Departmental Competitive Examination for Promotion ofSEA to the Grade of Assistant Engineer - February 2002

Television EngineeringPaper – II-B

Time : 3 HoursMax. Marks : 100

This paper contains three Parts (A,B & C). Part A : contains 30 questions of 1 mark each. All are compulsory.Part B : contains 5 questions out of which three questions are to be

answered. This part carries total of 30 marks.Part C : contains 7 questions out of which four questions are to be

answered. This part carries total of 40 marks.

Part (A)

Q.No. 1 Answer all the following questions:- (30x1)

i) 2T pulse is used for quick checking of :(a) Differential at phase (b) Time error (c) S/N (d) High frequency response.

ii) The fault of changing hues, when monochrome picture is normal in a colour TV receiver can be mainly due to defective(a) band pass amplifier (b) burst gate amplifier (c) beam focussing unit (d) tuner circuit

iii) Channel width in VHF band for Digital Terrestrial Television Transmission is(a) 8 MHz (b) 7 MHz (c) 5.5 MHz (d) 6 MHz

iv) Duration of back porch in PAL-B CCVS signal is(a) 12 S (b) 5.8 S (c) 4.7 S (d) 0.2 S

v) The ‘threshold’ level of a digital satellite TV receiver is usually specified as a (a) bit error rate (b) megabits per second (c) gigabits per second (d)bit rate

vi) The transmission lines ‘X’ and ‘Y’ are 10 m and 20 m long respectively. If they are of same type then the(a) characteristic impedance of ‘X’ is greater than that of ‘Y’(b) characteristic impedance of ‘Y’ is greater than that of ‘X’(c) characteristic impedance of ‘X’ and that of ‘Y’ are equal.(d) None of these.

vii) Equivalent noise figure in decibel for the noise temperature of 120 K of a LNBC is(a) 0.4138 (b) 4.138 (c) 0.5138 (d) 1.5038

viii) In the spectrum of a frequency modulated wave (a) carrier frequency vanishes when modulation index is large.(b) The number of significant side bands depends upon modulation index.(c) Carrier frequency cannot disappear (d) None of these.

ix) Which of the following colour is produced by additive mixing of primary colours of Blue and Green.(a) Yellow (b) Red (c) Magenta (d) Cyan

x) The test pattern ‘white circle on grey back ground’ is for checking(a) colour parity (b) correct focussing of the picture (c) mains hum interference (d) overall picture linearity

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The ‘16’ in 16-QAM refers to(a) The 16 bits of information normally used in MPEG-2 digital compression block coding

systems.(b) The number of variables that are present in the transparent digital trans-modulator’s

digital mixer circuit.(c) The maximum number of megabits per second that the digital encoder can send at

any given moment of time.(d) The number of discrete signal-state values of vector magnitude that the QAM signal

supports.xi) In order to have reduced beam current, normally video signal from the output of the video

detector can be fed to the (a) cathode of the picture tube (b) grid of the picture tube(c) grid and cathode of the picture tube (d) none of these

xii) The junction capacitance of the varactor diode can be varied inversely with the amount of(a) reverse bias voltage applied across it(b) forward bias voltage applied across it(c) constant bias voltage applied across it.(d) None of the above

xiii) Number of cycles in colour burst in PAL-B colour television system is equal to(a) 25 + 1 cycles (b) 10 + 1 cycles (c) 50 + 1 cycles (d) 12.5 + 1 cycles

xiv) TV receiver employs(a) electrostatic focussing and magnetic deflection (b) magnetic focussing and electrostatic deflection(c) electrostatic focussing and deflection (d) magnetic focussing and deflection

xv) Depth of field in a Television Camera can be increased by(a) working of a lower F-stop (b) working of a higher F-stop(c) working at less lighting level (d) Decreasing the distance between the

camera and the objectxvi) Smaller the beam width angle of an antenna

(a) smaller will be the directivity (b) higher will be the directivity (c) higher will be the antenna bandwidth (d) none of these

xvii) Three main factors used to distinguish one colour from another are(a) its wave length, luminance and chrominance (b) hue, saturation and luminance(c ) wave length, hue and saturation (d) none of these.

xviii) Linear amplifiers are essential in vision transmitters employing(a) High level modulation (b) I.F. modulation (c) Frequency modulation (d) none of these.

xix) If the video sampling frequency is 13.5 MHz with format 4 : 2 : 2 using 10 bits, what is the data rate ?(a) 540 Mbps (b) 2700 Mbps (c) 270 Mbps (d) 5400 Mbps

xx) In R.F. monitoring of a TV Transmitter the Nyquist demodulator takes into account(a) Differential phase error (b) Differential gain error(c) VSB characteristics error (d) Pre-emphasis error

xxi) Higher peak to peak amplitude of 4.43 MHz chrominance signal indicates excess of (a) white colour (b) yellow colour (c) hue (d) saturation

xxii) To determine the correct azimuth bearing when using a compass, the magnetic factor for the site location should be :(a) added to the compass reading(b) subtracted from the compass reading(c) either added to or subtracted from the compass reading, if the site is East or West of

true North South line.(d) Multiplied by compass reading.

xxiii) The higher the noise temperature of C-band LNBC,(a) the better is its performance (b) the poorer is its performance(c) the more constant is its performance (d) none of these

