PAL (Phase Alternating Line) is a television signal standard developed by Telefunken engineer Walter Bruch in Germany in 1963.

Like all analog television standards, PAL is adapted and compatible with older monochrome (black and white) television broadcasts. In adapted analog color television standards, an additional chrominance signal is transmitted at the end of the monochrome television signal spectrum.

It is known that any color perceived by human vision can be made up of the primary colors: red (R), green (G) and blue (B). This color model is abbreviated RGB. Due to the predominance of the green color component in the average television picture and to avoid redundant coding, R-Y and B-Y differences are used as additional color signals (where Y is the total brightness of a monochrome television signal). The PAL system uses the YUV color model.

Both additional color signals in the PAL standard are transmitted simultaneously in quadrature modulation (a type of amplitude modulation - is the sum of two carrier oscillations of the same frequency, but shifted in phase relative to each other by 90 degrees, each of which is modulated in amplitude by its own modulating signal), typical frequency subcarrier - 4433618.75 Hz (4.43 MHz). In this case, the "red" color difference signal is repeated in the next line with a phase rotation of 180 degrees. To eliminate the phase error, the PAL decoder adds the current line and the previous one from memory, thereby completely eliminating phase errors (typical for the NTSC system). When two signals are added, the “red” color-difference components are mutually destroyed, because their sign has changed. When two signals are subtracted, the "blue" signals cancel each other out. Thus, at the outputs of the adder-subtractor, separated U and V signals are obtained, which are scaled R-Y and B-Y.

In analog television receivers, an ultrasonic delay line is used to store the color difference signal from the previous line, in digital ones, RAM per line.

Thus, unlike NTSC, in the PAL standard, when using a standard analog decoder, the vertical color resolution is slightly lower than the resolution of a monochrome image (due to the summation of two adjacent lines across the field). This is quite acceptable, since the horizontal resolution in color is also less due to the reduction in bandwidth. Subjectively, due to the greater sensitivity of the eye to the brightness component, such a deterioration is almost not noticeable in average statistical pictures. At the same time, it should be understood that in the transmitted signal, the vertical color resolution is complete, resolution degradation occurs only in analog PAL decoders.

The use of digital signal processing makes it possible to restore both full vertical color resolution and improve the brightness/chrominance separation through the use of comb (or even more complex, so-called 3D) subcarrier filtering.

The use of quadrature modulation is a distinctive feature of PAL from the SECAM standard, the phase rotation of the "red" signal by lines distinguishes it from, the YUV color model distinguishes it from all analog systems.

A television frame of the PAL standard consists of 576 lines (a total of 625, some of which are service), each line consists of 720 fragments, i.e. is a 720*576 matrix.

Each frame consists of "fields" - alternating even and odd lines, alternating even and odd fields to reduce picture flicker.

Several modifications of the PAL standard are used, with differences in broadcasting ranges, video signal bandwidth and audio carrier frequency.

Most analog video cameras for video surveillance systems work in the PAL D standard.

Unlike the black-and-white image transmission standard, which was more or less uniform all over the world (only the distance between the image and sound transmission frequencies differed), there are several color television standards. The main color television systems are SECAM, PAL, NTSC. System SECAM adopted in the countries of the former USSR, as well as in France. System PAL adopted in Western European countries, except France. System NTSC adopted in the Americas and Japan. Standards PAL And SECAM were developed on the basis of a single black-and-white image standard and with the ability to receive a new TV signal by old TVs, therefore they are partially compatible with each other (the image scan and brightness are encoded the same way, but the color balance is encoded differently). Standard NTSC developed independently of the old standard. At the moment, there is a refinement, and in some countries the introduction of digital standards, the advantage of which is increased picture resolution, increased picture frequency, as well as signal noise immunity. In Russia, the transition to digital broadcasting is planned for 2010.

NTSC standard

NTSC (National Television System Color) is the first color television system to find practical application. It was developed in the USA and adopted for broadcasting already in 1953, and at present this system is also broadcast in Canada, most countries of Central and South America, Japan, South Korea and Taiwan. It was during its creation that the basic principles of color transmission in television were developed. This standard defines a method for encoding information into a composite video signal. According to the standard NTSC, each video frame consists of 525 horizontal lines of the screen, through which an electron beam passes every 1/30 second. When drawing a frame, the electron beam makes two passes over the entire screen: first along the odd lines, and then along the even lines (interlacing). Support for 16 million different colors is provided. New versions of the NTSC standard "Super NTSC" and "16 x 9" are currently being developed and will be part of the MPEG standard and the DVD authoring standard.

