The FDR technique uses a swept RF signal instead of TDR DC pulses.FDR is far more sensitive than TDR and can precisely locate faults and degradation in system performance, not just DC open or short circuit conditions.This dual role of predicting future failure conditions and isolating existing problems makes DTF an important part of service and maintenance on transmission lines.DTF displays RF return loss or VSWR data versus distance.Thus, the actual return loss versus distance is shown in Figure 1. Distance TEST TIP Cable manufacturers specify the propagation velocity (Vp) of cables.
Preventative maintenance has another set of benefits even more important than cost. Overall quality is improved giving greater customer satisfaction.For the majority of transmission lines and antennas, the absence of DTF capability severely impacts the time to repair transmission lines and renders preventative maintenance procedures impractical.RF failure conditions at the top of a tower or through a bulkhead frequently are not measurable with traditional tools such as TDR and spectrum analyzers with tracking generators.The effects of poor connections, damaged cables, or faulty antennas are quickly identified.Since DTF automatically accounts for attenuation versus distance, the display accurately indicates the return loss or VSWR of the antenna.
The FDR measurement technique requires a swept frequency input to the transmission line.