![ CCIR-B Standard
1) Video characteristics:
Number of lines/picture-625
Interlace ratio-2:1
Scanning sequence for lines-left to right
Scanning sequence for field-Top to bottom
Field freq-50 fields/sec
Line freq-15625 Hz
Aspect ratio-4:3
Video bandwidth-5 MHz
Vertical resolution-0.7 x (625-40)=409lines.
Horizontal resolution =[410 x (4/3)]=546
alternate Black & white lines.](https://image.slidesharecdn.com/ave1ppt-161116095320/85/Audio-Video-Engineering-5-320.jpg)
Audio Video Engineering
- 2. ANALOG & DIGITAL T.V. TRANSMISSION & RECEPTION: • T.V. BROADCAST CHANNELS • CCIR-B STANDARD • VESTIGIAL SIDE BAND TECHNIQUE • INTERLACE SCANNING •COMPOSITE VIDEO SIGNAL •COMPATIBILITY REQUIREMENT •COLOUR TV FUNDAMENTALS. • FREQUENCY INTERLEAVING • PAL, NTSC, SECAM SYSTEMS • ANALOG T.V. TRANSMITTERS • T.V.RECEPTION
- 3. TELEVISION BROADCAST CHANNELS For television broadcasting channels have been assigned in the VHF and UHF range. The allocated frequencies are: Lower VHF range band I - 41…………68 MHz. Upper VHF range band III - 174………230MHz. UHF range band IV - 470………582MHz. UHF range band V - 606………790MHz. (Band II , 88 to 108 MHz is allocated for FM broadcasting ) The channel allocation in band I and III are given below. There are four channels in band I, of which channel I is no longer used for T. V. broadcasting.
- 4. TELEVISION CHANNEL ALLOCATION CCIR: Band range Channel MHz Frequency Range Picture carrier MHz Sound carrier MHz I (41-68MHz) 1 2 3 4 41-47 47-54 54-61 61-68 Not in use 48.25 55.25 62.25 53.75 60.75 67.75 III (174- 223MHz) 5 6 7 8 9 10 174-181 181-188 188-195 195-203 202-209 209-216 175.25 182.25 189.25 169.25 203.25 210.25 180.75 187.75 194.75 201.75 208.75 215.75 Additional channel 11 12 216.23 223.23 217.25 224.25 222.75 229.75
- 5. CCIR-B Standard 1) Video characteristics: Number of lines/picture-625 Interlace ratio-2:1 Scanning sequence for lines-left to right Scanning sequence for field-Top to bottom Field freq-50 fields/sec Line freq-15625 Hz Aspect ratio-4:3 Video bandwidth-5 MHz Vertical resolution-0.7 x (625-40)=409lines. Horizontal resolution =[410 x (4/3)]=546 alternate Black & white lines.
- 6. 2) Composite video signal: • Line period-64μs • Line blanking period-12μs • Front porch-1.5μs • Back porch-5.8μs • Sync pulse period-4.7μs • Post and pre equalizing pulse-160μs • Vertical blanking pulse-1280μs • Field period-20ms • Sync level-100% • Blanking level-75% • White level-10%
- 7. 3) Radio freq. Characteristics: • Channel B.W.-7MHz • Sound to Picture carrier difference-5.5MHz • Picture modulation-AM VSB • Sound modulation-FM. • Carrier deviation-±50KHz. • Pre- emphasis-50μs • Colour sub carrier burst-4.43 MHz. • Space wave (Line of sight) Propagation. • Horizontal Polarization.
- 11. COMPATIBILITY COLOUR SIGNAL IS INSERTED WITHIN 7MHz CHANNEL B.W. FOR PAL SYSTEM, 6MHz FOR NTSC & 8MHz FOR SECAM COLOUR SIGNALS ARE COMPATIBLE WITH BLACK & WHITE SYSTEM. COLOUR TRANSMISSION SYSTEM PRODUCES A NORMAL BLACK & WHITE PICTURE ON MONOCHROME RECEIVER. A NORMAL BLACK & WHITE TRANSMISSION SHOULD PRODUCE A BLACK & WHITE PICTURE ON A COLOUR TV SCREEN. COLOUR TV SYSTEM MUST HAVE SAME VIDEO B.W. IT MUST USE SAME LINE & FRAME SYNCHRONISING PULSES.
