Communication miscellaneous Easy Questions and Answers | Page - 3

Communication miscellaneous

The percentage increase in signal power of a carrier amplitude modulated 100% by a square wave—

1. 50%
1. 100%
1. 200%
1. None of these

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Let the given square wave looks like as shown below.
Since the average value of square wave i.e.m(t) = 1 and, on 100% modulation the amplitude of the carrier will be twice for half the time and zero for the other half time. Now, P_t = P_c [1+ m²(t)] = P_c [1 + 1] = 2P_c
Percentage increase in power
= 2 P_c − P_c ×100 = 100
P_c

Correct Option: B

Let the given square wave looks like as shown below.
Since the average value of square wave i.e.m(t) = 1 and, on 100% modulation the amplitude of the carrier will be twice for half the time and zero for the other half time. Now, P_t = P_c [1+ m²(t)] = P_c [1 + 1] = 2P_c
Percentage increase in power
= 2 P_c − P_c ×100 = 100
P_c

The d.c. power to a modulated class C amplifier is 500 W. The power that modulator must supply for 100% modulation applied at the output electrode—

1. 500 W
1. 250 W
1. 1000 W
1. 2000 W

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P_modulated = μ² P_dc
2

Given μ = 1 P_dc = 500 W

P_modulated or P_dc = 1² .500 = 250 W.
2

Correct Option: B

P_modulated = μ² P_dc
2

Given μ = 1 P_dc = 500 W

P_modulated or P_dc = 1² .500 = 250 W.
2

C (t) and m(t) are used to generate an AM signal. The μ = 0·5 of generated AM, then the quantity
Total sideband power
carrier power

1. 1
  2
1. 1
  4
1. 1
  3
1. 1
  8

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We know that,
Total sideband power = μ² . A²_c + μ² . A²_c
4 2 4 2

and
Carrier power = A²_c
2

Now
Total sideband power = μ²/4 . A²_c/2 + μ²/4 . A²_c/2
Carrier power A²c/2

= 2. μ² = 1 (0.5)²
4 2

= 0.25 = 1
2 8

Correct Option: D

We know that,
Total sideband power = μ² . A²_c + μ² . A²_c
4 2 4 2

and
Carrier power = A²_c
2

Now
Total sideband power = μ²/4 . A²_c/2 + μ²/4 . A²_c/2
Carrier power A²c/2

= 2. μ² = 1 (0.5)²
4 2

= 0.25 = 1
2 8

Two identical matched hybrid T-S are joined by the Eplane arms at ports 4 and 4' to produce a 6-port device as shown in Fig. If 16 mW power is fed into port 1, what will be the power output from other five ports?

1. 2 3 1' 2' 3'
  8 4 2 2 0 mW
1. 2 3 1' 2' 3'
  0 8 4 4 0 mW
1. 2 3 1' 2' 3'
  0 8 2 2 4 mW
1. 2 3 1' 2' 3'
  8 2 4 2 0 mW

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NA

Correct Option: B

NA

A superheterodyne receiver is to operate in the frequency range of 550 kHz-1650 kHz with the intermediate frequency of 450 kHz. The receiver is tuned to 700. The capacitance ratio R = C_max/C_min of the local oscillator would be—

1. 4.41
1. 2.1
1. 3
1. 9

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Given that frequency range (550-1650) kHz, where 1650 kHz is maximum and 550 is minimum value
f_IF = 450 kHz
When the local oscillator frequency is kept higher, the maximum to minimum capacitance ratio required is
R = C_max
2100 ² = 4.41
C_min 1000

Correct Option: A

Given that frequency range (550-1650) kHz, where 1650 kHz is maximum and 550 is minimum value
f_IF = 450 kHz
When the local oscillator frequency is kept higher, the maximum to minimum capacitance ratio required is
R = C_max
2100 ² = 4.41
C_min 1000