original analog continuous-time U signal is recovered. For V, a 90-degree shifted subcarrier briefly gates the chroma signal every 280 nanoseconds, and the rest of the process is identical to that used for the U signal.
Gating at any other time than those times mentioned above will yield an additive mixture of any two of U, V, -U, or -V. One of these ''off-axis'' (that is, of the U and V axis) gating methods is called I/Q demodulation. Another much more popular off-axis scheme was the X/Z demodulation system. Further matrixing recovered the original U and V signals. This scheme was actually the most popular demodulator scheme throughout the 60s.
The above process uses the subcarrier. But as previously mentioned, it was deleted before transmission, and only the chroma is transmitted. Therefore, the receiver must reconstitute the subcarrier. For this purpose, a short burst of the subcarrier, known as the colorburst, is transmitted during the back porch (re-trace blanking period) of each scan line. A subcarrier oscillator in the receiver locks onto this signal (see
phase-locked loop
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a ...
) to achieve a phase reference, resulting in the oscillator producing the reconstituted subcarrier.
![Hanoverbars without PAL delay](https://upload.wikimedia.org/wikipedia/commons/7/74/Hanoverbars_without_PAL_delay.png)
NTSC uses this process unmodified. Unfortunately, this often results in poor color reproduction due to phase errors in the received signal, caused sometimes by multipath, but mostly by poor implementation at the studio end. With the advent of solid-state receivers, cable TV, and digital studio equipment for conversion to an over-the-air analog signal, these NTSC problems have been largely fixed, leaving operator error at the studio end as the sole color rendition weakness of the NTSC system. In any case, the PAL D (delay) system mostly corrects these kinds of errors by reversing the phase of the signal on each successive line, and averaging the results over pairs of lines. This process is achieved by the use of a 1H (where H = horizontal scan frequency) duration delay line. Phase shift errors between successive lines are therefore canceled out and the wanted signal amplitude is increased when the two in-phase (
coincident) signals are re-combined.
NTSC is more spectrum efficient than PAL, giving more picture detail for a given bandwidth. This is because sophisticated comb filters in receivers are more effective with NTSC's 4 field color phase cadence compared to PAL's 8 field cadence. However, in the end, the larger channel width of most PAL systems in Europe still give their PAL systems the edge in transmitting more picture detail.
SECAM system
In the
SECAM
SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog color television system that was used in France, some parts of Europe and Africa, and Russia. It was one of th ...
television system, U and V are transmitted on ''alternate'' lines, using simple
frequency modulation
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 Run-length limited#FM: .280. ...
of two different color subcarriers.
In some analog color CRT displays, starting in 1956, the brightness control signal (
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls withi ...
) is fed to the
cathode
A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
connections of the electron guns, and the color difference signals (
chrominance
Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying luma signal (or Y' for short). Chrominance is usually represente ...
signals) are fed to the control grids connections. This simple CRT matrix mixing technique was replaced in later
solid state designs of signal processing with the original matrixing method used in the 1954 and 1955 color TV receivers.
Synchronization
Synchronizing pulses added to the video signal at the end of every
scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernible ...
and video frame ensure that the sweep oscillators in the receiver remain locked in step with the transmitted signal so that the image can be reconstructed on the receiver screen.
[
][
][
]
A ''sync separator'' circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync.
Horizontal synchronization
The horizontal synchronization pulse (''horizontal sync'', or ''HSync''), separates the
scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernible ...
s. The horizontal sync signal is a single short pulse which indicates the start of every line. The rest of the scan line follows, with the signal ranging from 0.3 V (black) to 1 V (white), until the next horizontal or
vertical synchronization pulse.
The format of the horizontal sync pulse varies. In the 525-line
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
system it is a 4.85
μs-long pulse at 0
V. In the 625-line
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
system the pulse is 4.7 μs synchronization pulse at 0
V . This is lower than the amplitude of any video signal (''blacker than black'') so it can be detected by the level-sensitive "sync stripper" circuit of the receiver.
Vertical synchronization
Vertical synchronization (also called vertical sync or VSync) separates the video fields. In PAL and NTSC, the vertical sync pulse occurs within the
vertical blanking interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...
. The vertical sync pulses are made by prolonging the length of HSYNC pulses through almost the entire length of the scan line.
