Wave Prob Flashcards
What composite field (composed of E & H fields) is found stored in the antenna?
Induction field
Which 2 composite fields are associated with every antenna?
Induction & radiation
What composite field (composed of E & H fields) is propagated into free space.
Radiation
What term is used to describe the basic freq. of a radio wave.
Fundamental freq
What term is used to describe a whole # multiple of the basic freq of a radio wave.
Harmonic freq. or harmonics
If a transmitting antenna is placed close to the ground how should the antenna be polarized to give the greatest signal strength.
Vertically.
What is one of the major reasons for the fading of radio waves which have been reflected from a surface?
Shifting of the phase relationships if the wave
What are the 3 layers if the atmosphere?
Troposphere
Stratosphere
Ionosphere
Which layer of the atmosphere has little to no effect on radio waves?
Stratosphere
What are the 2 components of a ground wave?
Surface & space wave
What type of polarization is preferred for a surface wave?
Vertical
What is the determining factor in classifying whether a radio wave is a ground wave or a space wave?
Whether the component is traveling 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.
Sea water
What are the 3 factors that must be considered in the transmission if surface waves to reduce attenuation.
- Electrical properties of the terrain
- freq
- polarization of the antenna
What is the hight of the D layer of the ionosphere.
30-55 miles
What is the hight of the E layer of the ionosphere.
55-90 miles
What is the hight of the F layers of the ionosphere.
90-240 miles
What factor determines whether a radio wave is reflected or refracted by the ionosphere.
Thickness if ionized layer
There is a maximum freq at which vertically transmitted radio waves can be refracted back to earth. What is this max freq called?
Critical freq
What 3 main factors determine the amount of refraction in the ionosphere.
- Density of the ionized layer
- freq
- angle of entry
What is the skip zone of a radio wave?
A zone of silence between the ground wave & sky wave where there is no reception.
Where does the greatest amount of ionospheric absorption occur in the ionosphere?
Where the density is the greatest.
What is meant by the term multipath?
Term used to describe the multiple pattern a radio wave may follow.
What are the 4 main classes of regular variations which effect the ionization of the ionosphere.
- Daily
- seasonal
- 11 year
- 26 year
What is luf?
Lowest usable freq
What is muf?
Max usable freq
What is fot?
Optimum working freq
What happens when luf is to low?
The signal will be absorbed & to weak for reception.
What are some disadvantages of operating transmitters at or near 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 muf?
Frequent signal fading & dropouts.
How do raindrops affect radio waves?
Can cause attenuation by scattering.
How does fog affect radio waves at freqs above 2 ghz?
Can cause attenuation by absorption.
What layer of the atmosphere is weather?
Troposphere.
Which radio freq bands use the tropospheric scattering principle for propagation of radio waves?
VHF & above.
What is the primary difference between the radio horizon & the natural horizon.
Radio horizon is about 1/3 farther.
