EXPERIMENT 1. PATTERN GENERATOR

Objectives:
1.1 Getting to know the basic patterns in the Pattern Generator.
1.2 Measuring standard composite video and voltage on each pattern.
1.3 Measuring on the modulator wave modulated video (RF).
1.4 Measuring video IF.

Equipment Used:

1 Pattern Generator TV signal, LODESTAR CPG-1367A
1 Oscilloscope 40 MHz and passive probe
1 Power Supply
A cable connecting the BNC - BNC 75
A BNC connector cable - RCA 75
1 T-BNC Connector
Circuit diagram:

Introduction:

Source of image patterns (pattern generator) is the technique of video (television) for the purpose of setting up or finding fault. There are various kinds of image patterns with a variety of needs. Pattern of so many images that exist, there are several commonly used image patterns are not very specific uses.

Types of Image and its Use Patterns

• The spots (Dot)

To check and adjust the static convergence in the middle of the screen with a low brightness. This should be done according to the television manufacturer's instructions.

• The boxes (crosshach)

Plaid pattern with horizontal lines and vertical lines with the background color of black and white color line.

1.   To check and adjust the horizontal and vertical dynamic convergence and the convergence angle.

2.   By linearity of deflection (deflection) the correct horizontal and vertical, horizontal white lines should be a  

      rectangular equilateral.

      >   If not, then the plane can be checked for truth response amplitudes. Vertical white line width should

           be 200 ns.

      >   If this line is not sharp and visible lower intensity than the horizontal line, the amplitude response is

           possible recipient is not enough.

      >   If vertical lines appear double, receiver circuit may be vibrating.

3.   To pin-cushion proofreaders check the receiver. With the convergence of the right, square in the corner of the screen should be approximately equal to a square in the middle of the screen at a distance of normal vision.

• White

This pattern contains a signal 100% white (without color information) with alternating burst.

1. Images for constant brightness on the entire screen (tida no hum, etc..)

2. Color picture tube for setting a good white (white-D).

3. Limitation of fire flow on the color picture tube.

4. For the video recorder is ideal pattern for the current setting of writing (recording) luminance. This pattern can also to set the FM demodulator (setting white level).

• Beam Color (color)

Blocks of colors (color bar) consists of 8 vertical color bar standard and a reference beam horizontally. Beams 8 colors are arranged in order of depreciation luminan. From left to right beams D color is white, yellow, cyan, green, magenta, red, blue, and black.
This pattern is used to set the operational control of the receiver at the correct position.
Horizontal beam (white level) on the bottom of this pattern is used as a standard when setting the amplitude signal of color differences with relationships with luminan signal in the picture tube.
Signals can be used for resetting the signal amplitude of the demodulator circuit and the matrix, as the output can be compared with the reference beam. In addition to the above purposes, this pattern can be used to check the overall color appearance. So can also be used checks and settings on the receiver or VCR:
1. Lock Inspection burst.
2. AGC examination of color and which create the color.
3. Examination series reactance of the subcarrier regenerator.
4. Examination of the regenerator subcarrier synchronization.
5. Checking circuit identifier (identification) PAL.



Experimental Procedure:

1. Set-up equipment such as in the picture above.
2. Connect the pattern generator with the power supply 8, 5 V, then ON the instrument.
3. Pattern generator output switches on and observe put on VIDEO waveforms for each pattern.

4. Observe and picture synchronizing signal and horizontal blanking, vertical blanking, front and rear porch,
     and image information of each pattern.

5. Images and specify voltage waveforms.
6. Pattern generator output switches on and observe put in the IF waveform for each pattern and the
     measuring frequency.

7. Image of the wave form and specify voltage.
8. Image signal for one frame (still image) in composite video, determine the level and its period

 

BASIC THEORY

Analog (or analogue ) television encodes television picture and sound information and transmits it as an analog signal : one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal. All systems preceding digital television were analog television systems.

Broadcasters using analog television systems encode their signal using NTSC , PAL or SECAM analog encoding and then modulate this signal onto a VHF or UHF carrier. An analog television picture is "drawn" on the screen an entire frame each time, in the manner of a motion picture (cinematograph) film.

Until the advent of digital television , all television was based on the transmission and reception of analog signals , displayed on a cathode-ray tube . Although a number of different broadcast television systems were in use worldwide, the same principles of operation apply.

The first commercial analog television systems were monochrome ; they were enhanced to include color beginning in the 1950s.

