   the mid-canada line, also known as the mcgill fence, was a line of radar stations across the "middle" of canada to provide early warning of a soviet bomber attack on north america. it was built to supplement the less-advanced pinetree line, which was located further south. the majority of mid-canada line stations were used only briefly from the late 1950s to the mid-1960s, as the attack threat changed from bombers to icbms; the early warning role passed almost entirely to the more capable dew line further north. ==history== ===impetus=== construction of the pinetree line had only just started when air planners started to have concerns about its capabilities and siting. by the time it detected a potential attack by jet-powered aircraft, there would be little time to do anything before the attack reached canadian or northern u.s. cities. additionally the pinetree systems used "old" pulse-based radars that were fairly easy to jam and were unable to detect targets close to the ground due to scattering. although expensive in terms of fuel use, it would be possible for soviet bombers to evade detection by flying lower. they would eventually be seen as they approached the stations, but possibly so late that there would be no possibility of intercepting them. this made the pinetree line's usefulness somewhat suspect even before it had become operational. dr. w.b. lewis, head of the aecl chalk river laboratories and former chief superintendent of the uk telecommunications research establishment (tre) had proposed to the defence research board (drb) a doppler radar system that avoided both of these problems. known today as a "forward scatter bistatic radar", it used two antennas, a transmitter and receiver, separated by about 60&nbsp;km. any aircraft flying between the antennas would be detected when it entered the beam, causing the received signal to change. since the system relied on the speed of the aircraft to "shift" the frequency due to the doppler effect, the radar could be aimed at static objects like the ground; although a signal would be reflected and received, since the ground is not moving this signal has no frequency shift and can be easily filtered out. another advantage of the system is that it requires much less power to operate effectively. a conventional pulse radar spends most of its time turned off, listening for the reflections of it
Aerospace_Defense_Command CanadaaUnited_States_relations Closed_facilities_of_the_United_States_Air_Force Cold_War_military_history_of_Canada Radar_networks Radar_stations_of_the_United_States_Air_Force Royal_Canadian_Air_Force