Editing Tropospheric scatter (section)

===Discovery===
Prior to [[World War II]], prevailing radio physics theory predicted a relationship between frequency and diffraction that suggested radio signals would follow the curvature of the Earth, but that the strength of the effect would fall off rapidly and especially at higher frequencies. In spite of this widespread belief, during the war there were numerous incidents in which high-frequency radar signals were able to detect targets at ranges far beyond the theoretical calculations. In spite of these repeated instances of anomalous range, the matter was never seriously studied.{{sfn|Stecker|1960}}

In the immediate post-war era, the limitation on [[television]] construction was lifted in the United States and millions of sets were sold. This drove an equally rapid expansion of new television stations. Based on the same calculations used during the war, the [[Federal Communications Commission]] (FCC) arranged frequency allocations for the new VHF and UHF channels to avoid interference between stations. To everyone's surprise, interference was common, even between widely separated<!--in distance, or frequency?--> stations. As a result, licenses for new stations were put on hold in what is known as the "television freeze" of 1948.{{sfn|Stecker|1960}}

[[Bell Labs]] was among the many organizations that began studying this effect, and concluded it was a previously unknown type of reflection off the [[tropopause]]. This was limited to higher frequencies, in the UHF and microwave bands, which is why it had not been seen prior to the war when these frequencies were beyond the ability of existing electronics. Although the vast majority of the signal went through the troposphere and on to space, the tiny amount that was reflected was useful if combined with powerful transmitters and very sensitive receivers. In 1952, Bell began experiments with [[Lincoln Labs]], the MIT-affiliated [[radar]] research lab. Using Lincoln's powerful microwave transmitters and Bell's sensitive receivers, they built several experimental systems to test a variety of frequencies and weather effects. When [[Bell Canada]] heard of the system they felt it might be useful for a new communications network in [[Labrador]] and took one of the systems there for cold weather testing.{{sfn|Stecker|1960}}

In 1954 the results from both test series were complete and construction began on the first troposcatter system, the [[Pole Vault (communications system)|Pole Vault]] system that linked [[Pinetree Line]] radar systems along the coast of [[Labrador]]. Using troposcatter reduced the number of stations from 50 [[microwave relay]]s scattered through the wilderness to only 10, all located at the radar stations. In spite of their higher unit costs, the new network cost half as much to build as a relay system. Pole Vault was quickly followed by similar systems like [[White Alice Communications System|White Alice]], relays on the [[Mid-Canada Line]] and the [[DEW Line]], and during the 1960s, across the Atlantic Ocean and Europe as part of [[NATO]]'s [[ACE High]] system.