Editing Chain Home (section)

===Prior experiments===
From the earliest days of [[radio]] technology, signals had been used for navigation using the [[radio direction finding]] (RDF) technique. RDF can determine the bearing to a radio transmitter, and several such measurements can be combined to produce a [[radio fix]], allowing the receiver's position to be calculated.<ref>{{cite web |title=Federal Standard 1037C, Glossary of Telecommunication Terms |year=1996 |website=General Services Administration |url=http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |access-date=25 May 2015 |archive-date=2 March 2009 |archive-url=https://web.archive.org/web/20090302235918/http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |url-status=dead }}</ref> Given some basic changes to the broadcast signal, it was possible for the receiver to determine its location using a single station. The UK pioneered one such service in the form of the [[Orfordness Beacon]].<ref>{{cite book |first1=B. |last1=Sitterly |first2=D. |last2=Davidson |url=http://www.loran-history.info/downloads/MIT-Radiation-Lab-Series-V4-Long-Range-Navigation-LORAN.pdf |title=The LORAN System |publisher=McGraw Hill |date=1948 |page=4 |access-date=8 August 2016 |archive-date=25 September 2012 |archive-url=https://web.archive.org/web/20120925163857/http://www.loran-history.info/downloads/MIT-Radiation-Lab-Series-V4-Long-Range-Navigation-LORAN.pdf |url-status=dead }}</ref>

Through the early period of radio development it was widely known that certain materials, especially metal, reflected radio signals. This led to the possibility of determining the location of objects by broadcasting a signal and then using RDF to measure the [[Bearing (navigation)|bearing]] of any reflections. Such a system saw patents issued to Germany's [[Christian Hülsmeyer]] in 1904,<ref name=bauer>{{cite book |last=Bauer |first=Arthur |title=Christian Hülsmeyer and about the early days of radar inventions |publisher=Foundation Centre for German Communications and Related Technologies |url=http://aobauer.home.xs4all.nl/Huelspart1def.pdf |date=15 January 2005}}</ref> and widespread experimentation with the basic concept was carried out from then on. These systems revealed only the bearing to the target, not the range, and due to the low power of radio equipment of that era, they were useful only for short-range detection. This led to their use for iceberg and collision warning in fog or bad weather, where all that was required was the rough bearing of nearby objects.<ref name=bauer/>

The use of radio detection specifically against aircraft was first considered in the early 1930s. Teams in the UK, US,{{sfn|Bowen|1998|p=6}} Japan,<ref>{{cite book |first= Shigeru |last=Nakajima |chapter=The history of Japanese radar development to 1945 |pages=245–258 |title=Radar Development to 1945 |editor-first=Russell |editor-last=Burns |publisher=Peter Peregrinus |year=1988 |isbn= 978-0863411397}}</ref> Germany<ref name=holl>{{cite web|author=Hollmann |url=http://www.radarworld.org/germany.html |title=Radar Development in Germany |publisher=Radarworld.org |access-date=10 February 2013}}</ref> and others had all considered this concept and put at least some amount of effort into developing it. Lacking ranging information, such systems remained of limited use in practical terms; two angle measurements could be used, but these took time to complete using existing RDF equipment and the rapid movement of the aircraft during the measurement would make coordination difficult.<ref name=holl/>