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Why top loading is used with an antenna?
To increase its impedance
To increase its beamwidth
To increase its effective height
To increase its bandwidth
Top loading is used to increase the effective height of an antenna. When the length of the antenna is shorter than a quarter wavelength (λ/4), top loading compensates for the reduced height.
Which among the following is not a reason for the use of antenna coupler?
To prevent re-radiation of the local oscillator
To provide the output amplifier with correct load impedance
To discriminate against harmonics
To make the antenna look resistive
Antenna coupler is a device connected between a radio transmitter or receiver and its antenna to improve power transfer between them. Antenna coupler is never used to prevent re-radiation of the local oscillator.
Which one of the following is very useful as a multiband HF receiving antenna?
Rectangular horn
Folded dipole
Conical horn
Log periodic
A log periodic antenna is a multi-element, directional, antenna designed to operate over a wide band of frequencies. Whereas, folded dipole and rest work over short band frequencies.
Which one of the following consists of non-resonant antennas?
Simple dipole
Broadside array
Folded dipole
Rhombic antenna
Non-resonant antennas are like non-resonant transmission lines. Non-resonant transmission lines do not have standing waves. Hence they do not have any reflected wave and they have only forward travelling wave. Whereas resonant antennae have standing wave patterns.
Antennas are often tested in ________
An anechoic chamber
A vacuum chamber
Atmosphere
An RF reflective chamber
An antenna is basically a transducer that converts radio frequency fields into alternating current or vice versa. They can be used for both transmission and reception of radio signals. They are often tested in an anechoic chamber. An antenna is used to transmit high frequency waves and plays significant role in the communication process.
The energy picked up by a parabolic antenna is concentrated at the ________
edges
corners
center
focus
A parabolic antenna is one with parabolic reflector. Energy picked up by a parabolic antenna is concentrated at the focus.
An array with one driven element, a reflector, and one or more directors is called ________
Marconi
Folded Dipole
Simple Dipole
Yagi
A Yagi-Uda antenna is a directional antenna consisting of many parallel elements in a line. It consists of a single driven element which is connected to the transmitter or receiver with a transmission line and also contains parasitic elements which are not connected to the transmitter or receiver. Thus, there are three or four directors and one reflector.
An antenna can be matched to a feed line by using an LC network only.
False
True
An antenna can be matched to a feed line, also known as a transmission line, by using an LC network. But it can also be matched to feed line by a loading coil.
Which of the following term is not applied to the Yagi-Uda array?
Low impedance
Reception of signals
Good bandwidth
High gain
A Yagi-Uda antenna is a directional antenna consisting of many parallel elements in a line. It consists of a single driven element and also contains parasitic elements. It consists of 3 or 4 directors and 1 reflector.
Which statement is true about indirect FM modulator?
Varies the phase of carrier oscillator
It differentiates the modulating signal
Varies the frequency of carrier oscillator
It integrates the modulating signal
Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator, thus being known as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.
Which statement is true about direct FM modulator?
It integrates the modulating signal
Varies the frequency of carrier oscillator
Varies the phase of carrier oscillator
It differentiates the modulating signal
Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator, thus being known as frequency discrimination method, while indirect FM modulator varies the phase of carrier oscillator, thus being called phase discrimination method.
To generate a SSB signal ________
High frequency signal is needed
Quadrature signal is required
DSB-SC is required
Full carrier AM is required
Single side band suppressed carrier modulation technique suppresses the carrier and transmits either of the two sidebands. Thus, this not only reduces the power consumed but also reduces the bandwidth. SSB-SC technique requires a DSB-SC to be passed through a bandpass filter.
In high level amplitude modulation, power in the sidebands comes from _________
Modulating amplifier
RF amplifier
Carrier
Driver stage
In amplitude modulated system, amplitude of the carrier wave is varied in proportion to the amplitude of the original message wave which is to be transmitted. For high level amplitude modulation, power amplifiers are not required and modulating amplifiers is used to give power to sidebands.
What is the full form of ALC?
Automatic Limiter Control
Amplitude Level Control
Automatic Level Control
Amplitude Limiter Control
ALC stands for Automatic Level Control. It is a technology that is used for automatic control of output power.
A resonant circuit is used in narrowband RF amplifiers.
True
False
The quality factor Q, of a resonant circuit is a measure of a quality of resonant circuit, thus indicating the performance of the resonant circuit. Bandwidth can be seen as the ratio of the resonant frequency to quality factor. A higher value for Q means a more narrow bandwidth, which we want in many application.
The ability to change the operating frequency rapidly without a lot of retuning is called ________
Mixing
Filtering
VCO
Agility
Agility is the process of changing operating frequency rapidly without a lot of returning.
What is the use of bypass capacitor?
to couple RF around an amplifier
acts as high pass filter
to remove RF from non-RF circuits
acts as low pass filter
A bypass capacitor is generally used to dampen the AC or noise present at all frequencies. In communication, it is used to remove RF from non-RF circuits.
The person who sent the first radio signal across the atlantic ocean was ________
Marconi
Maxwell
Hertz
Bell
Marconi is the first person who sent the first radio signal across the atlantic ocean. It was Maxwell who originated the theory of radio waves. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.
The time taken by the charge carrier to cross from the emitter to the collector is called ________
Transit time
Charge time
Relaxing time
Miller time
Transit time is that time which is taken by the charge carriers to move from emitter to collector.
