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Sensitive Time Domain Reflectometer for Observing Complex Reflections

IP.com Disclosure Number: IPCOM000082920D
Original Publication Date: 1975-Feb-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Elliott, J: AUTHOR

Abstract

Time Domain reflectometry (TDR) is a powerful technique for such purposes as: matching and reducing reflections in transmission systems; studying and measuring electrical properties of materials; locating faults in transmission lines; and studying, designing and optimizing the mounting of circuit elements that are part of transmission systems. Commercial TDR systems have limited sensitivity to small reflections and, whereas they can differentiate between reactive reflectors alone (shunt L or C, series L or C) and resistive reflectors alone, they cannot, however, measure the individual components of complex loads (shunt R with shunt C, series L with series R, etc.)

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Sensitive Time Domain Reflectometer for Observing Complex Reflections

Time Domain reflectometry (TDR) is a powerful technique for such purposes as: matching and reducing reflections in transmission systems; studying and measuring electrical properties of materials; locating faults in transmission lines; and studying, designing and optimizing the mounting of circuit elements that are part of transmission systems. Commercial TDR systems have limited sensitivity to small reflections and, whereas they can differentiate between reactive reflectors alone (shunt L or C, series L or C) and resistive reflectors alone, they cannot, however, measure the individual components of complex loads (shunt R with shunt C, series L with series R, etc.)

Described is a method that allows simultaneous measurement of the elements of complex unknowns and has greatly increased sensitivity. These virtues allow improved performance and applicability over commercial systems, in general, and, in particular, yield a powerful method for the measurement of the properties of materials - particularly those samples with very small dimensions and small values of electrical parameters. This feature is important with today's trend towards microminiaturization.

The basic scheme is to use "Lock-In" detection (LI) to examine the reflection pattern from a commercial TDR, after the sampling processing in the latter (channel A). This way the replicated, audio-frequency signal from the TDR can be Lock-In analyzed so as to sort out very small signals from below the noise (hence the high sensitivity), and use the amplitude and phase selectivity of the LI to sort out, from the reflected signal, the resistive and reactive components of the unknown reflecting discontinuity.

These concepts are illustrated with the aid of Figs. 1, 2 and 3 and...