Line-of-sight propagation

line of sightline-of-sightradio horizonterrain shieldingLOSEffective Earth radiusline-of-sight communication40 kilometersis unable to communicate with Earthk''-factor
Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves travel in a direct path from the source to the receiver.wikipedia
300 Related Articles

Shortwave radio

shortwaveshort waveshort-wave
Additionally, frequencies in the shortwave bands between approximately 1 and 30 MHz, can be reflected back to Earth by the ionosphere, called skywave or "skip" propagation, thus giving radio transmissions in this range a potentially global reach.
Thus shortwave radio can be used for very long distance communication, in contrast to radio waves of higher frequency which travel in straight lines (line-of-sight propagation) and are limited by the visual horizon, about 64 km (40 miles).

Radio wave

radio wavesradioradio signal
In contrast to line-of-sight propagation, at low frequency (below approximately 3 MHz) due to diffraction, radio waves can travel as ground waves, which follow the contour of the Earth.
Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.

Microwave

microwavesmicrowave radiationmicrowave tube
Low-powered microwave transmitters can be foiled by tree branches, or even heavy rain or snow.
Microwaves travel by line-of-sight; unlike lower frequency radio waves they do not diffract around hills, follow the earth's surface as ground waves, or reflect from the ionosphere, so terrestrial microwave communication links are limited by the visual horizon to about 40 mi.

Very high frequency

VHFVHF radioVHF band
However, at frequencies above 30 MHz (VHF and higher) and in lower levels of the atmosphere, neither of these effects are significant.
Radio waves in the VHF band propagate mainly by line-of-sight and ground-bounce paths; unlike in the HF band there is only some reflection at lower frequencies from the ionosphere (skywave propagation).

Radio receiver

receiverreceiversRadios
Thus, any obstruction between the transmitting antenna (transmitter) and the receiving antenna (receiver) will block the signal, just like the light that the eye may sense.
Like FM, DAB signals travel by line of sight so reception distances are limited by the visual horizon to about 30–40 miles (48–64 km).

Non-line-of-sight propagation

non-line-of-sightBLOSNLOS
See also Non-line-of-sight propagation for more on impairments in propagation.
Many types of radio transmissions depend, to varying degrees, on line of sight (LOS) between the transmitter and receiver.

Skywave

ionospheric reflectionsky waveionospheric propagation
Additionally, frequencies in the shortwave bands between approximately 1 and 30 MHz, can be reflected back to Earth by the ionosphere, called skywave or "skip" propagation, thus giving radio transmissions in this range a potentially global reach.

Multipath propagation

multipathmultipath interferencemultipath fading
Where one component (often, but not necessarily, a line of sight component) dominates, a Rician distribution provides a more accurate model, and this is known as Rician fading.

Rayleigh fading

fadingtarget fading
Rayleigh fading is most applicable when there is no dominant propagation along a line of sight between the transmitter and receiver.

Fresnel zone

first Fresnel zoneFresnel zone conceptFresnel zone equations
For the best propagation, a volume known as the first Fresnel zone should be free of obstructions.
To maximize signal strength, one needs to minimize the effect of obstruction loss by removing obstacles from both the direct radio frequency line of sight (RF LoS) line and also the area around it within the primary Fresnel zone.

Horizon

visual horizonacceleration horizoncurvature of the Earth
The rays or waves may be diffracted, refracted, reflected, or absorbed by the atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles.

Radio propagation

propagationpropagation moderadio wave propagation
Radio wave propagation is affected by atmospheric conditions, ionospheric absorption, and the presence of obstructions, for example mountains or trees.
Line-of-sight propagation means radio waves which travel in a straight line from the transmitting antenna to the receiving antenna.

Ionosphere

ionosphericD layerionospheric physics
Additionally, frequencies in the shortwave bands between approximately 1 and 30 MHz, can be reflected back to Earth by the ionosphere, called skywave or "skip" propagation, thus giving radio transmissions in this range a potentially global reach.

Transmitter station

transmitterbroadcasting facilitymicrowave transmitter
Assuming a perfect sphere with no terrain irregularity, the distance to the horizon from a high altitude transmitter (i.e., line of sight) can readily be calculated.
The location may be chosen to fit the coverage area and for VHF-UHF-applications line of sight considerations.

Radio

radio communicationradio communicationswireless
If the Earth were a perfect sphere without an atmosphere, the radio horizon would be a circle.
In the very high frequency band, greater than 30 megahertz, the Earth's atmosphere has less of an effect on the range of signals, and line-of-sight propagation becomes the principle mode.

Ground plane

ground plane antennareference planereflector screen
Reflected radiation from the surface of the surrounding ground or salt water can also either cancel out or enhance the direct signal.

Antenna (radio)

antennaantennasradio antenna
The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth.
For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location.

Rician fading

Ricean fading
Rician fading occurs when one of the paths, typically a line of sight signal or some strong reflection signals, is much stronger than the others.

Slant range

rangeSlant directionslant distance
In radio electronics, especially radar terminology, slant range is the line-of-sight distance along a slant direction between two points which are not at the same level relative to a specific datum.

Ionospheric absorption

absorption of HF radio waves
Radio wave propagation is affected by atmospheric conditions, ionospheric absorption, and the presence of obstructions, for example mountains or trees.

Electromagnetic radiation

electromagnetic waveelectromagnetic waveselectromagnetic
Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves travel in a direct path from the source to the receiver.

Wave propagation

propagationpropagatespropagate
Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves travel in a direct path from the source to the receiver.

Transmission (telecommunications)

transmissiontransmissionstransmit
Electromagnetic transmission includes light emissions traveling in a straight line.

Line (geometry)

linestraight linelines
Electromagnetic transmission includes light emissions traveling in a straight line.