PAL standard

SECAM standard

System SECAM (SEquentiel Couleur A Memoire), like PAL uses a screen image of 625 lines at 25 frames per second. This system was originally proposed in France as early as 1954, but regular broadcasting, after lengthy improvements, was only started in 1967 simultaneously in France and the USSR. Currently, it is also adopted in Eastern Europe, Monaco, Luxembourg, Iran, Iraq and some other countries. The main feature of the system is sequential, through the line, transmission of color difference signals with further restoration in the decoder by repeating the lines. At the same time, in contrast to PAL And NTSC frequency modulation of subcarriers is used. As a result, hue and saturation do not depend on illumination, but color fringing appears at sharp transitions in brightness. Typically, after bright areas of the image, the fringing is blue, and after dark areas, it is yellow. Moreover, as in the system PAL, vertical color sharpness is halved.
Sources:
http://www.videodata.ru/palsecam.htm
http://ru.wikipedia.org/wiki/%D0%92%D0%B8%D0%B4%D0%B5%D0%BE

IEEE1394 interface

(FireWire, i-Link) is a serial high-speed bus designed to exchange digital information between a computer and other electronic devices.

Various companies promote the standard under their own brand names:

Apple - FireWire

History

in 1986, members of the Microcomputer Standards Committee decided to merge the different versions of the serial bus (Serial Bus) that existed at that time

in 1992, Apple took over the development of the interface

IEEE 1394 standard adopted in 1995

Advantages

Digital interface - allows you to transfer data between digital devices without loss of information

Small size - a thin cable replaces a bunch of bulky wires

Easy to use - no terminators, device IDs or presets

Hot plug - the ability to reconfigure the bus without turning off the computer

Low cost for end users

Various data rates - 100, 200 and 400 Mbps (800, 1600 Mbps IEEE 1394b)

Flexible topology - equality of devices, allowing various configurations (the ability to "communicate" devices without a computer)

High speed - real-time multimedia signal processing capability

Open architecture - no need for special software

Availability of power directly on the bus (low-power devices can do without their own power supplies). Up to one and a half amperes and voltage from 8 to 40 volts.

Connect up to 63 devices.

The IEEE 1394 bus can be used with:

computers

Audio and video multimedia devices

Printers and scanners

Hard drives, RAID arrays

Digital camcorders and VCRs

Organization of IEEE 1394 Devices

IEEE 1394 devices are organized in a 3-layer scheme - Transaction, Link and Physical, corresponding to the three lower layers of the OSI model.

Transaction Layer - data stream routing with support for asynchronous write-read protocol.

Link Layer - forms data packets and ensures their delivery.

Physical Layer - conversion of digital information to analog for transmission and vice versa, control of the signal level on the bus, control of access to the bus.

Communication between the PCI bus and the Transaction Layer is carried out by the Bus Manager. It assigns the type of devices on the bus, numbers and types of logical channels, detects errors.

Data is transmitted in frames of 125 microseconds. Time slots for channels are placed in the frame. Both synchronous and asynchronous modes of operation are possible. Each channel can occupy one or more time slots. To transmit data, the transmitter device asks for a synchronous channel of the required bandwidth. If the transmitted frame has the required number of timeslots for the given channel, an affirmative response is received and the channel is granted.

FireWire Specifications

IEEE 1394

At the end of 1995, the IEEE adopted the standard under serial number 1394. In Sony digital cameras, the IEEE 1394 interface appeared before the adoption of the standard and was called iLink.

The interface was originally positioned for transmitting video streams, but manufacturers of external drives also liked it, providing high bandwidth for modern high-speed drives. Today, many motherboards, as well as almost all modern laptop models, support this interface.

Data transfer rate - 100, 200 and 400 Mbps, cable length up to 4.5 m.

IEEE 1394a

In 2000, the IEEE 1394a standard was approved. A number of improvements have been made to improve device compatibility.

A timeout of 1/3 second for bus reset has been introduced until the transition process of establishing a secure connection or disconnection of a device has been completed.

IEEE 1394b

In 2002, the IEEE 1394b standard appears with new speeds: S800 - 800 Mbps and S1600 - 1600 Mbps. Also, the maximum cable length is increased to 50, 70 and when using high-quality fiber optic cables up to 100 meters.

