e- MonotonIC VisiON ( MICON ) at This now electronic block block on an LED TV for the modern Super Block MICON of Modern TV goes to the Super Block Electronics to be include a series of filter TV filters AMNIMARJESLOW GOVERNMENT 91220017 XI XAM PIN PING HUNG CHOP 02096010014 LJBUSAF + We Forward to electronic system e- Super Block MICON __ Yes MICON to JESS PIT MICON STRUCTURE SYSTEM ___ UP GOING TO GOOD WET ( Work ---> Energy ---> Time ) ON the Lord Jesus Bless ___ Gen. Mac Tech

                               


In the establishment of the television electronics industry in this century many formed by the form of block blocks that are installed in sequence different from analog TV that many components are installed in one PCB (printed circuit board) while for digital television is installed in the position of block blocks connected behind LED TV screens Digital; block block is:

1. Block monitor screen
2. LED block
3. Program Block
4. Lighting Block
5. SMPSS power supply block (Switch Mode Power Supply)
5. TX and RX (Antenna) Blocks
6. Block Control and dynamic motion sensors

This block block contains electronic circuits which are SMT or SMD components, namely surface mount device / technology, in times of change where components are found that can be made more modern in the science of electronics which can be conditioned in motion and temperature components will be developed which is upgraded in an electronic super block arrangement (e- Super Block MICON), where the electronic device or device can control and maintain the system automatically integrated . 


                  

Flat Panel Display TV Sets Block Diagram

RF reception stageSet top boxes can be very simple, but some boxes are complex gateways that are able to received several streams of information simultaneously. NXP offers single and multi-tuner solutions, as well as the option to easily connect several silicon tuners in parallel. Thanks to their high performance they can be used without external LNAs. NXP’s zero power loop-through switches enable TV reception even when the STB is shut-down. External LNAs are available for even better performance.

HDMI interfaceIn addition to a legacy analog audio video interfaces, for which NXP offers high-bandwidth switches and audio converters, today’s STB’s include a HDMI output interface for digital HD content output. NXP’s family of HDMI Rx, Tx and switches allow a switch-box function to be added to the STB, enabling the STB to become the main AV hub in the living-room

ESD protectionsTo increase the reliability of STBs and ensure a low return rate, NXP offers an extensive portfolio of solutions, integrated and discrete, for the protection of all interfaces.
• ESD protections and level shifters for HDMI
• ESD protections for USB, SATA, Ethernet
• ESD protections for analog AV interfaces

Content access systemTo ensure the authentication of viewing rights and protect high-value content, most STBs use a smart-card. As the leader of security ICs, NXP offers a large range of smart-card reader interfaces, which comply with the industry standards.

Low speed control functions and interfacesEven when based on a highly integrated solution, STB systems will need additional IOs, temperature sensors and LED controllers. NXP offers a large portfolio of I2C controlled interfaces, GPIO expanders and sensors

Power managementAs power efficiency becomes more important, manufacturer’s need efficient AC-DC controllers and high-performance microcontrollers to build power saving solutions, in active mode as well as in stand-by. NXP has a wide range of highly efficient AC-DC controllers and 8-bit and 32-bit micro-controllers.

RF remote controlThe storage of STBs in the home is becoming more remote, and there is an increasing need for higher data rates and bidirectional communication between remote controller and STB. The regular infra-red remote control is progressively being replaced with very low power RF, such as 802.15.4/ RF4CE solutions.

Logic
To complete system-on-chip solutions, NXP offers a large portfolio of single functions in a small package, with different packaging options to prevent probing for enhanced security.

DiscretesNXP Semiconductors has a comprehensive port-folio of discrete components, including transistors, diodes and ESD protections. 

 

                                                                              LED TV  


  



  




                                         

                             

We used to understand an equipment block diagram samsung tv schematic diagram . who are in the tv repair line would like it 555 timer ic block diagram working pin out configuration a plete of 555 timer ic with its block diagram working of se ne 555 timer pin configuration and pin out diagram download 555 data sheet schematics technical drawings block diagram blue print pirate radio kits fm transmitter schematic hobby broadcast rf circuit antenna surveillance spy links for fm transmitter kits circuits electronics sweep frequency generator working block diagram parameters working of sweep frequency generator is explained working and block diagram of electronically tuned sweep frequency generator is also given satellite tv at sea lnb low noise block down converter satellite tv in the americas uses circular polarization instead of transmitting the signal in a vertical or horizontal plane they somehow manage to send the signal led lcd backlights explained cnet home entertainment led lcd backlights explained the leds in "led tvs" e in several different configurations and some are better than others electronic circuit schematics electronic circuit schematics note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy panasonic tc l37s1 37 " lcd tv manuals manuals brands panasonic manuals tv tc l37s1 37" lcd tv panasonic tc l37s1 37" lcd tv manuals manuals and user guides for panasonic tc l37s1 37" lcd tv interactive block diagrams interactive block diagrams build a customized list of products to plete your design by using these application interactive block diagrams mouse over a green box

led backlight controller tc xbg nxp flat panel display tv block diagram pdp tv pyrope training manual ppt video online led block diagram led block diagram 238 best library ✈ ee │pics figures diagrams images on led block diagram circuit board for samsung led tv bablu notes how to work lcd tft monitor bablu notes solution on automotive led signal lighting

LED Backlight Controller TC XBG from block diagram of led tv , source:toshiba.semicon-storage.com

NXP Flat Panel Display TV Block Diagram from block diagram of led tv
PDP TV  TRAINING MANUAL

Led Block Diagram from block diagram of led tv

Led Block Diagram from block diagram of led tv 

led block diagram 230v led driver circuit diagram working and applications tv panasonic tc 21 fj30la auto intensity control of street lights circuit using microcontroller 652 best elektronics auto intensity control of street lights circuit using microcontroller schematic street lights that glow on detecting vehicle movement circuit nxp flat panel display tv block diagram led knight rider circuit .

Block Diagram Of Led Tv Elegant 40 Watt Led PWM Controll Circuit Diagram Knowledge

led block diagram 230v led driver circuit diagram working and applications tv panasonic tc 21 fj30la auto intensity control of street lights circuit using microcontroller 652 best elektronÄ°auto intensity control of street lights circuit using microcontroller schematic street lights that glow on detecting vehicle movement circuit nxp flat panel display tv block diagram led knight rider circuit This particular picture (Block Diagram Of Led Tv Elegant 40 Watt Led Pwm Controll Circuit Diagram Knowledge) . 

Led Tv Elegant Auto Intensity Control Of Street Lights Circuit Using Microcontroller 

                              What’s the difference between LCD and LED

LCD stands for “liquid crystal display” and technically, both LED and LCD TVs are liquid crystal displays. The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light. So really, LED TVs are a subset of LCD TVs.

LED, which stands for “light emitting diodes,” differs from general LCD TVs in that LCDs use fluorescent lights while LEDs use those light emitting diodes. Also, the placement of the lights on an LED TV can differ. The fluorescent lights in an LCD TV are always behind the screen. On an LED TV, the light emitting diodes can be placed either behind the screen or around its edges. The difference in lights and in lighting placement has generally meant that LED TVs can be thinner than LCDs, although this is starting to change. It has also meant that LED TVs run with greater energy efficiency and can provide a clearer, better picture than the general LCD TVs. 

                                           

LED TVs provide a better picture for two basic reasons. First, LED TVs work with a color wheel or distinct RGB-colored lights (red, green, blue) to produce more realistic and sharper colors. Second, light emitting diodes can be dimmed. The dimming capability on the back lighting in an LED TV allows the picture to display with a truer black by darkening the lights and blocking more light from passing through the panel. This capability is not present on edge-lit LED TVs; however, edge-lit LED TVs can display a truer white than the fluorescent LED TVs.

Because all these LCD TVs are thin-screen, each has particular angle-viewing and anti-glare issues. The backlit TVs provide better, cleaner angle viewing than the edge-lit LED TV. However, the backlit LED TV will usually have better angle viewing than the standard LCD TV. Both LED and LCD TVs have good reputations for their playback and gaming quality. 

                               XO__XO  Smart TV ( e- SMART MICON )

A smart TV, sometimes referred to as connected TV or hybrid TV, is a television set with integrated Internet and interactive "Web 2.0" features. Smart TV is a technological convergence between computers and flatscreen television sets and set-top boxes. Besides the traditional functions of television sets and set-top boxes provided through traditional broadcasting media, these devices can also provide Internet TV, online interactive media, over-the-top content (OTT), as well as on-demand streaming media, and home networking access.

Smart TV should not be confused with Internet TV, IPTV or Web television. Internet TV refers to receiving television content over the Internet instead of traditional systems (terrestrial, cable and satellite) (although Internet itself is received by these methods). IPTV is one of the Internet television technology standards for use by television broadcasters. Web television is a term used for programs created by a wide variety of companies and individuals for broadcast on Internet TV.

In smart TVs, the operating system is preloaded or is available through the set-top box. The software applications or "apps" can be preloaded into the device, or updated or installed on demand via an app store or marketplace, in a similar manner to how the apps are integrated in modern smartphones.

The technology that enables smart TVs is also incorporated in external devices such as set-top boxes and some Blu-ray players, game consoles, digital media players, hotel television systems, smartphones, and other network-connected interactive devices that utilize television-type display outputs. These devices allow viewers to find and play videos, movies, TV shows, photos and other content from the Web, cable or satellite TV channel, or from a local storage device . 

                                                     

A smart TV displaying content from a museum website; unlike traditional TVs, a smart TV enables the viewer to interact with icons or images on the screen. For example, on a museum website, viewers can "click" on items depicted onscreen to learn more about them. 

In the early 1980s, "intelligent" television receivers were introduced in Japan. The addition of an LSI chip with memory and a character generator to a television receiver enabled Japanese viewers to receive a mix of programming and information transmitted over spare lines of the broadcast television signal. A patent was published in 1994 (and extended the following year) for an "intelligent" television system, linked with data processing systems, by means of a digital or analog network. Apart from being linked to data networks, one key point is its ability to automatically download necessary software routines, according to a user's demand, and process their needs. The mass acceptance of digital television in late 2000s and early 2010s greatly improved smart TVs. Major TV manufacturers have announced production of smart TVs only, for their middle-end to high-end TVs in 2015. Smart TVs are expected to become the dominant form of television by the late 2010s. At the beginning of 2016, Nielsen reported that 29 percent of those with incomes over $75,000 a year had a smart TV.

Definition

Smart TVs on display

A smart TV device is either a television set with integrated Internet capabilities or a set-top box for television that offers more advanced computing ability and connectivity than a contemporary basic television set. Smart TVs may be thought of as an information appliance or the computer system from a handheld computer integrated within a television set unit, as such a smart TV often allows the user to install and run more advanced applications or plugins/addons based on a specific platform. Smart TVs run a complete operating system or mobile operating system software providing a platform for application developers.

Smart TV platforms or middleware have a public Software development kit (SDK) and/or Native development kit (NDK) for apps so that third-party developers can develop applications for it, and an app store so that the end-users can install and uninstall apps themselves. The public SDK enables third-party companies and other interactive application developers to “write” applications once and see them run successfully on any device that supports the smart TV platform or middleware architecture which it was written for, no matter who the hardware manufacturer is.

Smart TVs deliver content (such as photos, movies and music) from other computers or network attached storage devices on a network using either a Digital Living Network Alliance / Universal Plug and Play media server or similar service program like Windows Media Player or Network-attached storage (NAS), or via iTunes. It also provides access to Internet-based services including traditional broadcast TV channels, catch-up services, video-on-demand (VOD), electronic program guide, interactive advertising, personalisation, voting, games, social networking, and other multimedia applications.^[20] Smart TV enables access to movies, shows, video games, apps and more. Some of those apps include Netflix, Spotify, YouTube, and Amazon.

Functions

Smart TV devices also provide access to user-generated content (either stored on an external hard drive or in cloud storage) and to interactive services and Internet applications, such as YouTube, many using HTTP Live Streaming (also known as HLS) adaptive streaming. Smart TV devices facilitate the curation of traditional content by combining information from the Internet with content from TV providers. Services offer users a means to track and receive reminders about shows or sporting events, as well as the ability to change channels for immediate viewing. Some devices feature additional interactive organic user interface / natural user interface technologies for navigation controls and other human interaction with a Smart TV, with such as second screen companion devices,spatial gestures input like with Xbox Kinect, and even for speech recognition for natural language user interface.

