question paper of t.v engineering

1. SANT LONGOWAL INSTITUTE OF ENGINEERING & TECHNOLOGY, LONGOWAL
Class: DEC/12 Subject: T.V Engineering (EC -4103) Max. Marks: 15 Maximum Time Allowed: 1 Hour
PART-A
1. Objective Questions (choose one correct option among a,b,c,d) (1x4)
(i) If the raster is full bright at all times and variation of brightness has no effect, it suggests that
(1) there is a short in the cathode to control grid bias circuit
(2) it can also be due to excessive screen grid voltage
(3) it is always due to phosphor coating defect
Choose correct option
(a) only1 (b) 1 and 2 (c) only2 (d) 1,2 and 3
(ii) Which type of focusing is preferred in picture tubes?
(a) Electronics focusing (b) Magnetic focusing (c) Electromagnetic focusing (d) All
(iii) Choose correct options
(1)In picture transmission Positive modulation is preferred over negative modulation
(2) In positive modulation noise pulse will produce white blobs on the screen
(3) In negative modulation the noise pulses would tend to produce black spots
(4) Negative modulation reduces the effect of noise interference on picture signal
(a) 2,3 and 4 (b) 1,2,3 and 4 (c) 1,2 and 4 (d) 3 and 4
(iv) What is the function of Pre-emphasis circuit in sound signal transmission
(a) It boost only higher audio modulating frequencies
(b) It boost only lower audio modulating frequencies
(c) It boost both lower and higher audio modulating frequencies (d) None of these
Q2.Why is an aluminized coating provided on the phosphor screen? (1)
Q3.What is meant by deflection angle of the picture tube? What is the advantage of large deflection
angle (1)
Q4.Why amplitude modulation is preferred over frequency modulation for picture signal
transmission? (1)
PART B
Q1. Show that a total channel bandwidth of 11.25MHz would be necessary if both sidebands of the
modulated picture signal are fully transmitted. Explain how the channel width is reduced to 7MHz by
allowing vestigial sideband transmission. (2.5)
Q2. Explain why T.V transmission is done at frequency above 40MHz.justify that space wave
propagation is the only effective mode for T.V signal radiation above about 40MHz. (2.5)
Q3. Sketch composite video signal waveform for two successive lines and indicate (i) extreme white
level (ii) blanking level and (iii) pedestal height
Q4..Explain with a suitable sketch how electrons emitted at the cathode of a monochrome picture tube
are focused, accelerated and deflected to produce a raster on the screen. (3)