Pole Vault (communications system)

St. Anthony was a typical mid-line Pole Vault system with transmit and receive antennas facing the next stations to the north and south. A Pinetree radome is visible in the background.

Pole Vault was the first operational tropospheric scatter communications system. It linked radar sites and military airfields in Greenland and eastern Canada by telephone to send aircraft tracking and warning information across North America. The line stretched from Thule Air Force Base in northern Greenland, to Baffin Island and then along the eastern coast of Labrador and Newfoundland to St. John's for connection into existing commercial telecommunications networks.

The system was first proposed in 1952 to send information along the isolated Pinetree Line stations on the Labrador coast. This led to an initial proposal to use a microwave relay system, a relatively new technology at the time. The network would require 50 relays, many of them in the wilderness. Bell Canada won the contract to build the system after the USAF was convinced they could handle the job.

Before construction began, Bell learned of experiments with long-range troposcatter systems being carried out in the US by Bell Labs and MIT Lincoln Laboratory. These were limited by power, not the line of sight, greatly extending the range between stations. They borrowed one system for testing in Labrador and by late 1954 had successfully demonstrated links of several hundred kilometres. This allowed them to reduce the network to only 10 stations, all at the existing radar sites.

The first message was sent on the network on February 14, 1955, but due to the extension to Thule and upgrades to carry more lines at the behest of the USAF it was not finally handed over until December 31, 1956. The system was used operationally until 1975 when it was replaced by newer systems including ionospheric skip systems, underwater cables and, eventually, satellite communications.