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 (75 ohm)

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 contrast, 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 More recently, S-Video has been superseded by component video, which isolates not only the Y signal on its own cable, but the red and blue signals as well, while green values are inferred from reading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.