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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Hi, > The ideal TDR signal would be a step voltage change (infinitely fast rise > time) from a zero-impedance source. Not so. Firstly, the pulse generator impedance should be closely matched to that of the cable. Any mismatch causes severe multiple reflections which are extremely hard to understand, and which masks reflections which you do want to see. Secondly, the step voltage change causes ringing due to inductance, and that again masks the real reflections. Best is to adjust the risetime to minimum ringing and maximum resolution. Resolution is a factor of the length of the cable, the bandwidth of the pulse, and the attenuation slope of the cable. > Analysis of the reflection would > reveal every electromagnetic aspect of the media that carries the signal. > The amplitude of the transmitted signal needs to be sufficiently great > to overcome attenuation along the signal path, returning with adequate > level so that measurements can be supported in the presence of system > noise. Agreed. > > Unless pulsing, recording and computing resources are severly limited, a > pulse sufficiently close to ideal should be used so that maximum > information can be derived from test data. Once key reflection > properties have been identified, economics probably will dictate > limitations on resources for widespread application. > Agreed, depending on your definition of ideal. For instance, on a balanced line, an unbalanced pulser output is almost useless, especially on longer cables. The pulser output must closely match the cable characteristics. Regards Johan Smit P.O.Box 4742 George East 6539 Rep of South Africa Tel/fax +27 44 8745533 Mobile (082) 8644914 smitjs@mweb.co.za