To transmit electrical signals over an antenna through free space
To improve the signal to noise ratio
To make the low-frequency signals travel long distance
All of the above
Answer.4. All of the above
Explanation:-
Modulation is a process of varying one or more properties of a carrier signal (High-frequency signal) with a modulating signal (Low-frequency signal). Hence, Modulation is the process of combining signal and radiofrequency.
Need for Modulation:
It is needed in order to match the characteristics of the input signal to that of channel characteristics.
Low-frequency signals can be multiplexed with high-frequency signals to travel long distances.
Wireless transmission of low pass signal is made possible due to modulation.
Practically realization of antenna size can be achieved.
Some modulation technique reduces the effect of noise on the signal.
12. Signal modulation has proved to be advantageous in more than one way in the communication system. Which of the following is FALSELY stated?
Communication range increases
Reception quality improves
Antenna size gets enlarged
Adjustment in the bandwidth is allowed
Answer.3. Antenna size gets enlarged
Explanation:-
For efficient transmission from an antenna, its size should be comparable to the transmitted wavelength. As a result, using a high-frequency carrier wave in modulation allows the antenna size to be decreased, lowering the cost and increasing the performance. As frequency f ∝ 1/λ because the speed of the wave is a constant based on the medium.
f = c/λ
13. The main purpose of modulation is to
Combine two waves of different frequencies
Achieve wave shaping of the carrier wave
Transmit low-frequency information over long distances efficiently
Reduce sidebands
Answer.3. Transmit low-frequency information over long distances efficiently
Explanation:-
Modulation is the process in which some characteristics, usually an amplitude, frequency, or phase angle of a high-frequency carrier wave is varied in accordance with the instantaneous value of a low-frequency information signal called modulating signal.
A low-frequency wave cannot be transmitted to long distances. So, a low-frequency information signal is superimposed on a high-frequency wave, which acts as a carrier of the information.
14. What is the main disadvantage of Bluetooth technologies?
Used for voice and data transfer
Low power consumption
Affordable rates
Lower security
Answer.4. Lower security
Explanation:-
Bluetooth is a wireless technology that allows the exchange of data within a short distance. Usually, every network technology has some security built into it to prevent hackers from accessing your data without your permission. However, Bluetooth security is weak compared to Wi-Fi and other wireless data standards.
A determined attacker can, for example, gain access to your wireless device through a Bluetooth connection, although he or she would have to be nearby for the attempt to work. Hence Bluetooth technology Bluetooth uses short-wavelength UHF radio waves.
15. The process of super imposing information onto a carrier wave is called
Transmission
Communication
Modulation
Demodulation
Answer.3. Modulation
Explanation:-
The process of superimposing information onto a carrier wave is called Modulation.
Need for Modulation:
1. It is needed in order to match the characteristics of the input signal to that of channel characteristics.
2. Multiplexing is made possible due to modulation.
3. Wireless transmission of low pass signal is made possible due to modulation.
4. Practically realization antenna size can be achieved
5. Some modulation technique reduces the effect of noise on the signal.
16. If a total of 33 MHz of bandwidth is allocated to a particular FDD cellular telephone system which uses two 25 kHz simplex channels to provide full-duplex voice and control channels, compute the number of channels available per cell if a system uses 4-cell reuse
55
660
95
165
Answer.4. 165
Explanation:-
Given,
Cluster size (N) = 4
Total bandwidth = 33 MHz
Channel bandwidth = 25 kHz × 2 simplex channel
Channel bandwidth = 50 kHz/duplex channel
Total available channels = (33,000 × 103)/(50 × 103)
Total available channels = 660 channels
Total number of available channels per cell = (Total available channels)/N
Total number of available channels per cell = 660/4
Total number of available channels per cell = 165
17. The technique for decreasing co-channel interference and thus increasing system capacity by using directional antennas is called:
Sectoring
Cell splitting
Cell merging
Micro zoning
Answer.1. Sectoring
Explanation:-
Cell sectoring
In cell sectoring, a single omnidirectional antenna at the base station is replaced by several directional antennas, each radiating within a specified sector.
By using directional antennas power is transmitted in a single desired direction decreasing the number of interfering co-channel cells and co-channel interference.
The technique for decreasing co-channel interference and thus increasing system performance by using directional antennas is called sectoring.
The factor by which the co-channel interference is reduced depends on the amount of sectoring used. A cell is normally partitioned into three sectors.
When sectoring is employed, the channels used in a particular cell are broken down into sectored groups and are used only within a particular sector.
For cluster size 7, sectoring reduces co-channel cells from 6 to 2 for 120° sectoring and to 1 for 60° sectoring.
18. The process of superimposing a signal on the carrier wave is called:
Transmission
Communication
Modulation
Demodulation
Answer.3. Modulation
Explanation:-
The process of superimposing information or signal onto a carrier wave is called Modulation.
Need for Modulation:
1. It is needed in order to match the characteristics of the input signal to that of channel characteristics.
2. Multiplexing is made possible due to modulation.
3. Wireless transmission of low pass signal is made possible due to modulation.
4. Practically realization antenna size can be achieved
5. Some modulation technique reduces the effect of noise on the signal.
19. In case of which of the following, an increase on the modulation index leads to an increase in bandwidth
PM
FM
AM
Both (1) and (2)
Answer.4. Both (1) and (2)
Explanation:-
For both frequency and phase modulation, an increase in modulation index results in an increase in transmission bandwidth.
⇒ For AM, the Modulation index is given by:
µ = Am/AC
Bandwidth = 2 fm which is independent of modulation index
⇒ For PM, the Modulation index is given by:
β = KpAm
Bandwidth = 2 (1 +β ) fm bandwidth depends on modulation index β
⇒ For FM the modulation index is
β = KfAm/fm
Bandwidth = 2 (1 +β ) fm bandwidth depends on modulation index β
20. Which layer of the atmosphere is used the most for communication?
Stratosphere
Ionosphere
Mesosphere
Troposphere
Answer.2. Ionosphere
Explanation:-
The ionosphere is the atmospheric layer, which is mostly used for communication purposes.
Due to electrical conductivity, the ionosphere helps in radio communication.
21. On which of the following frequencies does a Wi-Fi network work?
2.4 MHz
5 MHz
10 GHz
5 GHz
Answer.2. Ionosphere
Explanation:-
Wi-Fi is the wireless network system most commonly used in homes to connect multiple electronic devices through the internet. An instrument called a router is needed to connect several instruments through the internet.
IEEE 802.11 specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN), Wi-Fi computer communication in various frequencies.
WiFi uses radio frequencies to send signals between devices.
