CHAPTER 14: Antennas and Wave Propagation

Question 1

The interface between the transmitter and free space and between free space and the receiver is the ______________.

Answer 1

Antenna

Question 2

A radio signal is called an ___________________wave because it is made up of both electric and magnetic fields.

Answer 2

Electromagnetic

Question 3

A radio signal is called an electromagnetic wave because it is made up of both electric and ________________.

Answer 3

Magnetic fields

Question 4

Whenever _________________ is applied to the antenna, an electric field is set up.

Answer 4

voltage

Question 5

This voltage causes ____________ to flow in the antenna, producing a magnetic field.

Answer 5

current

Question 6

The strength and direction of the magnetic field depend upon the _______ and ________ of the current flow.

Answer 6

magnitude and direction

Question 7

__________________ is the dielectric constant of the material between the two conductors.

Answer 7

Permittivity

Question 8

During one-half cycle of the ac input, one wire is positive and the other is negative.
During the negative half-cycle, the polarity __________.

Answer 8

reverses

Question 9

Transmission lines do not radiate signals efficiently. The closeness of the conductors keeps the ________________ concentrated in the transmission line dielectric.

Answer 9

electric field

Question 10

The electric field spreads out from conductor to _________.

Answer 10

conductor

Question 11

The higher the Q, the narrower the _________________.

Answer 11

bandwidth

Question 12

The __________________ of any antenna is the shape of the electromagnetic energy radiated from or received by that antenna.

Answer 12

radiation pattern

Question 13

___________ is a phenomenon caused by any support insulators used at the ends of the wire antenna and has the effect of adding capacitance to the end of each wire.

Answer 13

End effect

Question 14

A _______________ uses multiple transmitters, receivers, or antennas to mitigate the problems caused by multipath signals.

Answer 14

diversity system

Question 15

With __________________, two separate sets of transmitters and receivers operating on different frequencies are used to transmit the same information simultaneously.

Answer 15

frequency diversity

Question 16

______________________________ uses two receive antennas spaced as far apart as possible to receive the signals.

Answer 16

Space or spatial diversity

Question 17

__________is the variation in signal amplitude at the receiver caused by the characteristics of the signal path and changes in it.

Answer 17

Fading

Question 18

In a ___________________, multiple repeaters are under the control of a computer system that can transfer a user from an assigned but busy repeater to another, available repeater, thus spreading the communication load.

Answer 18

trunked repeater system

Question 19

Communication ____________ act as fixed repeater stations.

Answer 19

satellites

Question 20

The receiver-transmitter combination within the satellite is known as a _________.

Answer 20

transponder

Question 21

________________ waves leave an antenna and remain close to the earth.

Answer 21

Ground or surface

Question 22

AM broadcast signals are _________ primarily by ground waves during the day and by sky waves at night.

Answer 22

propagated

Question 23

Two basic types of antenna arrays are used to achieve
gain and directivity:

Answer 23

Parasitic array and driven array

Question 24

A ______________ consists of a basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line.

Answer 24

parasitic array

Question 24

_______________ usually consist of two or more half- wave dipoles mounted end to end.

Answer 24

Collinear antennas

Question 25

A __________________ is a stacked collinear antenna consisting of half-wave dipoles spaced from one another by one-half wavelengths.

Answer 25

broadside array

Question 26

The end-fire array uses two half-wave dipoles spaced one-half wavelength apart.