The ''vertical sync'' signal is a series of much longer pulses, indicating the start of a new field. The sync pulses occupy the whole line interval of a number of lines at the beginning and end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or midway through).
The format of such a signal in 525-line
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
is:
* pre-equalizing pulses (6 to start scanning odd lines, 5 to start scanning even lines)
* long-sync pulses (5 pulses)
* post-equalizing pulses (5 to start scanning odd lines, 4 to start scanning even lines)
Each pre- or post- equalizing pulse consists in half a
scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernible ...
of black signal: 2 μs at 0 V, followed by 30 μs at 0.3 V.
Each long sync pulse consists of an equalizing pulse with timings inverted: 30 μs at 0 V, followed by 2 μs at 0.3 V.
In video production and computer graphics, changes to the image are often kept in step with the vertical synchronization pulse to avoid visible discontinuity of the image. Since the
frame buffer
A framebuffer (frame buffer, or sometimes framestore) is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing data representing all the pixels in a complete video frame. Modern ...
of a
computer graphics
Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great de ...
display imitates the dynamics of a cathode-ray display, if it is updated with a new image while the image is being transmitted to the display, the display shows a mishmash of both frames, producing a
page tearing
Screen tearing is a visual artifact in video display where a display device shows information from multiple frames in a single screen draw.
The artifact occurs when the video feed to the device is not synchronized with the display's refresh ra ...
artifact partway down the image.
Vertical synchronization eliminates this by timing frame buffer fills to coincide with the
vertical blanking interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...
, thus ensuring that only whole frames are seen on-screen. Software such as video games and
computer-aided design
Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve c ...
(CAD) packages often allow vertical synchronization as an option, because it delays the image update until the vertical blanking interval. This produces a small penalty in latency because the program has to wait until the video controller has finished transmitting the image to the display before continuing.
Triple buffering
In computer science, multiple buffering is the use of more than one buffer to hold a block of data, so that a "reader" will see a complete (though perhaps old) version of the data, rather than a partially updated version of the data being create ...
reduces this latency significantly.
Two-timing intervals are defined – the ''front porch'' between the end of the displayed video and the start of the sync pulse, and the ''back porch'' after the sync pulse and before the displayed video. These and the sync pulse itself are called the ''horizontal blanking'' (or ''retrace'') ''interval'' and represent the time that the electron beam in the CRT is returning to the start of the next display line.
Horizontal and vertical hold
Analog television receivers and composite monitors often provide manual controls to adjust horizontal and vertical timing.
The sweep (or deflection) oscillators were designed to run without a signal from the television station (or VCR, computer, or other composite video source). This provides a blank canvas, similar to today's "CHECK SIGNAL CABLE" messages on monitors: it allows the television receiver to display a raster to confirm the basic operation of the set's most fundamental circuits, and to allow an image to be presented during antenna placement. With sufficient signal strength, the receiver's sync separator circuit would split timebase pulses from the incoming video and use them to reset the horizontal and vertical oscillators at the appropriate time to synchronize with the signal from the station.
The free-running oscillation of the horizontal circuit is especially critical, as the horizontal deflection circuits typically power the flyback transformer (which provides acceleration potential for the CRT) as well as the filaments for the high voltage rectifier tube and sometimes the filament(s) of the CRT itself. Without the operation of the horizontal oscillator and output stages, for virtually every analog television receiver since the 1940s, there will be absolutely no illumination of the CRT's face.
The lack of precision timing components in early television receivers meant that the timebase circuits occasionally needed manual adjustment.
If their free-run frequencies were too far from the actual line and field rates, the circuits would not be able to follow the incoming sync signals.
Loss of horizontal synchronization usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or down the screen.
The adjustment took the form of ''horizontal hold'' and ''vertical hold'' controls, usually on the front panel along with other common controls. These adjusted the free-run frequencies of the corresponding timebase oscillators.
Properly working, adjusting a horizontal or vertical hold should cause the picture to almost "snap" into place on the screen; this is called ''sync lock''. A slowly rolling vertical picture demonstrates that the vertical oscillator is nearly synchronized with the television station but is not locking to it, often due to a weak signal or a failure in the sync separator stage not resetting the oscillator. Sometimes, the black interval bar will almost stop at the right place, again indicating a fault in sync separation is not properly resetting the vertical oscillator.