Features

LG Smart TV using the web browser.

Smart TV develops new features to satisfy consumers and companies, such as new payment processes. LG and PaymentWall have collaborated to allow consumers to access purchased apps, movies, games, and more using a remote control, laptop, tablet, or smartphone. This is intended for an easier and more convenient way for checkout.

Technology

Platforms

Smart TV technology and software is still evolving, with both proprietary and open source software frameworks already available. These can run applications (sometimes available via an 'app store' digital distribution platform), interactive on-demand media, personalized communications, and have social networking features.

There are many Smart TV platforms used for individual purposes. Smart TV owners desire the most successful platform possible for their Smart TV. For this reason, platforms are ranked from best to worst. HbbTV, provided by the Hybrid Broadcast Broadband TV association, CE-HTML, part of Web4CE, OIPF, part of HbbTV, and Tru2way are framework platforms managed by technology businesses.

Android TV, Boxee, Firefox OS, Frog, Google TV, Horizon TV, httvLink, Inview, Kodi Entertainment Center, MeeGo, Mediaroom, OpenTV, Opera TV, Plex, Roku, RDK, which is Reference Development Kit, Smart TV Alliance, ToFu Media Platform, Ubuntu TV, and Yahoo! Smart TV are framework platforms managed by individual companies.

Current Smart TV platforms used by vendors are Amazon, Apple, Google, Haier, Hisense, Hitachi, Insigna, LG, Microsoft, Netgear, Panasonic, Philips, Samsung, Sharp, Sony, TCL, TiVO, Toshiba, Sling Media, and Western Digital. Sony, Panasonic, Samsung, LG, and Roku TV are some platforms ranked under the best Smart TV platforms.

Social networking

Some smart TV platforms come prepackaged, or can be optionally extended, with social networking technology capabilities. The addition of social networking synchronization to smart TV and HTPC platforms may provide an interaction with both on-screen content and other viewers than is currently available to most televisions, while simultaneously providing a much more cinematic experience of the content than is currently available with most computers.

Advertising

Some smart TV platforms also support interactive advertising, addressable advertising with local advertising insertion and targeted advertising,^[36] and other advanced advertising features such as ad telescoping using VOD and DVR, enhanced TV for consumer call-to-action and audience measurement solutions for ad campaign effectiveness.^[38][39] The marketing and trading possibilities offered by Smart TVs are sometimes summarized by the term t-commerce. Taken together, this bidirectional data flow means that smart TVs can be and are used for clandestine observation of the owners. Even in sets that are not configured off-the-shelf to do so, default security measures are often weak and will allow hackers to easily break into the TV.

Security and privacy

There is evidence that a smart TV is vulnerable to attacks. Some serious security bugs have been discovered, and some successful attempts to run malicious code to get unauthorized access were documented on video. There is evidence that it is possible to gain root access to the device, install malicious software, access and modify configuration information for a remote control, remotely access and modify files on TV and attached USB drives, access camera and microphone.

There have also been concerns that hackers may be able to remotely turn on the microphone or web-camera on a smart TV, being able to eavesdrop on private conversations. A common loop antenna may be set for a bidirectional transmission channel, capable of uploading data rather than only receiving. Since 2012, security researchers discovered a similar vulnerability present in more series of Smart Tvs, which allows hackers to get an external root access on the device .

Anticipating growing demand for an antivirus for a smart TV, some security software companies are already working with partners in digital TV field on the solution. At this writing it seems like there is only one antivirus for smart TVs available: 'Neptune', a cloud-based antimalware system developed by Ocean Blue Software in partnership with Sophos. However, antivirus company Avira has joined forces with digital TV testing company Labwise to work on software to protect against potential attacks.^[44] The privacy policy for Samsung's Smart TVs has been called Orwellian (a reference to George Orwell and the dystopian world of constant surveillance he depicted in 1984), and compared to Telescreens because of eavesdropping concerns.

Hackers have misused Smart TV's abilities such as operating source codes for applications and its unsecured connection to the Internet. Passwords, IP address data, and credit card information can be accessed by hackers and even companies for advertisement. A company caught in the act is Vizio.The confidential documents, codenamed Vault 7 and dated from 2013–2016, include details on CIA's software capabilities, such as the ability to compromise smart TVs.

Reliability

High-end Samsung Smart TVs stopped working for at least seven days after a software update. Application providers are rarely upgrading Smart TV apps to the latest version; for example, Netflix does not support older TV versions with new Netflix upgrades.

Restriction of access

Internet websites can block smart TV access to content at will, or tailor the content that will be received by each platform. Google TV-enabled devices were blocked by NBC, ABC, CBS, and Hulu from accessing their Web content since the launch of Google TV in October 2010. Google TV devices were also blocked from accessing any programs offered by Viacom’s subsidiaries.

Market share

According to a report from research group NPD In-Stat, in 2012 only about 12 million U.S. households had their Web-capable TVs connected to the Internet, although an estimated 25 million households owned a set with the built-in network capability. In-Stat predicted that by 2016, 100 million homes in North America and western Europe would be using television sets blending traditional programming with internet content.

The number of households using over-the-top television services has rapidly increased over the years. In 2015, 52% of U.S. households subscribed to Netflix, Amazon Prime, or Hulu Plus; 43% of pay-TV subscribers also used Netflix, and 43% of adults used some streaming video on demand service at least monthly. Additionally, 19% of Netflix subscribers shared their subscription with people outside of their households. Ten percent of adults at the time showed interest in HBO Now . 

                

                        Interactive television 

Interactive television (also known as ITV or iTV) is a form of media convergence, adding data services to traditional television technology. Throughout its history, these have included on-demand delivery of content, as well as new uses such as online shopping, banking, and so forth. Interactive TV is a concrete example of how new information technology can be integrated vertically (into established technologies and commercial structures) rather than laterally (creating new production opportunities outside existing commercial structures, e.g. the world wide web) 

                                              

                                                       Digital TV set-top box 

Interactive television represents a continuum from low (TV on/off, volume, changing channels) to moderate interactivity (simple movies on demand without player controls) and high interactivity in which, for example, an audience member affects the program being watched. The most obvious example of this would be any kind of real-time voting on the screen, in which audience votes create decisions that are reflected in how the show continues. A return path to the program provider is not necessary to have an interactive program experience. Once a movie is downloaded, for example, controls may all be local. The link was needed to download the program, but texts and software which can be executed locally at the set-top box or IRD (Integrated Receiver Decoder) may occur automatically, once the viewer enters the channel.

Back Light

The first patent of interactive connected TV was registered in 1994, carried on 1995 in the United States. It clearly expose this new interactive technology with content feeding and feedback through global networking. User identification allows interacting and purchasing.

Return path

The viewer must be able to alter the viewing experience (e.g. choose which angle to watch a football match), or return information to the broadcaster.

This "return path," return channel or "back channel" can be by telephone, mobile SMS (text messages), radio, digital subscriber lines (ADSL) or cable.

Cable TV viewers receive their programs via a cable, and in the integrated cable return path enabled platforms, they use the same cable as a return path.

Satellite viewers (mostly) return information to the broadcaster via their regular telephone lines. They are charged for this service on their regular telephone bill. An Internet connection via ADSL, or other, data communications technology, is also being increasingly used.

Interactive TV can also be delivered via a terrestrial aerial (Digital Terrestrial TV such as 'Freeview' in the UK). In this case, there is often no 'return path' as such - so data cannot be sent back to the broadcaster (so you could not, for instance, vote on a TV show, or order a product sample). However, interactivity is still possible as there is still the opportunity to interact with an application which is broadcast and downloaded to the set-top box (so you could still choose camera angles, play games etc.).

Increasingly the return path is becoming a broadband IP connection, and some hybrid receivers are now capable of displaying video from either the IP connection or from traditional tuners. Some devices are now dedicated to displaying video only from the IP channel, which has given rise to IPTV - Internet Protocol Television. The rise of the "broadband return path" has given new relevance to Interactive TV, as it opens up the need to interact with Video on Demand servers, advertisers, and website operators.

Forms of interaction

The term "interactive television" is used to refer to a variety of rather different kinds of interactivity (both as to usage and as to technology), and this can lead to considerable misunderstanding. At least three very different levels are important (see also the instructional video literature which has described levels of interactivity in computer-based instruction which will look very much like tomorrow's interactive television):

Interactivity with a TV set

The simplest, Interactivity with a TV set is already very common, starting with the use of the remote control to enable channel surfing behaviors, and evolving to include video-on-demand, VCR-like pause, rewind, and fast forward, and DVRs, commercial skipping and the like. It does not change any content or its inherent linearity, only how users control the viewing of that content. DVRs allow users to time shift content in a way that is impractical with VHS. Though this form of interactive TV is not insignificant, critics claim that saying that using a remote control to turn TV sets on and off makes television interactive is like saying turning the pages of a book makes the book interactive.

In the not too distant future, the questioning of what is real interaction with the TV will be difficult. Panasonic already has face recognition technology implemented its prototype Panasonic Life Wall. The Life Wall is literally a wall in your house that doubles as a screen. Panasonic uses their face recognition technology to follow the viewer around the room, adjusting its screen size according to the viewers distance from the wall. Its goal is to give the viewer the best seat in the house, regardless of location. The concept was released at Panasonic Consumer Electronics Show in 2008. Its anticipated release date is unknown, but it can be assumed technology like this will not remain hidden for long.

Interactivity with TV program content

In its deepest sense, Interactivity with normal TV program content is the one that is "interactive TV", but it is also the most challenging to produce. This is the idea that the program, itself, might change based on viewer input. Advanced forms, which still have uncertain prospect for becoming mainstream, include dramas where viewers get to choose or influence plot details and endings.

• As an example, in Accidental Lovers viewers can send mobile text messages to the broadcast and the plot transforms on the basis of the keywords picked from the messages.
• Global Television Network offers a multi-monitor interactive game for Big Brother 8 (US) "'In The House'" which allows viewers to predict who will win each competition, who's going home, as well as answering trivia questions and instant recall challenges throughout the live show. Viewers login to the Global website to play, with no downloads required.
• Another kind of example of interactive content is the Hugo game on Television where viewers called the production studio, and were allowed to control the game character in real time using telephone buttons by studio personnel, similar to The Price Is Right.
• Another example is the Clickvision Interactive Perception Panel used on news programmes in Britain, a kind of instant clap-o-meter run over the telephone.

Simpler forms, which are enjoying some success, include programs that directly incorporate polls, questions, comments, and other forms of (virtual) audience response back into the show. One example would be Australian media producer Yahoo!7's Fango mobile app, which allows viewers to access program-related polls, discussion groups and (in some cases) input into live programming. During the 2012 Australian Open viewers used the app to suggest questions for commentator Jim Courier to ask players in post-match interviews.

There is much debate as to how effective and popular this kind of truly interactive TV can be. It seems likely that some forms of it will be popular, but that viewing of pre-defined content, with a scripted narrative arc, will remain a major part of the TV experience indefinitely. The United States lags far behind the rest of the developed world in its deployment of interactive television. This is a direct response to the fact that commercial television in the U.S. is not controlled by the government, whereas the vast majority of other countries' television systems are controlled by the government. These "centrally planned" television systems are made interactive by fiat, whereas in the U.S., only some members of the Public Broadcasting System has this capability.

Commercial broadcasters and other content providers serving the US market are constrained from adopting advanced interactive technologies because they must serve the desires of their customers, earn a level of return on investment for their investors, and are dependent on the penetration of interactive technology into viewers' homes. In association with many factors such as

• requirements for backward compatibility of TV content formats, form factors and Customer Premises Equipment (CPE)
• the 'cable monopoly' laws that are in force in many communities served by cable TV operators
• consumer acceptance of the pricing structure for new TV-delivered services. Over the air (broadcast) TV is Free in the US, free of taxes or usage fees.
• proprietary coding of set top boxes by cable operators and box manufacturers
• the ability to implement 'return path' interaction in rural areas that have low, or no technology infrastructure
• the competition from Internet-based content and service providers for the consumers' attention and budget
• and many other technical and business roadblocks

Interactivity with TV-related content

The least understood, Interactivity with TV-related content may have most promise to alter how we watch TV over the next decade. Examples include getting more information about what is on the TV, weather, sports, movies, news, or the like.