- 12. COLOUR TV FUNDAMENTALS GRASSMAN’S LAW LUMINANCE OR BRIGHTNESS, HUE & SATURATION CHROMACITY DIAGRAM MIXING OF COLOUR 1. ADDITIVE MIXING 2. SUBTRACTIVE MIXING COLOUR DIFFERENCE
- 17. ANALOG TELEVISION RECEIVER • YAGI ANTENNA • RF TUNER • VIDEO IF AMPLIER • VIDEO DETECTOR • SOUND PROCESSING SECTION • LUMINANCE CHANNEL • SAW FILTER • PAL DEMATRIX • VIDEO DRIVE SECTION • DEFLECTION SECTION • EHT SECTION • HORIZANTAL OSCILLATOR • VERTICAL OSCILLATOR • SMPS
- 18. RF TUNER: It selects the channel to be received by switching pre-tuned circuits in the RF stage in the oscillator. It matches the impedance of the line at its i/p and amplifies it to maintain a good signal to noise ratio. It converts the RF into IF by mixing with the local oscillator frequency to feed it to the VIF amplifier. MULTISTAGE VIF AMPLIFIER: Used in conjunction with a surface acoustic wave(SAW) filter and a preamp to obtain a high controlled gain (upto 80db). For VSB reception, it amplifies picture if (38.9MHz), COLOUR SUBCARRIER IF(34.47mhz) at 50% and SOUND IF(33.4 MHz) AT 5 – 10% of the peak amplification between the 35-38MHz range. The last stage feeds into a video detector VIDEO DETECTOR It extracts the video signal from the modulated IF signal.A diode detector is commonly used to demodulate the amplitude modulated video if signal by rectification. Due to non linearities in the simple diode detectors,synchronous demodulators or balanced multipliers are used in modern receivers.
- 19. SYNCHRONOUS VIDEO IF DETECTION It works on the sampling principle to overcome nonlinearities and harmonics.The amplitude modulation is detected at the sampling intervals by limiting the carrier and selecting the pure carrier by tuned resonant ckts.The video modulated signal carrier is sampled by a pure unmodulated carrier of exactly the same frequency.The phase relation between the reference carrier and modulated signal are vital for detection SOUND SEPERATION AND PROCESSING The SOUND IF signal at 33.4MHz is taken off at the output of the second VIDEO I.F. Stage by means of a tuned circuit which feeds into a diode detector. The VIF and SIF are heterodyned in this detector to produce different frequency as the intercarrier SIF at 5.5MHz.The composite colour video signal is amplified and passed on to the luminance channel for amplification of the monochrome Y signal,and to the chroma section for decoding and further processing of the chrominance signal. LUMINANCE CHANNEL It provides normal video amplification for monochrome signals with facility of contrast adjustment by the amplifier gain control and brightness adjustment by suitable bias variation of picture tube.It has to incorporate a delay line to keep the luminance signal in step with the chrominance signal.A notch filter is used to block the colour sub carrier(4.43MHz) which would otherwise cause dot pattern interference.
- 20. . SYNCHRONOUS DETECTION The U & V signals from the pal dematrix are applied to two synchronous demodulators ,it passes only the signals that are in phase with the two quadrature phased with the two quadrature phased reference subcarrier signals . The colour burst signal required to synchronise the locally generated sub carriers separated from the CVS.
- 21. VIDEO DRIVE SECTION: The U & V signals obtained at the output of the synchronous detectors are amplified by the relative gain factor of 1.140 for V channel to get back the (R-Y),and 2.028 for U channel to (B-Y). The (G-Y) is obtained by matrixing (R-Y) &(B-Y).The three colours reclamped to get the maximum black and the luminance. DEFLECTION CIRCUITS: Sync separation synchronization of the horizontal and the vertical oscillator that drive the horizontal and vertical coils ,generation of the EHT the focus anode and other auxiliary voltages and blanking during fly back are provided by deflection ckts Degaussing coils are provided for removing stay colouring effects on the screen caused by stray magnetic field.
