DiSEqC

DiSEqC (Digital Satellite Equipment Control) is a special comunication protocol for use between a satellite receiver and a device such as a multi-dish switch or a small dish antenna rotor. It is compatible with the actuators used to rotate large C band dishes if used with a DiSEqC positioner. It relies only on the coaxial cable to transmit both bidirectional data/signals and power.

Applications of DiSEqC:DiSEqC 1.0 circuit max. 4 LNB`s

DiSEqC 1.0: 4 LNB's Separate Option/Position



Diseqc A = Position A Option A
Diseqc B = Position B Option A
Diseqc C = Position A Option B
Diseqc D = Position B Option B

DiSEqC 1.0 + 0/12 Volt: 8 LNB's



DiSEqC 1.0 + Toneburst + 0/12 Volt: 12 LNB's

Attitudes in the receiver menu:
LNB1 = DiSEqC A, 0 Volt, ToneBurst Sat A
LNB2 = DiSEqC A, 0 Volt, ToneBurst Sat B
LNB3 = DiSEqC B, 0 Volt, ToneBurst aus
LNB4 = DiSEqC C, 0 Volt, ToneBurst Sat A
LNB5 = DiSEqC C, 0 Volt, ToneBurst Sat B
LNB6 = DiSEqC D, 0 Volt, ToneBurst aus
LNB7 = DiSEqC A, 12 Volt, ToneBurst Sat A
and so on to LNB12.

DiSEqC 1.0 + Toneburst + 2 Tuner: 12 LNB's


DiSEqC 1.1: 16 LNB's


DiSEqC 1.1: 64 LNB's



DiSEqC 1.2 of 1.3 Motor : 1 LNB


DiSEqC 1.2: 10 LNB's without Motor


DiSEqC 1.0 + ToneBurst + DiSEqC 1.2 + 2 Tuner: 16 LNB's


DiSEqC 1.0 + 0/12 Volt + DiSEqC 1.2 or 1.3 Motor: 5 LNB's

Explanations of Digital Television Terms

What is free to view digital tv?

Free to view digital tv is a replacement technology for existing free-to-air analog services. It provides better picture quality and reception, plus a variety of new features that enhance the viewing experience.

The digital television industry in Australia is using the DVB-T standard, first developed in Europe, rather than the American-developed ATSC standard. DVB-T is proving to be a very high quality system and is being used in many countries around the world.

What benefits does free to view digital tv provide?

Free to view digital tv is a far more efficient and flexible transmission system than the current analog system. It allows broadcasters to offer viewers a range of new and different services.

Australian digital television features include:

• 'Ghost free' reception
• Widescreen 16:9 pictures
• Standard Definition pictures (SD)
• High Definition pictures (HD)
• High quality audio and surround sound
• Multi-channel programming on ABC and SBS
• Closed Captioning of programs for the hearing impaired
• Electronic Program Guides (EPGs) with 'now & next' program information for some channels
• In selected markets, on-screen program guide channel with today's program information for Nine Network, Seven Network, Network Ten & SBS
• In selected markets, HD demonstration channels
• Multi-camera views and enhancements during selected programs

Can my 4:3 analog TV set display digital TV to its full effect?

No. You can view digital television on your 4:3 analog receiver with a digital tv set top box, but you will not be able to see widescreen pictures displayed to full effect. Some set-top boxes give you the option of viewing widescreen pictures in 'letterbox' format (black bars top and bottom) or 'centre cut' full screen format (with the 4:3 section 'cut out' of the 16:9 picture).


Why are digital TV pictures sharper than with analog TV?

Analog television can suffer from multipath interference, which results in a 'ghosted' picture on your screen.

Free to view digital tv is not affected by multipath interference and picture 'flutter'. So the digital result is a sharper, cleaner and clearer picture.

In areas of low signal strength, viewers of analog tv may experience 'snowy' pictures. Without adequate signal strength to the set top box, digital tv may not improve the viewing experience compared to analog.

Is audio better on digital television than on analog?

Yes. Australian television has traditionally been broadcast with FM stereo sound.

Digital television will be transmitted with MPEG digital stereo sound (the equivalent of CD quality) and/or Dolby Digital Sound (2, 4 or 5 channels), thereby providing markedly superior audio services.

