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Which two composite fields (composed of E and H fields) are associated with every antenna?
Induction field and radiation field.
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What composite field (composed of E and H fields) is found stored in the antenna?
Induction field.
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What composite field (composed of E and H fields) is propagated into free space?
Radiation field.
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What is the term used to describe the basic frequency of a radio wave?
Fundamental frequency
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What is the term used to describe a whole number multiple of the basic frequency of a radio wave?
Harmonic frequency or harmonics.
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It is known that WWV operates on a frequency of 10 megahertz. What is the wavelength of WWV?
30 meters.
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A station is known to operate at 60-meters. What is the frequency of the unknown station?
5 megahertz.
-
If a transmitting antenna is placed close to the ground, how should the antenna be polarized to give the greatest signal strength?
Vertically polarized.
-
In the right-hand rule for propagation, the thumb points in the direction of the E field and theforefinger points in the direction of the H field. In what direction does the middle finger point?
Direction of wave propagation.
-
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.
-
What are the three layers of the atmosphere?
Troposphere, stratosphere, and ionosphere.
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Which layer of the atmosphere has relatively little effect on radio waves?
Stratosphere.
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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 is the best type of surface or terrain to use for radio wave transmission?
Radio horizon is about 1/3 farther.
-
What is the primary difference between the radio horizon and the natural horizon?
Sea water.
-
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 causes ionization to occur in the ionosphere?
High energy ultraviolet light waves from the sun.
-
How are the four distinct layers of the ionosphere designated?
D, E, F1, and F2 layers.
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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.
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What factor determines whether a radio wave is reflected or refracted by the ionosphere?
Thickness of ionized layer.
-
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.
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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 is the skip zone of a radio wave?
A zone of silence between the ground wave and sky wave where there is no reception.
-
Where does the greatest amount of ionospheric absorption occur in the ionosphere?
Where ionization density is greatest.
-
What is meant by the term "multipath"?
A term used to describe the multiple pattern a radio wave may follow.
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When a wide band of frequencies is transmitted simultaneously, each frequency will vary in the amount of fading. What is this variable fading called?
Selective fading.
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What are the two main sources of emi with which radio waves must compete?
Natural and man-made interference.
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Thunderstorms, snowstorms, cosmic sources, the sun, etc., are a few examples of emi sources.
What type of emi comes from these sources?
Natural.
-
Motors, switches, voltage regulators, generators, etc., are a few examples of emi sources. What
type of emi comes from these sources?
Man-made.
-
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
-
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
-
What are the two general types of variations in the ionosphere?
Regular and irregular variations.
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What is the main difference between these two types of variations?
Regular variations can be predicted but irregular variations are unpredictable.
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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.
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What are the three more common types of irregular variations in the ionosphere?
Sporadic E, sudden disturbances, and ionospheric storms.
-
What do the letters muf, luf, and fot stand for?
Muf is maximum usable frequency. Luf is lowest usable frequency. Fot is commonly known as optimum working frequency.
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When is muf at its highest and why?
Muf is highest around noon. Ultraviolet light waves from the sun are most intense.
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What happens to the radio wave if the luf is too low?
When luf is too low it is absorbed and is too weak for reception.
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What are some disadvantages of operating transmitters at or near the luf?
Signal-to-noise ratio is low and the probability of multipath propagation is greater.
-
What are some disadvantages of operating a transmitter at or near the muf?
Frequent signal fading and dropouts.
-
What is fot?
Fot is the most practical operating frequency that can be relied on to avoid problems of multipath,absorbtion, and noise.
-
How do raindrops affect radio waves?
They can cause attenuation by scattering.
-
How does fog affect radio waves at frequencies above 2 gigahertz?
It can cause attenuation by absorbtion.
-
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.
-
How does temperature inversion affect radio transmission?
It can cause vhf and uhf transmission to be propagated far beyond normal line-of-sight distances.
-
In what layer of the atmosphere does virtually all weather phenomena occur?
Troposphere.
-
Which radio frequency bands use the tropospheric scattering principle for propagation of radio waves?
Vhf and above.
-
Where is the tropospheric region that contributes most strongly to tropospheric scatter propagation?
Near the mid-point between the transmitting and receiving antennas, just above the radio horizon.
-
What are the two basic classifications of antennas?
Half-wave (Hertz) and quarter-wave (Marconi).
-
What are the three parts of a complete antenna system?
Coupling device, feeder, and antenna.
-
What three factors determine the type, size, and shape of an antenna?
- Frequency of operation of the transmitter, amount of power to be radiated, and general direction
- of the receiving set.
-
If a wave travels exactly the length of an antenna from one end to the other and back during the period of 1 cycle, what is the length of the antenna?