Displaying a picture

A CRT television displays an image by scanning a beam of electrons across the screen in a pattern of horizontal lines known as a raster. At the end of each line the beam returns to the start of the next line; at the end of the last line it returns to the top of the screen. As it passes each point the intensity of the beam is varied, varying the brightness (technically, luminance) of that point. A color television system is identical except that an additional signal known as chrominance controls the color of the spot.

Raster scanning is shown in a slightly simplified form below.

When analog television was developed, no affordable technology for storing any video signals existed; the luminance signal has to be generated and transmitted at the same time at which it is displayed on the CRT. It is therefore essential to keep the raster scanning in the camera (or other device for producing the signal) in exact synchronization with the scanning in the television.

The physics of the CRT require that a finite time interval is allowed for the spot to move back to the start of the next line (horizontal retrace) or the start of the screen (vertical retrace). The timing of the luminance signal must allow for this.

Raster scanning has to be performed sufficiently quickly that persistence of vision allows the eye to view a stable image, and such that moving images can be displayed without appearing jerky. The maximum frame rate achievable depends on the bandwidth of the electronics and transmission system, and the number of lines in the image. In practice, a rate of 50 or 60 hertz is a satisfactory compromise, with interlacing used to double the apparent number of lines.

Components of a television system

           A practical television system needs to take luminance, chrominance (in a color system), synchronization (horizontal and vertical), and audio signals, and broadcast them over a radio transmission. The transmission system must include a means of channel selection.

A typical analog television receiver is based around the block diagram shown below:

 

Receiving the signal

The television system for each country will specify a number of channels within the UHF or VHF frequency ranges. A channel actually consists of two signals: the picture information is transmitted using amplitude modulation on one frequency, and the sound is transmitted with frequency modulation at a frequency at a fixed offset (typically 4.5 to 6 MHz) from the picture signal.
The channel frequencies chosen represent a compromise between allowing enough bandwidth for video (and hence satisfactory picture resolution), and allowing enough channels to be packed into the available frequency band. In practice a technique called vestigial sideband is used to reduce the channel spacing, which would be at least twice the video bandwidth if purely AM was used.
Signal reception is invariably done via a superheterodyne receiver: the first stage is a tuner which selects a channel and frequency-shifts it to a fixed intermediate frequency (IF). Signal amplification (from the microvolt range to fractions of a volt) is then performed largely by the IF stages.
At this point the IF signal consists of a video carrier at one frequency and the sound carrier at a fixed offset. A demodulator recovers the video signal and sound as an FM signal at the offset frequency (this is known as intercarrier sound).
The FM sound carrier is then demodulated, amplified, and used to drive a loudspeaker. Until the advent of NICAM sound transmission was invariably monophonic.

Structure of a video signal

The video carrier is demodulated to give a composite video signal; this contains luminance (brightness), chrominance (color) and synchronization signals; this is identical to the video signal format used by analog video devices such as VCRs or CCTV cameras. Note that the RF signal modulation is inverted compared to the conventional AM: the minimum video signal level corresponds to maximum carrier amplitude, and vice versa. The carrier is never shut off altogether; this is to ensure that intercarrier sound demodulation can still occur.

Each line of the displayed image is transmitted using a signal as shown below. The same basic format (with minor differences mainly related to timing and the encoding of color) is used for PAL, NTSC and SECAM television systems. A monochrome signal is identical to a color one, with the exception that the elements shown in color in the diagram (the color burst, and the chrominance signal) are not present.

 Synchronization

Synchronization is transmitted via negative-going pulses; in a composite video signal of 1 volt amplitude, these are approximately 0.3 V below the "black level". The horizontal sync signal is a single short pulse which indicates the start of every line. Two timing intervals are defined - the front porch between the end of displayed video and the start of the sync pulse, and the back porch after the sync pulse and before displayed video. These and the sync pulse itself are called the horizontal blanking (or retrace) interval and represent the time that the electron beam in the CRT is returning to the start of the next display line.

The vertical sync signal is a series of much longer pulses, indicating the start of a new field. The sync pulses occupy the whole of line interval of a number of lines at the beginning and end of a scan; no picture information is transmitted during vertical retrace. The pulse sequence is designed to allow horizontal sync to continue during vertical retrace; it also indicates whether each field represents even or odd lines in interlaced systems (depending on whether it begins at the start of a horizontal line, or mid-way through).

