NAVEDTRA 14182A, NAVY ELECTRICITY AND ELECTRONICS TRAINING SERIES. MODULE 10-WAVE PROPAGATION, TRANSMISSION LINES, AND ANTENNAS Chapter 2

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Induction and radiation
Which two basic fields are associated with every antenna
Induction
Which field is associated with the energy stored in the antenna
HAlf-wave
Which type of antenna has an electrical length equal to half the wavelength of the signal being transmitted
Radio wave
What is an energy wave called that is generated by a transmitter
Sine wave
What is the basic shape of the wave generated by a transmitter
Frequency
What is the number of cycles of a sine wave that are completed in 1 second known as
300 GHz
The frequencies falling between 3 kHz and what are called radio frequencies (abbreviated rf) since they are commonly used in radio communications
100 gigahertz
The usable radio-frequency range is roughly 10 kilohertz to what
3-30 KHz
What is the VLF frequency range
30-300 KHz
What is the LF frequency range
300-3000 KHz
What is the MF frequency range
3-30 MHz
What is the HF frequency range
30-300 MHz
What is the VHF frequency range
300-300 MHz
What is the UHF frequency range
300-3000 MHz
What is the SHF frequency range
30-300 GHz
What is the EHF frequency range
Harmonic
Any frequency that is a whole number multiple of a smaller basic frequency is known as what property of that basic frequency
Period
What is the property of a radio wave which is simply the amount of time required for the completion of one full cycle
Wavelength
What is the space called occupied by one full cycle of a radio wave at any given instant
186,000
The velocity (or speed) of a radio wave radiated into free space by a transmitting antenna is equal to the speed of light—which is how many miles per second
Plane of polarization
Where must the receiving antenna be located for maximum absorption of energy from the electromagnetic fields
Ionosphere
Troposphere, Stratosphere, along with what else are the three separate regions, or layers that the Earth's atmosphere is divided int
11.2
The troposphere is the portion of the Earth's atmosphere that extends from the surface of the Earth to a height of about 3.7 miles (6 km) at the North Pole or the South Pole and how many miles at the equator
Stratosphere
Which atmosphere layer has relatively little effect on radio waves because it is a relatively calm region with little or no temperature changes
250
The Ionosphere extends upward from about 31.1 miles to a height of about how many miles
Ionosphere
What is the most important region of the atmosphere for long distance point-to-point communications
Ground and sky waves
What are the two principal ways in which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna
2 MHz
The surface wave is impractical for long distance transmissions at frequencies above what frequency
High Frequency
Which frequency band is used for sky wave propagation
Ionization
What is the process known as of upsetting electrical neutrality
Recombination
What occurs when the free electrons and positive ions collide with each other
3
How many layers is the Ionosphere composed of
Critical frequency
Each ionospheric layer has a maximum frequency at which radio waves can be transmitted vertically and refracted back to Earth which is known as what
Skip distance
What is the distance from the transmitter to the point where the sky wave is first returned to Earth
skip zone
What is a zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to Earth
Frequency diversity
In what practice are two transmitters and two receivers used, each pair tuned to a different frequency, with the same information being transmitted simultaneously over both frequencies
Selective fading
When a wide band of frequencies is transmitted simultaneously, each frequency will vary in the amount of fading. What is this variation called
Absorption
What results in the loss of energy of a radio wave and has a pronounced effect on both the strength of received signals and the ability to communicate over long distances
Free-space loss
The combined effects of absorption, ground reflection loss, and what else account for most of the energy losses of radio transmissions propagated by the ionosphere
30 MHz
There is little natural interference above what frequency
4
How many main classes can the regular variations that affect the extent of ionization in the ionosphere be divided into
Sunspots
What are responsible for variations in the ionization level of the ionosphere
Sudden ionospheric disturbance
Long distance propagation of hf radio waves is almost totally "blanked out" when what occurs
4
An ionospheric storm that is associated with sunspot activity may begin anytime from 2 days before an active sunspot crosses the central meridian of the sun until how many days after it passes the central meridian
Maximum usable frequency
For a given angle of incidence and time of day, there is a maximum frequency that can be used for communications between two given locations. What is this frequency known as
100 MHz
Raindrops cause greater attenuation by scattering than by absorption at frequencies above what
2 GHz
Fog can cause serious attenuation by absorption at frequencies above what
Temperature inversion
What is the condition when layers of warm air are formed above layers of cool air known as
7
As the lowest region of the Earth's atmosphere, the troposphere extends from the Earth's surface to a height of slightly over how many miles
Troposphere
What region does virtually all weather phenomena occur in
30 MHz
Radio waves of frequencies below what normally have wavelengths longer than the size of weather turbulences
10 GHz
The usable frequency range for tropospheric scattering is from about 100 megahertz to what
500
A correctly designed tropospheric scatter circuit will provide highly reliable service for distances ranging from 50 miles to how many miles