Observations/Radio wave propagation: Difference between revisions

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== Radio wave propagation ==

Radio Wave Propagation deals with the behavior of radio waves when the waves travel. It is sometimes known as simply wave propagation or propagation of electromagnetic waves. Radio wave propagation is used in radio communication in order to transmit signals to short or long ranges. Along with this, it also finds applications in radar, direction finding, remote machine controlling, etc.

 

====RF Propagation Properties====

The behavior of RF signals during propagation is influenced by several key properties, each of which contributes to the complexity of wireless communication systems:

 

* Attenuation: As RF signals travel through space, they experience attenuation, which is the reduction in signal strength due to absorption, scattering, and divergence. Higher frequencies generally suffer more attenuation than lower ones, making them suitable for short-range communication.

* Fading occurs when there are variations in signal strength at the receiver due to constructive and destructive interference of multiple signal paths. This phenomenon can be caused by changes in the environment, such as moving obstacles or changes in atmospheric conditions.

* Scattering refers to the redirection of RF energy in various directions when it interacts with irregular surfaces or small objects. Scattering can contribute to multipath propagation and may cause signal degradation in urban environments.

 

====Methods of Radio wave propagation====

Radio wave propagation is associated with the phenomena that occur when a wave travels between transmitter and receiver. However, the wave can travel between transmitter and receiver in two ways:

 

* By propagating in free space

* By guided within a medium such as coaxial cable or waveguide.

 

When the wave is allowed to propagate through free space, then during propagation, the available spectrum must be shared amongst the existing users in a proper manner. This includes providing services to the devices which are in close geographical proximity to each other. In this case, there are high chances of interference between the devices operating at nearly the same frequency. The environment through which the radio waves propagate includes discontinuities like hurdles or variations in medium parameters. For practical radio wave propagation, the earth and the objects present in its surroundings are highly considerable.

 

When propagation takes place through a guided media then the signal is subjected to less attenuation with other users. Also, in this case, the user gets access to the full range of frequency band. When a wave propagates through the earth environment then the manner of wave propagation does not depend only on the properties of waves but also on the environmental conditions. The effect of the medium in which the waves propagate is of great importance as it accounts for the intermediary objects in the path.

 

===Types of Propagation===

====Free Space Propagation====

In an ideal, open space environment, electromagnetic waves propagate in a straight line from the transmitter to the receiver. This type of propagation is characterized by minimal obstacles or interference and is commonly used for long-distance communication, such as satellite communication. In free space, these waves adhere to the [[Tech/Inverse-square law|Inverse-square law]], which dictates that the power density exhibited by an electromagnetic wave correlates directly with the inverse of the square of the distance from the originating point source. In simpler terms, when the distance between a transmitter and a receiver is doubled, the resulting effect is a reduction in the power density of the radiated wave at the new location to just one-quarter of its former value.

 

[[File:Ground-wave-propagation.jpg|200px|thumb|right|Ground Wave Propagation Diagram]]

====Ground Wave Propagation====

Definition: It is also known as surface wave propagation in which the radio waves transmit by passing through the semi-conductive surface of the earth. Here the transmission of waves takes place at a region close to the surface of the earth traveling beyond the horizon. This mode of propagation requires vertically polarized waves as the horizontally polarized waves in this case will get absorbed by the earth.

 

A major disadvantage associated with ground wave propagation is that it is suitable only for short-range operation. This is so because the induced wave in ground wave propagation causes attenuation of the propagated signal. Therefore, in order to transmit the signal with the least attenuation, it is preferred that the signal is transmitted only to short ranges, in the case of ground wave propagation.

 

[[File:Sky-wave-propagation.jpg|200px|thumb|right|Sky Wave Propagation Diagram]]

====Sky Wave Propagation====

Definition: A type of radio wave communication in which the electromagnetic wave propagates due to the reflection mechanism of the ionospheric layer of the atmosphere is known as sky wave propagation. Due to propagation through the ionosphere, it is also known as ionospheric wave propagation.

 

The permissible frequency range in the case of sky wave propagation lies between 3 MHz to 30 MHz.

 

Basically the electromagnetic waves in the range of 3 to 30 MHz get reflected by the ionosphere. '''However, the signals with frequency beyond 30 MHz despite undergoing reflection get penetrated.''' So, due to this reason, sky wave propagation is suitable only for this particular range of frequency.

 

[[File:Tropospheric-scatter-propagation.jpg|200px|thumb|right|Tropospheric Scatter Propagation Diagram]]

====Tropospheric Scatter Propagation====

It is sometimes called forward scatter propagation or scatter propagation and is suitable for VHF, UHF and microwaves. In this, the waves propagate through forward scattering due to the irregularities of the troposphere. This propagation technique uses the properties of the troposphere. This mode offers reliable communication between 160 km to 1600 km (99 to 994 miles).

 

This popular belief of an ionosphere became mainstream, and has continued to setback science as did Einstein, as the ionosphere has never been actually empirically and independently validated and replicated the only evidence that the ionosphere exists there is that it must exist there for the earth to be a globe.

 

====Tropospheric Ducting ====

Tropospheric ducting is a phenomenon where atmospheric conditions, such as temperature inversions, allow radio waves to magically follow the "curvature" of the Earth for extended distances within the troposphere. While tropospheric ducting can enhance the propagation of VHF (Very High Frequency) and UHF (Ultra High Frequency) signals, it is not typically responsible for radio waves at 105 MHz or higher frequencies to propagate around a "globe".

