Editing Gee (navigation) (section)

=== Prerequisite work ===

The basic idea of radio [[hyperbolic navigation]] was well known in the 1930s, but the equipment needed to build it was not widely available at the time. The main problem involved the accurate determination of the difference in timing of two closely spaced signals, differences in milli- and microseconds.{{sfn|Blanchard|1991|p=297}}

During the 1930s, the development of [[radar]] demanded devices that could accurately measure these sorts of signal timings. In the case of [[Chain Home]], transmission aerials sent out signals, and any reflections from distant targets were received on separate aerials. An [[oscilloscope]] (or oscillograph as it was known in the UK){{sfn|Blanchard|1991|p=297}} was used to measure the time between transmission and reception. The transmitter triggered a [[time base generator]] that started a "trace" moving quickly along the oscilloscope display. Any received signals caused the beam to deflect downward, forming a ''blip''. The distance that the trace had moved from the left side of the display could be measured to accurately calculate the difference in time between sending and receiving, which, in turn, could be used to calculate the [[slant range]] to the target.{{sfn|Blanchard|1991|p=297}}

Radar can also be used as a navigation system. If two stations are able to communicate, they could compare their measurements of the distance to a target, and use basic [[trilateration]] to determine the location. This calculation could then be sent to the aircraft by radio. This is a fairly manpower-intensive operation, and while it was used by both the British and Germans during the war, the workload meant it could generally only be used to guide single aircraft.<ref>{{Cite journal | doi = 10.1049/ji-3a-1.1946.0133| title = Oboe: A precision ground-controlled blind-bombing system| journal =  Journal of the Institution of Electrical Engineers - Part IIIA: Radiolocation| volume = 93| issue = 2| pages = 496–511| year = 1946| last1 = Jones | first1 = F. E. | author-link1 = Francis Jones (physicist)}}</ref>{{sfn|Jones|1978|pp=172–178}}