In the TV receiver, a sync separator circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync. These are fed to horizontal and vertical timebase circuits which generate sawtooth current waveforms, which are each reset by the appropriate sync pulse. These waveforms are fed to the horizontal and vertical scan coils wrapped around the CRT tube. These produce a magnetic field proportional to the changing current, and this deflects the electron beam, scanning it across the tube surface.

The lack of precision timing components available in early television receivers meant that the timebase circuits occasionally needed manual adjustment. The adjustment took the form of horizontal hold and vertical hold controls, usually on the rear of the set. Loss of horizontal synchronization usually resulted in an unwatchable picture; loss of vertical synchronization would produce an image rolling up or down the screen.

Synchronizing pulses added to the video signal at the end of every scan line and video frame ensure that the sweep oscillators in the receiver remain locked in step with the transmitted signal, so that the image can be reconstructed on the receiver screen.

There are two kinds of sync pulses: horizontal sync (HSYNC), which is responsible for horizontal synchronization pulse and separating the scan lines, and vertical sync (VSYNC), responsible for vertical synchronization and separating the video frames. In PAL and NTSC, the vertical sync pulse occurs within the vertical blanking interval. The vertical sync pulses are made by prolonging the length of HSYNC pulses through almost the entire length of the scan line.

Horizontal synchronization

A horizontal synchronization pulse is sent whenever the television set should start scanning a new line. The rest of the scan line follows, with the signal ranging from 0.3 V (black) to 1 V (white), until the next horizontal or vertical synchronization pulse.
The format of the horizontal sync pulse varies. In the 525-line NTSC system it is a 4.85 µs-long pulse at 0 V. In the 625-line PAL system the pulse is 4.7 µs synchronization pulse at 0 V . This is lower than the amplitude of any video signal (blacker than black) so it can be detected by the level-sensitive "sync stripper" circuit of the receiver.

Vertical synchronization

A vertical synchronization pulse is sent whenever the television set should start scanning a new frame from the top of the screen.
The format of such a signal in 525-line NTSC is:

·          

• pre-equalizing pulses (6 to start scanning odd lines, 5 to start scanning even lines)
• long-sync pulses (5 pulses)
• post-equalizing pulses (5 to start scanning odd lines, 4 to start scanning even lines)

Each pre- or post- equalizing pulse consists in half a scan line of black signal: 2 µs at 0 V, followed by 30 µs at 0.3 V.

Each long sync pulse consists in an equalizing pulse with timings inverted: 30 µs at 0 V, followed by 2 µs at 0.3 V.

In video production and computer graphics, changes to the image are often kept in step with the vertical synchronization pulse to avoid visible discontinuity of the image. Since the frame buffer of a computer graphics display imitates the dynamics of a cathode-ray display, if it is updated with a new image while the image is being transmitted to the display, the display shows a mishmash of both frames, producing a page tearing artifact partway down the image.

Vertical synchronization eliminates this by timing frame buffer fills to coincide with the vertical blanking interval, thus ensuring that only whole frames are seen on-screen. Software such as computer games and CAD packages often allow vertical synchronization as an option, because it delays the image update until the vertical blanking interval. This produces a small penalty in latency, because the program has to wait until the video controller has finished transmitting the image to the display before continuing. Triple buffering reduces this latency significantly.

VSYNC is also the name of the signal indicating this frame change in analog RGB component video.

Monochrome video

The luminance component of a composite video signal varies between 0 V and approximately 0.7 V above the 'black' level. In the NTSC system, there is a blanking signal level used during the front porch and back porch, and a black signal level 75 mV above it; in PAL and SECAM these are identical.
In a monochrome receiver the luminance signal is amplified to drive the control grid in the electron gun of the CRT. This changes the intensity of the electron beam and therefore the brightness of the spot being scanned. Brightness and contrast controls determine the DC shift and amplification, respectively.

Color video

A color signal conveys picture information for each of the red, green, and blue components of an image (see the article on Color space for more information). However, these are not simply transmitted as three separate signals, because:

• such a signal would not be compatible with monochrome receivers (an important consideration when color broadcasting was first introduced)
• it would occupy three times the bandwidth of existing television, requiring a decrease in the number of channels available
• typical problems with signal transmission (such as differing received signal levels between different colors) would produce unpleasant side-effects.

Instead, the RGB signals are converted into YUV form, where the Y signal represents the overall brightness, and can be transmitted as the luminance signal. This ensures a monochrome receiver will display a correct picture. The U and V signals are the difference between the Y signal and the B and R signals respectively. The U signal then represents how 'blue' the color is, and the V signal how 'red' it is. The advantage of this scheme is that the U and V signals are zero when the picture has no color content. As the eye is more sensitive to errors in luminance than in color, the U and V signals can be transmitted in a relatively lossy (specifically: bandwidth-limited) way with acceptable results. The G signal is not transmitted in the YUV system but is recovered algebraically at the receiving end.

