COMPOSITE VIDEO

COMPOSITE VIDEO

PURPOSE:

1.1  Getting to know the basic composite video.

1.2  Measure voltage and standard composite video.

1.3  Determining the parameters of composite video.


EQUIPMENT USED:

1 VCD / VTR
1 Oscilloscope 40 MHz and passive probe
An RCA cable connector - BNC (75W)

Circuit diagram:

 

INTRODUCTION:

The most fundamental job of a video decoder is to separate the color from the black and white information for video composite signals. This task has been achieved many ways since the introduction of color television over 50 years ago. Many different separation methods have been used through the years. With the availability of new cost effective technologies, the consumer has been seeing a gradual improvement in picture quality and detail. Advances in display tube technology and semiconductor processes have pushed the technological envelope providing sharper, more robust video. But separating the chrominance from the luminance information is especially challenging due to the fact that the signals overlap each other in the frequency spectrum. How do you separate them, while minimizing display artifacts?

Composite Signal Construction
The composite video signal is constructed with 3 basic elements:
- Luminance Information from DC to 5.5MHz (B&W Detail)
- Chrominance Information modulated onto a carrier (at 3.58MHz or 4.43MHz)
- Synchronization Information (Horizontal and Vertical Sync)

The three analog elements of a composite video signal carry all the information necessary to display a two dimensional picture on a cathode ray tube (CRT) television.

Luminance (a B&W World)

The luminance signal carries the black and white parts of the picture. This component of the composite video signal requires the most bandwidth (typically to 5MHz), and signal integrity, to convey sharp and clear images. Edge information, brightness, and contrast of the image are entirely contained in the luminance portion of the signal. Until 1947 the broadcast video signal was only black and white. To maintain compatibility with the installed equipment of the time, color or chrominance information was added to the luminance signal

to create the color composite signal as we know it today. Figure 1 shows the specified bandwidths for NTSC and PAL.

Chrominance (an Add-On)The chrominance information is quadrature modulated onto the luminance information. The chrominance is interleaved into the video signal bandwidth between luminance spectra. The chrominance modulation scheme utilizes an I, Q (U, V for PAL) coordinate system where hue and saturation is in vector format. A camera sensor captures light in Red, Green, and Blue (RGB) format. The RGB signal is converted into Y (luminance signal) and I, Q (Color Difference signal) format along with the synchronization information. The I, Q (commonly referred to as C) color information occupies a smaller bandwidth than the Y signal. C bandwidths typically range from 0.6MHz to 1.3MHz. The chrominance signal is modulated onto a carrier. The carrier resides at 3.58MHz for NTSC signals and 4.43MHz for PAL signals. The chroma information must be separated out of the video signal to demodulate it to baseband. This is difficult because luminance information that resides from 2MHz to 5MHz cannot be differentiated from chroma information. Several techniques have been tried over the years to improve separating Y and C, each increasing in complexity and performance.

Don’t Forget the SyncThe synchronization information is also imbedded in the composite video signal and occupies precious amplitude range of the video signal. Horizontal Sync, Vertical Sync (also know as Vertical retrace) and the Color Reference Bursts are embedded in the composite waveform. Figure 2 shows a typical composite signal.

Composite Video Signal Construction

            Composite video signal containing variations of the camera signal (image information), blanking pulses (blanking), and synchronization pulses (sync).

 

Figure 1. Three sets of composite video signal is a variation of the camera signal, blanking pulses, and synchronizing pulses. (A) camera signals (image information) to a single horizontal line, (b) H blanking pulse signal is added to the camera, (c) Toll-alignment of H added to the pulse discharge.

  Figure 2 composite video signals for two horizontal lines

In figure 2, the amplitude of voltage and current are shown sequentially for MRV two horizontal lines in the shadows, as time increases Dalan horizontal direction, the amplitude is changed to white shade, gray, or black in the picture. Starting from the far left at time zero, the signal at the level of white and MRV file located on the left image (the image).

                Once the first line dipayar from left to right, found different cameras with different amplitude signal corresponding to image information is required. After penjejakkan (trace) horizontal camera produces the desired signal for one line, MRV file located on the right image (image or image). Then the discharge pulse is inserted in order to restore the video signal amplitude to the top to the black level, so that repetition of traces can be left empty.

            After emptying time long enough to cover the trail repetition, emptying the voltage is removed. Then & MRV file located on the left, ready to memayar next line. In this way each horizontal line dipayar respectively. Note that the second line shows the dark image information near the black level.

            With regard to time, the amplitude of the signal-amplitude right after emptying in Figure 2 shows the information in accordance with the left side at the start line of MRV. Just before discharge, the signal variation corresponds to the right side. Appropriate information in the middle line of MRV is half the time between discharge pulses.

