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PHXII15:COMMUNICATION SYSTEMS

356756 In amplitude modulation

1 Only amplitude is change, but frequency, phase remains constant

2 Frequency, phase are change, but Amplitude remains constant

3 Amplitude, Frequency are constant but phase change

4 Amplitude, Phase are constant but frequency changes

PHXII15:COMMUNICATION SYSTEMS

356757 Assertion :
A portable AM radio set must be kept horizontal to receive the signals properly.
Reason :
Radio waves are polarised electromagnetic waves.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but reason is correct.

PHXII15:COMMUNICATION SYSTEMS

356758 A single frequency $20 k H z$ and peak voltage of 5 volt is used to modulate a carrier wave of frequency $1.2 M H z$ and peak voltage 25 volts.
Choose the correct statement.

1 Modulation index

= 5

, side frequency bands are at

1400 k H z a n d 1000 k H z

2 Modulation index

= 0.8

, side frequency bands are at

1180 k H z a n d 1220 k H z

3 Modulation index

= 0.2

, side frequency bands are at

1220 k H z a n d 1180 k H z

4 Modulation index

= 5

, side frequency bands are at

21 / 2 k H z a n d 18.8 k H z

Explanation:

Modulation index $= m = \frac{V_{m}}{V_{0}} = \frac{1}{5} = 0.2$
Frequency $= 12 \times 10^{3} kHz$
$\begin{aligned} F = 12.00 kHz \\ F_{1} = 1200 - 20 = 1180 kHz \\ F_{2} = 1200 + 20 = 1220 kHz \end{aligned}$

JEE - 2017

PHXII15:COMMUNICATION SYSTEMS

356759 A diode detector is used to detect an amplitude modulated wave of $60 %$ modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it.

1

10.62 M H z

2

10.62 k H z

3

5.31 M H z

4

5.31 k H z

Explanation:

supporting img
$τ = R C = 100 \times 10^{3} \times 250 \times 10^{- 12} \sec$
$\begin{aligned} = 2.5 \times 10^{7} \times 10^{- 12} \sec \\ = 2.5 \times 10^{- 5} \sec \end{aligned}$
The higher frequency which can be detected with tolerable distortion is
$f = \frac{1}{2 π m_{a} R C} = \frac{1}{2 π \times 0.6 \times 2.5 \times 10^{- 5}} H z$
$= \frac{100 \times 10^{4}}{25 \times 1.2 π} H z = \frac{4}{1.2 π} \times 10^{- 4} H z$
$= 10.61 K H z$
This condition is obtained by applying the condition that rate of decay of capacitor voltage must be equal or less than the rate of decay of modulated signal voltage for proper detection of modulated signal.

PHXII15:COMMUNICATION SYSTEMS

356756 In amplitude modulation

1 Only amplitude is change, but frequency, phase remains constant

2 Frequency, phase are change, but Amplitude remains constant

3 Amplitude, Frequency are constant but phase change

4 Amplitude, Phase are constant but frequency changes

PHXII15:COMMUNICATION SYSTEMS

356757 Assertion :
A portable AM radio set must be kept horizontal to receive the signals properly.
Reason :
Radio waves are polarised electromagnetic waves.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but reason is correct.

PHXII15:COMMUNICATION SYSTEMS

356758 A single frequency $20 k H z$ and peak voltage of 5 volt is used to modulate a carrier wave of frequency $1.2 M H z$ and peak voltage 25 volts.
Choose the correct statement.

1 Modulation index

= 5

, side frequency bands are at

1400 k H z a n d 1000 k H z

2 Modulation index

= 0.8

, side frequency bands are at

1180 k H z a n d 1220 k H z

3 Modulation index

= 0.2

, side frequency bands are at

1220 k H z a n d 1180 k H z

4 Modulation index

= 5

, side frequency bands are at

21 / 2 k H z a n d 18.8 k H z

Explanation:

Modulation index $= m = \frac{V_{m}}{V_{0}} = \frac{1}{5} = 0.2$
Frequency $= 12 \times 10^{3} kHz$
$\begin{aligned} F = 12.00 kHz \\ F_{1} = 1200 - 20 = 1180 kHz \\ F_{2} = 1200 + 20 = 1220 kHz \end{aligned}$

JEE - 2017

PHXII15:COMMUNICATION SYSTEMS

356759 A diode detector is used to detect an amplitude modulated wave of $60 %$ modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it.

1

10.62 M H z

2

10.62 k H z

3

5.31 M H z

4

5.31 k H z

Explanation:

supporting img
$τ = R C = 100 \times 10^{3} \times 250 \times 10^{- 12} \sec$
$\begin{aligned} = 2.5 \times 10^{7} \times 10^{- 12} \sec \\ = 2.5 \times 10^{- 5} \sec \end{aligned}$
The higher frequency which can be detected with tolerable distortion is
$f = \frac{1}{2 π m_{a} R C} = \frac{1}{2 π \times 0.6 \times 2.5 \times 10^{- 5}} H z$
$= \frac{100 \times 10^{4}}{25 \times 1.2 π} H z = \frac{4}{1.2 π} \times 10^{- 4} H z$
$= 10.61 K H z$
This condition is obtained by applying the condition that rate of decay of capacitor voltage must be equal or less than the rate of decay of modulated signal voltage for proper detection of modulated signal.