Horizontal sync errors cause the image to be torn diagonally and repeated across the screen as if it were wrapped around a screw or a barber's pole; the greater the error, the more "copies" of the image will be seen at once wrapped around the barber pole. Given the importance of the horizontal sync circuit as a power supply to many subcircuits in the receiver, they may begin to malfunction as well; and horizontal output components that were designed to work together in a resonant circuit may become damaged.
In the earliest electronic television receivers (1930s-1950s), the time base for the sweep oscillators was generally derived from RC circuits based on carbon resistors and paper capacitors. After turning on the receiver, the vacuum tubes in the set would warm up and the oscillators would begin to run, allowing a watchable picture. Resistors were generally simple pieces of carbon inside a Bakelite enclosure, and the capacitors were usually alternating layers of paper and aluminum foil inside cardboard tubes sealed with bee's wax. Moisture ingress (from ambient air humidity) as well as thermal instability of these components affected their electrical values. As the heat from the tubes and the electrical currents passing through the RC circuits warmed them up, the electrical properties of the RC timebase would shift, causing the oscillators to drift in frequency to a point that they could no longer be synchronized with the received pulses coming from the TV station via the sync separator circuit, causing tearing (horizontal) or rolling (vertical).
Hermetically-sealed passive components and cooler-running semiconductors as active components gradually improved reliability to the point where the horizontal hold was moved to the rear of the set first, and the vertical hold control (due to the longer period in the RC constant) persisted as a front panel control well into the 1970s as the consistency of larger-value capacitors increased.
By the early 1980s the efficacy of the synchronization circuits, plus the inherent stability of the sets' oscillators, had been improved to the point where these controls were no longer necessary. Integrated Circuits which eliminated the horizontal hold control were starting to appear as early as 1969.
The final generations of analog television receivers (most TV sets with internal on-screen displays to adjust brightness, color, tint, contrast) used "TV-set-on-a-chip" designs where the receiver's timebases were divided down from crystal oscillators, usually based on the 3.58 MHz NTSC colorburst reference. PAL and SECAM receivers were similar though operating at different frequencies. With these sets, adjustment of the free-running frequency of either sweep oscillator was either physically impossible (being derived inside the integrated circuit) or possibly through a hidden service mode typically offering only NTSC/PAL frequency switching, accessible through the On-Screen Display's menu system.
Horizontal and Vertical Hold controls were rarely used in CRT-based computer monitors, as the quality and consistency of components were quite high by the advent of the computer age, but might be found on some composite monitors used with the 1970s-1980s home or personal computers.
There is no equivalent in modern television systems.
Other technical information
Components of a television system
A typical analog monochrome
television receiver
A television set or television receiver, more commonly called the television, TV, TV set, telly, tele, or tube, is a device that combines a tuner, display, and loudspeakers, for the purpose of viewing and hearing television broadcasts, or using ...
is based around the block diagram shown below:
![TV-block-diagram](https://upload.wikimedia.org/wikipedia/commons/d/de/TV-block-diagram.svg)
The tuner is the object which "plucks" the television signals out of the air, with the aid of an antenna. There are two types of tuners in analog television,
VHF and
UHF tuners. The VHF tuner selects the VHF television frequency. This consists of a 4 MHz video bandwidth and a 2 MHz audio bandwidth. It then amplifies the signal and converts it to a 45.75 MHz
Intermediate Frequency
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sign ...
(IF) amplitude-modulated picture and a 41.25 MHz IF frequency-modulated audio carrier.
The IF amplifiers are centered at 44 MHz for optimal frequency transference of the audio and frequency carriers. What centers this frequency is the IF transformer. They are designed for a certain amount of bandwidth to encompass the audio and video. It depends on the number of stages (the amplifier between the transformers). Most of the early television sets (1939–45) used 4 stages with specially designed video amplifier tubes (the type 1852/6AC7). In 1946 the RCA presented a new innovation in television; the RCA 630TS. Instead of using the 1852 octal tube, it uses the 6AG5 7-pin miniature tube. It still had 4 stages, but it was 1/2 the size. Soon all of the manufactures followed RCA and designed better IF stages. They developed higher amplification tubes, and lower stage counts with more amplification. When the tube era came to an end in the mid-70s, they had shrunk the IF stages down to 1-2 (depending on the set) and with the same amplification as the 4 stage, 1852 tube sets. Like radio, television has
Automatic Gain Control
Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...
