Communication Systems problems
- 1. Which of the following is taken as reference antenna for directive gain?
Options- A. Half wave dipole
- B. Elementary doublet
- C. Isotropic
- D. Infinitesimal dipole Discuss
Correct Answer: Isotropic
Explanation:
Isotropic antenna is one which radiates equally in all directions. It is a standard reference antenna.
- 2. The number of noise sources in a BJT are
Options- A. 3
- B. 2
- C. 1
- D. 4 Discuss
Correct Answer: 3
Explanation:
Shot noise, partition noise and thermal noise.
- 3. An earth mat for a communication tower consists of
Options- A. one or two radials extending from base of tower at a depth of about 5 cm below ground
- B. a large number of radials extending from base of tower at a depth of about 3 m
- C. a large number of radials extending from base of tower at a depth of about 30 cm
- D. none of the above Discuss
Correct Answer: a large number of radials extending from base of tower at a depth of about 30 cm
Explanation:
The number of radials is large and depth is about 30 cm.
- 4. In CCIR-B system, the time between start of one H syn. pulse and next is
Options- A. 64 ?s
- B. 6.4 ?s
- C. 640 ?s
- D. 0.64 ?s Discuss
Correct Answer: 64 ?s
Explanation:
The frequency of H pulses is 15625 Hz.
Hence 
.
- 5. A cordless telephone using separate frequencies for transmission in base and portable units is known as
Options- A. duplex arrangement
- B. half duplex arrangement
- C. either (a) or (b)
- D. neither (a) nor (b) Discuss
Correct Answer: duplex arrangement
Explanation:
Separate frequencies for transmission from base and portable units allows two way transmission and is called duplex arrangement.
- 6. Signal to noise ratio of microphone is defined as the ratio of output when the sound pressure is __________ to the output in the absence of any sound signal.
Options- A. 0.5 Pa
- B. 0.2 Pa
- C. 0.1 Pa
- D. 0.01 Pa Discuss
Correct Answer: 0.1 Pa
Explanation:
0.1 Pa (= 0.5 x 10-4 W/m2) is taken as standard sound pressure for defining S/N ratio of microphones.
- 7. Some types of traps used in video IF amplifier of colour TV are
Options- A. shunt traps
- B. series traps
- C. absorption traps
- D. all of the above Discuss
Correct Answer: all of the above
Explanation:
All these are used.
- 8. Consider the following statements
- The amplitude of an FM wave is constant
- FM is more immune to noise than AM
- FM broadcasts operate in upper VHF and UHF frequency ranges
- FM transmitting and receiving equipments are simpler as compared to AM transmitting and receiving equipments
Options- A. 1, 2, 3, 4
- B. 1, 2, 3
- C. 2, 3, 4
- D. 1, 3, 4 Discuss
Correct Answer: 1, 2, 3
Explanation:
FM equipments are complex as compared to AM equipments.
- 9. The colour subcarrier and sidebands produced by its modulation with the chrominance signals are accommodated in the standard channel width by the process of
Options- A. frequency adjustment
- B. frequency interleaving
- C. frequency changing
- D. frequency amalgamation Discuss
Correct Answer: frequency interleaving
Explanation:
In frequency interleaving the space between bundles is used for colour signal.
- 10. As the frequency increases, the absorption of ground wave by earth's surface
Options- A. decreases
- B. increases
- C. remains the same
- D. either (a) or (c) Discuss
Correct Answer: increases
Explanation:
Because of this reason ground waves can be used for frequencies upto about 1600 kHz only.
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