Communication Mid Exam - Amplitude Modulation

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Questions and Answers

What is the modulation technique used to convert an analog signal into a digital signal?

AM modulation

Pulse code modulation (correct)

FM modulation

Phase Modulation

What is the expression for bandwidth BW of a PCM system, where n is the number of bits per sample and fm is the modulating frequency?

BW> = 1/2nfm

BW> = 2nfm (correct)

BW< = nfm

BW> = nfm

In uniform quantization process, what is true about the step size?

The quantizer has linear characteristics

Both b and c are correct

Step size varies according to the values of the input signal

The step size remains same (correct)

In pulse amplitude modulation, what is varied?

Amplitude of the pulse train Signup and view all the answers

A signal has the highest frequency component of 3.2MHz and peak to peak value 6 volt is transmitted using PCM. What is the signal to quantization noise ratio?

36.98dB Signup and view all the answers

What is the maximum bandwidth of the message in a PCM system that uses a uniform quantizer followed by a 7 bit binary encoder and has a bit rate of 49*10^6bps?

49Mbps Signup and view all the answers

What happens when the amplitude of the modulating signal is greater than the amplitude of the carrier?

Distortion Signup and view all the answers

What is the ratio between the modulating signal voltage and the carrier voltage called?

Modulation Index Signup and view all the answers

Which type of FM generation uses a varactor diode?

Indirect FM Signup and view all the answers

What is the circuit used for producing DSB-SC called?

Modulator Signup and view all the answers

When does over-modulation occur?

Modulating signal voltage > Carrier voltage Signup and view all the answers

What is the modulating signal voltage if the maximum and minimum voltages on the wave were observed to be 10V and 5V respectively?

2.5V Signup and view all the answers

What is the type of angle modulation that varies the frequency of the carrier wave?

Frequency Modulation Signup and view all the answers

Which type of modulation is an indirect form of frequency modulation?

Phase Modulation Signup and view all the answers

What is the effect on the deviation d of an FM signal when it is passed through a mixer?

Remains unchanged Signup and view all the answers

What is the output signal from a DSB-SC modulator?

Neither FM nor PM signal Signup and view all the answers

What is the purpose of an amplitude limiter in FM receivers?

Remove amplitude variations due to noise Signup and view all the answers

What is the bandwidth of an FM wave with a modulating frequency of 2 KHz and a frequency sensitivity of 40 Hz/volt?

4KHz Signup and view all the answers

What is the modulation index of an FM wave with a frequency deviation of 180 Hz and a modulating frequency of 2 KHz?

9 Signup and view all the answers

What is a characteristic of Frequency Modulation?

All of the above Signup and view all the answers

According to Carson's rule, how is the bandwidth B related to the modulating frequency fm?

B = 2(Δf + fm) Hz Signup and view all the answers

What are the disadvantages of PCM?

Encoding, decoding and quantizing circuitry of PCM is complex Signup and view all the answers

Study Notes

Amplitude Modulation

When the amplitude of the modulating signal is greater than the amplitude of the carrier, distortion occurs.
The ratio between the modulating signal voltage and the carrier voltage is called the modulation index.
Over-modulation occurs when the modulating signal voltage is greater than the carrier voltage.

Frequency Modulation

VCO is used to generate indirect FM.
The modulating frequency of a carrier wave varies between 900kHz and 1100KHz, and its bandwidth is 200KHz.
Phase modulation is an indirect form of frequency modulation.
The amount of frequency deviation is proportional to the amplitude of the intelligence signal in an FM signal.
The effect on the deviation d of an FM signal when it is passed through a mixer is that it remains unchanged.
In Frequency Modulation, the amplitude of the carrier remains the same, and the frequency of the carrier varies in accordance with the modulating signal.
The modulation index of FM is given by μ = frequency deviation/ modulating frequency.
According to Carson’s rule, Bandwidth B and modulating frequency fm are related as B = 2(Δf + fm) Hz.

Pulse Code Modulation

The modulation techniques used to convert analog signal into digital signal are Pulse Code Modulation (PCM).
The expression for bandwidth BW of a PCM system is given by BW > = 2nfm.
In uniform quantization process, the step size remains the same, and the quantizer has linear characteristics.
A PCM system uses a uniform quantizer followed by a 7-bit binary encoder, and the bit rate of the system is equal to 49*106bps.

Other Concepts

The circuit used for producing DSB-SC is called a modulator.
Amplitude limiter in FM receivers are used to remove amplitude variations due to noise.
The output signal from a DSB-SC modulator is a signal with a maximum and minimum voltage.
The disadvantages of PCM are that encoding, decoding, and quantizing circuitry of PCM is complex, and PCM requires a large bandwidth as compared to other systems.

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Description

This quiz assesses understanding of amplitude modulation concepts, including modulation index and effects of amplitude on modulating signals.