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.A TDR cannot detect small performance changes at RF frequencies, so it is not possible to monitor performance degradation between maintenance intervals with these traditional methods.Without FDR techniques, the “Fix after Failure” philosophy becomes the only alternative.FDR is a transmission line fault isolation method which precisely identifies signal path degradation for coax and waveguide transmission lines.Although the acronyms are similar, FDR technology is different from traditional Time Domain Reflectometry (TDR) techniques.For example, connector corrosion can be detected early and weather seals replaced before moisture destroys expensive cables.
Lightning can sever a portion of the antenna or damage the in-line lightning arrestor.
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.
Thus, the actual return loss versus distance is shown in Figure 1. Distance TEST TIP Cable manufacturers specify the propagation velocity (Vp) of cables.
Anritsu Handheld products incorporating DTF include tables of many standard cables and waveguides to simplify DTF measurements. If this specification is not available, it can easily be determined by measuring a known length of cable.