1. NTSC SYSTEM

2. INTRODUCTION It’s the national television system committee. Analog television – used in parts of North and South America,Myanmar,S.Korea,parts of pacific Islands. In 1941 - no color. 1953 – color provision was made. Widely accepted one and it was replaced by digital ATSC (advanced)systems – higher resolution. But frame rate and no of lines are same as analog NTSC.

3. Consists of 29.97 frames/sec. 525 lines - two fields- 262.5 scan lines for each field. National Television System Committee Lines/Field525/60 Horizontal Frequency15.734 kHz Vertical Frequency60 Hz Color Subcarrier Frequency 3.579545 MHz Video Bandwidth4.2 MHz Sound Carrier4.5 MHz

4. NTSC has 525 vertical lines. However lines number 248 to 263 and 511 to 525 are typically blanked to provide time for the beam to return to the upper left hand corner for the next scan. Notice that the beam does not return directly to the top, but zig- zags a bit.

5. ENCODING

6. Matrix produces the Y,I,Q signals. There is a B.limiting filters of different Mhz for each separate signals. – B.Widths are reduced in order to avoid crosstalk interference between monochrome and color signals. Delay lines – to compensate for delay produced by the filters. Oscillator – frequency -3.57 Mhz.

7. It is phase shifted and appropriate color bursts are added and given to modulators. Pulse generator - blank and sync pulses. Finally resistor combines all these signals and produces the complete color video signal.

8. DECODER

9. Here color difference signals are separated. Filter – passes only chrominance signals – Attenuates luminance, sound carrier and side bands. The I and Q demodulators – chrominance signal C.subcarrier – demodulation – B.filters –limited to respective color B.widhts Amplitude modulated – matrix - color difference signals are produced.

10. Sync and burst keyer - separates the synch and color respectively. AFC -maintains the frequency. Luminance signal is added – delay. All these signals are amplified and given to the matrix. Finally produces R,G, B colors are produced back from color difference signals.

11. Reduction in bandwidth If R-Y and B-Y are transmitted directly – 3Mhz is required. I and Q are active up to 0.5 MHz and Q drops after 0.5 & only I remains between 0.5 and 1.5 to produce colors. Double sideband transmission – Q signal VSB – I signal. For combined transmission 2Mhz is required and 1 Mhz is reduction is achieved.

12. SUBCARRIER FREQUENCY Exactly 3.5 Mhz is used – suppresses the dot patterns. In 525 line NTSC system the line frequency is 15750 Hz. Line frequency= t.no.lines X no of frames/s. 2

13. Sound carrier range = 4.5 Mhz Beat frequency range= 4.5 - 3.58=0.92 Mhz This interferes with the reproduced image. A new line frequency of 15734.26 hz is produced which exactly gives the subcarrier frequency as 3.579545Mhz

14. DOT PATTERN INTERFERENCE Each HZ line has three full cycle and one half cycle wave. Becoz of this the 1 st line ends with +ve cycle and 2 nd line begins with –ve cycle. This produces a dark and white patterns on the screen.

15. LIMITATIONS Sensitive to transmission paths – produces phase errors – changes colors. Program change occurs in local television network and VTR – phase errors are introduced. Phase of chrominance signal – signal level Cross talk between demodulator o/p - distortion

16. VTR

17. ATC – overcome these problems. Used in color television receivers to maintain correct flesh tones when a station changes cameras or switches Automatic tint control- automatically corrects the phase errors before the chroma signal is demodulated.