22 Questions
What is the effect on the deviation d of an FM signal when it is passed through a mixer?
Remains unchanged
What is the output signal from a DSB-SC modulator?
Neither FM nor PM signal
What is the purpose of an amplitude limiter in FM receivers?
To remove amplitude variations due to noise
What is the modulation index of an FM wave given by s(t)=20cos(8π×106t+9sin(2π×103t))?
9
What is true about Frequency Modulation?
All of the above
What does the amount of frequency deviation in FM signal depend on?
Amplitude of the modulating signal
What is the modulation index of FM given by?
μ = frequency deviation/ modulating frequency
What happens to the frequency deviation Δ when the modulating frequency is doubled?
Remains unchanged
What is the result of the amplitude of the modulating signal being greater than the amplitude of the carrier?
Distortion
What is the ratio of the modulating signal voltage to the carrier voltage called?
Modulation index
What type of frequency modulation is generated using a VCO?
Indirect FM
When does over-modulation occur in amplitude modulation?
Modulating signal voltage > Carrier voltage
What is the modulating signal voltage if the maximum and minimum voltages on the wave are 10v and 5v respectively?
2.5v
What is the circuit used for producing DSB-SC called?
Modulator
What modulation technique is used to convert analog signal into digital signal?
Pulse code modulation
What is the bandwidth of a carrier wave with a modulating frequency varying between 900kHz and 1100kHz?
200KHz
What is the expression for bandwidth BW of a PCM system?
BW> = 2nfm
Which of the following is an indirect form of frequency modulation?
Armstrong modulator
What is the characteristic of a uniform quantizer in PCM?
The step size remains the same
What is the maximum bandwidth of the message in a PCM system with a 7-bit binary encoder and a bit rate of 49*10^6bps?
7Mkbps
In which type of modulation is the amplitude of the pulse train varied?
Pulse amplitude modulation
What is the signal to quantization noise ratio for a signal with a highest frequency component of 3.2MHz and peak to peak value 6 volt, transmitted using PCM with 512 quantization levels?
36.98dB
Study Notes
Modulation Techniques
- Pulse Code Modulation (PCM) converts analog signal into digital signal
- Other modulation techniques: AM modulation, FM modulation
Bandwidth of PCM System
- Expression for bandwidth BW: BW > nfm, where n is the number of bits per sample and fm is the modulating frequency
Uniform Quantization
- Step size remains same in uniform quantization process
- The quantizer has linear characteristics
PCM System
- Bit rate of the system is equal to 49*10^6bps
- Maximum bandwidth of message: 7Mbps
Pulse Amplitude Modulation
- Amplitude of the pulse train is varied in pulse amplitude modulation
Signal to Quantization Noise Ratio
- For a signal with highest frequency component of 3.2MHz and peak to peak value 6 volt, signal to quantization noise ratio is 36.98dB
Amplitude Modulation
- The ratio between the modulating signal voltage and the carrier voltage is called modulation index
- Over-modulation occurs when the amplitude of the modulating signal is greater than the amplitude of the carrier
Voltage-Controlled Oscillator (VCO)
- VCO is used to generate indirect FM
DSB-SC Modulator
- The circuit used for producing DSB-SC is called a modulator
Frequency Modulation
- The two types of angle modulation are phase and frequency modulation
- 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
FM Signal
- The effect on the deviation d of an FM signal when it is passed through a mixer: doubles
- In Frequency Modulation, amplitude of the carrier remains same, frequency of the carrier varies in accordance with the modulating signal, and the number of side bands are infinite
- 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
Disadvantages of PCM
- Encoding, decoding and quantizing circuitry of PCM is complex
- PCM require large bandwidth as compared to the other systems
Test your knowledge of digital signal processing concepts, including modulation techniques, pulse code modulation, and quantization process.
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