(AGC). This controls the gain of the IF amplifier stages and the tuner. More of this will be discussed below.
The video amp and output amplifier consist of a low linear
pentode
A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode (called a ''tripl ...
or a high powered transistor. The video amp and output stage separate the 45.75 MHz from the 41.25 MHz. It simply uses a diode to detect the video signal. But the frequency-modulated audio is still in the video. Since the diode only detects AM signals, the FM audio signal is still in the video in the form of a 4.5 MHz signal. There are two ways to attach this problem, and both of them work. We can detect the signal before it enters into the video amplifier, or do it after the audio amplifier. Many television sets (1946 to late 1960s) used the after video amplification method, but of course, there is the occasional exception. Many of the later set late (1960s-now) use the before-the-video amplifier way. In some of the early television sets (1939–45) used its own separate tuner, so there was no need for a detection stage next to the amplifier. After the video detector, the video is amplified and sent to the sync separator and then to the picture tube.
At this point, we will now look at the audio section. The means of detection of the audio signal is by a 4.5 MHz traps coil/transformer. After that, it then goes to a 4.5 MHz amplifier. This amplifier prepares the signal for the 4.5Mhz detector. It then goes through a 4.5 MHz IF transformer to the detector. In television, there are 2 ways of detecting FM signals. One way is by the
ratio detector
The ratio detector is a type of detector circuit, commonly used in radio receivers for demodulating frequency modulated (FM) signal.
The ratio detector is a variant of the Foster–Seeley discriminator, but one diode conducts in an opposite d ...
. This is simple but very hard to align. The next is a relatively simple detector. This is the
quadrature detector
In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage. The term dates from the first three decades of radio (1888-1918). Unlike modern radio stations which transmit sound (an audi ...
. It was invented in 1954. The first tube designed for this purpose was the 6BN6 type. It is easy to align and simple in circuitry. It was such a good design that it is still being used today in the Integrated circuit form. After the detector, it goes to the audio amplifier.
The next part is the sync separator/clipper. This also does more than what is in its name. It also forms the AGC voltage, as previously stated. This sync separator turns the video into a signal that the horizontal and vertical oscillators can use to keep in sync with the video.
The horizontal and vertical oscillators form the raster on the CRT. They are kept in sync by the sync separator. There are many ways to create these oscillators. The first one is the earliest of its kind is the
thyratron
A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, pro ...
oscillator. Although it is known to drift, it makes a perfect sawtooth wave. This sawtooth wave is so good that no linearity control is needed. This oscillator was for the electrostatic deflection CRTs. It found some purpose for the electromagnetically deflected CRTs. The next oscillator is the blocking oscillator. It uses a transformer to create a sawtooth wave. This was only used for a brief time period and never was very popular after the beginning. The next oscillator is the
multivibrator
A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers, and flip-flops. The first multivibrator circuit, the astable multivibrator oscillator, was invented by Henri A ...
. This oscillator was probably the most successful. It needed more adjustment than the other oscillators, but it is very simple and effective. This oscillator was so popular that it was used from the early 1950s until today.
The oscillator amplifier is sorted into two categories. The vertical amplifier directly drives the yoke. There is not much to this. It is similar to an audio amplifier. The horizontal oscillator is a different situation. The oscillator must supply the high voltage and the yoke power. This requires a high power flyback transformer, and a high powered tube or transistor. This is a problematic section for CRT televisions because it has to handle high power.
Sync separator
![Videosignal frame](https://upload.wikimedia.org/wikipedia/commons/9/9b/Videosignal_frame.jpg)
Image synchronization is achieved by transmitting negative-going pulses; in a composite video signal of 1-volt amplitude, these are approximately 0.3 V below the "
black level
Video black level is defined as the level of brightness at the darkest (black) part of a visual image or the level of brightness at which no light is emitted from a screen, resulting in a pure black screen.
Video displays generally need to be cal ...
