Editing Tropospheric scatter (section)

{{Short description|Method of communicating with microwave radio signals over considerable distances}}
[[File:Tropospheric scatter.jpg|thumb|220px|A tropospheric scatter system can bridge large distances ''(white)'' while a [[microwave relay]] system ''(lines below)'' requires multiple relay stations due to its [[line-of-sight propagation|line of sight]] limitation. ]]
[[File:White Alice Site, Tropospheric Antennas HAER AK-21-A-2.jpg|thumb|[[Valdez-Cordova Census Area, Alaska|Boswell Bay, Alaska]] White Alice Site, Tropospheric scatter antenna and feeder.]]
[[File:Pacific Scatter.jpg|thumb|Pacific Scatter System]]

'''Tropospheric scatter''', also known as '''troposcatter''', is a method of communicating with [[microwave radio]] signals over considerable distances – often up to {{convert|500|km|mi}} and further depending on frequency of operation, equipment type, terrain, and climate factors. This method of propagation uses the tropospheric scatter phenomenon, where radio waves at [[Ultra high frequency|UHF]] and [[Super high frequency|SHF]] [[Frequency|frequencies]] are randomly scattered as they pass through the upper layers of the [[troposphere]]. Radio signals are transmitted in a narrow beam aimed just above the horizon in the direction of the receiver station. As the signals pass through the troposphere, some of the energy is scattered back toward the Earth, allowing the receiver station to pick up the signal.<ref>{{cite tech report |url= https://www.its.bldrdoc.gov/fs-1037/other/t.pdf |url-access= |title= Telecommunications: Glossary of Telecommunication Terms - tropospheric scatter | date = 2000-08-23 | page = T-21 | number = FED-STD-1037C | institution = [[National Telecommunications and Information Administration]] | language= en-us | format = pdf | access-date = 2021-07-13 | url-status = live | archive-url = https://web.archive.org/web/20161225065408/https://www.its.bldrdoc.gov/fs-1037/other/t.pdf | archive-date = 2016-12-25 | df = dmy-all}}</ref>

Normally, signals in the microwave frequency range travel in straight lines, and so are limited to ''[[Line-of-sight propagation|line-of-sight]]'' applications, in which the receiver can be 'seen' by the transmitter. Communication distances are limited by the [[horizon|visual horizon]] to around {{convert|30|-|40|mi|order=flip}}. Troposcatter allows microwave communication beyond the horizon. It was developed in the 1950s and used for military communications until [[communications satellite]]s largely replaced it in the 1970s.

Because the troposphere is turbulent and has a high proportion of moisture, the tropospheric scatter radio signals are [[refracted]] and consequently only a tiny proportion of the transmitted radio energy is collected by the receiving antennas. Frequencies of transmission around {{frequency|2|GHz}} are best suited for tropospheric scatter systems as at this frequency the wavelength of the signal interacts well with the moist, turbulent areas of the troposphere, improving [[signal-to-noise ratio]]s.