RADIO WAVE PROPAGATION

Question 1

is a general term applied to the reduction in
signal strength at the input to a receiver.

Answer 1

FADING

Question 2

It applies to propagation variables in the physical radio
path that affect changes in the path loss between
transmit and receive antennas.

Answer 2

FADING

Question 3

typically makes the received signal smaller.

Answer 3

FADING

Question 4

FADING
* Fading is caused by four factors:

Answer 4

1. Variation in distance between transmitter and receiver.
2. Changes in the environmental characteristics of the signal path.
3. The presence of multiple signal paths.
4. Relative motion between the transmitter and receiver.

Question 5

is also caused by objects coming between the
transmitter and receiver known as

Answer 5

FADING, shadow fading.

Question 6

To overcome fading, most communication systems have
a ————-. That is, they have a high enough
transmitter power and sufficient receiver sensitivity to
ensure that the weaker reflective signals do not degrade
the direct signal as much.

Answer 6

built-in fading margin

Question 7

Multipath fading can also be greatly minimized by using
———-, either at the transmitter or at
the receiver or at both.

Answer 7

highly directive antennas

Question 8

It is a fabricated engineering quantity that evolved from
manipulating communications system link budget
equations

Answer 8

FREE-SPACE PATH LOSS

Question 9

It is often defined as the loss incurred by an
electromagnetic wave as it propagates in a straight line
through vacuum with no absorption or reflection of
energy from nearby objects.

Answer 9

FREE-SPACE PATH LOSS

Question 10

The manipulation of antenna gain terms results is a
distance and frequency-dependent term called

Answer 10

free-space
path loss.

Question 11

Free-space path loss assumes ideal atmospheric
conditions, so no electromagnetic energy is actually lost
or dissipated—it merely spreads out as it propagates
away from the source, resulting in ——-

Answer 11

lower relative power
densities.

Question 12

Mathematically, free-space path loss is equal to

Answer 12

Lp = (
4πD/λ)^2 = (4πfD/c)^2

Question 13

FREE-SPACE PATH LOSS
* Mathematically, free-space path loss expressed in dB

Lp = 20log(4π/c) + 20logf(Hz) + 20logD(m)
Lp = 32. 4 + 20logf(MHz) + 20logD(km)
Lp = 92. 4 + 20logf(GHz) + 20logD(km)
Lp = 96. 6 + 20logf(GHz) + 20logD(miles)

Question 14

(sometimes called link margin) is essentially
a “fudge factor” included in system gain equations that
considers the nonideal and less predictable characteristics

Answer 14

Fade margin

Question 15

Fade margin (sometimes called link margin) is essentially
a “fudge factor” included in system gain equations that
considers the nonideal and less predictable characteristics
of radio wave propagation, such as

Answer 15

multipath
propagation (multipath loss) and terrain sensitivity.

Question 16

Fade margin also considers

Answer 16

system reliability objectives.

Question 17

These characteristics cause temporary, abnormal
atmospheric conditions that alter the free space loss and
are usually detrimental to the overall system
performance.

Answer 17

FADE MARGIN

Question 18

Fade margin is included in system gain equations as a

Answer 18

loss

Question 19

FADE MARGIN
* Solving the reliability equations for a specified annual
system availability for an unprotected, non-diversity
system yields the following expression:

Answer 19

Fm = 30logD + 10 log (6ABf) − 10 log( 1 − R )− 70

Question 20

Consider a space-diversity microwave radio system operating
at an RF carrier frequency of 1.8 GHz. Each station has a 2.4-
m-diameter parabolic antenna that is fed by 100 m of air-
filled coaxial cable. The terrain is smooth, and the area has a humid climate. The distance between stations is 40 km. A
reliability objective of 99.99% is desired. Determine the
amount of free space path loss and the fade margin being
consider in computing for the system gain.

Answer 20

ANS. Fm = 31.4 dB, Lp = 129.55 dB

Question 21

Determine the path loss for the following frequencies
and distances:

Answer 21

ANS. 72.4 dB
ANS. 88.52 dB
ANS. 115.92 dB
ANS. 126.38 dB
ANS. 138.42 dB
ANS. 137.51 dB

Question 22

Electromagnetic waves traveling within Earth’s
atmosphere are called and
communications between two or more points on Earth is
called terrestrial radio communications.