Similar (and most likely to pay the bills), getting more information about what is being advertised, and the ability to buy it—(after futuristic innovators make it) is called "tcommerce" (short for "television commerce"). Partial steps in this direction are already becoming a mass phenomenon, as Web sites and mobile phone services coordinate with TV programs (note: this type of interactive TV is currently being called "participation TV" and GSN and TBS are proponents of it). This kind of multitasking is already happening on large scale—but there is currently little or no automated support for relating that secondary interaction to what is on the TV compared to other forms of interactive TV. Others argue that this is more a "web-enhanced" television viewing than interactive TV. In the coming months and years, there will be no need to have both a computer and a TV set for interactive television as the interactive content will be built into the system via the next generation of set-top boxes. However, set-top-boxes have yet to get a strong foothold in American households as price (pay per service pricing model) and lack of interactive content have failed to justify their cost.

One individual who is working to radically disrupt this field is Michael McCarty, who is the Founder and CEO of a new wave of interactive TV products that will be hitting the market in early 2013. As he suggested in his presentation to the "Community for Interactive Media", "Static media is on its way out, and if Networks would like to stay in the game, they must adapt to consumers needs."

Many think of interactive TV primarily in terms of "one-screen" forms that involve interaction on the TV screen, using the remote control, but there is another significant form of interactive TV that makes use of Two-Screen Solutions, such as NanoGaming.^[6] In this case, the second screen is typically a PC (personal computer) connected to a Web site application. Web applications may be synchronized with the TV broadcast, or be regular websites that provide supplementary content to the live broadcast, either in the form of information, or as interactive game or program. Some two-screen applications allow for interaction from a mobile device (phone or PDA), that run "in synch" with the show.

Such services are sometimes called "Enhanced TV," but this term is in decline, being seen as anachronistic and misused occasionally. (Note: "Enhanced TV" originated in the mid-late 1990s as a term that some hoped would replace the umbrella term of "interactive TV" due to the negative associations "interactive TV" carried because of the way companies and the news media over-hyped its potential in the early 90's.)

Notable Two-Screen Solutions have been offered for specific popular programs by many US broadcast TV networks. Today, two-screen interactive TV is called either 2-screen (for short) or "Synchronized TV" and is widely deployed around the US by national broadcasters with the help of technology offerings from certain companies. The first such application was Chat Television™ (ChatTV.com), originally developed in 1996. The system synchronized online services with television broadcasts, grouping users by time-zone and program so that all real-time viewers could participate in a chat or interactive gathering during the show’s airing.^[7]

One-screen interactive TV generally requires special support in the set-top box, but Two-Screen Solutions, synchronized interactive TV applications generally do not, relying instead on Internet or mobile phone servers to coordinate with the TV and are most often free to the user. Developments from 2006 onwards indicate that the mobile phone can be used for seamless authentication through Bluetooth, explicit authentication through Near Field Communication. Through such an authentication it will be possible to provide personalized services to the mobile phone.

Interactive TV services

Notable interactive TV services are:

• ActiveVideo (formerly known as ICTV) - Pioneers in interactive TV and creators of CloudTV™: A cloud-based interactive TV platform built on current web and television standards. The network-centric approach provides for the bulk of application and video processing to be done in the cloud, and delivers a standard MPEG stream to virtually any digital set-top box, web-connected TV or media device.
• T-commerce - Is a commerce transaction through the set top box return path connection.
• BBC Red Button
• ATVEF - 'Advanced Television Enhancement Forum' is a group of companies that are set up to create HTML based TV products and services. ATVEF's work has resulted in an Enhanced Content Specification which makes it possible for developers to create their content once and have it display properly on any compliant receiver.
• MSN TV - A former serice originally introduced as WebTV. It supplied computerless Internet access. It required a set-top box that sold for $100 to $200, with a monthly access fee. The service was discontinued in 2013, although customer service remained available until 2014.
• Philips Net TV - solution to view Internet content designed for TV; directly integrated inside the TV set. No extra subscription costs or hardware costs involved.
• An Interactive TV purchasing system was introduced in 1994 in France. The system was using a regular TV set connected together with a regular antenna and the Internet for feedback. A demo has shown the possibility of immediate purchasing, interactively with displayed contents.
• QUBE - A very early example of this concept, it was introduced experimentally by Warner Cable (later Time Warner Cable, now part of Charter Spectrum) in Columbus, Ohio in 1977. Its most notable feature was five buttons that could allow the viewers to, among other things, participate in interactive game shows, and answer survey questions. While successful, going on to expand to a few other cities, the service eventually proved to be too expensive to run, and was discontinued by 1984, although the special boxes would continue to be serviced well into the 1990s.

Closed-circuit Interactive television

Television sets can also be used as computer displays or for video games.

User interaction

Interactive TV has been described in human-computer interaction research as "lean back" interaction,^[8] as users are typically relaxing in the living room environment with a remote control in one hand. This is a very simplistic definition of interactive television that is less and less descriptive of interactive television services that are in various stages of market introduction. This is in contrast to the descriptor of personal computer-oriented "lean forward" experience of a keyboard, mouse and monitor. This description is becoming more distracting than useful as video game users, for example, don't lean forward while they are playing video games on their television sets, a precursor to interactive TV. A more useful mechanism for categorizing the differences between PC- and TV-based user interaction is by measuring the distance the user is from the Device. Typically a TV viewer is "leaning back" in their sofa, using only a Remote Control as a means of interaction. While a PC user is 2 ft or 3 ft (60 or 100 cm) from his high resolution screen using a mouse and keyboard. The demands of distance, and user input devices, requires the application's look and feel to be designed differently. Thus Interactive TV applications are often designed for the "10-foot user interface" while PC applications and web pages are designed for the "3ft user experience". This style of interface design rather than the "lean back or lean forward" model is what truly distinguishes Interactive TV from the web or PC.^[9] However even this mechanism is changing because there is at least one web-based service which allows you to watch internet television on a PC with a wireless remote control^{[citation needed]}.

In the case of Two-Screen Solutions Interactive TV, the distinctions of "lean-back" and "lean-forward" interaction become more and more indistinguishable. There has been a growing proclivity to media multitasking, in which multiple media devices are used simultaneously (especially among younger viewers). This has increased interest in two-screen services, and is creating a new level of multitasking in interactive TV. In addition, video is now ubiquitous on the web, so research can now be done to see if there is anything left to the notion of "lean back" "versus" "lean forward" uses of interactive television.

For one-screen services, interactivity is supplied by the manipulation of the API of the particular software installed on a set-top box, referred to as 'middleware' due to its intermediary position in the operating environment. Software programs are broadcast to the set-top box in a 'carousel'.

On UK DTT (Freeview uses ETSI based MHEG-5), and Sky's DTH platform uses ETSI based WTVML in DVB-MHP systems and for OCAP, this is a DSM-CC Object Carousel.

The set-top box can then load and execute the application. In the UK this is typically done by a viewer pressing a "trigger" button on their remote control (e.g. the red button, as in "press red").

Interactive TV Sites have the requirement to deliver interactivity directly from internet servers, and therefore need the set-top box's middleware to support some sort of TV Browser, content translation system or content rendering system. Middleware examples like Liberate are based on a version of HTML/JavaScript and have rendering capabilities built in, while others such as OpenTV and DVB-MHP can load microbrowsers and applications to deliver content from TV Sites. In October 2008, the ITU's J.201 paper on interoperability of TV Sites recommended authoring using ETSI WTVML to achieve interoperability by allowing dynamic TV Site to be automatically translated into various TV dialects of HTML/JavaScript, while maintaining compatibility with middlewares such as MHP and OpenTV via native WTVML microbrowsers.

Typically the distribution system for Standard Definition digital TV is based on the MPEG-2 specification, while High Definition distribution is likely to be based on the MPEG-4 meaning that the delivery of HD often requires a new device or set-top box, which typically are then also able to decode Internet Video via broadband return paths.

Emergent approaches such as the Fango app^[5] have utilised mobile apps on smartphones and tablet devices to present viewers with a hybrid experience across multiple devices, rather than requiring dedicated hardware support.

Interactive television projects

Some interactive television projects are consumer electronics boxes which provide set-top interactivity, while other projects are supplied by the cable television companies (or multiple system operator, or MSO) as a system-wide solution. Even other, newer, approaches integrate the interactive functionality in the TV, thus negating the need for a separate box. Some examples of interactive television include:

• MSOs
  • Cox Communications (US)
  • Time Warner (US)
  • Comcast (US)
  • Cablevision (US)
• Previous MSO trials or demos
  • Tele-TV from Bell Atlantic, NYNEX, Pacific Telesis, Creative Artists Agency (US) - no longer in operation
  • Full Service Network from Time Warner (US) - no longer in operation
  • GTE mainStreet (US) a former product of GTE, also provided over select Continental Cablevision and Daniels cable television systems.
  • Smartbox from TV Cabo, Novabase and Microsoft (PT) - this no longer in operation, although some of the equipment is still used for the digital TV service. This was the pioneer project.
• Consumer electronics solutions
  • TiVo
  • ReplayTV
  • UltimateTV
  • Miniweb Interactive
  • Microsoft Windows XP Media Center
  • Philips Net TV
  • Mirada products
• Two-Screen Solutions, or "enhanced TV" solutions
  • See Enhanced TV
  • Chat Television (IBSC),^[10] purchased by Charter Communications, Inc. in May 2001.
• Hospitality & healthcare solutions
  • LodgeNet

Mobile phone interaction with the STB and the TV

• ITEA WellCom Project using Bluetooth and NFC for authentication, pairing and seamless service access

Interactive Video and Data Services

IVDS is a wireless implementation of interactive TV, it utilizes part of the VHF TV frequency spectrum (218–219 MHz

                                           XO__XO XI PING  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.^[1] The signals are received via an outdoor parabolic antenna commonly referred to as a satellite dish and a low-noise block downconverter.

A satellite receiver then decodes the desired television programme for viewing on a television set. Receivers can be external set-top boxes, or a built-in television tuner. Satellite television provides a wide range of channels and services. It is usually the only television available in many remote geographic areas without terrestrial television or cable television service.

Modern systems signals are relayed from a communications satellite on the K_u band frequencies (12–18 GHz) requiring only a small dish less than a meter in diameter.^[2] The first satellite TV systems were an obsolete type now known as television receive-only. These systems received weaker analog signals transmitted in the C-band (4–8 GHz) from FSS type satellites, requiring the use of large 2–3-meter dishes. Consequently, these systems were nicknamed "big dish" systems, and were more expensive and less popular.^[3]

Early systems used analog signals, but modern ones use digital signals which allow transmission of the modern television standard high-definition television, due to the significantly improved spectral efficiency of digital broadcasting. As of 2018, Star One C2 from Brazil is the only remaining satellite broadcasting in analog signals, as well as one channel (C-SPAN) on AMC-11 from the United States.

Different receivers are required for the two types. Some transmissions and channels are unencrypted and therefore free-to-air or free-to-view, while many other channels are transmitted with encryption (pay television), requiring the viewer to subscribe and pay a monthly fee to receive the programming. 

Technology

Satellite television dishes in Malaysia.

An Inview Neelix set-top box.

Back view of a linear polarised LNB.

Corrugated feedhorn and LNB on a Hughes DirecWay satellite dish.

