Electromagnetic Fields and Signal Modulation Quiz

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What is the main reason that the polarization of waves changes during transmission over long distances?

Various propagation effects in free space cause the polarization to change (correct)

The wavelength of the signal changes over long distances

The conductor length is not properly matched to the frequency

The shape of the antenna changes over long distances

What is the most common length for antennas in terms of the wavelength of the transmitted signal?

Three-quarters wavelength

Two wavelengths

One-eighth wavelength

One-half wavelength (correct)

What is the wavelength of a 3-kHz audio signal?

$30,000$ m

$100,000$ m (correct)

$300,000$ m

$3,000$ m

What is the main reason that little radiation occurs with a signal carried by a cable or transmission line?

The arrangement of the conductors in a cable or transmission line prevents radiation Signup and view all the answers

How can an open transmission line be made into an antenna?

By bending the conductors out at a right angle with the transmission line Signup and view all the answers

What is the primary characteristic of the radiation pattern of most antennas?

Directional Signup and view all the answers

What type of wave do most wireless applications use?

Far field wave Signup and view all the answers

In which field are measurements valid for antenna radiation patterns?

Far field Signup and view all the answers

What is the significance of polarization in antennas?

Determines the orientation of electric and magnetic fields Signup and view all the answers

What type of wave will a vertically polarized antenna produce 0 V in?

Horizontally polarized wave Signup and view all the answers

Why is it important for both transmitting and receiving antennas to be of the same polarization?

For optimal transmission and reception Signup and view all the answers

Which type of antennas produce horizontal polarization?

Horizontal antennas Signup and view all the answers

What causes the generation of a sinusoidal magnetic field?

A sinusoidally varying electric field Signup and view all the answers

What is the ratio of the electric field strength to the magnetic field strength in a radiated wave called?

Wave impedance Signup and view all the answers

What is the value of the wave impedance mentioned in the text?

377 Ω Signup and view all the answers

At what speed are the resulting fields radiated into space?

The speed of light ($3 \times 10^8$ m/s) Signup and view all the answers

What component of an antenna does not dissipate power in the form of heat?

The radiation resistance Signup and view all the answers

What describes the region directly around the antenna where the electric and magnetic fields are distinct?

The near field Signup and view all the answers

What is the main purpose of a parasitic array?

To increase the signal strength and directionality Signup and view all the answers

Which of the following statements about reflectors in a parasitic array is true?

Reflectors are slightly longer than the driven element Signup and view all the answers

How do directors in a parasitic array contribute to the radiation pattern?

They induce a voltage and produce radiation that reinforces the driven element's signal Signup and view all the answers

What is the typical configuration of the driven element in a parasitic array?

A half-wave dipole or variation Signup and view all the answers

What is the approximate spacing between the directors and the driven element in a parasitic array?

One-tenth to two-tenths of a wavelength Signup and view all the answers

Which of the following statements about parasitic elements is false?

They are connected to the transmission line Signup and view all the answers

What type of transmission line is ideal for a dipole antenna?

RG-58/U coaxial cable Signup and view all the answers

How is the Marconi or ground-plane vertical antenna fed?

With coaxial cable Signup and view all the answers

What role does the earth ground play in a Marconi antenna setup?

Acts as a mirror, providing the other one-quarter wavelength of the antenna Signup and view all the answers

At very high frequencies, what can serve as an effective ground plane for antennas?

Metallic surface like a car roof Signup and view all the answers

What is the impedance of a vertical ground-plane antenna compared to a dipole?

One-half the impedance of the dipole Signup and view all the answers

How does the actual impedance of a vertical ground-plane antenna vary?

It decreases with the length/diameter ratio of the conductor Signup and view all the answers