PHXII15:COMMUNICATION SYSTEMS

356756 In amplitude modulation

1 Only amplitude is change, but frequency, phase remains constant

2 Frequency, phase are change, but Amplitude remains constant

3 Amplitude, Frequency are constant but phase change

4 Amplitude, Phase are constant but frequency changes

PHXII15:COMMUNICATION SYSTEMS

356757 Assertion :
A portable AM radio set must be kept horizontal to receive the signals properly.
Reason :
Radio waves are polarised electromagnetic waves.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but reason is correct.

PHXII15:COMMUNICATION SYSTEMS

356758 A single frequency $20 k H z$ and peak voltage of 5 volt is used to modulate a carrier wave of frequency $1.2 M H z$ and peak voltage 25 volts.
Choose the correct statement.

1 Modulation index

= 5

, side frequency bands are at

1400 k H z a n d 1000 k H z

2 Modulation index

= 0.8

, side frequency bands are at

1180 k H z a n d 1220 k H z

3 Modulation index

= 0.2

, side frequency bands are at

1220 k H z a n d 1180 k H z

4 Modulation index

= 5

, side frequency bands are at

21 / 2 k H z a n d 18.8 k H z

Explanation:

Modulation index $= m = \frac{V_{m}}{V_{0}} = \frac{1}{5} = 0.2$
Frequency $= 12 \times 10^{3} kHz$
$\begin{aligned} F = 12.00 kHz \\ F_{1} = 1200 - 20 = 1180 kHz \\ F_{2} = 1200 + 20 = 1220 kHz \end{aligned}$

JEE - 2017

PHXII15:COMMUNICATION SYSTEMS

356759 A diode detector is used to detect an amplitude modulated wave of $60 %$ modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it.

1

10.62 M H z

2

10.62 k H z

3

5.31 M H z

4

5.31 k H z

Explanation:

supporting img
$τ = R C = 100 \times 10^{3} \times 250 \times 10^{- 12} \sec$
$\begin{aligned} = 2.5 \times 10^{7} \times 10^{- 12} \sec \\ = 2.5 \times 10^{- 5} \sec \end{aligned}$
The higher frequency which can be detected with tolerable distortion is
$f = \frac{1}{2 π m_{a} R C} = \frac{1}{2 π \times 0.6 \times 2.5 \times 10^{- 5}} H z$
$= \frac{100 \times 10^{4}}{25 \times 1.2 π} H z = \frac{4}{1.2 π} \times 10^{- 4} H z$
$= 10.61 K H z$
This condition is obtained by applying the condition that rate of decay of capacitor voltage must be equal or less than the rate of decay of modulated signal voltage for proper detection of modulated signal.

PHXII15:COMMUNICATION SYSTEMS

356756 In amplitude modulation

1 Only amplitude is change, but frequency, phase remains constant

2 Frequency, phase are change, but Amplitude remains constant

3 Amplitude, Frequency are constant but phase change

4 Amplitude, Phase are constant but frequency changes

PHXII15:COMMUNICATION SYSTEMS

356757 Assertion :
A portable AM radio set must be kept horizontal to receive the signals properly.
Reason :
Radio waves are polarised electromagnetic waves.

1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.

2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.

3 Assertion is correct but Reason is incorrect.

4 Assertion is incorrect but reason is correct.

PHXII15:COMMUNICATION SYSTEMS

356758 A single frequency $20 k H z$ and peak voltage of 5 volt is used to modulate a carrier wave of frequency $1.2 M H z$ and peak voltage 25 volts.
Choose the correct statement.

1 Modulation index

= 5

, side frequency bands are at

1400 k H z a n d 1000 k H z

2 Modulation index

= 0.8

, side frequency bands are at

1180 k H z a n d 1220 k H z

3 Modulation index

= 0.2

, side frequency bands are at

1220 k H z a n d 1180 k H z

4 Modulation index

= 5

, side frequency bands are at

21 / 2 k H z a n d 18.8 k H z

Explanation:

Modulation index $= m = \frac{V_{m}}{V_{0}} = \frac{1}{5} = 0.2$
Frequency $= 12 \times 10^{3} kHz$
$\begin{aligned} F = 12.00 kHz \\ F_{1} = 1200 - 20 = 1180 kHz \\ F_{2} = 1200 + 20 = 1220 kHz \end{aligned}$

JEE - 2017

PHXII15:COMMUNICATION SYSTEMS

356759 A diode detector is used to detect an amplitude modulated wave of $60 %$ modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance of 100 kilo ohm. Find the maximum modulated frequency which could be detected by it.

1

10.62 M H z

2

10.62 k H z

3

5.31 M H z

4

5.31 k H z

Explanation:

supporting img
$τ = R C = 100 \times 10^{3} \times 250 \times 10^{- 12} \sec$
$\begin{aligned} = 2.5 \times 10^{7} \times 10^{- 12} \sec \\ = 2.5 \times 10^{- 5} \sec \end{aligned}$
The higher frequency which can be detected with tolerable distortion is
$f = \frac{1}{2 π m_{a} R C} = \frac{1}{2 π \times 0.6 \times 2.5 \times 10^{- 5}} H z$
$= \frac{100 \times 10^{4}}{25 \times 1.2 π} H z = \frac{4}{1.2 π} \times 10^{- 4} H z$
$= 10.61 K H z$
This condition is obtained by applying the condition that rate of decay of capacitor voltage must be equal or less than the rate of decay of modulated signal voltage for proper detection of modulated signal.