Analog Communications : Practice Questions and Answers

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.

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.

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.

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.

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.

A parabolic antenna is one with parabolic reflector. Energy picked up by a parabolic antenna is concentrated at the focus.

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, also known as a transmission line, by using an LC network. But it can also be matched to feed line by a loading coil.

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.

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.

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.

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 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.

ALC stands for Automatic Level Control. It is a technology that is used for automatic control of output power.

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.

Agility is the process of changing operating frequency rapidly without a lot of returning.

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.

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.

Transit time is that time which is taken by the charge carriers to move from emitter to collector.