Is digital television likely to cause interference?

Typically no. Digital television is not inherently prone to causing interference and is markedly superior to analog television in that respect. But the planning of channel allocations for digital television has entailed the occupation by digital television broadcasts of some channels formerly used for other purposes, eg, as output channels for VCRs.

What is widescreen?

Digital television will be broadcast in widescreen mode. Widescreen television has a different aspect ratio (ratio of width to height) than traditional analog. The aspect ratio of a widescreen is 16:9, while Australian viewers have been accustomed to viewing a 4:3 aspect ratio since television began in this country.

Widescreen will, in many cases, literally mean you see more of the picture. Most movies are currently made in 16:9 and are converted to 4:3 to allow us to watch them on television or video, so there is a lot of information that you don't see on your television that you would see in the cinema version of the film. Live sporting events will benefit in particular from the extra detail and wider frame.

For some time now television production has been converting to widescreen, both locally and overseas. Widescreen programming is becoming more readily available and will eventually become the global standard.

What is a digital tv set top box receiver?

A digital tv set top box receives and decodes digital terrestrial tv transmissions into a form suitable for display on analog television sets or other display devices, eg computer monitors or projection screens.

Analog television sets currently in use in Australia cannot display digital transmissions on their screens without being connected to such a digital tv set top box receiver.

What does a digital tv set top box do?

The capability of a digital tv set top box will depend upon its specifications.

A digital tv set top box, when connected to a 4:3 analog television set, will usually give viewers an improved signal, better picture quality and multichannelling. Some set-top boxes may also provide viewers with data casting services and video, audio and data enhancements.

What is an integrated digital television?

This is a television set with built-in digital tv capabilities to receive and display digital transmissions.

Integrated digital televisions (IDTV) are generally distinguished by wide screens, high-level audio capability and high quality displays. They will not require a digital tv set top box for video and audio services.

What are Standard Definition (SD) pictures?

SD picture quality is superior to that obtained from analog 4:3 sets, and is 'ghost free' and in widescreen format.

The SD picture resolution is 576 lines x 720 pixels @ 50Hz interlaced (576i).

What are High Definition (HD) pictures?

HD pictures have image resolution which is superior to SD pictures and to the existing analog, with up to three times the improvement in detail.

Australian broadcasters are using two different levels of high definition;

– 1920 pixels x 1080 lines @ 50Hz interlaced

– 720 pixels x 576 lines @ 50Hz progressive

The benefits of HD pictures at the highest resolution are particularly noticeable on larger screen sets and when using projection equipment.

HD pictures are also ghost free and in widescreen format. When viewed on an HDTV screen the viewer can enjoy cinema-quality viewing with Dolby Digital sound (some HD programs).

Commercial free to air broadcasters are required to transmit a minimum of 1040 hours of 'native' HD programs (including advertisements) each year. In regional areas this is a requirement after two years from the commencement of digital tv transmissions in an area. Programs transmitted in High Definition will also be simultaneously broadcast in Standard Definition.

What is multi-view?

Multi-view lets you select from a variety of camera angles or may provide additional information related to an event. Multi-view is particularly suited to sporting events like cricket, tennis and motor racing.

On additional channels to the main program the viewer can select, via remote control, a different full screen views of the event, alternative audio commentary or related information.

What is multichannelling?

Because a digital signal can carry much more data than an analog signal, more than one channel of television programs can be broadcast in SDTV at the same time. This is known as multichannelling.

The Federal Government has decided that commercial broadcasters are not allowed to multichannel, but that the ABC and SBS may do so.

The ABC and SBS are allowed to broadcast, in addition to their main services, a wide range of programs including educational programs, regional news and current affairs, science and arts programs, children's programs, subtitled foreign programs, foreign language news and occasional dramas.

The ABC and SBS are able to transmit their radio services through their television channels, extending the reach of these services. The ABC also broadcasts its internet radio service - DiG - via digital television.

Broadcasters are also offering a number of program guide and information data channels and some are providing High Definiton demonstration channels.

What are program enhancements?

Viewers of digital television will have a wide choice of 'enhancements' to regular programming. Enhancements are separate channels of video, data or audio, which are related to the program on the primary channel.

Sports programs may offer the choice of a different camera angle, altenative audio commentary, action replays, player profiles or other information.