Eligible devices are referred to as FireWire 800 or FireWire 1600, depending on the maximum speed.

The cables and connectors used have changed. To achieve maximum speeds at maximum distances, the use of optics is provided, plastic - for lengths up to 50 meters, and glass - for lengths up to 100 meters.

Despite the change in connectors, the standards remained compatible, which can be achieved using adapters.

On December 12, 2007, the S3200 specification was introduced with a maximum speed of 3.2 Gbps.

IEEE 1394.1

In 2004, the IEEE 1394.1 standard was released. This standard was adopted to enable the construction of large-scale networks and dramatically increases the number of connected devices to a mammoth 64,449.

IEEE 1394c

Introduced in 2006, the 1394c standard allows the use of Cat 5e cable from Ethernet. It is possible to use in parallel with Gigabit Ethernet, that is, to use two logical and independent networks on one cable. The maximum declared length is 100 m. The maximum speed corresponds to the S800 - 800 Mbps.

FireWire Connectors

There are three types of connectors for FireWire:

4pin (IEEE 1394a without power) is found on laptops and camcorders. Two wires for signal transmission (information) and two for reception.

6pin (IEEE 1394a). In addition, two wires for power.

9pin (IEEE 1394b). Additional wires for receiving and transmitting information.

Integration

Audio and video equipment (digital CD, MD, VideoCD and DVD players, digital STB and Digital VHS) can now be integrated with and controlled by computers. Systems can be made from this equipment - by simply connecting devices to each other using a single cable. After that, using a personal computer acting as a controller, you can perform the following operations: record from a CD player to a mini-disc, store digital radio broadcasts received via STB, enter digital video into a personal computer for subsequent editing and editing. Of course, this also retains the possibility of direct data exchange between audio and video equipment without the use of a computer, or, on the contrary, data exchange between two computers, regardless of audio or video, as in local networks based on traditional Ethernet technologies.

NEC Corporation recently announced the development of a chip designed to support hardware routing between two IEEE-1394-based networks and enable them to interoperate in future IEEE-1394 high-bandwidth home multimedia networks. This dual-port chip is also equipped with firmware that performs automatic network configuration and allows you to establish connections with other network devices, including mobile devices. In this way, the home network can be extended beyond the boundaries of a particular home to a distance of up to one kilometer. In the meantime, Sony continues to advance the IEEE-1394-based home networking concept and intends to support practical developments with even larger, high-speed, low-power, compact components for a wide range of applications and integration into system chipsets. Today, Sony is showcasing new consumer electronics that can form a home network based on i.Link. All this architecture has a proud name Home Audio/Video Interoperability (HAVi). It looks like Sony will soon really live, if not in a digital home, then at least in a digital apartment. However, the IEEE-1394 standard, which is increasingly attracting the attention of not only manufacturers of audio and video devices, but also developers of equipment for personal computers, will no doubt soon become a new network standard that brings the coming digital age closer.

In the operating system released in autumn 2000 Microsoft Windows Millennium Edition for the first time there was built-in support for local area networks based on IEEE-1394 controllers. Such a network has a data transfer rate four times faster than Fast Ethernet, and is very convenient for a home or small office. The only inconvenience in building such a network is the small maximum length of one segment (cable length up to 4.2 m). To eliminate this drawback, signal amplifiers are produced - repeaters, as well as multipliers-hubs for several ports (up to 27). Recently, the new USB interface (version 2.0) has been actively competing with the IEEE-1394 interface, which provides data transfer at speeds up to 480 Mbps versus the old 12 Mbps, that is, 40 times faster than the existing USB standard! The USB bus has become widespread due to its low cost and powerful support in the form of a controller built directly into motherboard chipsets. At the same time, it was stated that high-speed USB 2.0 would also be implemented as a controller built into the chipset (Intel ICH3). However, Microsoft has prioritized IEEE-1394 support over USB 2.0, and USB's asynchronous transmission prevents it from competing seriously with FireWire in digital video.