The satellites used for broadcasting television are usually in a geostationary orbit 37,000 km (23,000 mi) above the earth's equator. The advantage of this orbit is that the satellite's orbital period equals the rotation rate of the Earth, so the satellite appears at a fixed position in the sky. Thus the satellite dish antenna which receives the signal can be aimed permanently at the location of the satellite, and does not have to track a moving satellite. A few systems instead use a highly elliptical orbit with inclination of +/−63.4 degrees and orbital period of about twelve hours, known as a Molniya orbit.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility.^[6] Uplink satellite dishes are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter.^[6] The increased diameter results in more accurate aiming and increased signal strength at the satellite.^[6] The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite.^[7] The transponder re-transmits the signals back to Earth at a different frequency (a process known as translation, used to avoid interference with the uplink signal), typically in the C-band (4–8 GHz), K_u-band (12–18 GHz), or both.^[6] The leg of the signal path from the satellite to the receiving Earth station is called the downlink.^[8]

A typical satellite has up to 32 K_u-band or 24 C-band transponders, or more for K_u/C hybrid satellites.^[9] Typical transponders each have a bandwidth between 27 and 50 MHz.^[9] Each geostationary C-band satellite needs to be spaced 2° longitude from the next satellite to avoid interference; for K_u the spacing can be 1°.^[10] This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites or 360/1 = 360 geostationary K_u-band satellites.^[10] C-band transmission is susceptible to terrestrial interference while K_u-band transmission is affected by rain (as water is an excellent absorber of microwaves at this particular frequency).^[11] The latter is even more adversely affected by ice crystals in thunder clouds.^[11]

On occasion, sun outage will occur when the sun lines up directly behind the geostationary satellite to which the receiving antenna is pointed.^[12] The downlink satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected with a parabolic receiving dish, which reflects the weak signal to the dish's focal point.^[13] Mounted on brackets at the dish's focal point is a device called a feedhorn or collector.^[14] The feedhorn is a section of waveguide with a flared front-end that gathers the signals at or near the focal point and conducts them to a probe or pickup connected to a low-noise block downconverter (LNB).^[15] The LNB amplifies the signals and downconverts them to a lower block of intermediate frequencies (IF), usually in the L-band.^[15]

The original C-band satellite television systems used a low-noise amplifier (LNA) connected to the feedhorn at the focal point of the dish.^[16] The amplified signal, still at the higher microwave frequencies, had to be fed via very expensive low-loss 50-ohm impedance gas filled hardline coaxial cable with relatively complex N-connectors to an indoor receiver or, in other designs, a downconverter (a mixer and a voltage-tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency.^[16] The channel selection was controlled typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend, but this design evolved.^[16]

Designs for microstrip-based converters for amateur radio frequencies were adapted for the 4 GHz C-band.^[17] Central to these designs was concept of block downconversion of a range of frequencies to a lower, more easily handled IF.^[17]

The advantages of using an LNB are that cheaper cable can be used to connect the indoor receiver to the satellite television dish and LNB, and that the technology for handling the signal at L-band and UHF was far cheaper than that for handling the signal at C-band frequencies.^[18] The shift to cheaper technology from the hardline and N-connectors of the early C-band systems to the cheaper and simpler 75-ohm cable and F-connectors allowed the early satellite television receivers to use, what were in reality, modified UHF television tuners which selected the satellite television channel for down conversion to a lower intermediate frequency centered on 70 MHz, where it was demodulated.^[18] This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where only small numbers of systems costing thousands of US dollars were built, to a far more commercial one of mass production.^[18]

In the United States, service providers use the intermediate frequency ranges of 950–2150 MHz to carry the signal from the LNBF at the dish down to the receiver. This allows for transmission of UHF signals along the same span of coaxial wire at the same time. In some applications (DirecTV AU9-S and AT-9), ranges of the lower B-band.  and 2250–3000 MHz, are used. Newer LNBFs in use by DirecTV, called SWM (Single Wire Multiswitch), are used to implement single cable distribution and use a wider frequency range of 2–2150 MHz.

The satellite receiver or set-top box demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.).^[19] Often, the receiver includes the capability to selectively unscramble or decrypt the received signal to provide premium services to some subscribers; the receiver is then called an integrated receiver/decoder or IRD.^[20] Low-loss cable (e.g. RG-6, RG-11, etc.) is used to connect the receiver to the LNBF or LNB.^[15] RG-59 is not recommended for this application as it is not technically designed to carry frequencies above 950 MHz, but may work in some circumstances, depending on the quality of the coaxial wire, signal levels, cable length, etc.^[15]

A practical problem relating to home satellite reception is that an LNB can basically only handle a single receiver.^[21] This is because the LNB is translating two different circular polarizations (right-hand and left-hand) and, in the case of K-band, two different frequency bands (lower and upper) to the same frequency range on the cable.^[21] Depending on which frequency and polarization a transponder is using, the satellite receiver has to switch the LNB into one of four different modes in order to receive a specific "channel".^[21] This is handled by the receiver using the DiSEqC protocol to control the LNB mode.^[21] If several satellite receivers are to be attached to a single dish, a so-called multiswitch will have to be used in conjunction with a special type of LNB.^[21] There are also LNBs available with a multiswitch already integrated.^[21] This problem becomes more complicated when several receivers are to use several dishes (or several LNBs mounted in a single dish) pointing to different satellites.

A common solution for consumers wanting to access multiple satellites is to deploy a single dish with a single LNB and to rotate the dish using an electric motor. The axis of rotation has to be set up in the north-south direction and, depending on the geographical location of the dish, have a specific vertical tilt. Set up properly the motorized dish when turned will sweep across all possible positions for satellites lined up along the geostationary orbit directly above the equator. The disk will then be capable of receiving any geostationary satellite that is visible at the specific location, i.e. that is above the horizon. The DiSEqC protocol has been extended to encompass commands for steering dish rotors. 

There are five major components in a satellite system: the programming source, the broadcast center, the satellite, the satellite dish, and the receiver. "Direct broadcast" satellites used for transmission of satellite television signals are generally in geostationary orbit 37,000 km (23,000 mi) above the earth's equator.^[22] The reason for using this orbit is that the satellite circles the Earth at the same rate as the Earth rotates, so the satellite appears at a fixed point in the sky. Thus satellite dishes can be aimed permanently at that point, and don't need a tracking system to turn to follow a moving satellite. A few satellite TV systems use satellites in a Molniya orbit, a highly elliptical orbit with inclination of +/-63.4 degrees and orbital period of about twelve hours.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility.^[22] Uplink facilities transmit the signal to the satellite over a narrow beam of microwaves, typically in the C-band frequency range due to its resistance to rain fade.^[22] Uplink satellite dishes are very large, often as much as 9 to 12 metres (30 to 40 feet) in diameter^[22] to achieve accurate aiming and increased signal strength at the satellite, to improve reliability.^[22] The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite.^[22] The transponder then converts the signals to K_u band, a process known as "translation," and transmits them back to earth to be received by home satellite stations.^[22]

The downlinked satellite signal, weaker after traveling the great distance (see inverse-square law), is collected by using a rooftop parabolic receiving dish ("satellite dish"), which reflects the weak signal to the dish's focal point.^[23] Mounted on brackets at the dish's focal point is a feedhorn^[23] which passes the signals through a waveguide to a device called a low-noise block converter (LNB) or low noise converter (LNC) attached to the horn.^[23] The LNB amplifies the weak signals, filters the block of frequencies in which the satellite television signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range.^[23] The signal is then passed through a coaxial cable into the residence to the satellite television receiver, a set-top box next to the television.

The reason for using the LNB to do the frequency translation at the dish is so that the signal can be carried into the residence using cheap coaxial cable. To transport the signal into the house at its original K_u band microwave frequency would require an expensive waveguide, a metal pipe to carry the radio waves.^[24] The cable connecting the receiver to the LNB are of the low loss type RG-6, quad shield RG-6, or RG-11.^[25] RG-59 is not recommended for this application as it is not technically designed to carry frequencies above 950 MHz, but will work in many circumstances, depending on the quality of the coaxial wire.^[25] The shift to more affordable technology from the 50 ohm impedance cable and N-connectors of the early C-band systems to the cheaper 75 ohm technology and F-connectors allowed the early satellite television receivers to use, what were in reality, modified UHF television tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated.^[24]

An LNB can only handle a single receiver.^[21] This is due to the fact that the LNB is mapping two different circular polarisations – right hand and left hand – and in the case of the K_u-band two different reception bands – lower and upper – to one and the same frequency band on the cable, and is a practical problem for home satellite reception.^[21] Depending on which frequency a transponder is transmitting at and on what polarisation it is using, the satellite receiver has to switch the LNB into one of four different modes in order to receive a specific desired program on a specific transponder.^[21] The receiver uses the DiSEqC protocol to control the LNB mode, which handles this.^[21] If several satellite receivers are to be attached to a single dish a so-called multiswitch must be used in conjunction with a special type of LNB.^[21] There are also LNBs available with a multiswitch already integrated.^[21] This problem becomes more complicated when several receivers use several dishes or several LNBs mounted in a single dish are aimed at different satellites.^[21]

The set-top box selects the channel desired by the user by filtering that channel from the multiple channels received from the satellite, converts the signal to a lower intermediate frequency, decrypts the encrypted signal, demodulates the radio signal and sends the resulting video signal to the television through a cable.^[25] To decrypt the signal the receiver box must be "activated" by the satellite company. If the customer fails to pay his monthly bill the box is "deactivated" by a signal from the company, and the system will not work until the company reactivates it. Some receivers are capable of decrypting the received signal itself. These receivers are called integrated receiver/decoders or IRDs.

Analog television which was distributed via satellite was usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide a raw audio signal.

Later signals were digitized television signal or multiplex of signals, typically QPSK. In general, digital television, including that transmitted via satellites, is based on open standards such as MPEG and DVB-S/DVB-S2 or ISDB-S . 

The conditional access encryption/scrambling methods include NDS, BISS, Conax, Digicipher, Irdeto, Cryptoworks, DG Crypt, Beta digital, SECA Mediaguard, Logiways, Nagravision, PowerVu, Viaccess, Videocipher, and VideoGuard. Many conditional access systems have been compromised.

Sun outage

An event called sun outage occurs when the sun lines up directly behind the satellite in the field of view of the receiving satellite dish.^[26] This happens for about a 10-minute period daily around midday, twice every year for a two-week period in the spring and fall around the equinox. During this period, the sun is within the main lobe of the dish's reception pattern, so the strong microwave noise emitted by the sun on the same frequencies used by the satellite's transponders drowns out reception.^[26]

Uses

Direct broadcast via satellite

DBS satellite dishes installed on an apartment complex.

A Sky "minidish".

Direct-To-Home (DTHTV) can either refer to the communications satellites themselves that deliver service or the actual television service.^[27] Most satellite television customers in developed television markets get their programming through a direct broadcast satellite provider.^[27] Signals are transmitted using K_u band and are completely digital which means it has high picture and stereo sound quality.^[2]

Programming for satellite television channels comes from multiple sources and may include live studio feeds.^[28] The broadcast center assembles and packages programming into channels for transmission and, where necessary, encrypts the channels. The signal is then sent to the uplink ^[29] where it is transmitted to the satellite. With some broadcast centers, the studios, administration and up-link are all part of the same campus.^[30] The satellite then translates and broadcasts the channels.^[31]

Most systems use the DVB-S standard for transmission.^[27] With pay television services, the datastream is encrypted and requires proprietary reception equipment. While the underlying reception technology is similar, the pay television technology is proprietary, often consisting of a conditional-access module and smart card. This measure assures satellite television providers that only authorized, paying subscribers have access to pay television content but at the same time can allow free-to-air channels to be viewed even by the people with standard equipment available in the market.

Some countries operate satellite television services which can be received for free, without paying a subscription fee. This is called free-to-air satellite television. Germany is likely the leader in free-to-air with approximately 250 digital channels (including 83 HDTV channels and various regional channels) broadcast from the Astra 19.2°E satellite constellation.^[32] These are not marketed as a DBS service, but are received in approximately 18 million homes, as well as in any home using the Sky Deutschland commercial DBS system. All German analogue satellite broadcasts ceased on 30 April 2012.^[33][34]

The United Kingdom has approximately 160 digital channels (including the regional variations of BBC channels, ITV channels, Channel 4 and Channel 5) that are broadcast without encryption from the Astra 28.2°E satellite constellation, and receivable on any DVB-S receiver (a DVB-S2 receiver is required for certain high definition television services). Most of these channels are included within the Sky EPG, and an increasing number within the Freesat EPG.