". The ''horizontal sync'' signal is a single short pulse which indicates the start of every line. Two-timing intervals are defined – the ''front porch'' between the end of the displayed video and the start of the sync pulse, and the ''back porch'' after the sync pulse and before the displayed video. These and the sync pulse itself are called the ''horizontal blanking'' (or ''retrace'') ''interval'' and represent the time that the electron beam in the CRT is returning to the start of the next display line.
The ''vertical sync'' signal is a series of much longer pulses, indicating the start of a new field. The sync pulses occupy the whole of line interval of a number of lines at the beginning and end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or midway through).
In the television receiver, a ''sync separator'' circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync.
Loss of horizontal synchronization usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or down the screen.
Counting sync pulses, a
video line selector {{short description, Electronic device used to select between different analog video signals
A video line selectorteletext
A British Ceefax football index page from October 2009, showing the three-digit page numbers for a variety of football news stories
Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipp ...
,
on-screen display
An on-screen display (OSD) is an image superimposed on a screen picture, commonly used by modern television sets, VCRs, and DVD players to display information such as volume, channel, and time.
History
In the past, most adjustments on TV sets ...
s,
station identification
Station identification (ident, network ID or channel ID or bumper) is the practice of radio and television stations and broadcast network, networks identifying themselves on-air, typically by means of a call sign or brand name (sometimes known, ...
logos as well as in the industry when cameras were used as a sensor.
Timebase circuits
In an analog receiver with a
CRT display sync pulses are fed to horizontal and vertical ''timebase'' circuits (commonly called "sweep circuits" in the United States), each consisting of an oscillator and an amplifier. These generate modified
sawtooth and
parabola
In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves.
One descript ...
current waveforms to scan the electron beam in a
linear
Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
way. The waveform shapes are necessary to make up for the distance variations from the electron beam source and the screen surface. The oscillators are designed to free-run at frequencies very close to the field and line rates, but the sync pulses cause them to reset at the beginning of each scan line or field, resulting in the necessary synchronization of the beam sweep with the originating signal. The output waveforms from the timebase amplifiers are fed to the horizontal and vertical ''deflection coils'' wrapped around the CRT tube. These coils produce
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s proportional to the changing current, and these deflect the electron beam across the screen.
In the 1950s, the power for these circuits was derived directly from the mains supply. A simple circuit consisted of a
series
Series may refer to:
People with the name
* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
Arts, entertainment, and media
Music
* Series, the ordered sets used in ...
voltage dropper
resistance and a
rectifier
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...
valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
(
tube
Tube or tubes may refer to:
* ''Tube'' (2003 film), a 2003 Korean film
* ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom
* "Tubes" (Peter Dale), performer on the Soccer AM television show
* Tube (band), a ...
) or
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
. This avoided the cost of a large high voltage mains supply (50 or 60 Hz)
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
. This type of circuit was used for the thermionic valve (
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
) technology. It was inefficient and produced a lot of heat which led to premature failures in the circuitry. Although failure was common, it was easily repairable.
In the 1960s,
semiconductor
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
technology was introduced into timebase circuits. During the late 1960s in the UK,
synchronous
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
(with the scan line rate) power generation was introduced into
solid state receiver designs. These had very complex circuits in which faults were difficult to trace, but had very efficient use of power.
In the early 1970s
AC mains (50 or 60 Hz), and line timebase (15,625 Hz),
thyristor
A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...
based switching circuits were introduced. In the UK use of the simple (50 Hz) types of power, circuits were discontinued. The reason for design changes arose from the electricity supply contamination problems arising from
EMI
EMI Group Limited (originally an initialism for Electric and Musical Industries, also referred to as EMI Records Ltd. or simply EMI) was a British transnational conglomerate founded in March 1931 in London. At the time of its break-up in 201 ...
, and supply loading issues due to energy being taken from only the positive half cycle of the mains supply waveform.
CRT flyback power supply
Most of the receiver's circuitry (at least in
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
- or
IC-based designs) operates from a comparatively low-voltage
DC power supply. However, the
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
connection for a
cathode-ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictur ...
requires a very high voltage (typically 10–30 kV) for correct operation.
This voltage is not directly produced by the main
power supply
A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...
circuitry; instead, the receiver makes use of the circuitry used for horizontal scanning.
Direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
(DC), is switched through the line output transformer, and
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC) is induced into the scan coils. At the end of each horizontal scan line the
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
, which has built up in both transformer and scan coils by the current, is a source of latent electromagnetic energy. This stored collapsing magnetic field energy can be captured. The reverse flow, short duration, (about 10% of the line scan time) current from both the line output transformer and the horizontal scan coil is discharged again into the
primary winding
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's c ...
of the
flyback transformer
A flyback transformer (FBT), also called a line output transformer (LOPT), is a special type of electrical transformer. It was initially designed to generate high voltage sawtooth signals at a relatively high frequency. In modern applications, ...
by the use of a rectifier which blocks this negative reverse
emf. A small value
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
is connected across the scan switching device. This tunes the circuit
inductance
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the ...
s to
resonate
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillat ...
at a much higher
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
. This slows down (lengthens) the flyback time from the extremely rapid decay rate that would result if they were electrically isolated during this short period. One of the secondary windings on the flyback transformer then feeds this brief high voltage pulse to a
Cockcroft–Walton generator
The Cockcroft–Walton (CW) generator, or multiplier, is an electric circuit that generates a high DC voltage from a low-voltage AC or pulsing DC input. It was named after the British and Irish physicists John Douglas Cockcroft and Ernest Tho ...
design
voltage multiplier 280px, Villard cascade voltage multiplier.
A voltage multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage, typically using a network of capacitors and diodes.
Voltage multipliers can ...
. This produces the required
EHT supply. A
flyback converter
The flyback converter is used in both AC/DC, and DC/DC conversion with galvanic isolation between the input and any outputs. The flyback converter is a buck-boost converter with the inductor split to form a transformer, so that the voltage ra ...
is a power supply circuit operating on similar principles.
A typical modern design incorporates the flyback transformer and rectifier circuitry into a single unit with a captive output lead, (known as a diode split line output transformer or an Integrated High Voltage Transformer (IHVT)), so that all high-voltage parts are enclosed. Earlier designs used a separate line output transformer and a well-insulated high voltage multiplier unit. The high frequency (15 kHz or so) of the horizontal scanning allows reasonably small components to be used.
Transition to digital
In many countries, over-the-air
broadcast television
Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
Analog television systems were standardized b ...
of
analog audio
Analog recording is a technique used for the recording of analog signals which, among many possibilities, allows analog audio for later playback.
Analog audio recording began with mechanical systems such as the phonautograph and phonograph. L ...
and
analog video
Video is an electronic medium for the recording, copying
Copying is the duplication of information or an artifact based on an instance of that information or artifact, and not using the process that originally generated it. With analog f ...
signals has been discontinued, to allow the re-use of the television broadcast
radio spectrum
The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...
for other services such as
datacasting
Datacasting (data broadcasting) is the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital terrestrial television (DTT), but may also be applied ...
and
subchannel
In broadcasting, digital subchannels are a method of transmitting more than one independent program stream simultaneously from the same digital radio or television station on the same radio frequency channel. This is done by using data compressi ...
s.
The first country to make a wholesale
switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
to digital over-the-air (terrestrial television) broadcasting was Luxembourg in 2006, followed later in 2006 by the Netherlands; in 2007 by Finland, Andorra, Sweden and Switzerland; in 2008 by Belgium (Flanders) and Germany; in 2009 by the United States (high power stations), southern Canada, the Isle of Man, Norway, and Denmark. In 2010, Belgium (Wallonia), Spain, Wales, Latvia, Estonia, the Channel Islands, San Marino, Croatia, and Slovenia; in 2011 Israel, Austria, Monaco, Cyprus, Japan (excluding
Miyagi Miyagi may refer to:
Places
* Miyagi Prefecture, one of the 47 major divisions of Japan
* Miyagi, Gunma, a village in Japan, merged into Maebashi in 2004
*Miyagi District, Miyagi, a district in Miyagi Prefecture, Japan
Other uses
* Miyagi (surna ...