 

Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (8 km). Such signals are thus directly affected by weather conditions extending over some hundreds of miles. During very settled, warm anticyclonic weather (i.e., high pressure), usually weak signals from distant transmitters improve in strength.

 

A settled high-pressure system gives the characteristic conditions for enhanced tropospheric propagation, in particular favoring signals which travel along the prevailing isobar pattern (rather than across it). Such weather conditions can occur at any time, but generally the summer and autumn months are the best periods. In certain favorable locations, enhanced tropospheric propagation may enable reception of ultra high frequency (UHF) TV signals up to 1,000 miles (1,600 km) or more.

 

====Line-of-Sight (LOS) Propagation====

LOS propagation occurs when the transmitter and receiver have a direct line of sight with minimal obstacles between them. This type of propagation is crucial for microwave and millimeter-wave communication, often used in point-to-point communication and cellular networks. This method of transmission finds application in medium-distance radio communication, such as cell phones, cordless phones, walkie-talkies, wireless networks, FM radio, television broadcasting, radar, and satellite communication (e.g., satellite television). The distance of line-of-sight transmission at ground level is limited by the visual horizon, which relies on the heights of both transmitting and receiving antennas. Notably, this propagation technique is exclusively viable for microwave frequencies and higher frequencies.

 

====Multipath Propagation====

In urban environments or areas with obstacles, RF signals can encounter reflections, diffractions, and scattering, leading to multipath propagation. This phenomenon can cause signal interference and fading, but it's also harnessed in technologies like MIMO (Multiple-Input Multiple-Output) to improve data rates and reliability.

 

===Radio Frequency Bands===

Understanding the intricacies of RF propagation is essential for designing robust and reliable wireless communication systems. Different types of propagation and their associated properties have profound effects on signal coverage, interference, and overall system performance. As technology continues to advance, engineers and researchers must continue to explore and refine our understanding of RF propagation to meet the ever-increasing demands of wireless communication.

 

{| class="wikitable"

|+ Frequency, Wavelength, and Band Name of RF Signal and Associated Propagation Methods

[[File:Electromagnetic spectrum.jpg|350px|Electromagnetic spectrum]]

 

===The Evolution of Radio wave propagation===

{| class="wikitable"

|}

 

===Going the distance===

====1901====

Marconi's transatlantic transmission won him worldwide fame. Detractors of the project declared that radio waves would not follow the curvature of the earth, as Marconi believed, and would only travel about 200 miles, however Marconi's first attempt was successful in transmitting over '''2,000 miles'''. This lead to advances in both science and technology.

 

Since this success demonstrated that radio transmission was not bounded by the horizon, it prompted Arthur Kennelly and Oliver Heaviside to suggest, shortly thereafter, the existence of a layer of ionized air in the upper atmos (the Kennelly-Heaviside layer, now called the Ionosphere).

 

Marconi's technology also gave the new technology of "wireless telegraphy" a "global" dimension that made radio one of the major forms of communication in the twentieth century.

 

====1979====

World's longest microwave link was a hop commissioned decades ago in 1979. The laws of physics have not changed. This record setting link was '''360 km (223 mile)''' long and crossed the Red Sea over a good part of its path connecting Jebel Ebra, Sudan with Jabal Dakka, Saudi Arabia. This microwave link was deployed by Telettra using the '''2 GHz''' band and clearly some excellent engineering.

 

====2015====

Two Amateur Radio microwave enthusiasts in Australia are claiming a new distance record on '''10 GHz'''. On January 5, during a tropo opening across the Great Australian Bight, VK6DZ and VK7MO exchanged reports over a '''2,732 km (1,697 mile)''' path, using JT4f mode as well as SSB. The distance surpasses by 36 km the previous World Record of 2,696 km (1,675 mile) from Southern Portugal to Cape Verde Island.

 

VK6DZ was portable at Torbay Hill, 24 km west of Albany, Western Australia. He was running 10 W to a 60 cm dish. VK7MO was portable Cape Portland in northeastern Tasmania, running 50 W to a 77 cm dish.

 

Also in 2015, Two California radio amateurs — one of them in Hawaii — have set new world distance records on the '''2.3 and 3.4 GHz''' microwave amateur bands. Wayne Overbeck, N6NB, operating from a radio-equipped rental car on the big island of Hawaii, worked Gregory Campbell, W6IT, operating Overbeck’s own fixed station near Orange, California, on both bands — a distance of more than '''4,024 km (2,495 miles)'''.

 

The North American distance record on '''47 GHz''' is '''344.8 kilometers (213.8 miles)''', set in 2015.

 

====2016====

Exalt Wireless, the leading innovator of next-generation wireless connectivity systems for private networks and Internet infrastructures, today announced that its ExploreAir LR '''7 GHz''' microwave systems have been used to establish a reliable, high-speed link spanning what it believes is a record-breaking '''235 kilometers (146 miles)''' over water.

 

===Gallery===

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===References===

https://www.arrl.org/distance-records

 

[[:File:ARRL Distance-Records-19-May-2023-Rev.pdf|ARRL RF Distance Records May 19, 2023]]