1A Flashcards
The HF band extends from
3MHz - 30MHz
HF is vulnerable to what three things?
weather, atmospheric disturbances, and the time of day.
We characterize an AM radio wave as having what three things?
an amplitude, a frequency, and a wavelength
This is the magnitude of change in the height of the radio wave. This is the amount of power introduced to the signal.
Amplitude
This is the number of cycles completed by a periodic quantity in a unit of time.
Frequency
This is the distance over which the wave’s shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests or troughs.
Wavelength
Frequency and wavelength have an ___ relationship.
inverse
The symbol for wavelength is…?
Greek letter lambda (λ)
What is the formula for wavelength?
the speed of light divided by the frequency of the signal
The following describes what?
How radio waves move in free space and over the surface of the earth.
The study of radio wave propagation
Radio waves passing through different environments experience what five things?
reflection, refraction, polarization, diffraction, and absorption
Ground waves travel at or near the…?
earth’s surface
___ allows these wave to propagate beyond the horizon, traveling as surface waves which follow the contour of the earth. This allows
mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon out to hundreds of miles.
Diffraction
What two frequencies communication systems can communicate over most of the earth and with submarines hundreds of feet underwater?
Very Low Frequency (VLF) and Extremely Low Frequency (ELF)
This refers to radio waves that travel in a straight line from the transmitting antenna to the receiving antenna.
Line of Sight (LOS)
True or False: LOS requires a cleared sight path?
False - as lower frequency radio waves can pass through buildings, foliage, and other obstructions.
What is the only propagation method possible at frequencies above 30MHz?
LOS
On the surface of the earth, LOS propagation is limited by the visual horizon to about…?
64km (40 miles)
By using ___ to transmit beams of microwaves, point-to-point microwave relay links transmit telephone and television signals over long distances up to the visual horizon.
parabolic dish antennas
What can communicate with satellites and spacecraft billions of miles from earth?
Ground stations
Skywave propagation is also called what?
Skip propagation
The ionosphere is the region of the atmosphere that extends from about ___ miles above the earth’s surface.
30-250 miles
The ionosphere has several layers of electrically charged gas atoms called…?
Ions
The ion arrangement is dependent to some degree upon what? Due to this, the conditions change as the time of day changes.
The Sun