What is Closed Captioning?

Closed captioning provides deaf and hearing-impaired viewers with the text of what is being spoken on television. The text is usually shown in a black box at the bottom of the picture. Hearing-impaired viewers will be familiar with current analog captioning which can be received on analog receivers with teletext capability. Captioning is normally 'closed' to viewers but can be accessed by those who need it.

Closed captioning does not interfere with normal viewing.

The Australia digital terrestrial television (DTT) receiver standard is non-mandatory but currently says that all receivers should have closed captioning decoding capability, including the ability to -

(a) decode and display teletext page 801 closed captioning,
(b) decode and display DVB bitmapped Subtitles - (a different system used in some other countries but not by Australian broadcasters), and
(c) pass teletext closed caption data out on the SD video output in the VBI (Vertical Blanking Interval) so that a standard PAL receiver fitted with teletext decoding can display it.

As captions are currently provided in the teletext style with all Australian broadcasters’ prime time programs, this is the more important digital set top box (STB) capability to those viewers who wish to see closed captions.

Many digital STBs have teletext closed captioning display capabilities - with these STBs, a TV connected to them doesn't also need to be able to decode teletext closed captions, as the feature is provided by the STB.

There are some digital STBs that do not include closed captioning decoding and display capability. However a few of these do pass the closed caption data out on the video output (via the VBI - see (c) above), and when these STBs are connected to a standard teletext-capable TV set, access to the closed captions can be had by viewers.

Therefore, any consumer intending to purchase a DTT STB and use closed captioning should, before purchase, check on the STB's capabilities.

Closed captioning of programming is incorporated in all English language news and current affairs programs as well as for all prime time programs (6.00pm to 10.30pm).

Of course, when available, closed captions can continue to be viewed on a standard PAL teletext-capable TV set that is tuned to analog broadcasts. However, many more digital TV programs incorporate closed captioning than do analog TV programs.

What is an EPG (Electronic Program Guide)?

An EPG is the electronic version of a printed program guide. Using your remote control you will be able to see on-screen "what's on now" and "what's on next" for all free-to-air services. You may also be able to search for a particular program by theme or category, eg sporting programs, movies etc. Extra text and picture information (eg story line, episode description etc) can be called up as well. The EPG is always up-to-date and available at the click of a remote control button.

What is interactive television (iTV)?

iTV allows the viewer to receive more information from television broadcast than analog can provide. iTV can be one-way (unconnected) or two-way (connected).

One-way iTV delivers information to your receiver that is additional to the main program and that allows you the option to view it or not. The viewer is able to view travel deals, concert dates etc.

Full, two-way iTV enables you to send information back to the broadcaster via a back channel. The viewer is able to vote in a poll, reserve concert tickets, etc.

Both one-way and two-way iTV can be added to commercials as well as programs.

A special icon will appear on the screen to notify the viewer iTV is available.

Currently no interactive tv enhancements are available on free to view digital tv.

courtesy : Had some doubts about Digital tv ..searched net got the above..did CCP

Binary number !!

We can use "int v = 0xFF;" to use hexadecimal numbers.
We can use still other base numbers, but..., how to use binary numbers in ANSI compiler??

solve this

if(X)
{
printf("Hello");
}
else
{
printf("World");
}

Question: What should be the value of "X" so that the output is HelloWorld?

MACRO

What does the message ``warning: macro replacement within a string literal'' mean?

Some pre-ANSI compilers/preprocessors interpreted macro definitions like

#define TRACE(var, fmt) printf("TRACE: var = fmt\n", var)

such that invocations like

TRACE(i, %d);


were expanded as

printf("TRACE: i = %d\n", i);


In other words, macro parameters were expanded even inside string literals and character constants.

Macro expansion is not defined in this way by K&R or by Standard C. When you do want to turn macro arguments into strings, you can use the new # preprocessing operator, along with string literal concatenation (another new ANSI feature):

#define TRACE(var, fmt) printf("TRACE: " #var " = " #fmt "\n", var)


What's the best way to write a multi-statement macro?