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xxiv) The tape speed of Betacam SP cassette recorder is normally(a) 111.5 mm/sec (b) 101.5 mm/sec (c) 100.5 mm/sec (d) 150.5 mm/sec

xxv) The video signal (from 25 Hz to 5 MHz) has an octave range of(a) 6 octave (b) 10 octaves (c) 18 octaves (d) none of these

xxvi) The colour temperature of average day light is(a) 1930o K (b) 6500o K (c) 18000o K (d) 2760o K

xxvii) Constant impedance band pass Diplexer is used in solid state Television transmitter mainly for(a) filtering spurious frequencies(b) filtering signals higher than 2nd harmonic of visual carrier frequency and aural carrier

frequency.(c) Combining visual and aural carrier signals.(d) For rejecting aural carrier frequencies.

xxviii) The digital modulation used in Digital terrestrial video broadcasting is

(a) QPSK (b) 16-QAM(c) COFDM (d) BPSK.

xxix) The dominant mode used in rectangular wave guide is

(a) TE11 (b) TE01

(c) TE10 (d) TE12

Part (B) (Answer any three questions)

Q.2 (7+3)(a) Find the magnitude of the colour vector representing 100% Magenta in PAL

system. Also show the location of the colour vector on U-V plane.

(b) (i) Find the luminance of 25% red in PAL system.(ii) If the degree of saturation for green is 75% in another case, find its luminance.(iii) What will be the degree of saturation of Blue if the luminance is 0.055.

Q.3 (5+5)(a) Calculate the bandwidth requirement of 625 line, 15625 Hz, television system.

Assume a Kell factor of 0.75, horizontal blanking time of 12 sec, lines lost during vertical blanking 50 and aspect ratio of screen 4 : 3.

(b) The following waveform on a WFM represents the vision frequency response of a video amplifier under test. Calculate the figures to represent frequency responses in dB of different frequencies with respect to 1 MHz.

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Q.4 (7+3)(a) A satellite at a distance of 40,000 km from a point on the earth’s surface radiates a

power of 2 W from an antenna with a gain of 17 dB in the direction of observer. Find the flux density in watts as well as dBW at the receiving point. Also find the power received by an antenna with an effective area of 10m2.

(b) If the above satellite operates at a frequency of 11 GHz and the receiving antenna has a gain of 52.3 dB, find the received power in dBW

Q.5 (4+6)(a) A 52 ohms transmission line is to be matched to a load of 300 ohms by means

of a quarter wave transmission line section. Determine the length and characteristic impedance of the quarter wave section. Assume operating frequency and velocity factor to be 100 MHz and 0.9 respectively.

(b) A transmission line with a characteristic impedance of 75 ohms is terminated in apurely resistive load. While making measurements it was observed that the load reflected a power of 100 watts. Calculate load resistance if the reflected voltage is 100V. What is the reflection coefficient and the incident power ? Also calculate the power absorbed by the load.

Q.6 (3+3+2+2)(a) Calculate the ERP and EIRP in dBm as well as in kW at the output of transmitting

antenna having a gain of 7 dB, when the through line power meter connected at the output of a television transmitter reads 5.97 kW, with an input signal of pure sync only.

(b) A Neutral Density Filter (NDF) has density 0.6 ND. How much percentage oflight intensity (Transmission Factor) will be transmitted through the NDF, when attached to a TV camera ?

(c) In respect of the following arrangement in a TV studio, if the change in exposure between interior and exterior is 3f stops, what ND filter is required on the window ?

(d) What will be the new colour temperature if a – 35 MIRED shift filter is applied to a light source of 3200 K ?

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(PART C)(Answer any four questions)

Q.7 (8+2)

(a) Draw the block schematic diagram of a PAL Encoder and explain how composite colour video signal is formed in not more than 200 words.

(b) How are colour filters and neutral density filters used in TV lighting.

Q.8 (4+4+2)

(a) Explain the main features of three points lighting in not more than 100 words.(b) Briefly mention the functioning of Dichroic Block with the help of a diagram.(c) What do you understand by ‘depth of field’ related with camera optics ?

Q.9 (3+4+3)

(a) Reason out the necessity of employing frequency modulation in Video Cassette Recorder.

(b) Draw the tape path in a Betacam Video Cassette recorder and label.(c) How is the accuracy in tape tension and speed is maintained in it ?

Q.10 (4+3+3)

(a) Mention the advantages in employing negative modulation for modulating video signals in analogue television transmission.

(b) Is that necessary to maintain residual carrier in negative modulation technique ? Justify your reply.

(c) What are the minimum requirements that should be fulfilled by an antenna to broadcast terrestrial television signals.

Q.11 (5+3+2)

(a) Detail the working of a ‘visual modulator’ with the help of a diagram and how are VSB signals obtained ?

(b) Valve type TV transmitters are being replaced by solid state TV transmitters. Justify this statement.

(c) What do you understand by the indication ‘CH 26 (-) on a name plate of a TV transmitter.

Q.12 (6+4)

(a) Explain the working principle of a Satellite TV Receiver (analogue or digital) at a TVRO terminal with the help of a block schematic diagram.

(b) Write a short note on remote control system associated with TV receiver.

Q.13 (6+4)

(a) List at least three main advantages and three main disadvantages of digital video over analogue counterpart.

(b) What is the difference between DVD – RW and DVD – R ? Which is economical for end users and for video developers and why ?

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