NEETS MODULE 10-Wave Propagation, Transmission Lines, and Antennas CH2

The polarity of a radio wave is determined by the orientation of (a) what moving field with respect to (b) what reference?

(a) Electric (b) earth

After the radiation field leaves an antenna, what is the relationship between the E and H fields with respect to (a) phase and (b) physical displacement in space?

(a) In phase (b) 90 degrees

A space wave (a) is primarily a result of refraction in what atmospheric layer and (b) extends approximately what distance beyond the horizon? 2-22

(a) Troposphere (b) One-third farther

Long range, surface-wave communications are best achieved when the signal is transmitted over seawater with (a) what polarization at (b) what relative frequency? 2-19

(a) Vertical (b) Low

Radio communications can be diffracted to exceptionally long distances through the use of (a) what frequency band at (b) what relative power level?

(a) Very low frequency (b) High power

What three main factors determine the amount of refraction in the ionosphere?

(a) density of ionization of the layer (b) frequency (c) angle at which it enters the layer

What three factors must be considered in the transmission of a surface wave to reduce attenuation?

(a) electrical properties of the terrain (b) frequency (c) polarization of the antenna

What are three ways of controlling radiated EMI during transmission?

(a) physical separation of the antenna (b) limiting bandwidth of the antenna (c) use of directional antennas

The most consistent communications can be expected at which of the following frequencies?

Optimum working frequency

Radio waves that arrive at a receiving site along different paths can cause signal fading if these waves have different

phase relationships

Sky waves

reflect back to earth from ionosphere

The bending of a radio wave because of a change in its velocity through a medium is known as

refraction *as they move between mediums

Compared to the other ionospheric layers at higher altitudes, the ionization density of the D layer is

relatively low

The distance between the transmitter and the nearest point at which refracted waves return to earth is referred to as the 2-32

skip distance

Ground waves

travel near the surface of the earth

The surface wave reaches the receiving site by

traveling along the surface of the ground

What is the skip zone of a radio wave?

A zone of silence between the ground wave and sky wave where there is no reception

Under certain conditions, such as ducting, line-of-sight radio waves often propagate for distances far beyond their normal ranges because of which of the following factors?

Temperature inversions

The amount of rf energy lost because of ground reflections depends on which of the following factors? 2-37

1. Angle of incidence 2. Ground irregularities 3. Frequency of the wave

Refraction of a sky wave in the ionosphere is influenced by which of the following factors?

1. Ionospheric density 2. Frequency of the wave 3. Angle of incidence of the wave

When ducting is present in the atmosphere, multi hop refraction of line-of-sight transmission can occur because of which of the following factors? 2-49

1. Operating frequency of the transmitter 2. Height of the transmitting antenna 3. Angle of incidence of the radio wave

Which irregular variation in ionospheric conditions can cause a waiting period of several days before communications return to normal?

1. Sporadic E 2. Ionospheric storms 3. Sudden ionospheric disturbance

The ability of a reflecting surface to reflect a specific radio wave depends on which of the following factors?

1. Striking angle 2. Wavelength of the wave 3. Size of the reflecting area

The space wave follows two distinct paths from the transmitting antenna to the receiving antenna

1.through the air directly to the receiving antenna, 2. reflected from the ground to the receiving antenna

Which of the following ionospheric variation causes densities to vary with the axial rotation of the sun? 2-41

27-day sunspot cycle

shf ehf

3-30 Ghz 30-300 Ghz

vlf lf mf

3-30 khz 30-300 khz 300-3000 khz

hf vhf uhf

3-30 mhz 30-300 mhz 300-3000 mhz

If the optimum working frequency for a communications link is 4,250 kHz, what is the approximate maximum usable frequency?

4,500 kHz

A radio wavelength expressed as 250 meters may also be expressed as how many feet? 2-8

820 as 1meter =3.28 feet ....250 *3.28

If the two reflected radio waves shown in the figure are received at the same instant at the receiving site, what will be the effect, if any, on signal quality?

A stronger signal will be produced *note out of phase signal would be weak or fading

When ground-wave coverage is LESS than the distance between the transmitter and the nearest point at which the refracted waves return to earth, which of the following reception possibilities should you expect?

A zone of silence

Energy radiated from an antenna is considered horizontally polarized under which of the following conditions? 2-12

ANS:If the electric field is in the horizontal plane E-Field-horizantal-parallel plane e-field- vertical - perpendicular plane

If the signal strength of an incoming signal is reduced for a prolonged period, what type of fading is most likely involved?

Absorption

The density of ionized layers is normally greatest during which of the following periods? 2-25

Between early morning and late afternoon

The induction field is made up of which of the following fields?

Both E and H fields

There is a maximum frequency at which vertically transmitted radio waves can be refracted back to Earth. What is this maximum frequency called?

Critical frequency

The density of what ionosphere layer increases because of a violent eruption on the surface of the sun?