ANSWER:
#define MACRO(arg1, arg2) do { \
/* declarations */ \
stmt1; \
stmt2; \
/* ... */ \
} while(0) /* (no trailing ; ) */


How can I write a macro which takes a variable number of arguments?
One popular trick is to define and invoke the macro with a single, parenthesized ``argument'' which in the macro expansion becomes the entire argument list, parentheses and all, for a function such as printf:

#define DEBUG(args) (printf("DEBUG: "), printf args)

if(n != 0) DEBUG(("n is %d\n", n));

The obvious disadvantage is that the caller must always remember to use the extra parentheses.

gcc has an extension which allows a function-like macro to accept a variable number of arguments, but it's not standard. Other possible solutions are to use different macros (DEBUG1, DEBUG2, etc.) depending on the number of arguments, to play games with commas:

#define DEBUG(args) (printf("DEBUG: "), printf(args))
#define _ ,

DEBUG("i = %d" _ i)

What is ATSC?

ATSC (Advanced Television Systems Committee) is a group which defines the standards for digital television transmission in the United States and many other counties.

ATSC is the digital replacement for the earlier analog standard, NTSC.

The ATSC standards are created by the Advanced Television Steering Committee, whose charter members are the Electronic Industries Association (EIA), the Institute of Electrical and Electronic Engineers (IEEE), the National Association of Broadcasters (NAB), the National Cable Television Association (NCTA), and the Society of Motion Picture and Television Engineers (SMPTE).

The ATSC standards include high definition television (HDTV), standard definition television (SDTV), data broadcasting, multichannel surround-sound audio, and satellite direct-to-home broadcasting.

In addition to the United States, ATSC is also used in Canada, South Korea, Argentina, and Mexico.

ATSC uses 8VSB (8-level Vestigal Side-Band) modulation and MPEG-2 compression.

What is HDTV?

HDTV (High Definition Television) is one of the DTV (Digital TV) standards. HDTV will eventually replace analog television.

HDTV offers resolutions of 720p, 1080i, and 1080p.

The 720p format offers 720 lines of horizontal resolution with progressive scan. Progressive scan means that every line is refreshed in each frame update.

The 1080i format offers 1080 lines of horizontal resolution with interlacing. Interlacing means that every other line is refreshed in each frame update. This means that it requires two frame updates to repaint the entire screen.

1080p offers the best of both worlds, 1080 lines of progressively scanned video.

HDTV features an aspect ratio of 16:9.

The HDTV standard also includes the use of 5.1 Dolby Digital surround sound (AC-3).

Each HDTV channel provides 19.39Mbps of bandwidth.

HDTV utilizes MPEG-2 compression.

HDTV is part of a larger set of standards called ATSC.

The FCC (Federal Communications Commission) has mandated that all licensed television stations be capable of broadcasting DTV by 2007.

What is aspect ratio?

Aspect Ratio is the ratio of a picture's width to its height.

NTSC television uses a 4:3 aspect ratio.

HDTV and SDTV feature a 16:9 aspect ratio.

Movie theaters typically use an aspect ration of 1.85:1 or 2.35:1.

Converting a movie to television requires either pan and scan or letterboxing.

Pan and scan is a process where technicians remove portions of the left or right side of the video to convert the aspect ratio.

Letterboxing is displaying the full picture in the center of the screen, with black bars above and below it.

What is MPEG-2?

MPEG-2 (Motion Picture Experts Group - 2) is a compression standard for digital television.

MPEG-2 compression enables digital television broadcasters to transmit video streams with higher resolution and audio streams with higher quality sound while using as little bandwidth as possible.

MPEG-2 is capable of reducing the amount of bandwidth utilized by as much as 55 to 1.

MPEG-2 is utilized by DVB, HDTV, and DVD.

MPEG-2 has been adopted as ISO Standard 13818-1.

sizeof() Vs strlen()

In C language Difference between sizeof() and strlen()

Consider the following example:

/* Example for sizeof( ) , strlen( ) */
#include 
main()
{
       char String[]="Hello";

       printf("\n SIZE OF String %d STRING LENGTH %d", 
       sizeof( String ), strlen( String ) );
}

Result:
SIZE OF String 6 STRING LENGTH 5.

Every String contains a NULL character( '\0' ) at the end. The sizeof() function will include that NULL character also for calculating string size but strlen() function not.

Why is sizeof('a') not 1?
Perhaps surprisingly, character constants in C are of type int, so sizeof('a') is sizeof(int) (though it's different in C++).