Thus, IEEE-1394 remains the international standard for a low-cost interface that allows you to combine all kinds of digital devices for entertainment, communications and computing equipment into a home multimedia digital complex. In other words, all IEEE-1394 devices, such as digital cameras, camcorders, DVD devices, and other devices, interface perfectly both with personal computers equipped with a similar interface (both Mac and PC computers support it), and between yourself. This means that users can now transfer, process and store data (including images, sound and video) at high speeds with virtually no degradation in quality. All these distinctive features of IEEE-1394 make it the most attractive universal digital interface of the future.

http://www.videodive.ru/scl/ieee1394.shtml http://www.youtube.com/watch?v=3fLggMWeiVQ(video on how to remake the IEEE 1394 connector) http://www.youtube.com/watch?v=xrJA54IdREc(a video about a laptop with connectors IEEE 1394)

Video standards

Since it's about video formats has already risen and quite a lot has already been said about it, including about analog And digital video recording formats, so I decided to talk directly about such common video standards how: NTSC, PAL And SECAM. Let's see how they differ from each other.

If you decide to purchase a camera abroad, especially in the US and Japan, be extremely careful. Prices in these countries are extremely attractive, only all video equipment is designed to work in NTSC(however, especially for Russian tourists there are shops selling electronics in the system PAL, but you have to be doubly vigilant here).

In this regard, it makes sense to delve into the concept of such abbreviations as NTSC, PAL, SECAM.

What does "NTSC" mean?

NTSC- this is abbr. English National Television Standards Committee - National Television Standards Committee - standard analog color television developed in the USA. On December 18, 1953, for the first time in the world, color television broadcasting was launched using this very systems. NTSC adopted as the standard for color television ( video) also in Canada, Japan and a number of countries in the Americas.

Technical features NTSC:

• number of fields - 60 Hz (more precisely 59.94005994 Hz);
• number of lines (resolution) - 525;
• subcarrier frequency - 3579545.5 Hz.
• number of frames per second - 30.
• beam scanning is interlaced (interlacing).

What does "PAL" mean?

PAL- this is abbr. from English. phase-alternating line- standard analog color television, developed by Walter Bruch, an engineer from the German company Telefunken, and presented as standard television ( video) broadcast in 1967.

Like all analog televisions ( video) standards, PAL is adapted and compatible with older monochrome (black and white) television broadcasts. In adapted analog standards For color television, an additional color signal is transmitted at the end of the monochrome television spectrum.

As is known from the nature of human vision, the perception of color consists of three components: red (R), green (G) and blue (B) colors. This color model is abbreviated RGB. Due to the predominance of the green color component in the average television picture and to avoid redundant coding, the difference between R-Y and B-Y is used as an additional color signal (Y is the total brightness of a monochrome television signal). In system PAL use color model YUV.

Both additional chrominance signals in PAL standard transmitted simultaneously in quadrature modulation (a variation of AM), the typical subcarrier frequency is 4433618.75 Hz (4.43 MHz).

In this case, each color difference signal is repeated in the next line with a phase rotation with a frequency of 15.625 kHz by 180 degrees, due to which the decoder PAL completely eliminates phase errors (typical for a system NTSC). To eliminate the phase error, the decoder adds the current line and the previous one from memory (analog television receivers use a delay line). Thus, objectively, a color television image in PAL video has half the vertical resolution of a monochrome image.

Subjectively, due to the greater sensitivity of the eye to the brightness component, such a deterioration is almost not noticeable in average statistical pictures. The use of digital signal processing further smoothes this drawback.

What does SECAM mean?

SECAM- this is abbr. from fr. Séquentiel couleur avec mémoire, later Séquentiel couleur à mémoire - consistent color with memory - standard analog color television, first used in France. Historically, it is the first European color television standard.

Chroma signal in the standard SECAM transmitted in frequency modulation (FM), one color component in one television line, in turn. The previous R-Y or B-Y signal, respectively, is used as the missing lines, receiving it from memory (in analog television receivers, a delay line is used for this). Thus, objectively, a color television image in a standard SECAM has half the vertical resolution of a monochrome image. Subjectively, due to the greater sensitivity of the eye to the brightness component, such a deterioration is almost not noticeable in average statistical pictures. The use of digital signal processing further smoothes this drawback.

As a joke, it is customary to decipher the abbreviation SECAM as "System Essentially Contrary to AMerican" (a system essentially opposed to the American one).

By the way, video cassettes marked NTSC the quality and duration of the recording do not meet the standard PAL.

I bet many of you have heard the terms PAL, SECAM and NTSC. TVs and TV tuners in the process of tuning channels often sin with questions about choosing one of them. The situation is aggravated when, in addition, it offers several subspecies of any of the three formats to choose from. And what to choose? And most importantly, how do all these formats differ from each other? In all this, we will now understand.