Figure 3. Details of horizontal blanking and synchronizing pulses.

Details of the horizontal blanking period as figure 3. Intervals marked H is the time required to memayar a complete line including tracking and loop trail.

Pulse-Pulse Alignment in Time Decommissioning V

            Sync pulses are inserted in the composite video signal during vertical blanking pulse width shown in Figure 4. This includes pulses to equalize, pulses vertical alignment and horizontal alignment of multiple pulses. Signal-signal is shown at intervals of time at the end of the field and the next one, to describe what happens during the vertical blanking time. Both signals are shown one above the other are the same, except for half-line shift between successive fields are required for MRV intertwined odd lines.

            Starting from the left in Figure 4, the fourth-last line of MRV horizontal raster shown on the basis of joint discharge pulses and horizontal alignment is needed. Immediately after following the last visible line, the video signal is made into the black by the vertical blanking pulse in preparation for the repetition of vertical trace. Vertical blanking period begins with a group of six pulses MRV, which separate the half-line intervals. Next is the vertical alignment pulse produces real jagged vertical flyback in a series of MRV. Serration also occur at intervals of half a line. Thus, a complete vertical alignment pulse width is three lines. Following the vertical alignment is a another group of six pulse equation and a series of horizontal pulses.During the vertical blanking period as a whole, there is no information on the resulting image, because the signal level is black or blacker than black so that the repetition of vertical traces can be left empty.

Simak

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            In a signal at the summit, the first pulse is a full line of credit beyond the previous horizontal alignment; in signals below for the next field, the first pulse is as far as half a line. The difference this time and a half lines between the even fields and odd continues through all subsequent pulses, so that the pulses of the vertical alignment for successive fields MRV interwoven set time for the odd lines.

Decommissioning & MRV V and V (V Blanking and V Scanning)

            Serrated vertical sync pulses that force the vertical deflection circuit to start the flyback. However, the flyback generally will not begin with the start of vertical alignment because the alignment must build a toll-charge in a capacitor in order to trigger circuits & MRV. If we assume that the vertical flyback starts with the leading edge of the third serration, the elapsed time from one line for vertical alignment before the flyback starts. Also six pulses to equalize the same with the three lines before the vertical alignment. So 3 1 = 4 lines left blank at the bottom of the image, right before the vertical loop trail begins.

            How much time is required for the flyback circuit depends on MRV, but the repetition time of a typical vertical traces are 5 lines. Once the loop trail MRV file from the bottom to the top of raster, produced five complete horizontal lines. Repetition vertical trail can be completed with ease during vertical blanking time. With 4 lines left blank at the base before the flyback and 5 lines emptied during flyback, 12 lines remaining from a total of 21 during during vertical blanking. The 12 blank lines at the top raster in the vertical direction of the surface tracking down. In summary, 4 lines left blank at the bottom and 12 on the top line in each field. In the framework of a total of two fields, 8 lines emptied at the base and 24 lines at the top. MRV lines generated during vertical tracking, but that made black by the vertical blanking, forming black rods at the top and the bottom of the image.
High image is slightly reduced by the discharge, compared with a raster that is not emptied. However, height can be fixed easily by enlarging the amplitude of the sawtooth waveform for vertical & MRV.

EXPERIMENT PROCEDURE:

1.     Set-up equipment as shown above, connect the video out VCR / VCD with CRO input.

2.     ON the instrument.

3.    Set the appropriate CRO to be easily observed (use MODE switch on the TV-H position and / or TV-V, in accordance with the observed images.) When seeing a wave of horizontal synchronization MODE switch put on the TV-H position, while to see a wave of vertical sync put the MODE switch on the TV-V position.

4.    Observe and picture synchronization pulses and horizontal blanking, vertical blanking pulse, the front porch and rear, and image information.

5.   Image of the wave forms and determine the voltage.

QUESTION:
1. What is the frequency of horizontal sync and vertical sync?
2. What system is used in the video? 


EXPERIMENT RESULTS :

1. Without Cassette CD

TV IMAGES V   : 

  1.
                                                                     

  
2. 
 
note : T/D = 2 ms  & V/D = 0,2 V                                                                                   

2 . Cassette CD has not been in play

TV IMAGES V   : 

1.                                                                                                        

                                                                                                                                                                      

 2.

Note : T/D = 2ms & V/D = 0,2V

3. With cassette CD after the play

TV IMAGES V   :

   1. 

2.

