How it Works | Propagation Flashcards
The ionosphere begins at about __ miles up
60
The nitrogen ionises at ___ levels
higher
The oxygen ionises at ___ levels
lower
Ionisation occurs mostly during the ___, and least just before ___
day, sunrise
Recombination is the recombining of the ___ with the ___
atoms electrons
A warmer ionosphere with ___ ionisation reflects signals ___
increased, better
The reflection is best towards the ___ in the mornings, to the South around ___, and the west in the ___ and ___.
East, Midday, evenings, evenings
_ layers of electrically charged gas atoms are produced between __ and ___km above the Earth
4 50 300
The D layer is between __ and __ km
50 100
The D layer exists during __ hours
daylight
The D layer experiences ___ ionisation as ___ UV waves penetrate so far into the atmosphere.
low, few
The D layer can refract _LF when large antenna and ___ power transmitters are used.
VLF high
The D layer is mainly responsible for absorbing and blocking _F and _F waves, whilst being transparent to _F.
LF MF HF
As it fades, _F signals can reach higher layers where they can be reflected back.
M
The E layer is between __ and ___ km
100 150
The E layer returns _F and _F bands, and waves longer than ___m
LF HF 100
The E layer is normally transparent to _HF
VHF
Sporadic E are strong patches of ionisation which can return _HF
VHF
The F layer exists in ___, and splits into __ and __
daylight, F1, F2
The F layer is responsible for most _F communications, wavelengths of less than ___m
HF, 10m
F layer atoms can stay ionised all ___ during maximum sunspot activity
night
The single hop capability in the F layer is up to ____ miles for horizontal waves.
3000
As the circumference of a wave front increases, the energy ___ per unit of length
reduces
The signal strength at any point is called the ___ strength, and is measured in ___
field, volts
Attenuation concerns the loss of ___ and ___ in various parts of the radio wave
energy velocity
Attenuation is the result of the radio wave’s energy being absorbed by the ___/___/___, on top of the normal ___ power with range.
Earth/atmosphere/ionosphere, decreasing
The only way to control attenuation is by alteration of the __
frequency
Radar attenuation ___ with frequency, and can be affected by water droplets.
increases
Radio waves can change direction as a result of ___, ___, and ___
refraction, reflection, diffraction
Refraction is the change of ___/___ as the wave travels across different media.
speed/bending
Refraction happens at the ionosphere with _F, according to the ___, ___, and ___
HF, temp, pressure, humidity.
The ___ does not change when refraction occurs
frequency
The initial and reflected waves have the ____ angle
same
A phase shift occurs, depending on the angle of ___ and the wave ___
incidence, polarisation
Diffraction of the wave is the ___ of the wave as it passes through a gap/around an edge
spreading
Radio waves bend around ___/___, and over mountains
dawn dusk
Multipath propagation is the receiving of signals from ___ sources, out of ___ with each other at the antenna
many, phase
AM will generally reflect off of different layers of the ___, arriving out of ___ at the antenna
ionosphere, phase
AM VHF will reflect off the ____, but not with SSB.
ionosphere
Reflection off of the ionosphere can severely affect ___ modulation used by GPS sats, but not in the ___ latitudes.
PSK, mid
Ground waves are associated with _LF and _F, sometimes _F
VLF, LF, MF
Ground waves don’t leave the ___ atmosphere
lower
The two factors which influence how closely ground waves follow the curve of the Earth are ___ and ___
scattering attenuation