Earth bulge
Encyclopedia
Earth bulge is a term used in telecommunication
s. It refers to the circular segment of earth profile which blocks off long distance communications.
(ie., line of sight) can readily be calculated.
Let R be the radius of Earth and h be the altitude of a telecommunication station. Line of sight distance d of this station is given by the Pythagorean theorem
;
Since the altitude of the station is much less than the radius of the Earth,
The mean radius of the earth is about 6378 kilometres (3,963.1 mi). (See Earth radius
) Using the same units for both the altitude of the station and the radius of the earth,
If the height is given in m. and distance in km.
If the height is given in ft. and the distance in miles,
distance. Usually a factor k is used in the equation above
k > 1 means geometrically reduced bulge and a longer service range. On the other hand, k < 1 means a shorter service range.
Experience has shown that, under normal weather conditions k is 4/3. That means that, the maximum service range increases by % 15
for h in m. and d in km.
for h in ft. and d in miles ;
But in stormy weather, k may decrease to cause fading in transmission. (In extreme cases k can be less than 1.) That is equivalent to a hypothetical decrease in Earth radius and an increase of Earth bulge.
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
s. It refers to the circular segment of earth profile which blocks off long distance communications.
Distance to horizon
Assuming a perfect sphere with no terrain irregularity, the distance to horizon from a high altitude transmitterTransmitter station
Transmitter station refers to terrestrial infrastructure for transmitting radio frequency signals. The station maybe used for, wireless communication, broadcasting, microwave link, mobile telephone etc.-Choice of location:...
(ie., line of sight) can readily be calculated.
Let R be the radius of Earth and h be the altitude of a telecommunication station. Line of sight distance d of this station is given by the Pythagorean theorem
Pythagorean theorem
In mathematics, the Pythagorean theorem or Pythagoras' theorem is a relation in Euclidean geometry among the three sides of a right triangle...
;
Since the altitude of the station is much less than the radius of the Earth,
The mean radius of the earth is about 6378 kilometres (3,963.1 mi). (See Earth radius
Earth radius
Because the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km...
) Using the same units for both the altitude of the station and the radius of the earth,
If the height is given in m. and distance in km.
If the height is given in ft. and the distance in miles,
The actual service range
The above analysis doesn’t take the effect of atmosphere on the propagation path of the RF signals into consideration. In fact, the RF signals don’t propagate in straight lines. Because of the canalizing effects of atmospheric layers, the propagation paths are somewhat curved. Thus, the maximum service range of the station, is not equal to the line of sightLine-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
distance. Usually a factor k is used in the equation above
k > 1 means geometrically reduced bulge and a longer service range. On the other hand, k < 1 means a shorter service range.
Experience has shown that, under normal weather conditions k is 4/3. That means that, the maximum service range increases by % 15
for h in m. and d in km.
for h in ft. and d in miles ;
But in stormy weather, k may decrease to cause fading in transmission. (In extreme cases k can be less than 1.) That is equivalent to a hypothetical decrease in Earth radius and an increase of Earth bulge.
Example
In normal weather conditions, the service range of a station at an altitude of 1500 m. with respect to receivers at sea level can be found as,
See also
- Radial (radio)Radial (radio)In RF engineering, radial has two different meanings, both referring to lines which radiate from a radio antenna.-Planning:...
- TransmitterTransmitterIn electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
- Field strength in free spaceField strength in free spaceField strength in free space is a term in telecommunications. It is the field strength caused by a half wave dipole under ideal conditions. The actual field strength in terrestrial environments is calculated by empirical formulas based on this field strength....
- Line-of-sight propagationLine-of-sight propagationLine-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
External links
- http://wiki.answers.com/Q/What_is_the_formula_to_calculate_earth_bulge
- http://www.wireless-center.net/Cisco-Wireless-Networking/728.html
- http://web.telia.com/~u85920178/data/pathlos.htm#bulges
- http://www.scribd.com/doc/52528816/64/The-Earth-bulge