India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD Free Dish", which is provided as in-fill for the country's terrestrial transmission network. It is broadcast from GSAT-15 at 93.5°E and contains about 80 FTA channels.

While originally launched as backhaul for their digital terrestrial television service, a large number of French channels are free-to-air on satellites at 5°W, and have recently been announced as being official in-fill for the DTT network.

In North America (United States, Canada and Mexico) there are over 80 FTA digital channels available on Galaxy 19 (with the majority being ethnic or religious in nature). Other FTA satellites include AMC-4, AMC-6, Galaxy 18, and Satmex 5. A company called GloryStar promotes FTA religious broadcasters on Galaxy 19.

Television receive-only

A C-band satellite dish used by TVRO systems.

The term Television receive-only, or TVRO, arose during the early days of satellite television reception to differentiate it from commercial satellite television uplink and downlink operations (transmit and receive). This was the primary method of satellite television transmissions before the satellite television industry shifted, with the launch of higher powered DBS satellites in the early 1990s which transmitted their signals on the K_u band frequencies.^[3][35] Satellite television channels at that time were intended to be used by cable television networks rather than received by home viewers.^[36] Early satellite television receiver systems were largely constructed by hobbyists and engineers. These early TVRO systems operated mainly on the C-band frequencies and the dishes required were large; typically over 3 meters (10 ft) in diameter.^[37] Consequently, TVRO is often referred to as "big dish" or "Big Ugly Dish" (BUD) satellite television.

TVRO systems were designed to receive analog and digital satellite feeds of both television or audio from both C-band and K_u-band transponders on FSS-type satellites.^[38][39] The higher frequency K_u-band systems tend to resemble DBS systems and can use a smaller dish antenna because of the higher power transmissions and greater antenna gain. TVRO systems tend to use larger rather than smaller satellite dish antennas, since it is more likely that the owner of a TVRO system would have a C-band-only setup rather than a K_u band-only setup. Additional receiver boxes allow for different types of digital satellite signal reception, such as DVB/MPEG-2 and 4DTV.

The narrow beam width of a normal parabolic satellite antenna means it can only receive signals from a single satellite at a time.^[40] Simulsat or the Vertex-RSI TORUS, is a quasi-parabolic satellite earthstation antenna that is capable of receiving satellite transmissions from 35 or more C- and K_u-band satellites simultaneously.

Back Light

Early history

In 1945 British science fiction writer Arthur C. Clarke proposed a worldwide communications system which would function by means of three satellites equally spaced apart in earth orbit.^[42][43] This was published in the October 1945 issue of the Wireless World magazine and won him the Franklin Institute's Stuart Ballantine Medal in 1963.^[44][45]

The first public satellite television signals from Europe to North America were relayed via the Telstar satellite over the Atlantic ocean on 23 July 1962, although a test broadcast had taken place almost two weeks earlier on 11 July.^[46] The signals were received and broadcast in North American and European countries and watched by over 100 million.^[46] Launched in 1962, the Relay 1 satellite was the first satellite to transmit television signals from the US to Japan.^[47] The first geosynchronous communication satellite, Syncom 2, was launched on 26 July 1963.^[48]

The world's first commercial communications satellite, called Intelsat I and nicknamed "Early Bird", was launched into geosynchronous orbit on April 6, 1965.^[49] The first national network of television satellites, called Orbita, was created by the Soviet Union in October 1967, and was based on the principle of using the highly elliptical Molniya satellite for rebroadcasting and delivering of television signals to ground downlink stations.^[50] The first commercial North American satellite to carry television transmissions was Canada's geostationary Anik 1, which was launched on 9 November 1972.^[51] ATS-6, the world's first experimental educational and direct broadcast satellite (DBS), was launched on 30 May 1974.^[52] It transmitted at 860 MHz using wideband FM modulation and had two sound channels. The transmissions were focused on the Indian subcontinent but experimenters were able to receive the signal in Western Europe using home constructed equipment that drew on UHF television design techniques already in use.^[53]

The first in a series of Soviet geostationary satellites to carry direct-to-home television, Ekran 1, was launched on 26 October 1976.^[54] It used a 714 MHz UHF downlink frequency so that the transmissions could be received with existing UHF television technology rather than microwave technology.^[55]

Beginning of the satellite TV industry, 1976–1980

The satellite television industry developed first in the US from the cable television industry as communication satellites were being used to distribute television programming to remote cable television headends. Home Box Office (HBO), Turner Broadcasting System (TBS), and Christian Broadcasting Network (CBN, later The Family Channel) were among the first to use satellite television to deliver programming. Taylor Howard of San Andreas, California became the first person to receive C-band satellite signals with his home-built system in 1976.^[56]

In the US, PBS, a non-profit public broadcasting service, began to distribute its television programming by satellite in 1978.^[57]

In 1979, Soviet engineers developed the Moskva (or Moscow) system of broadcasting and delivering of TV signals via satellites. They launched the Gorizont communication satellites later that same year. These satellites used geostationary orbits.^[58] They were equipped with powerful on-board transponders, so the size of receiving parabolic antennas of downlink stations was reduced to 4 and 2.5 metres.^[58] On October 18, 1979, the Federal Communications Commission (FCC) began allowing people to have home satellite earth stations without a federal government license.^[59] The front cover of the 1979 Neiman-Marcus Christmas catalogue featured the first home satellite TV stations on sale for $36,500.^[60] The dishes were nearly 20 feet (6.1 m) in diameter^[61] and were remote controlled.^[62] The price went down by half soon after that, but there were only eight more channels.^[63] The Society for Private and Commercial Earth Stations (SPACE), an organisation which represented consumers and satellite TV system owners, was established in 1980.^[64]

Early satellite television systems were not very popular due to their expense and large dish size.^[65] The satellite television dishes of the systems in the late 1970s and early 1980s were 10 to 16 feet (3.0 to 4.9 m) in diameter,^[66] made of fibreglass or solid aluminum or steel,^[67] and in the United States cost more than $5,000, sometimes as much as $10,000.^[68] Programming sent from ground stations was relayed from eighteen satellites in geostationary orbit located 22,300 miles (35,900 km) above the Earth.^[69][70]

TVRO/C-band satellite era, 1980–1986

By 1980, satellite television was well established in the USA and Europe. On 26 April 1982, the first satellite channel in the UK, Satellite Television Ltd. (later Sky1), was launched.^[71] Its signals were transmitted from the ESA's Orbital Test Satellites.^[71] Between 1981 and 1985, TVRO systems' sales rates increased as prices fell. Advances in receiver technology and the use of gallium arsenide FET technology enabled the use of smaller dishes. Five hundred thousand systems, some costing as little as $2000, were sold in the US in 1984.^[68][72] Dishes pointing to one satellite were even cheaper.^[73] People in areas without local broadcast stations or cable television service could obtain good-quality reception with no monthly fees.^[68][70] The large dishes were a subject of much consternation, as many people considered them eyesores, and in the US most condominiums, neighborhoods, and other homeowner associations tightly restricted their use, except in areas where such restrictions were illegal.^[3] These restrictions were altered in 1986 when the Federal Communications Commission ruled all of them illegal.^[65] A municipality could require a property owner to relocate the dish if it violated other zoning restrictions, such as a setback requirement, but could not outlaw their use.^[65] The necessity of these restrictions would slowly decline as the dishes got smaller.^[65]

Originally, all channels were broadcast in the clear (ITC) because the equipment necessary to receive the programming was too expensive for consumers. With the growing number of TVRO systems, the program providers and broadcasters had to scramble their signal and develop subscription systems.

In October 1984, the U.S. Congress passed the Cable Communications Policy Act of 1984, which gave those using TVRO systems the right to receive signals for free unless they were scrambled, and required those who did scramble to make their signals available for a reasonable fee.^[70][74] Since cable channels could prevent reception by big dishes, other companies had an incentive to offer competition.^[75] In January 1986, HBO began using the now-obsolete VideoCipher II system to encrypt their channels.^[66] Other channels used less secure television encryption systems. The scrambling of HBO was met with much protest from owners of big-dish systems, most of which had no other option at the time for receiving such channels, claiming that clear signals from cable channels would be difficult to receive.^[76] Eventually HBO allowed dish owners to subscribe directly to their service for $12.95 per month, a price equal to or higher than what cable subscribers were paying, and required a descrambler to be purchased for $395.^[76] This led to the attack on HBO's transponder Galaxy 1 by John R. MacDougall in April 1986.^[76] One by one, all commercial channels followed HBO's lead and began scrambling their channels.^[77] The Satellite Broadcasting and Communications Association (SBCA) was founded on December 2, 1986 as the result of a merger between SPACE and the Direct Broadcast Satellite Association (DBSA).^[72]

Videocipher II used analog scrambling on its video signal and Data Encryption Standard–based encryption on its audio signal. VideoCipher II was defeated, and there was a black market for descrambler devices which were initially sold as "test" devices.^[77]

The necessity for better satellite television programming than TVRO arose in the 1980s. Satellite television services, first in Europe, began transmitting K_u band signals in the late 1980s. On 11 December 1988 Luxembourg launched Astra 1A, the first satellite to provide medium power satellite coverage to Western Europe.^[78] This was one of the first medium-powered satellites, transmitting signals in K_u band and allowing reception with small(90 cm) dishes for the first time ever.^[78] The launch of Astra beat the winner of the UK's state Direct Broadcast Satellite licence, British Satellite Broadcasting, to the market, and accelerated its demise.

1990s to present

By 1987, nine channels were scrambled, but 99 others were available free-to-air.^[74] While HBO initially charged a monthly fee of $19.95, soon it became possible to unscramble all channels for $200 a year.^[74] Dish sales went down from 600,000 in 1985 to 350,000 in 1986, but pay television services were seeing dishes as something positive since some people would never have cable service, and the industry was starting to recover as a result.^[74] Scrambling also led to the development of pay-per-view events.^[74] On November 1, 1988, NBC began scrambling its C-band signal but left its K_u band signal unencrypted in order for affiliates to not lose viewers who could not see their advertising.^[79] Most of the two million satellite dish users in the United States still used C-band.^[79]ABC and CBS were considering scrambling, though CBS was reluctant due to the number of people unable to receive local network affiliates.^[79] The piracy on satellite television networks in the US led to the introduction of the Cable Television Consumer Protection and Competition Act of 1992. This legislation enabled anyone caught engaging in signal theft to be fined up to $50,000 and to be sentenced to a maximum of two years in prison.^[80] A repeat offender can be fined up to $100,000 and be imprisoned for up to five years.^[80]

Satellite television had also developed in Europe but it initially used low power communication satellites and it required dish sizes of over 1.7 metres. On 11 December 1988 Luxembourg launched Astra 1A, the first satellite to provide medium power satellite coverage to Western Europe.^[81] This was one of the first medium-powered satellites, transmitting signals in K_u band and allowing reception with small dishes (90 cm).^[81] The launch of Astra beat the winner of the UK's state Direct Broadcast Satellite licence holder, British Satellite Broadcasting, to the market.

In the US in the early 1990s, four large cable companies launched PrimeStar, a direct broadcasting company using medium power satellites. The relatively strong transmissions allowed the use of smaller (90 cm) dishes. Its popularity declined with the 1994 launch of the Hughes DirecTV and Dish Network satellite television systems.

