Electronics &Communication Engineering Subject code: 080290057 Subject: Television and Video Engineering (For seventh semester ECE ) 2 Mark Questions and Answers 1. Mention the major function of the camera tube? The function of the camera tube is to convert an optical image into electrical signals. 2. Define visual acuity? Visual acuity can be defined as the ability of human eye to resolve finer details in a picture 3. What do you refer by persistence of eye? The persistence of eye refers to the storage capability of the human eye 4.Define luminous intensity? It is the measure of intensity responsible for stimulating visual sensation. 5.Define aspect ratio? Aspect ratio can be defined as the ratio of width to height of the picture frame. For television, it is standardized as 4:3. 6.Define luminous flux? Luminous flux can be defined as the radiated luminous power or power of visible light expressed interms of its effect on the average or normal human eye. 7.Define luminance? Luminance can be defined as the quantity of light intensity emitted per square centimeter of an illuminated area. 8.What do you understand by illuminance? Illuminance is the average luminous flux incident on to a surface. 9.what do you mean by resolving power or resolution? It is the ability of the image reproducing system to represent the fine structure of an object.
scanning. Hence the total number of lines are divided into two groups called fields. Each field is scanned alternately. This way of scanning is called interlaced scanning. 17.Define vertical resolution? The capability of resolving picture details in the vertical direction is called vertical resolution. 18.What is horizontal resolution? The ability of the system to resolve maximum number of picture elements along the scanning lines determines horizontal resolution. 19.List the contents of a composite video signal? Composite video signal consists of a camera signal, blanking pulses and synchronizing pulses. 20.What do you mean by pedestal? The difference between the black level and blanking level is known as the pedestal. 21.Define level? The peak-white level is defined as the level of the video signal when the picture detail being transmitted corresponds to the maximum whiteness to be handled 22.Define pedestal height? Pedestal height is the distance between the pedestal and the average value axis of the video signal. 23.What is the main function of the blanking pulses? The composite video signal consist of blanking pulses to make the retrace lines invisible by increasing the signal amplitude little above the black level of 75percent during the time scanning the circuits develop retrace. 24.What are per the post equalizing pulses? To rectify the drawback occurs on account of half-line discrepancy five narrow pulses are added on either side of the vertical sync pulse. These are called pre-equalising and post-equalising pulses . 25. Differentiate monochrome and colour camera tube. In black and white camera only one pickup tube is needed but three such tubes or its equivalent is necessary in color cameras to develop separate signals for red ,green and blue information present in the scene. 26. Why do we prefer horizontal polarization for television receiving antenna?
A is used ,which is suitably polarized to rectify either positive or negative peaks of the input signal. 9. Draw diagram of a monochrome TV receiver and briefly explain the operation of TV receiver. A black and white receiver has six main sections:- Tuner section, IF sub system ,Video section ,Audio section, Deflection and power supply. section: This section consists of RF amplifier ,mixer and local oscillator.It selects the desired channel signal from those picked up by the antenna and converts it into the IF band. IF subsystem: The IF subsystem includes IF section ,AGC circuit and video detector.The IF section provides large amplification to the weak IF signals and the video detector that follows IF amplifiers produces composite video and intercarrier FM sound signals. Video section: The Video signal is accorded large amplification and fed to the picture tube. Audio section: The sound associated with the picture is transmitted as an FM signal with a center frequency 5.5MHz above the station picture carrier frequency. The sound signal BW is only about 150Khz as compared to the large bandwidth of 5MHz for the picture signal. Sync separation and processing: The horizontal and vertical sync pulses that form part of the composite video signal are separated in the sync separator. The composite video signal is either taken from the video detector output or after one stage of video amplification. DC supplies: All the active devices ,ICs and picture tube need a dc source for their operation. Rectifiers are used to convert ac to dc and filters provided to eliminate ac ripple in the dc output. 10. Explain briefly the operation of IF subsystem. The IF subsystem includes IF section ,AGC circuit and video detector.The IF section provides large amplification to the weak IF signals and the video detector that follows IF amplifiers produces composite video and intercarrier FM sound signals. The factors that influence the choice of intermediate frequencies in TV receivers are: Image Rejection Ratio: Image rejection ratio is defined as the output due to desired station divided by output due to image signal. Pickup due to local oscillator radiation from TV receivers Image Frequencies should not lie in the FM band Interference or direct pickup from bands assigned for other services