   

Note : T/D = 1 ms & V/D = 0,2 V

Data analysis

   ANSWER QUESTIONS:

1. What is the frequency of horizontal sync and vertical sync?
          Frequency = 31.68 KHz horizontal synchronization
          Frequency = 70.71 Hz vertical synchronization
2. What system is used in the video?
          The system used is to use the system pemodulasian AM because it can be seen from the changes in amplitude and has a spectrum of AM.

CONCLUSION:

1. Comprises a composite video signal consisting of variations of image information, pulse blanking (blanking), and pulse alignment (synchronization), each based on a function of time.
2. Interval marked H is the time required to memayar a complete line including tracking and loop trail.
   front porch pulse = 0.02 H
   horizontal sync pulse H = 0.08
   back porch pulse = 0.06 H
   horizontal blanking pulse = 0.16 H

Cable TV

A. Objectives:
1. Determining the modulator output attenuation before being distributed to customers.
2. Determine the amount of attenuation along the channel.
3. Knowing the strengthening of the cable television amplifier.

B. Equipment used:

• 1 Spectrum Analyzer
• 1 Modulator 3 channel
• 1 Connector  matching impedance 75 W
• 2 Television
• 2 VCD player
• Connecting cable 75 W (± 2 m)
• Coaxial cable RG-59 75 W (± 140 m)
• Connector  N male to BNC female

C. Circuit diagram

D. Theory
 

                        Cable television is a system of providing television to consumers via radio frequency signals transmitted to televisions through fixed optical fibers or coaxial cables located on the subscriber's property, much like the over-the-air method used in traditional television broadcasting (via radio waves) in which a television antenna is required. FM radio programming, high-speed Internet, telephony, and similar non-television services may also be provided. The major difference is the change of radio frequency signals used and optical connections to the subscriber property.

                        The abbreviation CATV is often used to mean "Cable TV". It originally stood for Community Antenna Television, from cable television's origins in 1948: in areas where over-the-air reception was limited by distance from transmitters or mountainous terrain, large "community antennas" were constructed, and cable was run from them to individual homes. The origins of cable broadcasting are even older as radio programming was distributed by cable in some European cities as far back as 1924.

It is most commonplace in North America, Europe, Australia and East Asia, though it is present in many other countries, mainly in South America and the Middle East. Cable TV has had little success in Africa, as it is not cost-effective to lay cables in sparsely populated areas. So-called "wireless cable" or microwave-based systems are used instead.

Edge Head (Head End)

Edge provides event signals (programs) for all channels. Local broadcasting and a much captured by an antenna mounted on top of a very high tower in order to extend the distance limit of view. These signals can be distributed it as their home channel number or frequencies diheterodinkan into different channels.

Distribution Cables

Frequency losses in coaxial cables is high, especially those working in the super frequency region from cable TV. However, loss-loss of channel offset by using a radio frequency amplifier (RF amplifier) with a wide field of frequencies that are placed along the cable network as shown in Figure 2.3.

In distribution systems, main channel is the trunk. From this main line, branch cables extended to groups of customers. Channel for each customer referred to the drop.

Each amplifier channel has a strengthening of the same trunk with a loss channel for the distance between the amplifier. Typical value is 40 dB, or a strengthening of the voltage at 100.

Block diagram of a cable television distribution system

Definition

Cable television or cable television is a television broadcasting system via radio frequency signals transmitted via fiber optic or coaxial cables are fixed and not through the air like a regular television broadcasts that must be captured antenna (over-the-air). In addition to television, FM radio show, internet, and phones also can be delivered via cable.
This system is often found in North America, Europe, Australia, East Asia, South America, and Middle East.

 Cable television was less successful in Africa because of low population densities in various regions. Like radios, different frequencies are used to distribute many channels through one cable. A receiver box used to select a television channel. Modern cable systems now use digital technology to broadcast more channels than analogue systems.

 How it works In a cable system, the signal may have exceeded 30 or 40 amplifiers before reaching your home, one for each 1000 feet or more, with each amplifier you can get noise and distortion. Plus if one of the amplifiers fails you will lose the image. Posts cable systems do not have good image quality and can not be trusted. At the end of 1970, cable TV amplifiers find a solution to the problem. Since then they also make the technology they can add programming to cable service.

Adding channelsIn the early 1950s, cable systems began to experiment with how to use microwave sender and receiver tower to catch signals from distant stations. In some cases, this way to make television available to the people who live outside the area of broadcast standards. In other cases, especially in the northeastern U.S..

That means cable TV subscribers may be able to access to several broadcasting stations that have the same network. For the first time the TV cable is used to increase the spectacle, not only the usual spectacle. This started a trend that started the boom in its cable TV in the 1970s.The addition of the station CATV (Community Antenna Television) and cable distribution system directs the author to add a switch most of the television setting.

