Quantization is the process through which a range of continuous analog values are quantized or rounded off to a single value, thereby forming samples of a discrete digital signal.
Quantization Error occurs when there is a difference between an input value and its quantized value.
Quantization occurs when an analog signal is converted into its digital form, thus it occurs in Pulse Code Modulation (PCM).
2. A telephone signal with a cut-off frequency of 4 kHz is digitalized into 8-bit samples at a Nyquist sampling rate of s = 2 W. Calculate the baseband transmission bandwidth.
8 kHz
64 kHz
16 kHz
2 kHz
Answer.2. 64 KHz
Explanation:-
Number of samples produced each sec : 2 × 4000 = 8000 (Nyquist criteria)
Each sample is encoded into 8 bits
Bit rate = 8 × 8000 = 64 kilo bits/sec
For PCM bit rate = Transmission bandwidth
Hence transmission bandwidth is 64 kHz
3. The main advantage of PCM is:
Less bandwidth
Better performance in presence of a noise
Possibility of multiplexing
Less power
Answer.2. Better performance in presence of a noise
Explanation:-
PCM (Pulse Code Modulation) is a digital scheme for transmitting analog data.
The amplitude of an analog signal can take any value over a continuous range, i.e. it can take on infinite values.
But, digital signal amplitude can take on finite values.
Analog signals can be converted into digital by sampling and quantizing.
Advantages of PCM:
Encoding is possible in PCM.
Very high noise immunity, i.e. better performance in the presence of noise.
Convenient for long-distance communication.
Good signal-to-noise ratio.
4. The bit rate of a digital communication system is R Kbits/sec. The modulation used is 32-QAM. The minimum bandwidth for inter-symbol interference-free transmission is –
R/10 Hz
R/10 KHz
R/5 Hz
R/5 KHz
Answer.4. R/5 KHz
Explanation:-
For M-ary signaling B.W ≥ $\frac{{{R_b}}}{{{{\log }_2}M}}$
Bit Rate Rb = R k bits/sec
32-ary signaling is used:
$\frac{R}{{{{\log }_2}32}} \cdot kHz$
Minimum Bandwidth = R/5 KHz
5. The number of bits used in a 4096 level PCM system is:
12
16
20
10
Answer.1. 12
Explanation:-
The number of levels for an n-bit PCM system is given by:
L = 2n
We can also state that the number of bits for a given quantization level will be:
n = log2 L
Calculation:
The number of levels given = 4096, i.e. L = 4096
The number of bits used will be:
n = log2 (4096)
= log2 (212)
= 12 log2 (2)
n = 12
6. The disadvantage of FM over AM is that ________
The noise is very high for high-frequency signal
High modulating power is required
Larger bandwidth is required
High output power is required
Answer.3. Larger bandwidth is required
Explanation:-
Advantages of FM over AM are:
Improved signal to noise ratio.
Smaller geographical interference between neighbouring stations.
Less radiated power.
Well-defined service areas for given transmitter power.
Disadvantages of FM:
Much more Bandwidth
More complicated receiver and transmitter.
7. To avoid slope overload error in delta modulation, the maximum amplitude of the input signal is
9. In TV, an electrical disturbance (noise) affects
neither the video nor the audio signals
only the audio signals
both the video and audio signals
only the video signals
Answer.4. only the video signals
Explanation:-
In TV transmission:
A video is Vestigial sideband modulated, which is a type of amplitude-modulated waveform
The Video signals are thus encoded in amplitude variations of the carriers
The Audio signal is encoded in FM waveform
Thus, the audio signals are encoded as frequency variations of the carrier
Noise is the signal that affects amplitude majorly. Thus, the video signal is distorted from amplitude variations.
10. A signal contains components at 400 Hz and 2400 Hz This signal modulates a carrier of frequency 100 MHz. However, after demodulation, it is found that the 400 Hz signal component is present. The channel bandwidth is 15 kHz. What is the reason for the higher frequency signal not being detected properly?
Modulation used in FM and BW is insufficient
Modulation used in AM and BW is insufficient
Modulation used in FM but pre-emphasis is not used
Modulation used in AM but detector is for FM
Answer.3. Modulation used in FM but pre-emphasis is not used
Explanation:-
In FM broadcasting, pre-emphasis improvement is the improvement in the signal-to-noise ratio of the high-frequency portion of the baseband. The higher frequency signal is not to be detected properly because modulation is used in FM but pre-emphasis is not used.
In the process of detecting a frequency modulated signal, the receiver produces a noise spectrum that rises in frequency (a so-called triangular spectrum). This is the reason why a preemphasis is required. Without pre-emphasis, the received audio would sound unacceptably noisy at high frequencies, especially under conditions of low carrier-to-noise ratio, i.e., during fringe reception conditions. Preemphasis increases the magnitude of the higher signal frequencies, thereby improving the signal-to-noise ratio.