There are three systems in the world analog color television - NTSC, PAL And SECAM, which are similar in many respects, and at the same time differ in a number of parameters. This situation often requires the use of special decoders to convert video from one standard to another.

A television picture consists of lines (lines) displayed sequentially on the screen. This imaging method is called line scanning, and the cycle of a complete change of the image (frame) - personnel scan. The more lines on the screen, the better the vertical clarity of the image, and the increased frame rate eliminates the possible effect of flicker.

The figure shows the predominant use of color TV standards by region.

Basic parameters of TV signals

Due to the limited bandwidth of communication channels, each frame in all TV standards is transmitted in two steps, or, as they say, consists of two fields. Initially (in the first field) even lines are displayed, then odd ones. Such a scan is called interlaced and, unlike horizontal, it somewhat degrades the image quality, but allows you to fit the TV signal into the standard frequency band of communication channels.

The frequency spectrum of the complete color TV signal is shown in the figure, which shows that the TV signal consists of brightness, color and sound signals transmitted over communication channels using separate carrier frequencies. The main differences between the standards are in the methods of color coding based on the modulation of the carrier frequency of the color signal.

When displaying the received TV signal, the color component is superimposed on the brightness. Therefore, when using equipment that does not support one or another standard, it is usually possible to obtain at least a black and white picture. The audio carrier frequency can be different even in versions of the same standard, which is sometimes the reason for the lack of sound during normal video playback.

NTSC

This color television standard ( NTSC) was developed in the USA. The first version appeared in 1941, and regular television broadcasts began in 1954. In development NTSC involved the largest, at that time, electronic companies that were part of the national committee on television systems (eng. National Television System Committee(NTSC)). The current standard NTSC used in most of the American continent, as well as in Japan, South Korea, Taiwan and the Philippines.

There are two widely used options NTSC, denoted by the letter indices M and N. Historically, the first was, and now the most common option, NTSC M. Then came NTSC N (sometimes called PAL N), today it is used in some countries in South America. True, NTSC J also works in Japan, but this option differs slightly from the main one - NTSC M.

Key Features of the NTSC Format

The horizontal scanning frequency for NTSC M is 525 lines per screen, the frame rate is 30. The bandwidth occupied by the video signal is 4.2 MHz. NTSC N uses a few more lines - 625 and a lower frame rate - 25 Hz.

system based NTSC allows you to provide high quality color images, but imposes very stringent requirements on the receiving and transmitting equipment. Due to the peculiarities of signal formation in this format, when decoding, it is not always possible to completely separate the signal into separate components, so the color signals are mixed with the brightness. And, depending on the brightness of the image area, it may slightly change its color tone.

Phase distortions of the signal, which sometimes occur during transmission, also contribute to not quite natural transmission of color tone, and amplitude-frequency distortions cause a change in color saturation.

PAL

Standard PAL(English) Phase Alternation Line) was first used in 1967 in Germany and the UK. Broadcasting in these countries began with several different options, which are now even more. PAL is widely used in most of Western Europe, Africa, Asia, Australia and New Zealand.

In fact, PAL is an advanced NTSC system that eliminates the sensitivity of the transmitted signal to phase distortion by changing the method of modulating the color carrier frequency. True, this led to some deterioration in clarity, which is partly compensated (in some versions of the standard) by an increased number of lines.

The PAL standard has the largest number of varieties in use.

SECAM

Standard SECAM(French Sequential Couleur Avec Memoire) - sequential color transmission with memorization was developed in France. Regular broadcasting with its use began in 1967 in France and the USSR. IN SECAM 625 lines are used at 25 frames, or 50 fields per second. Now SECAM used in France and some countries in Europe, in some countries of the former CCCP and Africa.

The peculiarity of the system is that the color difference signals are transmitted by means of frequency modulation. Whereas in PAL and NTSC quadrature amplitude modulation is used. Frequency modulation, as well as alternate (through a line) transmission of two color signals, made it possible to get rid of excessive sensitivity to distortion, but somewhat worsened clarity, which, however, in the conditions of receiving on-air television is not always important and is most noticeable in cable systems. SECAM allows you to achieve more natural color reproduction due to improved separation of color signals from luminance.

For recording on magnetic tape, a variation of the standard was used - MESECAM, in which the color difference subcarriers are moved to lower frequencies (approximately 1.1 MHz), which minimizes the effect of tape speed variability on color quality.

