Tiêu đề 30. Communication Systems.pdf ✅

1. If maximum and minimum amplitude of amplitude modulated wave is 8V and 2V respectively then calculate modulation index :- (1) 0.8 (2) 0.4 (3) 0.6 (4) 1 2. Three waves A, B and C of frequencies 1600 kHz, 5 MHz and 60 MHz, respectively are to be transmitted from one place to another. Which of the following is the most appropriate mode of communication: (1) A is transmitted via space wave while B and C are transmitted via sky wave (2) A is transmitted via ground wave, B via sky wave and C via space wave (3) B and C are transmitted via ground wave while A is transmitted via sky wave (4) B is transmitted via ground wave while A and C are transmitted via space wave 3. A 100m long antenna is mounted on a 500m tall building. The complex can become a transmission tower for waves with  (aprox) - (1) 400 m (2) 25 m (3) 150 m (4) 2400 m 4. A basic communication system consists of (A) transmitter (B) information source (C) user of information (D) channel (E) receiver Choose the correct sequence in which these are arranged in a basic communication system : (1) ABCDE (2) BADEC (3) BDACE (4) BEADC 5. Arrange the following communication frequency bands in the increasing order of frequencies: (A) AM broadcast (B) Cellular mobile radio (C) FM broadcast (D) Television UHF (E) Satellite communication (1) A, C, D B, E (2) A, B, C, D, E (3) E, B, D, C, A (4) A, C, B, D, E 6. A TV transmission tower antenna is at a height of 20 m. How much area on earth can avail the TV services ? (1) 20 km2 (2) 80.4 km2 (3) 200.4 km2 (4) 804 km2 7. Assertion :- On a certain day the maximum frequency reflected from ionosphere is 10 MHz, which reduces to 8 MHz on an other day. The maximum electron densities of ionosphere on these two days is in the ratio 25 : 16. Reason :- If fc be the critical frequency and the maximum electron density of the corresponding ionosphere be Nmax, then Nmax 2 c  f . (1) A (2) B (3) C (4) D 8. Assertion :- For frequencies less than 40 MHz-50 MHz communication is possible only through line of sight communication. Reason :- Lesser the frequency of waves than 40 MHz - 50 MHz the lesser is the diffraction effect experienced by them. (1) A (2) B (3) C (4) D 9. A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequency of the side bands will be :- (1) 1.003 MHz and 0.997 MHz (2) 3001 kHz and 2997 kHz (3) 1003 kHz and 1000 kHz (4) 1 MHz and 0.997 MHz KEY 1 – 9 3 2 1 2 1 4 1 4 1 Communication Systems