The frequency range (since modern DTF measurements are usually FDR - frequency domain reflectometry) is user selectable. Clearly you would want a frequency range that covers the frequencies that would be used in your system, but there's also a tradeoff between frequency range and distance : greater frequency ranges show more detail, but decrease max distance. I discuss all of this in the upcoming presentation "Understanding VNAs - Distance to Fault Measurements", so please stay tuned!
Similar, but not the same. TDR (time domain reflectometry) basically sends a pulse and then determines how long it takes for that pulse to be reflected back from the other end of the cable (which is ideally open or short). Most modern analyzers use FDR (frequency domain reflectometry), where the analyzer sweeps a frequency range and then uses an inverse fast Fourier transform to convert the frequency domain reflections into the time domain (and therefore into distances). FDR has many, many advantages over TDR for this application, and my upcoming presentation "Understanding VNAs - Distance to Fault Measurements" discuses these differences.
What is the Freq that is used when measuring distance to fault?
The frequency range (since modern DTF measurements are usually FDR - frequency domain reflectometry) is user selectable. Clearly you would want a frequency range that covers the frequencies that would be used in your system, but there's also a tradeoff between frequency range and distance : greater frequency ranges show more detail, but decrease max distance. I discuss all of this in the upcoming presentation "Understanding VNAs - Distance to Fault Measurements", so please stay tuned!
Is this measuremt similar to TDR?
Similar, but not the same. TDR (time domain reflectometry) basically sends a pulse and then determines how long it takes for that pulse to be reflected back from the other end of the cable (which is ideally open or short). Most modern analyzers use FDR (frequency domain reflectometry), where the analyzer sweeps a frequency range and then uses an inverse fast Fourier transform to convert the frequency domain reflections into the time domain (and therefore into distances). FDR has many, many advantages over TDR for this application, and my upcoming presentation "Understanding VNAs - Distance to Fault Measurements" discuses these differences.