On March 4, 1996 EchoStar introduced Digital Sky Highway (Dish Network) using the EchoStar 1 satellite.^[82] EchoStar launched a second satellite in September 1996 to increase the number of channels available on Dish Network to 170.^[82] These systems provided better pictures and stereo sound on 150–200 video and audio channels, and allowed small dishes to be used. This greatly reduced the popularity of TVRO systems. In the mid-1990s, channels began moving their broadcasts to digital television transmission using the DigiCipher conditional access system.^[83]

In addition to encryption, the widespread availability, in the US, of DBS services such as PrimeStar and DirecTV had been reducing the popularity of TVRO systems since the early 1990s. Signals from DBS satellites (operating in the more recent K_u band) are higher in both frequency and power (due to improvements in the solar panels and energy efficiency of modern satellites) and therefore require much smaller dishes than C-band, and the digital modulation methods now used require less signal strength at the receiver than analog modulation methods.^[84] Each satellite also can carry up to 32 transponders in the K_u band, but only 24 in the C band, and several digital subchannels can be multiplexed (MCPC) or carried separately (SCPC) on a single transponder.^[85] Advances in noise reduction due to improved microwave technology and semiconductor materials have also had an effect.^[85] However, one consequence of the higher frequencies used for DBS services is rain fade where viewers lose signal during a heavy downpour. C-band satellite television signals are less prone to rain fade.^[86]

In a return to the older (but proven) technologies of satellite communication, the current DBS-based satellite providers in the USA (Dish Network and DirecTV) are now utilizing additional capacity on the K_u-band transponders of existing FSS-class satellites, in addition to the capacity on their own existing fleets of DBS satellites in orbit. This was done in order to provide more channel capacity for their systems, as required by the increasing number of High-Definition and simulcast local station channels. The reception of the channels carried on the K_u-band FSS satellite's respective transponders has been achieved by both DirecTV & Dish Network issuing to their subscribers dishes twice as big in diameter (36") than the previous 18" (& 20" for the Dish Network "Dish500") dishes the services used initially, equipped with 2 circular-polarized LNBFs (for reception of 2 native DBS satellites of the provider, 1 per LNBF), and 1 standard linear-polarized LNB for reception of channels from an FSS-type satellite. These newer DBS/FSS-hybrid dishes, marketed by DirecTV and Dish Network as the "SlimLine" and "SuperDish" models respectively, are now the current standard for both providers, with their original 18"/20" single or dual LNBF dishes either now obsolete, or only used for program packages, separate channels, or services only broadcast over the providers' DBS satellites.

On 29 November 1999 US President Bill Clinton signed the Satellite Home Viewer Improvement Act (SHVIA). The act allowed Americans to receive local broadcast signals via direct broadcast satellite systems for the first time.

Satellite Television for the Asian Region (STAR), a service based in Mumbai and Hong Kong which now provides satellite TV coverage to Asia and Australia, introduced satellite TV to the Asian region in the early 1990s. It began broadcasting signals using the AsiaSat 1 satellite on 1 January 1991. 

                                    XO___XO XI PING X  The Signal Diode 

Signal Diodes are small two-terminal which conducts current when forward biased and blocks current flow when reverse biased . 

                                   

The semiconductor Signal Diode is a small non-linear semiconductor devices generally used in electronic circuits, where small currents or high frequencies are involved such as in radio, television and digital logic circuits.

Signal diodes, also sometimes known by its older name of the Point Contact Diode or the Glass Passivated Diode, are physically very small in size compared to their larger Power Diode cousins.

Generally, the PN junction of a small signal diode is encapsulated in glass to protect the PN junction, and usually have a red or black band at one end of their body to help identify which end is the cathode terminal. The most widely used of all the glass encapsulated signal diodes is the very common 1N4148 and its equivalent 1N914 signal diode.

Small signal and switching diodes have much lower power and current ratings, around 150mA, 500mW maximum compared to rectifier diodes, but they can function better in high frequency applications or in clipping and switching applications that deal with short-duration pulse waveforms.

The characteristics of a signal point contact diode are different for both germanium and silicon types and are given as:

• 1. Germanium Signal Diodes – These have a low reverse resistance value giving a lower forward volt drop across the junction, typically only about 0.2 to 0.3v, but have a higher forward resistance value because of their small junction area.
• 2. Silicon Signal Diodes – These have a very high value of reverse resistance and give a forward volt drop of about 0.6 to 0.7v across the junction. They have fairly low values of forward resistance giving them high peak values of forward current and reverse voltage.

The electronic symbol given for any type of diode is that of an arrow with a bar or line at its end and this is illustrated below along with the Steady State V-I Characteristics Curve.

Silicon Diode V-I Characteristic Curve

The arrow always points in the direction of conventional current flow through the diode meaning that the diode will only conduct if a positive supply is connected to the Anode, ( a ) terminal and a negative supply is connected to the Cathode ( k ) terminal thus only allowing current to flow through it in one direction only, acting more like a one way electrical valve, ( Forward Biased Condition ).

However, we know from the previous tutorial that if we connect the external energy source in the other direction the diode will block any current flowing through it and instead will act like an open switch, ( Reversed Biased Condition ) as shown below.

Forward and Reversed Biased Diode

Then we can say that an ideal small signal diode conducts current in one direction ( forward-conducting ) and blocks current in the other direction ( reverse-blocking ). Signal Diodes are used in a wide variety of applications such as a switch in rectifiers, current limiters, voltage snubbers or in wave-shaping circuits.

Signal Diode Parameters

Signal Diodes are manufactured in a range of voltage and current ratings and care must be taken when choosing a diode for a certain application. There are a bewildering array of static characteristics associated with the humble signal diode but the more important ones are.

1. Maximum Forward Current

The Maximum Forward Current ( IF(max) ) is as its name implies the maximum forward current allowed to flow through the device. When the diode is conducting in the forward bias condition, it has a very small “ON” resistance across the PN junction and therefore, power is dissipated across this junction ( Ohm´s Law ) in the form of heat.

Then, exceeding its ( IF(max) ) value will cause more heat to be generated across the junction and the diode will fail due to thermal overload, usually with destructive consequences. When operating diodes around their maximum current ratings it is always best to provide additional cooling to dissipate the heat produced by the diode.

For example, our small 1N4148 signal diode has a maximum current rating of about 150mA with a power dissipation of 500mW at 25oC. Then a resistor must be used in series with the diode to limit the forward current, ( IF(max) ) through it to below this value.

2. Peak Inverse Voltage

The Peak Inverse Voltage (PIV) or Maximum Reverse Voltage ( VR(max) ), is the maximum allowable Reverse operating voltage that can be applied across the diode without reverse breakdown and damage occurring to the device. This rating therefore, is usually less than the “avalanche breakdown” level on the reverse bias characteristic curve. Typical values of VR(max) range from a few volts to thousands of volts and must be considered when replacing a diode.

The peak inverse voltage is an important parameter and is mainly used for rectifying diodes in AC rectifier circuits with reference to the amplitude of the voltage were the sinusoidal waveform changes from a positive to a negative value on each and every cycle.

3. Total Power Dissipation

Signal diodes have a Total Power Dissipation, ( PD(max) ) rating. This rating is the maximum possible power dissipation of the diode when it is forward biased (conducting). When current flows through the signal diode the biasing of the PN junction is not perfect and offers some resistance to the flow of current resulting in power being dissipated (lost) in the diode in the form of heat.

As small signal diodes are non-linear devices the resistance of the PN junction is not constant, it is a dynamic property then we cannot use Ohms Law to define the power in terms of current and resistance or voltage and resistance as we can for resistors. Then to find the power that will be dissipated by the diode we must multiply the voltage drop across it times the current flowing through it: PD = V*I

4. Maximum Operating Temperature

The Maximum Operating Temperature actually relates to the Junction Temperature ( TJ ) of the diode and is related to maximum power dissipation. It is the maximum temperature allowable before the structure of the diode deteriorates and is expressed in units of degrees centigrade per Watt, ( oC/W ).

This value is linked closely to the maximum forward current of the device so that at this value the temperature of the junction is not exceeded. However, the maximum forward current will also depend upon the ambient temperature in which the device is operating so the maximum forward current is usually quoted for two or more ambient temperature values such as 25oC or 70oC.

Then there are three main parameters that must be considered when either selecting or replacing a signal diode and these are:

• The Reverse Voltage Rating
• The Forward Current Rating
• The Forward Power Dissipation Rating

Signal Diode Arrays

When space is limited, or matching pairs of switching signal diodes are required, diode arrays can be very useful. They generally consist of low capacitance high speed silicon diodes such as the 1N4148 connected together in multiple diode packages called an array for use in switching and clamping in digital circuits. They are encased in single inline packages (SIP) containing 4 or more diodes connected internally to give either an individual isolated array, common cathode, (CC), or a common anode, (CA) configuration as shown.

Signal Diode Arrays

Signal diode arrays can also be used in digital and computer circuits to protect high speed data lines or other input/output parallel ports against electrostatic discharge, (ESD) and voltage transients.

By connecting two diodes in series across the supply rails with the data line connected to their junction as shown, any unwanted transients are quickly dissipated and as the signal diodes are available in 8-fold arrays they can protect eight data lines in a single package.

CPU Data Line Protection

Signal diode arrays can also be used to connect together diodes in either series or parallel combinations to form voltage regulator or voltage reducing type circuits or even to produce a known fixed reference voltage.

We know that the forward volt drop across a silicon diode is about 0.7v and by connecting together a number of diodes in series the total voltage drop will be the sum of the individual voltage drops of each diode.

However, when signal diodes are connected together in series, the current will be the same for each diode so the maximum forward current must not be exceeded.

Connecting Signal Diodes in Series

Another application for the small signal diode is to create a regulated voltage supply. Diodes are connected together in series to provide a constant DC voltage across the diode combination. The output voltage across the diodes remains constant in spite of changes in the load current drawn from the series combination or changes in the DC power supply voltage that feeds them. Consider the circuit below.

Signal Diodes in Series

As the forward voltage drop across a silicon diode is almost constant at about 0.7v, while the current through it varies by relatively large amounts, a forward-biased signal diode can make a simple voltage regulating circuit. The individual voltage drops across each diode are subtracted from the supply voltage to leave a certain voltage potential across the load resistor, and in our simple example above this is given as 10v - ( 3*0.7V ) = 7.9V.

This is because each diode has a junction resistance relating to the small signal current flowing through it and the three signal diodes in series will have three times the value of this resistance, along with the load resistance R, forms a voltage divider across the supply.

By adding more diodes in series a greater voltage reduction will occur. Also series connected diodes can be placed in parallel with the load resistor to act as a voltage regulating circuit. Here the voltage applied to the load resistor will be 3*0.7v = 2.1V. We can of course produce the same constant voltage source using a single Zener Diode. Resistor, RD is used to prevent excessive current flowing through the diodes if the load is removed.

Freewheel Diodes

Signal diodes can also be used in a variety of clamping, protection and wave shaping circuits with the most common form of clamping diode circuit being one which uses a diode connected in parallel with a coil or inductive load to prevent damage to the delicate switching circuit by suppressing the voltage spikes and/or transients that are generated when the load is suddenly turned “OFF”. This type of diode is generally known as a “Free Wheeling Diode”, “Flywheel Diode” or simply Freewheel diode as it is more commonly called.

The Freewheel diode is used to protect solid state switches such as power transistors and MOSFET’s from damage by reverse battery protection as well as protection from highly inductive loads such as relay coils or motors, and an example of its connection is shown below.

Use of the Freewheel Diode

Modern fast switching, power semiconductor devices require fast switching diodes such as free wheeling diodes to protect them form inductive loads such as motor coils or relay windings. Every time the switching device above is turned “ON”, the freewheel diode changes from a conducting state to a blocking state as it becomes reversed biased.

However, when the device rapidly turns “OFF”, the diode becomes forward biased and the collapse of the energy stored in the coil causes a current to flow through the freewheel diode. Without the protection of the freewheel diode high di/dt currents would occur causing a high voltage spike or transient to flow around the circuit possibly damaging the switching device.

Previously, the operating speed of the semiconductor switching device, either transistor, MOSFET, IGBT or digital has been impaired by the addition of a freewheel diode across the inductive load with Schottky and Zener diodes being used instead in some applications. But during the past few years however, freewheel diodes had regained importance due mainly to their improved reverse-recovery characteristics and the use of super fast semiconductor materials capable at operating at high switching frequencies.

Other types of specialized diodes not included here are Photo-Diodes, PIN Diodes, Tunnel Diodes and Schottky Barrier Diodes. By adding more PN junctions to the basic two layer diode structure other types of semiconductor devices can be made.

For example a three layer semiconductor device becomes a Transistor, a four layer semiconductor device becomes a Thyristor or Silicon Controlled Rectifier and five layer devices known as Triac’s are also available.