D

Which of the following layers provide the greatest amount of absorption to the ionospheric wave? 2-34

D and E

What two layers in the ionosphere recombine and largely disappear at night? 2-26

D and E layers

What is the height of the individual layers of the ionosphere?

D layer is 30-55 miles, E layer 55-90 miles, and F layers are 90-240 miles

How are the four distinct layers of the ionosphere designated?

D, E, F1, and F2 layers

Which of the following ionospheric variation causes densities to vary with the time of the day? 2-40

Daily variation

What are the four main classes of regular variation which affect the extent of ionization in the ionosphere?

Daily, seasonal, 11-year, and 27-days variation.

The Navy's long-range vlf broadcasts are possible because of the advantages of which of the following types of propagation?

Diffraction

In the right-hand rule for propagation, the thumb points in the direction of the E field and the forefinger points in the direction of the H field. In what direction does the middle finger point?

Direction of wave propagation

For hf-radio communications covering long distances, what is the most important layer of the ionosphere? 2-16

F

What is the term used to describe the basic frequency of a radio wave?

Fundamental frequency

The signal of a space wave is sometimes significantly reduced at the receiving site because of which of the following interactions?

Ground-wave reflections

A sudden and intense burst of ultraviolet light is especially disruptive to communications in which of the following frequency bands? 2-43

HF

What relative range of operating frequencies is required during periods of maximum sunspot activity?

Higher

Which two composite fields (composed of E and H fields) are associated with every antenna?

Induction field and radiation field.

What composite field (composed of E and H fields) is found stored in the antenna?

Induction field.

Electrically charged particles that affect the propagation of radio waves are found in what atmospheric layer? 2-19

Ionosphere

How does temperature inversion affect radio transmission?

It can cause vhf and uhf transmission to be propagated far beyond normal line-of sight distances.

How is the term "temperature inversion" used when referring to radio waves?

It is a condition where layers of warm air are formed above layers of cool air.

What factor significantly affects the frequency of occurrence of the sporadic-E layer? 2-41

Latitude

Ultraviolet waves of higher frequencies produce ionized layers at what relative altitude(s)?

Lower

Receiving sites located near industrial areas can expect to have exceptionally large losses in signal quality as a result of which of the following propagation situations?

Man-made interference

For a radio wave entering the atmosphere of the earth at a given angle, the highest frequency at which refraction will occur is known by which of the following terms? 2-44

Maximum usable frequency ?

When is muf at its highest and why?

Muf is highest around noon. Ultraviolet light waves from the sun are most intense.

What are the two main sources of EMI with which radio waves must compete?

Natural and man-made interference.

What composite field (composed of E and H fields) is propagated into free space?

Radiation field.

What is the best type of surface or terrain to use for radio wave transmission?

Radio horizon is about 1/3 farther.

The ground wave is actually composed of two separate component waves

SURFACE WAVE and the SPACE WAVE

At frequencies above 100 MHz, the greatest attenuation of rf energy from raindrops is caused by which of the following factors?

Scattering

What is the primary difference between the radio horizon and the natural horizon?

Sea water

Which of the following ionospheric variation causes densities to vary with the position of the earth in its orbit around the sun?

Seasonal variation

What is one of the major reasons for the fading of radio waves which have been reflected from a surface?

Shifting in the phase relationships of the wave.

For long-range communications in the hf band, which of the following types of waves is most satisfactory? 2-24

Sky wave -ionospheric waves

The technique of reducing multipath fading by using several receiving antennas at different locations is known as what type of diversity?

Space

What are the three more common types of irregular variations in the ionosphere?

Sporadic E, sudden disturbances, and ionospheric storms.

Radio wave propagation has the least effect because of its constancy on which of the following atmospheric layers?

Stratosphere

A frequency of 3.5 GHz falls into what rf band?

Super high

Most weather phenomena take place in which of the following region of the atmosphere?

Troposphere

Ionization in the atmosphere is produced chiefly by which of the following types of radiation?

Ultraviolet radiation

If a transmitting antenna is placed close to the ground, how should the antenna be polarized to give the greatest signal strength?

Vertically polarized.

Which radio frequency bands use the tropospheric scattering principle for propagation of radio waves?

Vhf and above

In determining the success of radio transmission, which of the following factors is the LEAST predictable?

Weather conditions along the path of communication

The greatest amount of absorption takes place in the ionosphere under which of the following conditions? 2-34

When precipitation is greatest

What is the determining factor in classifying whether a radio wave is a ground wave or a space wave?

Whether the component of the wave is travelling along the surface or over the surface of the earth.

What are three ways of controlling the amount of transmitter-generated EMI?

a) filtering and shielding of the transmitter (b) limiting bandwidth (c) cutting the antenna to the correct frequency

A radio wave with a frequency of 32 kHz is part of which of the following frequency bands?

lf band

Surface waves

on the ground alone the earth

Space waves

over the surface