54 terms

# NAVEDTRA 14182A, Navy Electricity and Electronics Training Series. Module 10-Wave Propagation, Transmission Lines, and Antennas ****Chapter 2****

#### Terms in this set (...)

Which two basic fields are associated with every antenna?
Which field is associated with the energy stored in the antenna?
Induction
Which type of antenna has an electrical length equal to half the wavelength of the signal being transmitted?
Half-wave
What is an energy wave called that is generated by a transmitter?
What is the basic shape of the wave generated by a transmitter?
Sine Wave
What is the number of cycles of a sine wave that are completed in 1 second known as?
Frequency
The frequencies falling between 3kHz and what are called radio frequencies since they are commonly used in radio communications?
300 GHz
The usable radio-frequency range is roughly 10 kilohertz to what?
100 gigahertz
What is the VLF frequency range?
3 to 30 KHz
What is the LF frequency range?
30 to 300 KHz
What is the MF frequency range?
300 to 3000 KHz
What is the HF frequency range?
3 to 30 MHz
What is the VHF frequency range?
30 to 300 MHz
What is the UHF frequency range?
300 to 3000 MHz
What is the SHF frequency range?
3 to 30 GHz
What is the EHF frequency range?
30 to 300 GHz
Any frequency that is a whole number multiple of a smaller basic frequency is known as what property of that basic frequency?
Harmonic
What is the property of a radio wave which is simply the amount of time required for the completion of one full cycle?
Period
What is the space called occupied by one full cycle of a radio wave at any given instant?
Wavelength
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?
186,000
Where must the receiving antenna be located for maximum absorption of energy from the electromagnetic fields?
Plane of polarization
Troposphere, Stratosphere, along with what else are the three separate regions, or layers that the Earth's atmosphere is divided into?
Ionosphere
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 (6km) att the North Pole or the South Pole and how many miles at the equator?
11.2 miles
Which atmosphere layer has relatively little effect on radio waves because it is a relatively calm region with little or no temperature changes?
Stratosphere
The Ionosphere extends upward from about 31.1 miles to a height of about how many miles?
250
What is the most important region of the atmosphere for long distance point-to-point communications?
Ionosphere
What are the two principal ways in which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna?
Ground and Sky Waves
The surface wave is impractical for long distance transmissions at frequencies above what frequency?
2 megahertz
Which frequency band is used for sky wave propagation?
High Frequency
What is the process known as of upsetting electrical neutrality?
Ionization
What occurs when the free electrons and positive ions collide with each other?
Recombination
How many layers is the Ionosphere composed of?
Three
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?
Critical frequency
What is the distance from the transmitter to the point where the sky wave is first returned to Earth?
Skip Distance
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?
Skip Zone
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?
Absorption
Fading on ionosphere circuits is mainly a result of what?
Multipath Propagation
In what practice are two transmitters and two receivers used, each pair tuned to different frequency, with the same information being transmitted simultaneously over both frequencies?
Frequency diversity
When a wide band of frequencies is transmitted simultaneously, each frequency will vary in the amount of fading. What is this variation called?
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?
Free Space Loss
There is little natural interference above what frequency?
30 megahertz
How many main classes can the regular variations that affect the extent of ionization in the ionosphere be divided into?
Four
What are responsible for variations in the ionization level of the ionosphere
Sunspots
Long distance propagation of hf radio waves is almost totally "blanked out" when what occurs?
Sudden Ionospheric Disturbance (SID)
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?
Four
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?
Maximum Usable Frequency (MUF)
Raindrops cause greater attenuation by scattering than by absorption at frequencies above what?
100 megahertz
Fog can cause serious attenuation by absorption at frequencies above what?
2 gigahertz
What is the condition when layers of warm air are formed above layers of cool air known as?
Temperature inversion
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?
7
What region does virtually all weather phenomena occur in?
Troposphere
Radio waves of frequencies below what normally have wavelengths longer that the size of weather turbulences?
30 megahertz
The usable frequency range for tropospheric scattering is from about 100 megahertz to what?
10 gigahertz
A correctly designed tropospheric scatter circuit will provide highly reliable service for distances ranging from 50 miles to how many miles?
500