Browse Prior Art Database

Sensitive Time Domain Reflectometer for Observing Multiple Reflections

IP.com Disclosure Number: IPCOM000083061D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Elliott, BJ: AUTHOR

Abstract

Commercial Time Domain Reflectometers (TDR) have limited sensitivity for observing small reflections, because of the intrinsic background reflections in the instrument itself. Described here is a modified TDR system which reduces, by subtraction, this intrinsic background pattern.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 60% of the total text.

Page 1 of 2

Sensitive Time Domain Reflectometer for Observing Multiple Reflections

Commercial Time Domain Reflectometers (TDR) have limited sensitivity for observing small reflections, because of the intrinsic background reflections in the instrument itself. Described here is a modified TDR system which reduces, by subtraction, this intrinsic background pattern.

Use is made of the ADD, STORE and SUBTRACT capabilities of a Signal Averager (SA) which monitors the replicated, audio-frequency output of the Sampling Oscilloscope (SO) that is used to observe a chosen "time window" on the transmission line, that carries the incident test step waveform and the reflected signals. To measure one or several small reflecting perturbations the SO output signal is stored and smoothed in the SA (ADD MODE) for a suitable time (typically 1 minute). Then, with the reflectors removed (by, for example, replacing the signal line with a length of precision line of the same characteristic impedance), the SO output is stored in SA for the same time but in the SUBTRACT mode. Now, provided the amplitude and particularly the time position stability of the SO are adequate, the SA displays the reflection pattern while the background cancels out. Also, the incoherent noise in S0 is simultaneously smoothed by SA thus affording greater sensitivity.

Good time stability is essential, otherwise the effect of the background is exaggerated. To correct for the intrinsic SO time drift it is only necessary to trig...