In the NTSC and PAL color systems, U and V are transmitted by adding a color subcarrier to the composite video signal, and using quadrature amplitude modulation on it. In NTSC, the subcarrier is at approximately 3.58 MHz, in PAL it is roughly 4.43 MHz - these frequencies are within the luminance signal band, but the exact frequency is chosen so that it is midway between two harmonics of the line repetition rate, thus ensuring that the majority of the energy of the luminance signal does not overlap with the energy of the chroma signal.

The two signals (U and V) modulate both the amplitude and phase of the color carrier, so to demodulate them it is necessary to have a reference signal against which to compare it. For this reason a short burst of reference signal known as the color burst is transmitted during the back porch of each line. A reference oscillator in the receiver locks onto this signal (see phase-locked loop) to achieve a phase reference, and uses its amplitude to set an AGC system to achieve an amplitude reference.

The U and V signals are then demodulated by band-pass filtering to retrieve the color subcarrier, mixing it with the in-phase and quadrature signals from the reference oscillator, and low-pass filtering the results.
NTSC uses this process unmodified; unfortunately this often results in poor color reproduction due to phase errors in the received signal. The PAL system corrects this by reversing the phase of the signal on each successive line and averaging the result over pairs of lines. Phase errors therefore tend to be cancelled out.
In the SECAM television system, U and V are transmitted on alternate lines, using simple frequency modulation of the color subcarrier.

Power supply

Most of the receiver's circuitry (at least in Transistor or IC based designs) operates from a comparatively low-voltage DC power supply. However, the anode connection for a cathode-ray tube requires a very high voltage (typically 10-30 kV) for correct operation.

This voltage is not directly produced by the main power supply circuitry; instead the receiver makes use of the circuitry used for horizontal scanning. At the end of each horizontal scan line, the magnetic field which has built up in the scan coils contains electromagnetic energy. This must be dissipated when the field is reversed during horizontal retrace. Instead of being dissipated as waste heat, the horizontal scan coil is discharged into the primary winding of a flyback transformer. The secondary of this is fed to a high-voltage rectifier which produces the required EHT supply (see flyback converter for a detailed description of this form of power supply).

Typically, the flyback transformer and rectifier circuitry are incorporated into a single unit with a captive output lead, so that all high-voltage parts are enclosed. The high frequency (15 kHz or so) of the horizontal scanning allows reasonably small components to be used.
Such high voltages are not required for LCD screens.

Television standards

Analog broadcast television systems come in a variety of frame rates and resolutions. Further differences exist in the frequency and modulation of the audio carrier. The monochrome combinations still existing in the 1950s are standardized by the ITU as capital letters A through N. When color television was introduced, the hue and saturation information was added to the monochrome signals in a way that black & white televisions ignore. This way backwards compatibility was achieved. That concept is true for all analog television standards.

However there are three standards for the way the additional color information can be encoded and transmitted. The first was the American NTSC (National Television Systems Committee) color television system. The European/Australian PAL (Phase Alternation Line rate) and the French-Former Soviet Union SECAM (Séquentiel Couleur Avec Mémoire) standard were developed later and attempt to cure certain defects of the NTSC system. PAL's color encoding is similar to the NTSC systems. SECAM, though, uses a different modulation approach than PAL or NTSC.

In principle all three color encoding systems can be combined with any of the scan line/frame rate combinations. Therefore, in order to describe a given signal completely, it's necessary to quote the color system and the broadcast standard as capital letter. For example the United States uses NTSC-M, the UK uses PAL-I, France uses SECAM-L, much of Western Europe and Australia uses PAL-B/G, most of Eastern Europe uses PAL-D/K or SECAM-D/K and so on.

However not all of these possible combinations actually exist. NTSC is currently only used with system M, even though there were experiments with NTSC-A (405 line) and NTSC-I (625 line) in the UK. PAL is used with a variety of 625-line standards (B,G,D,K,I) but also with the North American 525-line standard, accordingly named PAL-M. Likewise, SECAM is used with a variety of 625-line standards.

