COMPOSITE VIDEO PRACTICE

COMPOSITE VIDEO PRACTICE

OBJECTIVES:

1.1 To know the base of composite video

1.2 To measure composite video and standart voltage

1.3 To determine the parameter of composite video

INSTRUMENTATIONS:

1 VCD/VTR

1 Oscilloscope 40 MHz and passive probe

1 Conector cable RCA - BNC (750 µohm)

CIRCUIT DIAGRAM :

THEORY :

Composite video is the most common type of video interface for sending or receiving an analog video signal to or from a television set. A composite video interface might connect a VHS tape player, DVD player or game console to a television

Composite video is a yellow, female RCA jack, normally found next to two audio jacks, one red, the other white. The three jacks together provide an interface for audiovisual connections. The red RCA jack connects the right channel of a stereo system, while the white RCA jack connects the left. The yellow composite video jack rounds out the set.

A video stream is composed of a Y signal for luminescence or black and white values and a C signal for chrominance or color. The Y signal provides brightness and contras allowing for deep rich blacks and startling bright whites. The quality of this signal is especially evident in low-lit scenes where a degraded signal will translate to "faded" blacks and muted whites, making it difficult to differentiate scenery or action. The color signal —- or RGB for red, green and blue-- carries the information needed to create changing hues. A degraded C signal can result in coloration that is not true to its source.

Composite video is so named because the Y/C signals are compressed and channeled through a single wire to be separated by a "comb filter" inside the television set. Though composite video was the standard for many years, the very process causes some degradation of signal integrity. This wasn't a problem in the past as television resolution and audiovisual equipment in general was inferior to today's standards. However, with the advent of high-definition television and DVD, the drawbacks of composite video have become evident on screen.

Limitations of composite video led to S-Video, a mini-DIN interface that carries the Y/C signals separately, each getting their own wire wrapped inside a single sheath to appear as a single cable. S-Video is also analog and still requires audio cables. More recently, S-Video has been superseded by component video, which isolates not only the Y signal on its own cable, but the red and blue signals as well, while green values are inferred from reading the other data streams. Component video requires three cables plus audio cables, for a total of five cables. The latest enhancement in audiovisual interfaces is High-Definition Multimedia Interface (HDMI), a true digital interface that combines video and audio into a single cable while preserving perfect integrity. This all-digital standard is the most desirable interface currently available.

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)

Step :

1. Set up the device like inte picture above, then connect the video out VCR/VCD with CRO input.

2. Turn ON the instrument.

3. Set the CRO to get a good picture (use the switch MODE at TV-H position but to look the

vertical synchronization wave put the switch MODE at TV-V)

4. See and draw the pulses of synchronization and horizontal blanking, vertical blanking pulse, front

of and back, and picture information.

5. Draw the shape of that wave and determine the voltage.

Question:

1. How much the horizontal synchronization frequencies and vertical synchronization?

2. What system that be used in that video?

Result

Analyze

Answer:
1. The horizontal synchronization frequencies =31,68 KHz
The vertical synchronization frequencies =70,71 Hz

2. The system that be used in that video is the AM modulation because can be seen at the

difference of amplitude and have the AM spectrum.

Conclusion

· A Composite Video is analog television signal's format before a sound signal is combined with it

and modulated onto an RF carrier.

· A composite video consist of blanking signal and synchronization signal.

· From the voltage of the signal we can determine the frequencies that be used in that video.

video modulator

video modulator

A. OBJECTIVES:

· Measuring the frequency spectrum of video transmission
· Determine the carrier frequency range image and sound carrier frequency.
· Specifies the field width (bandwidth) on video transmission.
· Specify the type of modulation on the picture and sound.

B. EQUIPMENT USED:

· 1 Modulator video (VCD / VTR / video sender).
· A Spectrum Analyzer.
· An RCA cable connector - BNC.


C. CIRCUIT DIAGRAM:




How to emit (transmit) signal is amplitude modulated image similar to a radio broadcasting system that has been known. In both cases, the amplitude of a carrier wave radio frequency (RF) is made varies with the modulating voltage. Modulation is a signal of fundamental frequency (baseband). On television, this baseband signal is a composite video signal. Broadcast television is really such a radio system, but includes pictures and sound. Sound signal emitted by joining in it frequency modulation (FM) on a separate carrier wave transmitter in the same channel as the image signal.
Understanding the image signal is used here to mean a modulated carrier wave. The video signal is a signal to a picture tube. Video signal to television audio signal corresponds to the sound system. Details are clearer than the image signal AM (amplitude modulation picture) and an FM voice signal.




Figure 2.a shows the frequency spectrum of video transmission that produces an image signal comprising AM picture carrier frequency (center frequency) and sound carrier frequencies (frequency side of the upper and lower side frequencies) - without VSB, while Figure 2b shows the frequency spectrum in transmission generate video image signals of AM frequencies only have the upper side only (with VSB).

E. EXPERIMENTAL PROCEDURE:

1. Calibration Spectrum Analyzer to determine the reference spectrum.
2. Set-up instruments like in the picture above.
3. ON the instrument.
4. Measure the output video modulator (RF) using the Spectrum Analyzer and observe the frequency spectrum.
5. Image of the frequency spectrum.
6. Determine how much an image carrier frequency, carrier frequency sounds, and the difference frequency picture carrier and sound carrier frequency.
7. Observe the spectrum, determine the type of modulation used in transmission, by way of changing the freq. SPAN (reduced scale).
8. Figure spktrum frequencies multiples of the base frequency.