Worksheet

1.

A 1 KW signal is transmitted using a communication channel which provides attenuation at the rate of – 2dB per km. If the communication channel has a total length of 5 km, the power of the signal received is [gain in dB = $10 \log \frac{P_o}{P_i}$]

a. 900 W. b. 100 W. c. 990 W. d. 1010 W.

2.

A message signal of frequency (\omega_{m}) is superposed on a carrier wave of frequency (\omega_{c}) to get an amplitude modulated wave (AM). The frequency of the AM wave will be

a. (\omega_{m}). b. (\omega_{c}). c. (\frac{\omega_{c} + \omega_{m}}{2}). d. (\frac{\omega_{c} - \omega_{m}}{2}).

3.

A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequencies of the side bands will be

a. 1.003 MHz and 0.997 MHz. b. 3001 kHz and 2997 kHz. c. 1003 kHz and 1000 kHz. d. 1 MHz and 0.997 MHz.

4.

I-V characteristics of four devices are shown in Fig. 15.1 Identify devices that can be used for modulation:

a.

‘i’ and ‘iii’.

b.

only ‘iii’.

c.

‘ii’ and some regions of ‘iv’.

d.

All the devices can be used.

5.

A male voice after modulation-transmission sounds like that of a female to the receiver. The problem is due to

a. poor selection of modulation index (selected $0 < m < 1$) b. poor bandwidth selection of amplifiers. c. poor selection of carrier frequency d. loss of energy in transmission.

6.

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:

a. ABCDE. b. BADEC. c. BDACE. d. BEADC.

7.

Identify the mathematical expression for amplitude modulated wave:

a. (A_{c} \sin [\{\omega_{c} + k_{1} v_{m}(t)\}t + \phi ]). b. (A_{c} \sin \{\omega_{c}t + \phi + k_{2} v_{m}(t)\}). c. (\{A_{c} + k_{2} v_{m}(t)\} \sin (\omega_{c}t + \phi )). d. (A_{c} v_{m}(t) \sin (\omega_{c}t + \phi )).

8.

A male voice after modulation-transmission sounds like that of a female to the receiver. The problem is due to

a. poor selection of modulation index (selected (0 < m < 1)) b. poor bandwidth selection of amplifiers. c. poor selection of carrier frequency d. loss of energy in transmission.

9.

Identify the mathematical expression for amplitude modulated wave:

a. $A_c \sin [\{\omega_c + k_1 v_m(t)\}t + \phi]$. b. $A_c \sin \{\omega_c t + \phi + k_2 v_m(t)\}$. c. $\{A_c + k_2 v_m(t)\} \sin (\omega_c t + \phi)$. d. $A_c v_m(t) \sin (\omega_c t + \phi)$.

10.

A 100m long antenna is mounted on a 500m tall building. The complex can become a transmission tower for waves with (\lambda)

a. ~ 400 m. b. ~ 25 m. c. ~ 150 m. d. ~ 2400 m.

11.

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:

a. A is transmitted via space wave while B and C are transmitted via sky wave. b. A is transmitted via ground wave, B via sky wave and C via space wave. c. B and C are transmitted via ground wave while A is transmitted via sky wave. d. B is transmitted via ground wave while A and C are transmitted via space wave.

12.

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:

a. A is transmitted via space wave while B and C are transmitted via sky wave. b. A is transmitted via ground wave, B via sky wave and C via space wave. c. B and C are transmitted via ground wave while A is transmitted via sky wave. d. B is transmitted via ground wave while A and C are transmitted via space wave.

13.

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:

a. ABCDE. b. BADEC. c. BDACE. d. BEADC.

14.

A message signal of frequency $\omega_m$ is superposed on a carrier wave of frequency $\omega_c$ to get an amplitude modulated wave (AM). The frequency of the AM wave will be

a. $\omega_m$. b. $\omega_c$. c. $\frac{\omega_c + \omega_m}{2}$. d. $\frac{\omega_c - \omega_m}{2}$.

15.

I-V characteristics of four devices are shown in Fig. 15.1. Identify devices that can be used for modulation:

a.

‘i’ and ‘iii’.

b.

only ‘iii’.

c.

‘ii’ and some regions of ‘iv’.

d.

All the devices can be used.

16.

A speech signal of 3 kHz is used to modulate a carrier signal of frequency 1 MHz, using amplitude modulation. The frequencies of the side bands will be

a. 1.003 MHz and 0.997 MHz. b. 3001 kHz and 2997 kHz. c. 1003 kHz and 1000 kHz. d. 1 MHz and 0.997 MHz.

17.

A 100m long antenna is mounted on a 500m tall building. The complex can become a transmission tower for waves with $\lambda$

a. ~ 400 m. b. ~ 25 m. c. ~ 150 m. d. ~ 2400 m.

18.

A 1 KW signal is transmitted using a communication channel which provides attenuation at the rate of – 2dB per km. If the communication channel has a total length of 5 km, the power of the signal received is [gain in dB = (10 \log \frac{P_{i}}{P_{0}})]

a. 900 W. b. 100 W. c. 990 W. d. 1010 W.