For this reason many people refer to any 625/25 type signal as "PAL" and to any 525/30 signal as "NTSC", even when referring to digital signals, e.g., on DVD-Video which don't contain any analog color encoding, thus no PAL or NTSC signals at all. Even though this usage is common, it is misleading as that is not the original meaning of the terms PAL/SECAM/NTSC.

Shutdown and transition to digital

Further information: Digital television transition

As of late 2009, ten countries had completed the process of turning off analog terrestrial broadcasting. Many other countries had plans to do so or were in the process of a staged conversion. The first country to make a wholesale switch to digital over-the-air (terrestrial) broadcasting was Luxembourg in 2006, followed later in 2006 by the Netherlands; in 2007 by Finland, Andorra, Sweden, Norway and Switzerland; in 2008 by Belgium (Flanders) and Germany; in 2009 by the United States (high power only), Isle of Man, Norway and Denmark. In 2010, Wallonia, Spain, Wales, Latvia and Estonia completed the transition. Croatia is fully covered with digital signal and last analog region will shut down in October 2010.

In the United States, high-power over-the-air broadcasts are solely in the ATSC digital format since June 12, 2009, the date that the Federal Communications Commission (FCC) set for the end of all high-power analog TV transmissions. As a result, almost two million households could no longer watch TV because they were not prepared for the transition. The switchover was originally scheduled for February 17, 2009, until the US Congress passed the DTV Delay Act. By special dispensation, some analog TV signals ceased on the original date

In Japan, the switch to digital is scheduled to happen July 24, 2011. In Canada, it is scheduled to happen August 31, 2011. China is scheduled to switch in 2015. In the United Kingdom, the digital switchover has different times for each part of the country; however, the whole of the UK will be digital by 2012. Brazil switched to digital on December 2, 2007 in major cities and it is estimated it will take seven years for complete signal expansion over all of the Brazilian territory. Australia will turn off analog signals between 2010 and 2013, region by region^.

In Malaysia, the Malaysian Communications & Multimedia Commission (MCMC) will call for tender bids in the third quarter of 2009 for the UHF 470–742 megahertz spectrum which will pave the way for the country to move into the digital television era. The awarding of the spectrum will see the winner having to build a single digital terrestrial transmission/TV broadcast (DTTB) infrastructure for all broadcasters to ride on to transmit their TV programs. The winner will be announced at the end of 2009 or early 2010 and has to commence digital roll-out soon after the award where the analog switch-off is planned for 2015.

While the majority of the viewers of over-the-air broadcasting in the USA watch full-power stations (which number about 1800), there are three other categories of TV stations in the US: low-power stations, Class A stations, and TV translator stations. There is presently no deadline for these stations, about 7100 in number, to convert to digital broadcasting.

Source Basic theory : WIKIPEDIA.COM 

 

 RESULT of PRACTICAL

PATTERN	PATTERN GENERATOR
DOTS
CROSH HAT
VERT LINES
HORIZ LINES
RASTER
COLOR

Data Analisys

Data Analisys

>  output voltage when the switch on the video
• DOT → 4.4 div x 0.1 V/div = 0.44 Volt
• CROSS HATCH → 4.3 div x 0.1 V/div = 0.43 Volt
• VERT LINES → 4.4 div x 0.1 V/div = 0.44 Volt
• HORIZ LINES → 4.6 div x 0.1 V/div = 0.46 Volt
• RASTER → 4.5 div x 0.1 V/div = 0.45 Volt
• COLOR → 3.2 div x 0.1 V/div = 0.32 Volt

>  voltage when the switch output at IF
• DOT → 4.4 div x 50 mV/div = 0.22 Volt
• CROSS HATCH → 1.1 div x 50 mV/div = 0.055 Volt
• VERT LINES → 0.8 div x 50 mV/div = 0.04 Volt
• HORIZ LINES → 1 div x 50 mV/div = 0.05 Volt
• RASTER → 1.1 div x 50 mV/div = 0.055 Volt
• COLOR → 1.1 div x 50 mV/div = 0.055 Volt


>  Frequency when the switch at the IF output

• T/Div = 0.2 µs = 2 x 10-7 s

F= 1 = 0.07 x 107 = 0.7 MHz
7 x 2 x 10-7

Note : The frequency of the same value for all patterns.


Conclusion

• The basic pattern of the Pattern Generator is Dot, Cross Hatch, Vert Lines, Horz Lines, Raster and Color.
• Voltage on the composite video standard is ± 0:04 Volt output when the switch on the
• VIDEO and ± 0055 volts when the switch at the IF.
• Frequency of each pattern of the same value that is 0.7 MHz.