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# Communication Mid Exam - Amplitude Modulation

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@MemorableIndium

### 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&gt; = 1/2nfm
• BW&gt; = 2nfm (correct)
• BW&lt; = nfm
• BW&gt; = 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?

<p>Amplitude of the pulse train</p> 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?

<p>36.98dB</p> 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?

<p>49Mbps</p> Signup and view all the answers

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

<p>Distortion</p> Signup and view all the answers

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

<p>Modulation Index</p> Signup and view all the answers

### Which type of FM generation uses a varactor diode?

<p>Indirect FM</p> Signup and view all the answers

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

<p>Modulator</p> Signup and view all the answers

### When does over-modulation occur?

<p>Modulating signal voltage &gt; Carrier voltage</p> 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?

<p>2.5V</p> Signup and view all the answers

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

<p>Frequency Modulation</p> Signup and view all the answers

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

<p>Phase Modulation</p> 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?

<p>Remains unchanged</p> Signup and view all the answers

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

<p>Neither FM nor PM signal</p> Signup and view all the answers

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

<p>Remove amplitude variations due to noise</p> 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?

<p>4KHz</p> 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?

<p>9</p> Signup and view all the answers

### What is a characteristic of Frequency Modulation?

<p>All of the above</p> Signup and view all the answers

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

<p>B = 2(Δf + fm) Hz</p> Signup and view all the answers

### What are the disadvantages of PCM?

<p>Encoding, decoding and quantizing circuitry of PCM is complex</p> 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.

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