Result:
In Turbo C output is: 2
In Turbo C++ output is: 1

Difference between Program Stream and Transport Stream

From ISO 13818-1

Transport Stream:

• Transport stream is a stream definition which is tailore for communicating or storing one ore more programs of coded data according to ITU-T Rec. H.262 ISO/IEC 13818-2 and ISO/IEC 13818-3 and other data in environments in which significant errors may occur. Such errors may be manifested as bit value errors or loss of packets.
• Transport Streams May be Fixed or Variable rate. In either case, the constituent elementary stream may be either fixed or variable rate.
• Transport Stream rate is defined by the values and locations of Program Clock Reference (PCR) fields, which in general are separate PCR fields for each program.
• Transport Stream may be constructed from
• a) from one or more elementary coded data streams
• b) from Program Streams
• c) from other Transport Streams which may themselves contain one or more programs.
• Transport Streams are constructed in two layers: a sytem layer and a compression layer. The input stream to the Transport Stream decoder has a system layer wrapped about a compression layer. Inpute Streams to the Video and Audio decoders have only the compression layer.
• Transport Stream system layer is divided into two syb-layers, one for multiplex-wide operations (the Transport stream Packet Layer), and one for stream-specific operations (the PES packet layer).

Program Stream:

• The Program Stream is a stream definition which is tailored for Commnucating or storing one program of coded data and other data in environments where errors are very unlikely, and where processing of system coding e.g by software, is a major consideration.
• Program Streams may be fixed or variable rate. In either case, the consituent elementary streams may be either fixed or variable rate.
• The Program Stream rate is defined by the values and locations of the System Clock Reference (SCR) and mux_rate fields.
• Program Streams are constructed in two layers: a system layer and a compression layer. The inpur to the Program Stream Decoder has a system layer wrapped about a compression layer. Input streams to the video and Audio decoders have only the compression layer.
• The Program Stream system layer is divided into two sub-layers, one for multiplex-wide operations (the pack layer), and one for stream-specific operations (the PES packet layer).

Analog Versus Digital Transmission

http://www.informit.com/articles/article.asp?p=24687&seqNum=5&rl=1

Feature Analog Characteristics Digital Characteristics

Signal Continuously Variable Discrete Signal 
Bandwidth Low bandwidth High Bandwidth 
Speed Low High 
Error Rate High 10^-5 bits Low 10^-7

Difference between Threads and Process

From the book Parallel and Distributed Programming Using C++ BY Tracey Hughes,
Cameron Hughes , Published by Addisioin-Wesley.

LINK:
{
http://books.google.com/books?ie=UTF-
8&hl=en&id=RQT5XeqaagEC&dq=Difference+between
+Thread+and+Process&prev=http://books.google.com/
books%3Fq%3DDifference%2Bbetween%2BThread%2Band%2BProcess&lpg
=PA102&pg=PA104&sig=
7XWb4nEO4BnjVFz1uGSAdwseDJs}

The major difference between Threads and Processes is each process has its own
address space and thread don't. If a process creates multiple threads, all the threads will be contained in its address space. This is why they share resources so easily and interthread communication is so simple. Child processes have their own address space and a copy of the data segment. Therefore, when a child changes its variables or data, it does not affect the data of its parent process. A shared memory area has to be created in order for parent and child processes to share data. Interprocess communication mechanisms, scuh as pipes and fifos, are used to communicate or pass data between them. Threads of the same process can pass data and communication by reading and writing directly to any data that is accesible to the parent process.

Similarites between Threads and Processes

• Both has an id, set of registers, state, priority and scheduling policy.
• Both have attributes that describe the entity to the OS.
• Both have an information block.
• Both share resources with the parent process.
• Both function as independent entities from the parent process.
• The creator cna exercise some control over the thread or process.
• Both can change their attributes.
• Both can create new resources.
• Neither can access the resources of another process.

Differences Between Threads and Processes

• Threads share the address space of the process that created it; processes have their own address.
• Threads have direct access to the data segment of its process; processes have their own copy of the data segment of the parent process.
• Threads can directly communicated with other threads of its process; processes muse use interprocess communication to communicate with sibling processes.
• Thread have almost no overload; processes have considerable overhead.
• New threads are easily created; new processes require duplication of the parent process.
• Threads can exercise considerable control over threads of the same process; processes can only exercise control over child processes.
• Changes to the main thread (cancellation, prority change, etc.) may affect the behavior of the other threads of the process; changes to the parent process does not affect childe processes.