Gain IF section : The main function of this section is to amplify modulated IF signal over its bandwidth with an of about 0.5mV signal from the mixer to deliver about 4V into the video detector. IF section is used to equalize amplitudes of sideband components ,because of vestigial side band transmission. IF section is used to reject the signals from adjacent channels. 11. Explain in detail the NTSC color receiver system. NTSC system is compatible with 525 line American system.In order to maintain compatibility two new colour difference signals are generated and they are represented as I and Q. Since eye is capable of resolving finer details in the regions around I,it is allowed to have a maximum bandwidth of 1.5MHz.The bandwidth of Q signal is restricted to 0.5MHz. Limitations of the NTSC system. The NTSC system is sensitive to transmission path differences introduces phase errors that result in colour changes in the picture. At the transmitter,phase changes in the chroma signal take place when change over between programmes of local and television network systems takes place and when video tape recorders are switched on .The phase angle is also affected by the level of the signal while passing through various circuits .In addition cross talk between demodulator outputs at the receiver causes colour distortion. 12. Explain working of a pAL system. The weighted (B-Y) and (R-Y) signals are modulated without being given a phase shift of 33 as is done in the NTSC system. On modulation both the color difference signals are allowed the same bandwidth of about 1.3MHz. The subcarrier frequency is chosen to be 4.43MHz. The weighted color difference signals are quadrature modulated with the subcarrier. 13.Describe with necessary diagrams the encoding of color difference signal. Quadrature modulation: It is used to combine two colour difference signals in to a single variable. Frequency interleaving: The technique of combining two distinct signal within the same bandwidth is as frequency interleaving. Colour burst: Sample of colour subcarrier output at the encoder are transmitted along with other sync pulses. 14.Describe the generation of Y signal and difference signals. Find the value for cyan. In a color camera ,the luminance or Y signal is obtained by adding R,G and B in the following proportions
second chroma amplifier from the color killer circuit ,it blocks the second chroma amplifier.Thus it prevents the color noise on black and white picture. 20.Briefly explain PAL-D system. The use of eye as the averaging mechanism for the correct hue is the basic concept of simple ‘PAL’ system. Beyond a certain limit , the human eye see the effect of colour changes on alternate lines hence the system needs modification. Considerable improvement found in the system of a delay line is used to do the averaging first and then present the color to the eye.This is called PAL-D or delay line PAL method and is most commonly employe in PAL receivers. 21.Briefly explain satellite TV broadcast system. Satellite TV is a TV from space. Broadcasters from earth transmit their programmes to specified satellites. Then, the transmissions are returned to receiving equipment on the ground. Therefore, the better the receiving equipment ,the higher the quality of the reception. Applications of satellite TV: The shear range of programmes currently available on satellite channel is very much impressive such as 24-hour music videos, news, and feature films. A variety of general entertainment programmes, sports ,children’s programmes , foreign language broadcasts and cultural programmes are all available for the keyboard dish owner. Some of these come through subscription channels and others by free to watch channels which are sponsored by advertising. Limitation: The limitation of the satellite TV is varying picture and quality .By adopting de-emphasis circuits we can avoid the variations. 22.Write short notes on Video disc system. The video disc is essentially a gramophone record with pictures on it.The first video disc was the laser optical and the second video disc system is based on the capacitance principle. 23.Write short notes on High definition Television. It aims at Improvement in both vertical and horizontal resolution of the reproduced picyure by approximately 2:1 over existing standards. Much improved colour rendition Higher aspect ratio of atleast 5:3 Stereophonic 24. Briefly explain CATV system. 25. Briefly explain Digital TV transmission and reception.