,
Iwate, and
Fukushima
may refer to:
Japan
* Fukushima Prefecture, Japanese prefecture
** Fukushima, Fukushima, capital city of Fukushima Prefecture, Japan
***Fukushima University, national university in Japan
*** Fukushima Station (Fukushima) in Fukushima, Fukushim ...
prefectures), Malta and France; in 2012 the Czech Republic, Arab World, Taiwan, Portugal, Japan (including Miyagi, Iwate, and Fukushima prefectures), Serbia, Italy, Canada, Mauritius, the United Kingdom, the Republic of Ireland, Lithuania, Slovakia, Gibraltar, and South Korea; in 2013, the Republic of Macedonia, Poland, Bulgaria, Hungary, Australia, and New Zealand, completed the transition. The United Kingdom made the transition to digital television between 2008 and 2012, with the exception of
Whitehaven
Whitehaven is a town and port on the English north west coast and near to the Lake District National Park in Cumbria, England. Historically in Cumberland, it lies by road south-west of Carlisle and to the north of Barrow-in-Furness. It is th ...
, which made the switch over in 2007. The first digital TV-only area in the United Kingdom was Ferryside in
Carmarthenshire
Carmarthenshire ( cy, Sir Gaerfyrddin; or informally ') is a county in the south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. The county is known as ...
.
The
Digital television transition in the United States
The digital transition in the United States was the switchover from analog to exclusively digital broadcasting of terrestrial television programming. According to David Rehr, then president and CEO of the National Association of Broadcasters, t ...
for high-powered transmission was completed on 12 June 2009, the date that the
Federal Communications Commission
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC) set. Almost two million households could no longer watch television because they had not prepared for the transition. The switchover had been delayed by the
DTV Delay Act
The digital transition in the United States was the switchover from Analog TV, analog to exclusively Digital television, digital broadcasting of terrestrial television programming. According to David Rehr, then president and CEO of the National ...
. While the majority of the viewers of over-the-air broadcast television in the U.S. watch full-power stations (which number about 1800), there are three other categories of television stations in the U.S.:
low-power broadcasting
Low-power broadcasting is broadcasting by a broadcast station at a low transmitter power output to a smaller service area than "full power" stations within the same region. It is often distinguished from "micropower broadcasting" (more commonly " ...
stations,
class A stations, and
television translator stations. They were given later deadlines. In broadcasting, whatever happens in the United States also influences southern Canada and northern Mexico because those areas are covered by television stations in the U.S.
In Japan, the switch to digital began in northeastern
Ishikawa Prefecture
is a prefecture of Japan located in the Chūbu region of Honshu island. Ishikawa Prefecture has a population of 1,140,573 (31 October 2019) and has a geographic area of 4,186 km2 (1,616 sq mi). Ishikawa Prefecture borders Toyama Prefecture to ...
on 24 July 2010 and ended in 43 of the country's 47 prefectures (including the rest of Ishikawa) on 24 July 2011, but in
Fukushima
may refer to:
Japan
* Fukushima Prefecture, Japanese prefecture
** Fukushima, Fukushima, capital city of Fukushima Prefecture, Japan
***Fukushima University, national university in Japan
*** Fukushima Station (Fukushima) in Fukushima, Fukushim ...
,
Iwate, and
Miyagi Miyagi may refer to:
Places
* Miyagi Prefecture, one of the 47 major divisions of Japan
* Miyagi, Gunma, a village in Japan, merged into Maebashi in 2004
*Miyagi District, Miyagi, a district in Miyagi Prefecture, Japan
Other uses
* Miyagi (surna ...
prefectures, the conversion was delayed to 31 March 2012, due to complications from the
2011 Tōhoku earthquake and tsunami
The occurred at 14:46 JST (05:46 UTC) on 11 March. The magnitude 9.0–9.1 (M) undersea megathrust earthquake had an epicenter in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region, and lasted approximately six minutes ...
and
its related nuclear accidents.
In Canada, most of the larger cities turned off analog broadcasts on 31 August 2011.
China is scheduled to end analog broadcasting between 2015 and 2018.
Brazil switched to digital television on 2 December 2007 in its major cities. It is now estimated that Brazil will end analog broadcasting in 2023.
In Malaysia, the Malaysian Communications & Multimedia Commission (MCMC) advertised for tender bids to be submitted in the third quarter of 2009 for the 470 through 742 MHz
UHF allocation, to enable Malaysia's broadcast system to move into DTV. The new
broadcast band
A broadcast band is a segment of the radio spectrum used for broadcasting.
