41) What is the function of blanking pulse in C.V.S.
To make a retrace period is invisible.
42). Mention the major function of the camera tube?
The major function of the camera tube is to convert an optical image into
electrical signals.
43). Define visual acuity?
Visual acuity can be defined as the ability of human eye to resolve finer
details in a picture
44). What do you refer by persistence of eye?
The persistence of eye refers to the storage capability of the human eye
45).Define luminous intensity?
It is the measure of light intensity responsible for stimulating visual sensation.
46).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.
47).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.
48).Define luminance?
Luminance can be defined as the quantity of light intensity emitted per
square centimeter of an illuminated area.
49).What do you understand by illuminance?
Illuminance is the average luminous flux incident on to a surface.
50).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.
51).Mention some important characteristics of human eye?
Visual acuity, persistence of vision, brightness and colour sensation are some of the important
characteristics of human eye.
52).What are rods and cones?
The retina of the human eye consists of light sensitive cellular structures
of two kinds namely rods and cones. The rods sense primarily the brightness
levels including very faint impressions. The cones are mainly responsible for
colour perception. There are 65 lakhs cones and about 10 crores rods connected
to the brain through 8 lakhs optic nerve fibres
53).Why is scanning necessary in television system?
Scanning is the important process carried out in a television system inorder
to obtain continuous frames and provides motion of picture. The scene is scanned
both in the horizontal and vertical directions simultaneously in a rabid rate. As a
result sufficient number of complete picture of frames per second is obtained to
give the illusion of continuous motion.
54).What do you understand by flicker?
The result of 24 pictures per second in motion pictures and that of scanning
25 frames per second in television pictures is enough to make an illusion of
continuity. But, they are not rapid enough to permit the brightness of one picture
or frame to blend smoothly in the next through the time when the screen is
blanked between successive frames. This develops in a definite flicker of light that
is very irritating to the observer when the screen is made alternately bright and
dark.
55).How will you solve the flickering problem?
The flickering problem is solved in motion pictures by showing each
picture twice. Hence 48 views of the scene are shown per second although they
are still the same 24 pictures frames per second. As a result of the increased
blanking rate, flicker is removed. In TV, Interlaced scaning is used to avoid flicker
56).What do you mean by interlaced scanning?
When the scanning beam reaches the bottom of the picture frame, it
quickly returns to the top to scan those lines that were missed in the previous 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.
57).Define vertical resolution?
The capability of resolving picture details in the vertical direction is called vertical resolution.
58).What is horizontal resolution?
The ability of the system to resolve maximum number of picture elements
along the scanning lines determines horizontal resolution.
59).List the contents of a composite video signal?
Composite video signal consists of a camera signal, blanking pulses and synchronizing pulses.
60).What do you mean by pedestal?
The difference between the black level and blanking level is known as the pedestal.
61).Define peak-white 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
62).Define pedestal height?
Pedestal height is the distance between the pedestal level and the average value axis of the video
Signal.
63).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.
64).What are per the post equalizing pulses?
To rectify the drawback which 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 .
65). 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.
66). Why do we prefer horizontal polarization for television receiving antenna?
We prefer horizontal polarization for television receiver antenna because it
results in more signal strength, less reflection and reduced ghost images.
67).Where can you employ indoor receiver antennas?
In strong signal areas it is sometimes feasible to use indoor antennas
provided the receiver is sufficiently sensitive.
68).A yagi antenna with a large number of directors is commonly used with
success in fringe areas for stations in the vhf band.
69).What do you understand by diplexer?
The outputs of both the video and the audio transmitter are
combined by the diplexer circuit and given to a common broadcast
transmitting antenna.
70). If two stations are operating at the same carrier frequency and located
nearby then they will interface with each other. This is called co-cannel
interference and it is common in fringe areas.
71) It is the interference due to stations located nearby and allocated as adjacent channels.
72).Define guard band?
Guard band can be defined as a small frequency band introduced
between two consecutive channels inorder to reduce interference .
73). Ghost interference arises as a result of discrete reflections of the signal
from the surface of hills, bridges, buildings, towers etc.
74).Mention the requirements of high level modulation?
In high level modulation, the video signal has to be modulated by
the picture carrier in the final power amplifier which has a high power
level. Grid bias modulation is employed.
75).What do you understand by ground waves?
Vertically polarized electromagnetic waves are radiated at zero or
small angles with ground. They are guided by the conducting surface of
the ground along which they are propagated. Such waves are known as
ground or surface waves. As the ground waves travel along the surface of
the earth, their attenuation is proportional to frequency. The attenuation is
reasonably low below 1500KHz.Therefore, all medium wave broadcast and long
wave telegraph and telephone communication is carried out by ground wave
propagation.
76).What are sky waves?
In ground wave propagation ,frequencies above 1600 KHz does not serve
any useful purpose as the signal gets very much attenuated within a short distance
of its transmission .Therefore ,most radio communication in short wave bands
upto 30MHz is carried out by sky waves.When these waves are transmitted high
up in the sky , they travel in the straight line until the ionosphere is reached. This
region begins about 120Km above the surface of the earth. The region consists of
large concentrations of charge gaseous ions, free electrons and neutral molecules.
The ions and free electrons cause to band all passing electromagnetic waves.
77).Describe briefly about space wave propagation.
Propagation of radio waves above about 40MHz is not possible through
either sky wave or surface wave propagation .Therefore ,the only alternative for
transmission in the VHF and UHF bands, despite large attenuation is by radio
waves which travel in a straight line from transmitter to receiver. This called
space wave propagation.
78).Why is AM preferred over FM broadcasting the picture signal?
If FM is adopted for picture transmission ,the changing beat frequency
between the multiple paths delayed with respect to each other would develop a
bar interference in the image with a shimmering effect as the bars continuously
changes as the beat frequency changes therefore ,no study picture is
produced.Apart from that ,circuit complexity and BW requirements are much less
in AM than FM.Hence AM is preferred to FM for broadcasting the picture signal.
79).What is Dipole array?
Dipole antenna is used for band I&III transmitters. It consists of diploe
pnels mounted on the four sides at the top of the antenna tower.Each panel has an
array of full wave dipoles mounted in front of reflectors. To get an unidirectional
pattern ,the four panels mounted on the four sides of the tower are so fed that the
current in each lags behind the previous by 90 degree . This is done by changing
the field cable length by λ/4 to the two alternate panels and by reversal of polarity
of the current.
80). Define Image rejection ratio.
Image rejection ratio is defined as the output due to desired station divided
by output due to image signal. 
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