In the next tutorial about diodes, we will look at the large signal diode sometimes called the Power Diode. Power diodes are silicon diodes designed for use in high-voltage, high-current mains rectification circuits. 

  

                                        The Light Emitting Diode

Light Emitting Diodes or simply LED´s, are among the most widely used of all the different types of semiconductor diodes available today and are commonly used in TV’s and colour displays. 

                                                  

They are the most visible type of diode, that emit a fairly narrow bandwidth of either visible light at different coloured wavelengths, invisible infra-red light for remote controls or laser type light when a forward current is passed through them.

The “Light Emitting Diode” or LED as it is more commonly called, is basically just a specialised type of diode as they have very similar electrical characteristics to a PN junction diode. This means that an LED will pass current in its forward direction but block the flow of current in the reverse direction.

Light emitting diodes are made from a very thin layer of fairly heavily doped semiconductor material and depending on the semiconductor material used and the amount of doping, when forward biased an LED will emit a coloured light at a particular spectral wavelength.

When the diode is forward biased, electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable number of these photons can leave the junction and radiate away producing a coloured light output.

LED Construction

Then we can say that when operated in a forward biased direction Light Emitting Diodes are semiconductor devices that convert electrical energy into light energy.

The construction of a Light Emitting Diode is very different from that of a normal signal diode. The PN junction of an LED is surrounded by a transparent, hard plastic epoxy resin hemispherical shaped shell or body which protects the LED from both vibration and shock.

Surprisingly, an LED junction does not actually emit that much light so the epoxy resin body is constructed in such a way that the photons of light emitted by the junction are reflected away from the surrounding substrate base to which the diode is attached and are focused upwards through the domed top of the LED, which itself acts like a lens concentrating the amount of light. This is why the emitted light appears to be brightest at the top of the LED.

However, not all LEDs are made with a hemispherical shaped dome for their epoxy shell. Some indication LEDs have a rectangular or cylindrical shaped construction that has a flat surface on top or their body is shaped into a bar or arrow. Generally, all LED’s are manufactured with two legs protruding from the bottom of the body.

Also, nearly all modern light emitting diodes have their cathode, ( – ) terminal identified by either a notch or flat spot on the body or by the cathode lead being shorter than the other as the anode ( + ) lead is longer than the cathode (k).

Unlike normal incandescent lamps and bulbs which generate large amounts of heat when illuminated, the light emitting diode produces a “cold” generation of light which leads to high efficiencies than the normal “light bulb” because most of the generated energy radiates away within the visible spectrum. Because LEDs are solid-state devices, they can be extremely small and durable and provide much longer lamp life than normal light sources.

Light Emitting Diode Colours

So how does a light emitting diode get its colour. Unlike normal signal diodes which are made for detection or power rectification, and which are made from either Germanium or Silicon semiconductor materials, Light Emitting Diodes are made from exotic semiconductor compounds such as Gallium Arsenide (GaAs), Gallium Phosphide (GaP), Gallium Arsenide Phosphide (GaAsP), Silicon Carbide (SiC) or Gallium Indium Nitride (GaInN) all mixed together at different ratios to produce a distinct wavelength of colour.

Different LED compounds emit light in specific regions of the visible light spectrum and therefore produce different intensity levels. The exact choice of the semiconductor material used will determine the overall wavelength of the photon light emissions and therefore the resulting colour of the light emitted.

Light Emitting Diode Colours

Typical LED Characteristics
Semiconductor Material	Wavelength	Colour	VF @ 20mA
GaAs	850-940nm	Infra-Red	1.2v
GaAsP	630-660nm	Red	1.8v
GaAsP	605-620nm	Amber	2.0v
GaAsP:N	585-595nm	Yellow	2.2v
AlGaP	550-570nm	Green	3.5v
SiC	430-505nm	Blue	3.6v
GaInN	450nm	White	4.0v

Thus, the actual colour of a light emitting diode is determined by the wavelength of the light emitted, which in turn is determined by the actual semiconductor compound used in forming the PN junction during manufacture.

Therefore the colour of the light emitted by an LED is NOT determined by the colouring of the LED’s plastic body although these are slightly coloured to both enhance the light output and to indicate its colour when its not being illuminated by an electrical supply.

Light emitting diodes are available in a wide range of colours with the most common being RED, AMBER,  YELLOW  and GREEN and are thus widely used as visual indicators and as moving light displays.

Recently developed blue and white coloured LEDs are also available but these tend to be much more expensive than the normal standard colours due to the production costs of mixing together two or more complementary colours at an exact ratio within the semiconductor compound and also by injecting nitrogen atoms into the crystal structure during the doping process.

From the table above we can see that the main P-type dopant used in the manufacture of Light Emitting Diodes is Gallium (Ga, atomic number 31) and that the main N-type dopant used is Arsenic (As, atomic number 33) giving the resulting compound of Gallium Arsenide (GaAs) crystalline structure.

The problem with using Gallium Arsenide on its own as the semiconductor compound is that it radiates large amounts of low brightness infra-red radiation (850nm-940nm approx.) from its junction when a forward current is flowing through it.

The amount of infra-red light it produces is okay for television remote controls but not very useful if we want to use the LED as an indicating light. But by adding Phosphorus (P, atomic number 15), as a third dopant the overall wavelength of the emitted radiation is reduced to below 680nm giving visible red light to the human eye. Further refinements in the doping process of the PN junction have resulted in a range of colours spanning the spectrum of visible light as we have seen above as well as infra-red and ultra-violet wavelengths.

By mixing together a variety of semiconductor, metal and gas compounds the following list of LEDs can be produced.

Types of Light Emitting Diode

• Gallium Arsenide (GaAs) – infra-red
• Gallium Arsenide Phosphide (GaAsP) – red to infra-red, orange
• Aluminium Gallium Arsenide Phosphide (AlGaAsP) – high-brightness red, orange-red, orange, and yellow
• Gallium Phosphide (GaP) – red, yellow and green
• Aluminium Gallium Phosphide (AlGaP) – green
• Gallium Nitride (GaN) – green, emerald green
• Gallium Indium Nitride (GaInN) – near ultraviolet, bluish-green and blue
• Silicon Carbide (SiC) – blue as a substrate
• Zinc Selenide (ZnSe) – blue
• Aluminium Gallium Nitride (AlGaN) – ultraviolet

Like conventional PN junction diodes, light emitting diodes are current-dependent devices with its forward voltage drop VF, depending on the semiconductor compound (its light colour) and on the forward biased LED current. Most common LED’s require a forward operating voltage of between approximately 1.2 to 3.6 volts with a forward current rating of about 10 to 30 mA, with 12 to 20 mA being the most common range.

Both the forward operating voltage and forward current vary depending on the semiconductor material used but the point where conduction begins and light is produced is about 1.2V for a standard red LED to about 3.6V for a blue LED.

The exact voltage drop will of course depend on the manufacturer because of the different dopant materials and wavelengths used. The voltage drop across the LED at a particular current value, for example 20mA, will also depend on the initial conduction VFpoint. As an LED is effectively a diode, its forward current to voltage characteristics curves can be plotted for each diode colour as shown below.

Light Emitting Diodes I-V Characteristics.

Light Emitting Diode (LED) Schematic symbol and I-V Characteristics Curves
showing the different colours available.

Before a light emitting diode can “emit” any form of light it needs a current to flow through it, as it is a current dependant device with their light output intensity being directly proportional to the forward current flowing through the LED.

As the LED is to be connected in a forward bias condition across a power supply it should be current limited using a series resistor to protect it from excessive current flow. Never connect an LED directly to a battery or power supply as it will be destroyed almost instantly because too much current will pass through and burn it out.

From the table above we can see that each LED has its own forward voltage drop across the PN junction and this parameter which is determined by the semiconductor material used, is the forward voltage drop for a specified amount of forward conduction current, typically for a forward current of 20mA.

In most cases LEDs are operated from a low voltage DC supply, with a series resistor, RSused to limit the forward current to a safe value from say 5mA for a simple LED indicator to 30mA or more where a high brightness light output is needed.

LED Series Resistance.

The series resistor value RS is calculated by simply using Ohm´s Law, by knowing the required forward current IF of the LED, the supply voltage VS across the combination and the expected forward voltage drop of the LED, VF at the required current level, the current limiting resistor is calculated as:

LED Series Resistor Circuit

Light Emitting Diode Example No1

An amber coloured LED with a forward volt drop of 2 volts is to be connected to a 5.0v stabilised DC power supply. Using the circuit above calculate the value of the series resistor required to limit the forward current to less than 10mA. Also calculate the current flowing through the diode if a 100Ω series resistor is used instead of the calculated first.

1). series resistor required at 10mA.

2). with a 100Ω series resistor.

We remember from the Resistors tutorials, that resistors come in standard preferred values. Our first calculation above shows that to limit the current flowing through the LED to 10mA exactly, we would require a 300Ω resistor. In the E12 series of resistors there is no 300Ω resistor so we would need to choose the next highest value, which is 330Ω. A quick re-calculation shows the new forward current value is now 9.1mA, and this is ok.

Connecting LEDs Together in Series

We can connect LED’s together in series to increase the number required or to increase the light level when used in displays. As with series resistors, LED’s connected in series all have the same forward current, IF flowing through them as just one. As all the LEDs connected in series pass the same current it is generally best if they are all of the same colour or type.

Connecting LED’s in Series

Although the LED series chain has the same current flowing through it, the series voltage drop across them needs to be considered when calculating the required resistance of the current limiting resistor, RS. If we assume that each LED has a voltage drop across it when illuminated of 1.2 volts, then the voltage drop across all three will be 3 x 1.2v = 3.6 volts.

If we also assume that the three LEDs are to be illuminated from the same 5 volt logic device or supply with a forward current of about 10mA, the same as above. Then the voltage drop across the resistor, RS and its resistance value will be calculated as:

Again, in the E12 (10% tolerance) series of resistors there is no 140Ω resistor so we would need to choose the next highest value, which is 150Ω.

LED Driver Circuits

Now that we know what is an LED, we need some way of controlling it by switching it “ON” and “OFF”. The output stages of both TTL and CMOS logic gates can both source and sink useful amounts of current therefore can be used to drive an LED. Normal integrated circuits (ICs) have an output drive current of up to 50mA in the sink mode configuration, but have an internally limited output current of about 30mA in the source mode configuration.

Either way the LED current must be limited to a safe value using a series resistor as we have already seen. Below are some examples of driving light emitting diodes using inverting ICs but the idea is the same for any type of integrated circuit output whether combinational or sequential.

IC Driver Circuit

If more than one LED requires driving at the same time, such as in large LED arrays, or the load current is to high for the integrated circuit or we may just want to use discrete components instead of ICs, then an alternative way of driving the LEDs using either bipolar NPN or PNP transistors as switches is given below. Again as before, a series resistor, RS is required to limit the LED current.

Transistor Driver Circuit

The brightness of a light emitting diode cannot be controlled by simply varying the current flowing through it. Allowing more current to flow through the LED will make it glow brighter but will also cause it to dissipate more heat. LEDs are designed to produce a set amount of light operating at a specific forward current ranging from about 10 to 20mA.

In situations where power savings are important, less current may be possible. However, reducing the current to below say 5mA may dim its light output too much or even turn the LED “OFF” completely. A much better way to control the brightness of LEDs is to use a control process known as “Pulse Width Modulation” or PWM, in which the LED is repeatedly turned “ON” and “OFF” at varying frequencies depending upon the required light intensity of the LED.

LED Light Intensity using PWM

When higher light outputs are required, a pulse width modulated current with a fairly short duty cycle (“ON-OFF” Ratio) allows the diode current and therefore the output light intensity to be increased significantly during the actual pulses, while still keeping the LEDs “average current level” and power dissipation within safe limits.

This “ON-OFF” flashing condition does not affect what is seen by the human eye as it “fills” in the gaps between the “ON” and “OFF” light pulses, providing the pulse frequency is high enough, making it appear as a continuous light output. So pulses at a frequency of 100Hz or more actually appear brighter to the eye than a continuous light of the same average intensity.

