Communication Engineering Set 1

Answer: 50%

Explaination:
the modulation is also expressed in percentage. it is also called percentage modulation. the signal is said to be 50% modulated if the peak message signal

Answer: 100%

Explaination:
a percentage of modulation greater than 100% will distort the message signal if detected by an envelope detector. in this case the lower excursion of the signal will drive the carrier amplitude below zero, making it negative (and hence changing its phase).

Answer: false

Explaination:
single sideband (ssb) am systems transmit only one of the sidebands (either upper or lower) about the carrier.

Answer: poor

Explaination:
ssb systems have the advantage of being very bandwidth efficient. but their performance in fading channels is very poor. for proper detection, the frequency of the oscillator at the product detector mixer in the receiver must be same as that of the incoming carrier frequency.

Answer: generation and reception of signal is complicated

Explaination:
tone-in-band ssb systems has the advantage of maintaining the low bandwidth property of the ssb signals, while at the same time providing good adjacent

Answer: feedforward signal regeneration

Explaination:
ffsr stands for feedforward signal regeneration. if the pilot tone and the information bearing signal undergo correlated fading, it is possible at the receiver to counteract the effects of fading through signal processing based on tracking of pilot tone.

Answer: coherent, noncoherent

Explaination:
am demodulation techniques may be broadly divide into two main categories. they are called coherent and noncoherent demodulation. they are differentiated by the knowledge of transmitted carrier frequency and phase at the receiver.

Answer: false

Explaination:
non coherent detection does require the knowledge of phase information. however, coherent detection requires knowledge of the transmitted carrier frequency and phase at the receiver.

Answer: phase detector

Explaination:
a product detector is also called a phase detector. it forms a coherent demodulator for am signals. it is a down converter circuit which converts the input bandpass signal to a baseband signal.

Answer: false

Explaination:
am systems can use either product detector or envelope detector for demodulation. as a rule, envelope detectors are useful when input signal power is at least 10db greater than noise power, whereas product detectors are able to process the am signals with input signal to noise ratios well below 0 db.

Answer: twisted nematic crystals

Explaination:
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.

Answer: amplitude limiter

Explaination:
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.

Answer: true

Explaination:
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.

Answer: true

Explaination:
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.

Answer: false

Explaination:
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.

Answer: low level amplitude modulated system

Explaination:
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.

Answer: sinusoidal

Explaination:
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.

Answer: am and fm both

Explaination:
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.

Answer: 35khz and 25khz

Explaination:
upper sideband frequency will be (30 + 5) = 35 khz and lower sideband frequency will be (30 – 5) = 25 khz.

Answer: true

Explaination:
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.

Answer: true

Explaination:
in duplex communication, two- way interaction is favourable simultaneously. thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units.

Answer: false

Explaination:
vestigial sideband modulation (vsb) is a type of amplitude modulation in which the carrier and only one sideband is completely transmitted and the other sideband is partly transmitted. thus, television production is done using vsb modulation as it reduces bandwidth to half.

Answer: duplex

Explaination:
in duplex communication, two- way interaction is favourable simultaneously. thus, a cordless telephone is duplex which uses separate frequencies for transmission in base and portable units.

Answer: circular polarization

Explaination:
in circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its

Answer: false

Explaination:
in circular polarization at each point the electric field of the electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate, in a plane perpendicular to the direction of propagation of the wave. it is used to reduce depolarization effect on received waves. it does not involve alignment between transmitting and receiving antenna.