Format Comparison

The list of the main differences between the standards is summarized in the table. As can be seen, there are significant differences in carrier frequencies and the total frequency band occupied in communication channels.

However, today it is unlikely that readers will have to suffer seriously due to problems, incompatibility of formats. Whichever way you output video from your computer, there will almost always be a choice of at least two formats PAL or NTSC.

| PAL(short for Phase Alternating Line) is an analog television standard. A color coding system used in television systems in many parts of the world. This system has a resolution of 625 lines at 25 frames (50 fields) per second.

PAL History

In the 1950s, during the mass production of color televisions in Western Europe, developers were faced with a problem found in the NTSC standard. The system exhibited a number of shortcomings, the main of which was the color shift of the image under poor signal reception conditions. Subsequently, to overcome the shortcomings of NTSC, alternative PAL and SECAM standards were developed. The new standard was intended for color television in European countries, had a frequency of 50 fields per second (50 hertz), and did not have the disadvantages of NTSC.

The PAL standard was developed by Walter Bruch at Telefunken in Germany. The first broadcasts in the new standard were made in the UK in 1964, then in Germany in 1967.

Later, Telefunken was acquired by the French electronics manufacturer Thomson. The company also acquired Compagnie Générale de Télévision, the founder of the European SECAM standard. Thomson (now called Technicolor SA) holds an RCA license from Radio Corporation of America, the founder of the NTSC standard.

In television systems, the term PAL is often interpreted as 576i resolution (625 lines/50 Hz), NTSC system as 480i (525 lines/60 Hz). The markings on the PAL or NTSC DVDs indicate the color rendering method, although the composite color itself is not recorded on them.

Color coding

Like NTSC, PAL uses amplitude modulation with a balanced chrominance subcarrier added to the luminance of the video signal as composite video. The subcarrier frequency for the PAL signal is 4.43361875 MHz, compared to 3.579545 MHz for NTSC. On the other hand, SECAM uses frequency modulation with two alternate color lines whose subcarriers are 4.25000 and 4.40625 MHz.

The very name of the standard Phase Alternating Line" indicates that the phase part of the color information in the video signal is restored from each line, which automatically corrects errors during signal transmission, canceling them, due to vertical resolution. Lines where color is restored are often called PAL or line phase interleaving, while as other lines are called NTSC lines.The first PAL TVs were very annoying to the human eye due to the so-called comb image effect, also known as Hanoverian bars, which occurs when phase errors occur.Thus, most receivers began to use chroma delay lines, storing information about the received color in each line of the kinescope.The disadvantage of the PAL system is the vertical color resolution, which is poorer than in NTSC, but since the human eye has the same color resolution, this effect is not visible.

A typical subcarrier frequency is 4.43361875 MHz and consists of 283.75 color cycles per line plus an offset of 25 Hz to avoid interference. Since the line frequency is 15625 Hz (625 lines x 50 Hz / 2), the color of the carrier frequency is calculated as follows: 4.43361875 MHz = 283.75* 15625 Hz + 25 Hz.

The original color subcarrier is required for the decoder to correct color differences. Since the color subcarrier is not transmitted along with the video information, it must be generated in the receiver. In order for the phase of the generated signal to match the transmitted information, 10 cycles of “color flashes” of the subcarrier are added to the video signal.

Benefits of PAL over NTSC

For NTSC receivers, color adjustment can be done manually. If the chroma is not adjusted correctly, the color display may be erroneous. The PAL standard automatically changes the color. Color phase errors in the PAL system have been eliminated by using a 1H delay line, resulting in a decrease in color saturation that is not as noticeable to the human eye as in NTSC.

However, even in PAL systems, color interleaving (Hanoverian bars) can lead to grainy images due to phase errors if first generation decoders are used. Often, such extreme phase shifts do not occur. Usually, this effect is observed when there are obstacles in the passage of the signal, and is observed in heavily built-up areas. The effect is more noticeable at ultra high frequencies (UHF) than at VHF.

In the early 1970s, some Japanese manufacturers developed new decoding methods to avoid paying royalties to Telefunken. The Telefunken license provided for any decoding method that was intended to reduce sub-carrier phase distortion. One development was to use a 1H delay line to decode only even or odd lines. For example, chroma on odd lines was switched on directly at the decoder, keeping the delay lines. Then, on even lines, the stored odd lines were decoded again. This method effectively converts the PAL system to NTSC. Such systems also have their drawbacks associated with NTSC and require the addition of manual color control.

