Editing Time-domain reflectometer (section)

=== Variations and extensions ===
The equivalent device for [[optical fiber]] is an [[optical time-domain reflectometer]].

{{anchor|TDT}}'''Time-domain transmissometry''' ('''TDT''') is an analogous technique that measures the transmitted (rather than reflected) impulse. Together, they provide a powerful means of analysing electrical or optical transmission media such as [[coaxial cable]] and [[optical fiber]].

Variations of TDR exist. For example, [[spread-spectrum time-domain reflectometry]] (SSTDR) is used to detect intermittent faults in complex and high-noise systems such as aircraft wiring.<ref>Smith, Paul, [[Cynthia Furse|Furse, Cynthia]] and Gunther, Jacob. "Analysis of Spread Spectrum Time Domain Reflectometry for [http://livewiretest.com/analysis-of-spread-spectrum-time-domain-reflectometry-for-wire-fault-location/ Wire Fault Location] {{Webarchive|url=https://web.archive.org/web/20101231231446/http://livewiretest.com/analysis-of-spread-spectrum-time-domain-reflectometry-for-wire-fault-location/ |date=2010-12-31 }}." IEEE Sensors Journal. December, 2005.</ref> Coherent optical time domain reflectometry (COTDR) is another variant, used in optical systems, in which the returned signal is mixed with a local oscillator and then filtered to reduce noise.<ref>José Chesnoy (ed.), ''Undersea Fiber Communication Systems'', Elsevier Science, 2002, {{ISBN|0-12-171408-X}}, p.171 (COTDR)</ref>