See also
* North American broadcast television frequencies
* AM broadcasting
* FM broadcasting
* Dead air
* Internet radio
* Radio network
* Music radio
* Old-time r ...
allocation would result in Malaysia's having to build an infrastructure for all broadcasters, using a single
digital terrestrial transmission/television broadcast (DTTB) channel. Large portions of Malaysia are covered by television broadcasts from Singapore, Thailand, Brunei, and Indonesia (from Borneo and Batam). Starting from 1 November 2019, all regions in Malaysia were no longer using the analog system after the states of Sabah and Sarawak finally turned it off on 31 October 2019.
In Singapore, digital television under
DVB-T2
DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial tele ...
began on 16 December 2013. The switchover was delayed many times until analog TV was switched off at midnight on 2 January 2019.
In the Philippines, the
National Telecommunications Commission
The National Telecommunications Commission (NTC; fil, Pambansang Komisyon sa Telekomunikasyon) is an attached agency of the Department of Information and Communications Technology responsible for the supervision, adjudication and control over ...
required all broadcasting companies to end analog broadcasting on 31 December 2015 at 11:59 p.m. Due to delay of the release of the implementing rules and regulations for digital television broadcast, the target date was moved to 2020. Full digital broadcast is expected in 2021 and all of the analog TV services should be shut down by the end of 2023.
In the Russian Federation, the
Russian Television and Radio Broadcasting Network
Russian Television and Radio Broadcasting Network (RTRN) (russian: Российская телевизионная и радиовещательная сеть) is a unitary enterprise created on August 13, 2001, by decree of the president of the ...
(RTRS) disabled analog broadcasting of federal channels in five stages, shutting down broadcasting in multiple
federal subjects
The federal subjects of Russia, also referred to as the subjects of the Russian Federation (russian: субъекты Российской Федерации, subyekty Rossiyskoy Federatsii) or simply as the subjects of the federation (russian ...
at each stage. The first region to have analog broadcasting disabled was
Tver Oblast
Tver Oblast (russian: Тверска́я о́бласть, ''Tverskaya oblast'', ), from 1935 to 1990 known as Kalinin Oblast (), is a federal subject of Russia (an oblast). Its administrative center is the city of Tver. It was named after Mikhai ...
on 3 December 2018, and the switchover was completed on 14 October 2019. During the transition, DVB-T2 receivers and monetary compensations for purchasing of terrestrial or satellite digital TV reception equipment were provided to disabled people, World War II veterans, certain categories of retirees and households with income per member below living wage.
See also
*
Amateur television
Amateur television (ATV) is the transmission of broadcast quality video and sound reproduction, audio over the wide range of frequencies of radio waves allocated for radio amateur (Ham) use. ATV is used for non-commercial experimentation, pleasure, ...
*
Narrow-bandwidth television Narrow-bandwidth television (NBTV) is a type of television designed to fit into a channel narrower than the standard bandwidth used for official television standards.
The three predominant worldwide broadcast television standards use either 6 ...
*
Overscan
*
Slow-scan television
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
A literal term for SSTV is narrowband television. Analog broadcast tel ...
*
Terrestrial television
Terrestrial television or over-the-air television (OTA) is a type of television broadcasting in which the signal transmission occurs via radio waves from the terrestrial (Earth-based) transmitter of a TV station to a TV receiver having an ant ...
*
Television 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 a ...
*
Vertical blanking interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...
*
Field (video)
In video, a field is one of the many still images which are displayed sequentially to create the impression of motion on the screen. Two fields comprise one video frame. When the fields are displayed on a video monitor they are "interlaced" so th ...
*
Video frame
In filmmaking, video production, animation, and related fields, a frame is one of the many '' still images'' which compose the complete '' moving picture''. The term is derived from the historical development of film stock, in which the sequenti ...
*
Glossary of video terms
This glossary defines terms that are used in the documen"Defining Video Quality Requirements: A Guide for Public Safety" developed by thVideo Quality in Public Safety (VQIPS) Working Group It contains terminology and explanations of concepts relev ...
Notes
References
External links
Video signal measurement and generation* [https://archive.today/20140923181048/http://www.productstat.com/engineering/18-6-story-color-television Designing the color television signal in the early 1950s as described by two engineers working directly with the NTSC]
{{DEFAULTSORT:Analog Television
Film and video technology
History of television
Television technology
Television terminology