The PAL and NTSC standards have several different color spaces, but the color difference is ignored by the decoder.

Advantages of PAL over SECAM

The first attempts at compatibility with color TVs were made in the SECAM standard, which also had the problem of NTSC shades. This was achieved by applying various methods of color transmission, namely alternative transmission of U and V vectors and modulation frequencies.

The SECAM standard is more reliable for signal transmission over long distances than NTSC or PAL. However, due to its nature, the color signal is only retained in a distorted form due to the decrease in amplitude, even in the black and white part of the image (there is a color overlap effect). Also PAL and SECAM receivers need delay lines.

PAL signal characteristics

The PAL-B/G signal has the following characteristics.

Types of PAL systems

* The PAL I system has never been used on UK VHF frequencies.

VHF - Very High Frequency (VHF)

UHF - Ultra High Frequency (UHF)

PAL-B/G/D/K/I

Most countries using PAL standards broadcast at 625 lines and 25 frames per second. The systems differ only in the carrier frequency of the audio signal and in the bandwidth of the channel. PAL B/G standards are used in most Western European countries, Australia and New Zealand, the UK, Ireland, Hong Kong, South Africa and Macau. PAL D/K standard in most CEE countries, PAL D standard in China. Analog CCTV cameras use the PAL D standard.

The PAL B and PAL G systems are very similar. System B uses 7 MHz and wide channels on VHF, while system G uses 8 MHz and UHF. Also systems D and K are similar: system D is used only on VHF, while system K is used only on UHF.

PAL-M (Brazil)

In Brazil, the PAL system uses 525 lines and 29.97 fps of system M, while using the NTSC color subcarrier. The exact PAL-M color subcarrier frequency is 3.575611 MHz.

The PAL color system can also match NTSC, a 525-line (480i) image is often referred to as PAL-60 (sometimes PAL-60/525, Quasi-PAL or Pseudo PAL). PAL is a broadcast standard, not to be confused with PAL-60.

PAL-N (Argentina, Paraguay, Uruguay)

This version of the system is used in Argentina, Paraguay and Uruguay. It uses 625 lines / 50 fields per second, the signal is from PAL-B / G, D / K, H, I. And the 6 MHz channel with a color subcarrier frequency of 3.582 MHz is very similar to NTSC.

VHS tapes recorded with PAL-N or PAL-B/G, D/K, H, I are indistinguishable due to the down conversion of the subcarriers on the tape. VHS recorded from TV in Europe will be played in PAL-N color. Also, any tape recorded in Argentina or Uruguay from PAL-N TV broadcast can be played in European countries that use PAL (Australia, New Zealand, etc.)

Typically, people in Uruguay, Argentina, and Paraguay own televisions that also display the NTSC-M standard, in addition to PAL-N. Live TV is also used in NTSC-M for North, Central and South America. Most DVD players sold in Argentina, Uruguay and Paraguay only play PAL discs (4.433618 MHz color subcarrier).

Some DVD players using a signal transcoder can encode NTSC-M, with some loss in picture quality due to system conversion from 625/50 PAL DVD to NTSC-M format (525/60 output).

Extended features of the PAL specification, such as teletext, are implemented in PAL-N. PAL-N supports modified 608 closed captioning, which is designed to facilitate NTSC compatibility.

PAL-L

The PAL L (Altered Sound System Phase L) standard uses the same video system in PAL-B/G/H quality (625 lines, 50 Hz, 15.625 kHz), but with a bandwidth of 6 MHz rather than 5.5 MHz. This requires an audio subcarrier of 6.5 MHz. The channel spacing used for PAL-L is 8 MHz.

Compatibility PAL standards

The PAL color system is commonly used with video formats that have 625 lines per frame (576 visible lines, the rest are used for overhead, data synchronization and subtitles) and a refresh rate of 50 interlaced fields per second (i.e. 25 full frames per second), such as B, G, H, I, and N.
PAL guarantees video compatibility. However, some of the standards (B/G/H, I and D/K) use different audio frequencies (5.5MHz, 6.0MHz 6.5MHz respectively). This may result in video without audio if the signal is on cable TV. Some countries in Eastern Europe that previously used SECAM D and K systems have switched to PAL, thereby paying more attention to the video signal. As a result, it became necessary to use various sound carriers.