- 28. Comparision between NTSC , SECAM & PAL transmission systems: NTSC SECAM PAL •Horizontal line •Field frequency •Bandwidth •SC_PC difference •Colour signal •Colour signal Modulation •Principle of operation •Phase error •Colour sub carrier burst •Application 525 50 Hz/60Hz 6-7MHz 5.5MHZ I & Q I=0.74(R-Y)-0.27(B-Y) Q=0.48(R-Y)+0.41(B-Y) QAM Simple Subjected to phase error 3.579MHz USA 625 50Hz 7-8MHZ 6.5MHz DR & DB DR=-1.9(R-Y) DB=-1.5(B-Y) FM Complicated Phase error is minimum 4.4MHz, 4.25MHz FRANCE 625 50Hz 6-7MHZ 5.5MHz U & V U=0.493(B-Y) V=0.877(R-Y) QAM Complicated No phase error 4.43MHz INDIA, AUSTRALIA G-Y signal is not transmitted. G-Y= -0.51(R-Y)-0.186(B-Y) (R-Y) & (B-Y) signals are transmitted. (G-Y) signal is derived from these two signals.
- 29. Principles of colour T.V. Transmitter T.V Transmission requirements: •T.V uses line of sight transmission.(Space Wave) •The height of the antenna should be as high as possible. •Omni directional antennas should be used. •The audio & Video powers should be adjusted properly. •The adjacent channel stations should be as apart as possible.
- 30. Design Principles of T.V. Transmitters: • Video signals amplitude modulated. Amplitude Modulation Low Level High Level • High Level Modulation: The signal & carrier both are amplified first to the power level required for transmission .The modulating signal then modulates the carrier. Thus the modulator operates at high power level. • Low Level Modulation: The modulation takes place at low voltage levels of modulating & carrier signal.The vestigial side band filter is located after modulator. Hence VSB filter operates at low power level.
- 31. VEDIO PROCESSING UNIT DIODE BRIDGE MODULATOR DELAY EQUALISER LINEAR AMPLIFIER VSB FILTER VIDEO UP CONVERTER PA ‘X’ TAL OSC FREQUENCY MULTIPLIER ‘X’ TAL OSC AUDIO PROCESSING UNIT MODULATED OSCILLATOR AUDIO UP CONVERTER LINEAR AMPLIFIER PA LPF PHASE DETECTER ‘X’TAL OSC DIPLEXER AFC LOOP 33.4MHZ 33.4MHZ SC 38.9MHZ (SC+33.4MHZ) (PC+38.9MHZ) PC38.9MHZ TO ANTENNA FIG: BLOCK DIAGRAM OF IF MODULATED TV TRANSMITTER VIDEO AUDIO
- 32. I/P AMP SYNC GENERATER EQUILISER PHASE COMPENSATOR V F AMPLIFIER MODULATING AMPILFIER ‘X’TAL M.O MULTIPLEXER *2*2*3*3 AMPILFIER P.A DRIVER P.A DRIVER VIDEO O/P AMPLIFIER VSBF & DIPLEXER PRE- AMPLIFIER FM MODULATOR MULTIPLEXER *2*2*3*3 AMPLIFIER P.A DRIVER PA AFC ‘X’ TAL OSC 500VA 350W 2KW 10KW (FILTER PLEXER) TO ANTENNA SYSTEM VF AF MONITOR RECEIVIER VIDEO AUDIO FIG: BLOCK DIAGRAM OF A 10KW VHF TRANSMITTER USING
- 33. SR NO. PARAMETERS LOW LEVEL MODULATION HIGH LEVEL MODULATION 1 POINT AT WHICH MODULATION TAKES PLACE MODULATION TAKES PLACE IN THE INITIAL STAGES OF AMPLIFICATION MODULATION TAKES PLACE IN THE FINAL STAGE OF AMPLIFICATION. 2 POWER LEVEL MODULATION CIRCUITARY HAS TO HANDLE LOW POWER MODULATION CIRCUITARY HAS TO HANDLE HIGH POWER 3 COMPLEXITY MODULATION CIRCUITARY IS SIMPLE AS IT HAS TO HANDLE LOW POWER MODULATION CIRCUITARY IS QUITE COMPLEX AS IT HAS TO HANDLE HIGH POWER. 4 PRIME FACTOR IN DESIGN SIMPLICITY IS THE PRIME REQUIRMENT PRIME REQUIREMENT IS HIGH EFFICIENY & LOW DISTORTION. 5 AMPLIFIER USED LINEAR AMPLIFIER SUCH AS CLASS A AMPLIFIER IS USED HIGH EFFICIENCY CLASS C AMPLIFIER IS USED 6 EFFICIENCY EFFICIENCY IS LOW EFFICIENCY IS HIGH DIFFERENCE BETWEEN LOW LEVEL & HIGHDIFFERENCE BETWEEN LOW LEVEL & HIGH LEVEL MODULATIONLEVEL MODULATION
- 37. THE END THANK YOU !!