81). What do you refer by Yagi uda Antenna?
This is a widely used antenna for television receivers .Generally ,for
locations within 40 to 60Km from the transmitter is the folded dipole with one
reflector and one director. This is commonly called Yagi antenna or Yagi-Uda
antenna
82). Name the essential parts of TV transmitter.
The essential parts of TV tranmitter includes a video processing unit . A
visual modulator which is a diode bridge modulator, phase compensator or delay
equalizer and frequency converter.
83). What is the main purpose of using VHF tuner?
The purpose tuner unit is to amplify both picture and sound signals picked
up the antenna and to convert the carrier frequencies and their associated side
bands into intermediate frequencies.
84). Name the essential components of RF section.
RF tuner section consists of RF amplifier ,mixer and local oscillator and is
normally mounted on a separate subchasis,called the front end.
85). What are the major tasks to be done by detector?
The video detector is designed to recover composite video signal and to
transform the sound signal to another lower carrier frequency.
86). Why is video amplifier required?
The amplitude of the composite video signal at the output of video
detector is not enough to drive the picture tube directly . Therefore further
amplification is required. This is done by video amplifier.
87). What are Sync pulses?
The Synchronizing pulses called ‘Sync’ are part of the composite video
signal as the top 25% of the signal amplitude. The sync pulses include horizontal
vertical and equalizing pulses. Sync separator separates these signals from the
video signal.
88). Define frequency Distortion.
The inequality in gain at different frequency components of the received
signal is called frequency distortion.
89). List out the advantages of IF sections.
The main function of this section is to amplify modulated IF signal over
its entire bandwidth with an input 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.
90). What is meant by high level modulation.
In high level modulation modulation occurs in the output circuit of the
final amplifier.
91). What do you understand by Hue?
Hue or tint can be defined as the predominant spectral colour of the received light.
The colour of any object is distinguished by its hue or tint.
92). Define Brightness.
Brightness can be defined as theamount of light intensity as perceived by
the eye regardless of the colour.
93). What do you mean by saturation?
Saturation refers to the spectral purity of the colour light.It indicates the degree by
which the colour is diluted by white.
94). List any three requirements to be satisfied for compatibility in television systems.
a. It should has the same bandwidth as the corresponding monochrome signal.
b. The colour signal should have the same brightness information as that of
monochrome signal.
c. The location and spacing of the picture and sound carrier frequencies
should remain the same.
95). What is additive mixing?
All light sensations to the eye are splitted in to three main colour groups
namely red,blue and green. The optic nerve system integratesthe different colour
impressions in accordance with the curve to perceive the actual colour of the
object.
96). State grassman’s law.
The brightness impression produced by the three primaries that constitute
the single light. This property of the eye of generating a response which depends
on the algebraic sum of the blue ,red and green inputs is called grassman’s law.
97). Explain the significance of generating colour difference signals.
Colour difference signals are generated to avoid the separate transmission
of R,G,B signals.
98). Why is (G-y) not suitable for transmission?
The proportion of G is large in luminance signal,hence magnitude of (GY) is relatively small so it requires amplifiers at the receiving end.
It affect the signal to noise ratio at the transmitting end.
99). What is gamma correction.
A colour camera is used develop three voltages proportional to red,green and blue
colour contents of the picture.These voltages are represented as R,G,B.a
correction is applied to these voltages to compensate for any nonlinearity of the
system and that of the picture tube.This is called gamma correction.i.e. the camera
tube output voltage amplitudes are normalized to I V p-p level.
100). what do you mean by compatibility?
Compatibility means that a colour TV signal can produce a black and white
picture on a monochrome receiver and signals from a black and white system can
provide a monochrome picture on a colour receiver.
101). What do you mean by colour burst?
In PAL system the two carrier components are suppressed in the balanced
quadrature modulator it is necessary to regenerate at the receiver for
demodulation .For this ,8 to 10 cycles of the colour subcarrier oscillator output at
the encoder are transmitted along with other sync pulses. This sample of the
colour subcarrier called colour burst,is placed at the back porch of each horizontal
blanking pulse pedestal.
102). What is swinging burst?
The PAL burst phase actually swings 45 about the –U axis from line to line and
indicates the same sign as that of the V signal;thus the switching mode
information is the swinging burst.this is known as swinging burst.
103). Merits of SECAM system.
SECAM system has several advantages because of frequency modulation
of the subcarrier and transmission of one line at a time.
SECAM receivers are immune to phase distortion.
Both the luminance and chrominance signals are not present at the same
time ,there is no possibility of cross talk between the colour difference
signals.
Ther is no need for the use of QAM at the transmitter and synchronous
detectors at the receiver.
The receiver does not need Automatic tuning control and Automatic color
Control
104). Demerits of SECAM system.
In SECAM system luminance is represented by the amplitude of voltage
but hue and saturation are represented by deviation of the subcarrier.when a
composite signal involving luminance and chrominance is faded out in studio
operation,it is the luminance signal that is readily attenuated and not6 the
chrominance.This makes the color more saturated during fade to black.
105). Limitations of the NTSC system.
The NTSC system is sensitive to transmission path differences which
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.
106). Mention some features of PAL system.
a. 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.
b. On modulation both the color difference signals are allowed the same
bandwidth of about 1.3MHz.
c. The color subcarrier frequency is chosen to be 4.43MHz.
d. The weighted color difference signals are quadrature modulated with the
subcarrier.
107). Write notes on NTSC 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.
108). What is the difference between NTSC,PAL and SECAM?
The difference between the SECAM system on one hand and NTSC and
PAL on the other is that the later transmit and receive two chrominance signals
simultaneously while in the SECAM system only one of the two color difference
signal is transmitted at a time.
109). What do you mean by high frequency preemphasis?
In SECAM system, the chrominance signals are pre-emphasized before
modulation. After modulating the carrier with the pre-emphasized and weighted
color difference signals, another form of preemphasis is carried out on the signals.
This takes the form of increasing amplitude of the sub carrier as its deviation
increases. Such a preemphasis is called high frequency preemphasis.
110). What is the use of line identification pulses?
In SECAM system ,the switching of Dr and Db signals line by line takes
place during the line sync pulse period.The sequence of switching continues
without interruption from one field to the next and is maintained through the field
blanking interval.However it is necessary for the receiver to be able to deduce as
to which line is being transmitted.Such an identification of the proper sequence of
color lines in each field is accomplished by identification pulses. 
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