1. LCD uses ________
a) sematic crystals
b) twisted nematic crystals
c) nematic crystals
d) cholesteric crystals
Explanation: LCD uses liquid crystal display. It uses twisted nematic crystals which are a type of liquid crystal, consisting of a substance called the nematic. The nematic liquid crystal is placed between two plates of polarized glass.
2. Which of the following stage is present in FM receiver but not in AM receiver?
a) Amplitude limiter
c) AM amplifier
Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.
3. Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception.
Explanation: A duplexer is being an electronic unit, allows bi-directional communication over the same path. The transmitter and receiver can communicate simultaneously. In radar, the duplexer isolates the receiver from the transmitter while allowing them to share a common antenna.
4. Single Sideband Modulation (SSB) is generally reserved for point-to-point communication.
Explanation: A point-to-point communication refers to bidirectional communication between only one transmitter and one receiver. In SSB-SC modulation technique, the carrier is suppressed and only one of the two side-bands are transmitted. Thus, it reduces power consumption and lessens bandwidth. Thus, it is preferred for point-to-point communication.
5. For an AM transmitter, class C amplifier can be used after the modulation stage.
Explanation: In an AM transmitter, the required transmission power is obtained from class C amplifier, as it is a power amplifier, for low-level or high-level modulation. So it is not used after the modulation stage.
6. For which of the modulated system, the linear amplified modulated stage is used?
a) low level amplitude modulated system
b) high level amplitude modulated system
c) high level frequency modulated system
d) low level frequency modulated system
Explanation: In low-level modulation, the generation of amplitude modulated signal takes place at low power levels. The generated AM signal is then amplified using a chain of linear amplifiers, which are required to avoid waveform distortion. Thus, linear amplified modulated stage is used in low level amplitude modulated system.
7. When noise is passed through a narrow band filter, the output of filter should be?
Explanation: Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. When noise gets passed through it, the output of it should be sinusoidal.
8. A narrow band noise can exist in _________
a) AM only
b) PCM only
c) FM only
d) AM and FM both
Explanation: Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. So it can be used in both AM and FM to pass a band of frequencies or to attenuate a band of frequencies.
9. The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be?
a) 35KHz and 25KHz
b) 34KHz and 24KHz
c) 25KHz and 35KHz
d) 0.35KHz and 0.25KHz
Explanation: Upper sideband frequency will be (30 + 5) = 35 KHz and Lower sideband frequency will be (30 – 5) = 25 KHz.
10. Phase array radar can track many targets together.
Explanation: A phased array radar is an array of radiating elements, with each having a phase-shifter. The phase of the signal being emitted from the radiating element is changed to produce beams, thereby producing constructive or destructive interference for steering the beams in the required direction. Thus, it can track many targets together.