Cross Compiler

A cross compiler is a compiler capable of creating executable code for another platform than the one on which the cross compiler is run. Such a tool is handy when you want to compile code for a platform that you don't have access to, or because it is inconvenient or impossible to compile on that platform (as is the case with embedded systems.)

(en.wikipedia.org/wiki/Cross_compiler)

About INLINE functions

Advantages:

1. It leads to a more readable program
2. It leads to much faster code (reducing fucntion calling time). That is improves program performence.
3. It accomplishes the same efficiency that the macro accomplishes.

Disadvantages:

1. Its frequent use can lead to increase in code size (that is output file size).

These advantages and disadvantages are part of the choice and/or trade off's that you have to make as a programmer. Speed over filesize or readability over lines of code, those are the types of choices that you as a programmer will have to make.

CI and CAM

Common Interface ( CI )
Common Interface ( CI ) To decode encrypted programmes, you need a subscription to the appropriate broadcaster along with hardware that enables you to use the decryption card (smart card) sent to you by the broadcaster. The first piece of hardwareis the Common Interface (CI), which is connected directly to the DVB card. A Conditional Access Module (CAM) isinserted into the CI, and the CAM is used to house the smartcard itself. Unfortunately it is easy to get these namesconfused.

Again and again Conditional Access Modules are referred to as CI modules - which can be confusing, since CIs themselves can also be designed in the form of pluggable modules(for example, the Siemens DVB-C module).

CIs are available in the form of PCI cards, DVB card daughterboards or as modules that can be installed in a 3.5" drive bay.Due to these different formats, you should ensure that the module you purchase can be used with your DVB card. Not all DVBcards have the connections required for CIs, so make sure in advance that the Ci fits your card.

Some broadcasters specify in their Terms and Conditions that you have to use a specific certified receiver to receive and decrypt their programmes - so far, however, there is not certified CI / CAM.



Conditional Access Module (CAM)
A Common interface (CI) module can be used to house many different peripheral devices, such as a modem, additional memory, games consoles, or more usually a Conditional Access Module (CAM) - sometimes referred to as a Common Interface Module (CIM, CI module). The CAM provides space for one or two smartcards (depending on the CI) supplied by the broadcaster.

Encryption systemsThere are various different encryption systems, which are not mutually compatible. The CAM must be suitable for the system you wish to decrypt - often a CAM is only suitable for one system, while other CAMs can be used with a number of systems (e.g. the Joker CAM).

Below are examples of encryption systems (their use and sample broadcasters are given in brackets):

Irdeto BetaCrypt (previously used by Premiere) Premiere Nagra (currently used by Premiere) Seca (Aston Canal+) Viaccess (previously used by Viasat) Conax (Canal+ Scandinavia, SVT) CryptoWorks (ORF, Xtra Music Payradio, Wizja +, MTV, DigiTurk, CzechLink, Easy.tv) NDS (Sky, currently used by Viasat)

The best-known CAM is probably in the Alphacrypt CAM, which works with VDR. Unfortunately CAMs are not usually particularly cheap, costing between 60 and 180 euros (the Alphacrypt CAM is at the top end of this price range). Obviously you can sometimes obtain them more cheaply on the second-hand market.

Mascom now produces an Alphacrypt Light CAM, which works well with VDR (tested with vdr-1.3.16 and Fujitsu-Siemens DVB-C PCI with CI) and KabelDeutschland Digital or Premiere. The high-street price for this CAM is 66 euros.

Volatile Pointer

Volatile is a variable which may change the valuewithout knowing of code.
A variable should be declared volatile whenever its value could change unexpectedly.

In practice, only three types of variables could change:
Memory-mapped peripheral registers
Global variables modified by an interrupt service routine
Global variables within a multi-threaded application

It is also used to avoid the compiler optimisation.

consider the below code,
volatile int *vp=0x5565;
.
.
.
.

code


while ( *vp!= 0 )
{
..code
}
In the above case, the vp pointer value may change during the run time.
To ensure that the volatile keyword is used.

so that the value of vp will not read often by compiler.
so the optimisation of the compiler will stop.
But in the ordinary pointer it is not done.

