Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
48 Cards in this Set
- Front
- Back
|
which two composite fields (Electric field and the Magnetic field) are associated with every antenna?
|
induction field and radiation field
|
|
|
which composite field is stored with in the antenna?
|
induction field
|
|
|
which composite field in emitted into free space?
|
radiation field
|
|
|
what term is used to describe the basic frequency of a wave?
|
fundamental frequency
|
|
|
what term is used to describe the whole number multiple of the basic frequency of a radio wave?
|
harmonic frequency
|
|
|
It is known that WWV operates and 10 Mhz what is the wavelength of WWV?
|
30 meters
|
|
|
A station is know to operate at a wavelength of 60 meters what is the frequency of the station?
|
5 Mhz
|
|
|
if an antenna is place close to the ground, how should the antenna be polarized to give it the bast signal strength?
|
vertically polarized
|
|
|
In the right rule of 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 represent?
|
direction of the wave of propagation
|
|
|
What is one of the major reasons for the fading of radio waves which have been reflected from a surface?
|
shifting in the face relationship of the wave
|
|
|
What are the three layers of the atmosphere
|
troposphere, stratosphere, and ionoshere
|
|
|
what layer of the atmosphere has little affect on radio waves?
|
stratosphere
|
|
|
what is the determining factor in determining whether a radio wave is a ground wave or a space wave?
|
whether the wave is traveling along the surface of the earth or over the surface of the earth
|
|
|
what is the best type of terrain or surface to transmit a radio wave?
|
sea water
|
|
|
what is the primary difference between radio horizon and the natural horizon?
|
the radio horizon is 1/3 times farther than the natural horizon
|
|
|
what three factors must be considered in the transmission of the surface wave to reduce attenuation?
|
the electrical properties of the terrain, frequency, and the polarization of the antenna
|
|
|
What causes ionization in the atmosphere?
|
high energy ultraviolet light waves from the sun enter the ionospheric region of the atmosphere, strike a gas atom, and literally knock an electron free from its parent atom
|
|
|
How are the four distinct layer in the ionosphere designated
|
they are designated D, E, F1 and F2
|
|
|
What are the heights of the individual layers of the ionosphere?
|
D layer is 30-55 miles, the E layer is 55-90 miles, the F layers are 90-240
|
|
|
what factor determines whether a radio wave is deflected or refracted by the ionosphere?
|
the thickness of the ionized layer
|
|
|
There is a maximum frequency at which vertically transmitted radio waves can be refracted back to earth. What is the frequency called?
|
critical frequency
|
|
|
what three factors determine the amount of refraction in the ionosphere?
|
depends on the frequency of the wave, the
angle of incidence, and the degree of ionization present. |
|
|
what is the skip zone of a radio wave?
|
a zone of silence where the ground wave becomes to weak for reception and the point where the sky wave first returns to earth
|
|
|
where does the greatest amount of absorption occur in the ionosphere
|
most ionospheric absorption occurs in the lowest layers of the ionosphere where ionization density is greatest
|
|
|
what is meant by the term multipath?
|
a term used to describe the multiple paths of a radio wave between the transmitter and receiver
|
|
|
when a wide band of frequencies is transmitted simultaneously, each frequency will vary in the amount of fading, what is this called?
|
selective fading
|
|
|
what are the two types of EMI radio waves have to deal with?
|
man made and natural
|
|
|
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?
|
EMI can be controlled by cutting transmitting antennas to the correct frequency, limiting bandwidth , and electronic filtering networks and metallic shielding
|
|
|
What are three ways of controlling radiated emi during transmission?
|
the physical separation of the transmitting and receiving antennas, the use of directional antennas, and limiting antenna bandwidth
|
|
|
what are two general types of variation in the ionosphere?
|
regular and irregular variations
|
|
|
what is the main difference between the two variations?
|
Regular is predictable and can be anticipated
Irregular is unpredictable |
|
|
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.
|
|
|
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
|
maximum usable frequency, lowest usable frequency, and frequence optimum de travail.
|
|
|
what is muf at its highest and why?
|
muf is highest around noon due to the fact ultraviolet light rays from the sun are at there highest
|
|
|
what happens to the radio wave if the luf is to low?
|
As the frequency of a radio wave is lowered, the rate of refraction increases. So a wave whose frequency is below the established luf is refracted back to Earth at a shorter distance than desired
|
|
|
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 transmitters 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 attenuation?
|
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.
|