One-half the wavelength.
-
What is the term used to identify the points of high current and high voltage on an antenna?
Current and voltage loops.
-
What is the term used to identify the points of minimum current and minimum voltage on an
antenna?
Current and voltage nodes.
-
The various properties of a transmitting antenna can apply equally to the same antenna when it is used as a receiving antenna. What term is used for this property?
Reciprocity of antennas.
-
The direction of what field is used to designate the polarization of a wave?
Electric (E) field.
-
If a wave's electric lines of force rotate through 360 degrees with every cycle of rf energy, what is the polarization of this wave?
Circular polarization.
-
What type of polarization should be used at medium and low frequencies?
Vertical polarization.
-
What is an advantage of using horizontal polarization at high frequencies?
Less interference is experienced by man-made noise sources.
-
What type of polarization should be used if an antenna is mounted on a moving vehicle at frequencies below 50 megahertz?
Vertical polarization.
-
What is the radiation resistance of a half-wave antenna in free space?
73 ohms.
-
A radiating source that radiates energy stronger in one direction than another is known as what type of radiator?
Anisotropic radiator.
-
A radiating source that radiates energy equally in all directions is known as what type of radiator?
Isotropic radiator.
-
A flashlight is an example of what type of radiator?
Anisotropic radiator.
-
What terms are often used to describe basic half-wave antennas?
Dipole, doublet and Hertz.
-
If a basic half-wave antenna is mounted vertically, what type of radiation pattern will be produced?
Nondirectional.
-
In which plane will the half-wave antenna be operating if it is mounted horizontally?
Vertical plane.
-
Since the radiation pattern of a dipole is similar to that of a doublet, what will happen to the
pattern if the length of the doublet is increased?
The pattern would flatten.
-
What is the simplest method of feeding power to the half-wave antenna?
To connect one end through a capacitor to the final output stage of the transmitter.
-
What is the radiation pattern of a quarter-wave antenna?
A circular radiation pattern in the horizontal plane, or same as a half wave.
-
Describe the physical arrangement of a ground screen.
-
It is composed of a series of conductors arranged in a radial pattern and buried 1 to 2 feet below
the ground.
-
What is the difference in the amount of impedance between a three-wire dipole and a simple center-fed dipole?
Nine times the feed-point impedance.
-
Which has a wider frequency range, a simple dipole or a folded dipole?
Folded dipole.
-
What is the purpose of antenna stubs?
To produce desired phase relationship between connected elements.
-
What is the primary difference between the major and minor lobes of a radiation pattern?
Major lobes have the greatest amount of radiation.
-
What is the maximum number of elements ordinarily used in a collinear array?
Four.
-
Why is the number of elements used in a collinear array limited?
As more elements are added, an unbalanced condition in the system occurs which impairs efficiency.
-
How can the frequency range of a collinear array be increased?
By increasing the lengths of the elements of the array.
-
How is directivity of a collinear array affected when the number of elements is increased?
Directivity increases.
-
What is the primary cause of broadside arrays losing efficiency when not operating at their
designed frequency?
Lower radiation resistance.
-
When more than two elements are used in a broadside array, how are the elements arranged?
Parallel and in the same plane.
-
As the spacing between elements in a broadside array increases, what is the effect on the major lobes?
They sharpen.
-
What are some disadvantages of the end-fire array?
- Extremely low radiation resistance, confined to one frequency, and affected by atmospheric
- conditions.
-
Where does the major lobe in the end-fire array occur?
Along the major axis
-
To maintain the required balance of phase relationships and critical feeding, how must the
end-fire array be constructed?
Symmetrically.
-
What two factors determine the directivity pattern of the parasitic array?
Length of the parasitic element (tuning) and spacing between the parasitic and driven elements.
-
What two main advantages of a parasitic array can be obtained by combining a reflector and a director with the driven element?
Increased gain and directivity.
-
The parasitic array can be rotated to receive or transmit in different directions. What is the name given to such an antenna?
Rotary array.
-
What are the disadvantages of the parasitic array?
Their adjustment is critical and they do not operate over a wide frequency range.
-
What is the advantage of adding parasitic elements to a Yagi array?
Increased gain.
-
The Yagi antenna is an example of what type of array?
Multielement parasitic array.
-
To radiate power efficiently, a long-wire antenna must have what minimum overall length?
One-half wavelength.
-
What is another name for the Beverage antenna?
Wave antenna.
-
What is the polarity of the currents that feed the V antenna?
Opposite.
-
What is the main disadvantage of the rhombic antenna?
It requires a large antenna site.
-
What is the primary reason for the development of the turnstile antenna?
For omnidirectional vhf communications.
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