What is mutex?

A synchronization object that provides mutual exclusion among tasks. A mutex is often used to ensure that shared variables are always seen by other tasks in a consistent state.

Another name of mutex is 'semaphore'.

Tuner

Tuner an electronic receiver that detects and demodulates and amplifies transmitted signals

Broadcasting TV systems

SECAM

SECAM (Sequentiel Couleur avec Mémoire, French for "sequential color with memory") is an analog television system, using frequency modulation to encode chrominance information. It is so named because it uses memory to store lines of color information, in order to eliminate the color artifacts found on systems using the NTSC standard.

It was developed for the same purpose as PAL, but uses a different (and many would argue inferior) mechanism to do so. R-Y and B-Y information is transmitted in alternate lines, and a video line store is used to combine the signals together. This means that the vertical colour resolution is halved relative to PAL and NTSC.

SECAM was introduced in France in 1967, where it is still used; it has also been adopted in many former French colonies, as well as parts of Eastern Europe (Bulgaria, Hungary) and the former Soviet Union. Many have argued that the primary motivation for the development of SECAM in France was to protect French television equipment manufacturers and make it more difficult to view non-French programming.

Political factors from the Cold War have also been attributed to the adoption of SECAM in Eastern Europe, as its use made it impossible for most Eastern Europeans to view television which was broadcast from outside the Iron Curtain which were mostly using PAL.

There are three varieties of SECAM:

1. French SECAM is used in France and its former colonies

2. MESECAM is used in the Middle East

3. D-SECAM is used in the Commonwealth of Independent States and Eastern Europe.

NTSC

The National Television Standards Committee sets the analog television standard for the United States; this format itself is also informally called "NTSC".

While a standard for the United States, it has been adopted in other countries as well, for example Japan. The current version replaced an older NTSC standard by adding chrominance information on a 3.579545 (exactly 315/88) MHz subcarrier, retaining compatibility with older black-and-white NTSC television receivers.

The NTSC format consists of 29.97 interlaced frames of video a second, each consisting of 480 lines of vertical resolution out of a total of 525 (the rest are used for sync, vertical retrace, and other data such as captioning).

NTSC interlaces its scanlines, drawing odd-numbered scanlines in odd-numbered fields and even-numbered scanlines in even-numbered fields, which gives a nearly flicker-free image at approximately 59.94 hertz (nominally 60 Hz / 1.001) refresh frequency, which is close to the nominal 60 Hz alternating current power used in the United States. (Compare this to the 50 Hz refresh rate of the 625-line PAL video format used in Europe, where 50 Hz (25 hertz is resonant) AC is the standard; PAL has noticeably more flicker than NTSC.) Synchronization of the refresh rate to the power cycle helped film cameras record early live television broadcasts, as it was very simple to sync a film projector to capture a frame of video to a film cell using the frequency of the alternating current.

Also, it was preferable to match the screen refresh rate to the power source so as to avoid wave interference that would produce rolling bars on the screen.

PAL

PAL, short for Phase Alternating Line, is the analogue video format used in television transmission in most of Europe (except France, Bulgaria, Russia, Yugoslavia, and some other countries in Eastern Europe, where SECAM is used), Australia and some Asian, African, and South American countries.

PAL was developed in Germany by Walter Bruch, and first introduced in 1967. The name "Phase Alternating Line" describes the way that part of the color information on the video signal is reversed in phase with each line, which automatically corrects phase errors in the transmission of the signal. NTSC receivers have a tint or hue control to perform the correction manually.

Some engineers jokingly expand NTSC to "Never Twice the Same Colour" while referring to PAL as "Perfect At Last" or "Peace At Last"! However, the alternation of colour information - Hanover bars - can lead to picture grain on pictures with extreme phase errors.

The PAL colour system is usually used with a video format that has 625 lines per frame and a refresh rate of 25 frames per second. Like NTSC this is an interlaced format. Each frame consists of two fields (half-a-frame), each field has half of the lines of a frame (one has all the even lines, one has all the odd lines). Fields are transmitted and displayed successively. There are 50 fields per second. At the time of its design, the interlacing of fields was a compromise between flicker and bandwidth.