People can manage their television channels to choose on the basis of the frequency allocation plan of the Federal Communications Commission (FCC) or they can set all to plan for the use by most cable systems. Two different plans its interests.In both search systems, each television station has provided six megahertz part of the radio spectrum. The FCC has become part of the spectrum of Very High Frequency (VHF) to 12 television channels.

Channel is not contained in one frequency block, but instead split into two groups to avoid interference with existing radio services. After that at the time of the growing popularity of television requires additional channels, the FCC allocated frequencies in the UHF (Ultra High Frequency) of the spectrum.

They create a channel 14 to 69 using a block of frequencies between 470 MHz and 812 MHz.
Because they use a cable instead of antenna, cable TV systems do not have to worry about existing services. Experts can use the so-called mid-band frequency has been passed by television broadcasters as well as for other signals, for channels 14-22. channels 1 through 6 are in a lower frequency while others are higher. CATV / Antenna change notice to the television seekers to look for around mid-band and looking through it.

While we are talking about the search channel, ought to consider why the CATV system does not use the same frequency for stations broadcasting on channels 1 through 6 who used the station used the station to broadcast over the airwaves. Equipment designed to protect cable signal carried on the cable from outside interference, and television is designed to receive signals only through the point of connection to the cable or antenna, but the disorder can still enter the system, especially at the connectors.

When the interference comes from the channel carried by cable, there is a problem caused by the difference in speed between the two signal broadcasting.Radio signals travel through the air at speeds that almost match the speed of light. In a coaxial cable such as that carried by the CATV signal into your house, radio signals running at two thirds the speed of light. When broadcast and cable signals to the television seekers breaking occurs for one second, you will see a shaded image known as ghosting

In 1972, a cable system in Wilkes-Barre, PA, starting with channel system offers pay-per-view first. Customers pay to watch individual movies or sporting events. They named this new service with a name or HBO Home Box Service. A pay-per-view continues as a regional service until 1975, when HBO began transmitting signals to the satellite in geosynchronous orbit and then into the cable system in Florida and Mississippi. Bill Wall said that the satellites in recent years can receive and send back up to 24 channels.

 Cable systems receive the signals using dish antennas 10 meters in diameter, with a separate dish for each channel. With the beginning of program delivery to cable systems, the basic architecture of a modern cable system is placed. As the number of program options continues to grow, the bandwidth of cable systems also increases. Current systems operate at 200 MHz, gain 33 channels. As process technology, the bandwidth increased to 300,400,500 and now to 550 MHz, with the number of channels that can be increased to 91 channels. Two additional technological advances, fiber optic and analog to digital conversion, improve the features and quality of broadcasting while continuing to increase the number of channels available.

E. Experimental Procedure
Prior to testing, calibration done prior to the Spectrum Analyzer. After that test the modulator output can be started.

Note: For each test, before being connected to the Spectrum Analyzer will be  matching impedance from 75 W to50 W (attenuasion 7,8 dB).

For each measurement of TP, do not connect the entire system to be measured. For example, measurements TP1 just installed only the modulator, modulator and cable TP2 just roll it, and so on.

1. Measure and image frequency spectrum at the measurement point (TP1) to see the modulator output signal level on each channel (± 2 m), with block diagram as shown below. The cable used in this test form koaxial cable 75 W.

2.  Repeat the test using a long cable (± 150 m) is TP2, with block diagram as shown below. Image of the frequency spectrum and determine the level., How many dB attenuation that occurred on the cable.

3. Repeat testing for TP3, TP4, TP5, TP6, and TP7 as in steps 1 and 2.

Determine the strengthening of the amplifier, the cable attenuation, attenuation at each port splitter.

4. Repeat to TP 2 and TP 4 with moving the cable roll.

F. Experimental Results

1. TP1

Note : REF=80dBµ      CF=2MHz             50MHz/DIV

           BW=1MHz        CP1∆F+92MHz    ∆V+16.8dB

           Signal Amplitude = 80dBµ

2. TP2

Note : REF=80dBµ    CF=4MHz           50MHz/DIV

          BW=1Mhz       CP1∆F+92MHz   ∆V+17,6dB

          Signal Amplitude = 62dBµ

3. TP3

Note : REF=80dBµ      CF=4MHz              50MHz/DIV

         BW=100KHz     CP1∆F-5.36MHz    ∆V+80dB

         Signal Amplitude = 73dBµ

G. Data Analysis

From TP1, TP2 and TP3 loss frequency is very large. While at TP4 and TP5 small. This is because at TP4 and TP5 already dimbangi channel using radio frequency amplifier (RF amplifier).

H. Conclusion

Loss will be a big loss in the channel when the channel is not matched with radip frequency amplifier (RF amplifier).