Multi-coloured Light Emitting Diode

LEDs are available in a wide range of shapes, colours and various sizes with different light output intensities available, with the most common (and cheapest to produce) being the standard 5mm Red Gallium Arsenide Phosphide (GaAsP) LED.

LED’s are also available in various “packages” arranged to produce both letters and numbers with the most common being that of the “seven segment display” arrangement.

Nowadays, full colour flat screen LED displays, hand held devices and TV’s are available which use a vast number of multicoloured LED’s all been driven directly by their own dedicated IC.

Most light emitting diodes produce just a single output of coloured light however, multi-coloured LEDs are now available that can produce a range of different colours from within a single device. Most of these are actually two or three LEDs fabricated within a single package.

Bi-colour Light Emitting Diodes

A bi-colour light emitting diode has two LEDs chips connected together in “inverse parallel” (one forwards, one backwards) combined in one single package. Bi-colour LEDs can produce any one of three colours for example, a red colour is emitted when the device is connected with current flowing in one direction and a green colour is emitted when it is biased in the other direction.

This type of bi-directional arrangement is useful for giving polarity indication, for example, the correct connection of batteries or power supplies etc. Also, a bi-directional current produces both colours mixed together as the two LEDs would take it in turn to illuminate if the device was connected (via a suitable resistor) to a low voltage, low frequency AC supply.

A Bi-colour LED

LED Selected Terminal A AC + – LED 1 ON OFF ON LED 2 OFF ON ON Colour Green Red Yellow

Tricoloured Light Emitting Diode

The most popular type of tricolour light emitting diode comprises of a single Red and a Green LED combined in one package with their cathode terminals connected together producing a three terminal device. They are called tricolour LEDs because they can give out a single red or a green colour by turning “ON” only one LED at a time.

These tricoloured LED’s can also generate additional shades of their primary colours (the third colour) such as Orange or Yellow by turning “ON” the two LEDs in different ratios of forward current as shown in the table thereby generating four different colours from just two diode junctions.

A Multi or Tricoloured LED

Output Colour Red Orange Yellow Green LED 1 Current 0 5mA 9.5mA 15mA LED 2 Current 10mA 6.5mA 3.5mA 0

LED Displays

As well as individual colour or multi-colour LEDs, several light emitting diodes can be combined together within a single package to produce displays such as bargraphs, strips, arrays and seven segment displays.

A 7-segment LED display provides a very convenient way when decoded properly of displaying information or digital data in the form of numbers, letters or even alpha-numerical characters and as their name suggests, they consist of seven individual LEDs (the segments), within one single display package.

In order to produce the required numbers or characters from 0 to 9 and A to F respectively, on the display the correct combination of LED segments need to be illuminated. A standard seven segment LED display generally has eight input connections, one for each LED segment and one that acts as a common terminal or connection for all the internal segments.

• The Common Cathode Display (CCD) – In the common cathode display, all the cathode connections of the LEDs are joined together and the individual segments are illuminated by application of a HIGH, logic “1” signal.
• The Common Anode Display (CAD) – In the common anode display, all the anode connections of the LEDs are joined together and the individual segments are illuminated by connecting the terminals to a LOW, logic “0” signal.

A Typical Seven Segment LED Display

Opto-coupler

Finally, another useful application of light emitting diodes is in Opto-coupling. An opto-coupler or opto-isolator as it is also called, is a single electronic device that consists of a light emitting diode combined with either a photo-diode, photo-transistor or photo-triac to provide an optical signal path between an input connection and an output connection while maintaining electrical isolation between two circuits.

An opto-isolator consists of a light proof plastic body that has a typical breakdown voltages between the input (photo-diode) and the output (photo-transistor) circuit of up to 5000 volts. This electrical isolation is especially useful where the signal from a low voltage circuit such as a battery powered circuit, computer or microcontroller, is required to operate or control another external circuit operating at a potentially dangerous mains voltage.

Photo-diode and Photo-transistor Opto-couplers

The two components used in an opto-isolator, an optical transmitter such as an infra-red emitting Gallium Arsenide LED and an optical receiver such as a photo-transistor are closely optically coupled and use light to send signals and/or information between its input and output. This allows information to be transferred between circuits without an electrical connection or common ground potential.

Opto-isolators are digital or switching devices, so they transfer either “ON-OFF” control signals or digital data. Analogue signals can be transferred by means of frequency or pulse-width modulation. 

       XO__XO XI PING X TRXX Filters in TV antenna installations 

Because of questions on the filters we manufacture, I would like to clarify the terms that are associated with this field - to eliminate possible mistakes when making an order or implementing the filters in antenna systems. As an example I will analyze band-stop filter, but the principles should be observed for all kinds of the equipment. 

We have taken the notation:

• FZK-(ch. number): channel-stop filter -(ch. number), e.g. FZK-52
• FZP-(ch. number, ch. number): band-stop filter -(ch. numbers), e.g. FZP-2934

An ideal band-stop filter has no attenuation in the pass-band, 90-degree steep slope, and infinitely high attenuation in the rejection band. The frequency characteristics (attenuation - T) would be like this:

In practice every filter is described by a set of parameters: 

Tp - pass attenuation (the lower the better)
Tz - stop attenuation (the higher the better)
Fp1- Pass frequency 1 (attenuated at the level of Tp)
Fz1- Stop frequency 1, (attenuated at the level of Tz)
Fz2- Stop frequency 2, (attenuated at the level of Tz)
Fp1- Pass frequency 2 (attenuated at the level of Tp)

The frequencies (bands) are given as TV channel numbers.

The customer should specify all the parameters listed above.

Theoretically, the width of the rejected band is determined by the two points (to the left and to the right from the center frequency) where the attenuation level drops by 3dB. In practice, however, in TV antenna systems, we are not so interested in these points, but in the the rejected TV channels. When making an order, it is enough to specify these channels. 

NOTICE 1.
Increase of the Tp /Tz ratio makes the filter more expensive.
The lower the difference between Fp1 and Fz1 (or between Fz2 and Fp2), the more expensive the filter.

NOTICE 2.
There are important only the four channels - the shape of the transitions ( between Fp1 and Fz1, and Fz2 and Fp2) is not essential - it depends on the kind of the filter and tuning method.

The shape of the transitions is not essential - all the filters fulfill their tasks: 

The offered filters are not generally suitable for cable TV systems (possibility of interferences coming in between Fz2 and Fp2). 

Below there are characteristics of two implementations of FZK-52 filter.

The filter on the right is not suitable for the application in the region, although it can be acceptable in another country (different Fp1). When ordering band-stop filters (FZK) it is important to specify not only stop channels, but also the active ones, especially in the case of close channels. 

Tp value depends only on the structure of the filter (0.5-2 dB).
Tz value: -18 dB or -25 dB (in the case of pass-band filters -30 to -50 dB).

Example characteristics of pass-band filters.

Due to different structure, they are classified as F-5 or F-6. Below - characteristic of F-5 filter (ch. 50). The vertical lines indicate video and audio carriers.

In the case of close channels (the active and unwanted - one or two channel gap) there should be used F-6 filters. These filters are additionally equipped with notch filter for required channel. In general, the filters work effectively for at least one channel gap.

Label of band-pass filter for ch.50, with notch filter for ch.52: Filter F-6 k50 p52. 

It is impossible to make LC filters that would pass one TV channel and stop the adjacent one - there is only several hundred kHz for the slope. 

The F-6 filters ensure typical attenuation of carriers at 25 dB level (one channel gap, UHF - band V), the F-5 filters - 18 dB. These parameters are suitable for the applications. 

Band-stop filters not only reduce reflections but also eliminate interferences coming from various transmitters operating close to antenna systems. Strongly attenuating their carriers, the filters eliminate possible intermodulation in antenna amplifiers caused by strong unwanted signals. Numerous base stations, cellular BTSs, local FM transmitters (up to several kW) are the typical sources of the unwanted signals.

This is the task of band-stop filters connected between the antenna and the amplifier (or being an integral part of the amplifier).

An example solution of band-stop filter for FM band (88-108 MHz) is shown below. The basic principle for the project has been minimum 30 dB attenuation of the unwanted signals. The best choice is 3-stage Chebyshev filter: 

The picture below shows the practical implementation (C8 is SMD type - not visible here). 

The A-130 antenna amplifiers are equipped with such filters, so they can be used in antenna installations operating close to local FM transmitters. Below - characteristics of the amplifier.

Other suitable type of filter that can be used for suppressing FM interferences is Cauer (or elliptic) filter.
This kind of filters is sharper than all the others, but the tolerances of LC elements have to be much smaller than in the case of Chebyshev filters. It also show ripples on the whole bandwidth.
Below- characteristic of band-stop Cauer filter (88-108 MHz, 40 dB).

In manufacturing practice it is difficult to select capacitors precisely, there are usually chosen values from the IEC 60063 preferred number series (E12 or E24). The following diagram depicts the characteristics obtained with capacitors from the series. 

It is clear that only E24 series ensures proper results. 

The schematic diagram of FM band-stop filter (75 ohm input/output impedance): 

The implementation shown above (Chebyshev filter) has been based on conventional components (lumped parameter system), the second solution (Cauer filter) involves microstrip technology (distributed parameter system).
The latter implementation is cheaper in mass production and eliminates the need of time-consuming adjustment.
After calculating the inductive components, we got the following PCB layout:
MASA=GROUND; We=In; Wy=Out

Electromagnetic analysis of the layout proves correctness of the solution:

The differences between the above graph and the specifications are of no significance.
For the computer simulation there were assumed the following parameters: 

• One-sided PCB.
• Epoxy-fiberglass substrate, relative permittivity: Er=5.
• PCB thickness: 1.5mm.
• Copper clad thickness: 0.035 mm.
• Dielectric loss factor: 0.04.

The picture of the physical prototype...

...and the characteristic taken on a wobbuloscope:

There is only needed a minor correction of frequency characteristic (to the left). The general requirements have been met - the FM band is effectively suppressed.

The discussion concerned use of RF filters in individual (or small community) antenna installations for filtering unwanted signals. Similar filters are also used in antenna diplexers/multiplexers, in band/channel amplifiers etc . 

    

                         Filter (signal processing) 

In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal^{[clarification needed]}. Most often, this means removing some frequencies or frequency bands. However, filters do not exclusively act in the frequency domain; especially in the field of image processing many other targets for filtering exist. Correlations can be removed for certain frequency components and not for others without having to act in the frequency domain. Filters are widely used in electronics and telecommunication, in radio, television, audio recording, radar, control systems, music synthesis, image processing, and computer graphics.

There are many different bases of classifying filters and these overlap in many different ways; there is no simple hierarchical classification. Filters may be:

• linear or non-linear
• time-invariant or time-variant, also known as shift invariance. If the filter operates in a spatial domain then the characterization is space invariance.
• causal or not-causal: A filter is non-causal if its present output depends on future input. Filters processing time-domain signals in real time must be causal, but not filters acting on spatial domain signals or deferred-time processing of time-domain signals.
• analog or digital
• discrete-time (sampled) or continuous-time
• passive or active type of continuous-time filter
• infinite impulse response (IIR) or finite impulse response (FIR) type of discrete-time or digital filter. 

Impedance matching

Impedance matching structures invariably take on the form of a filter, that is, a network of non-dissipative elements. For instance, in a passive electronics implementation, it would likely take the form of a ladder topology of inductors and capacitors. The design of matching networks shares much in common with filters and the design invariably will have a filtering action as an incidental consequence. Although the prime purpose of a matching network is not to filter, it is often the case that both functions are combined in the same circuit. The need for impedance matching does not arise while signals are in the digital domain.

Similar comments can be made regarding power dividers and directional couplers. When implemented in a distributed element format, these devices can take the form of a distributed element filter. There are four ports to be matched and widening the bandwidth requires filter-like structures to achieve this. The inverse is also true: distributed element filters can take the form of coupled lines.

Some filters for specific purposes

• Audio filter
• Line filter
• Scaled correlation, high-pass filter for correlations
• Texture filtering

Filters for removing noise from data

• Wiener filter
• Kalman filter
• Savitzky–Golay smoothing filter

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

                                               e- SUPER BLOCK MICON

                                                      

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++