An old-fashioned, but reliable, TDR for general use. Using a CRT and some low-tech controls, this TDR still does a great job. It is not really suitable for field use unless you have a lot of cables to check from a central location, as it does not have battery power. It will operate from a 22-28 VDC external power supply, which means it can be operated with an external battery pack, but the coaxial power connector is recessed almost 2" in the rear panel and is difficult to reach. As with most CRT instruments, the condition of the CRT display makes a big difference in performance. My unit is in pretty good condition and seems fairly accurate. Distances to faults are measured by deflecting the scan raster to bring the fault to a baseline on the reticle. The distance is then read from the mechanical numeric knob.

This is the unit I use when I'm first training someone to use a TDR. Since it responds to cable changes immediately, you can demonstrate what happens when you separate conductors, cut conductors, and otherwise manipulate conductors and cable. It also makes it much easier to visualize how a TDR works.

Like many TDRs, the 1401e was intended for use by telephone service technicians. It is battery-powered and designed for outdoor use. It uses an LCD display to show test results. Two cables or pairs can be tested simultaneously and the unit comes with two pairs of test leads. The 1401e also has a serial output that allows you to capture traces and test information to electronic files on your laptop or other computer. This unit performs pretty well and I use it on a regular basis.

This is the unit I carry in my car, though the batteries are getting a bit weak and I usually have to charge it for 30 minutes or so or connect it to a battery when I need to use it.

Again, this unit is designed for telephone technicians. It has quite a few features you don't find on most TDRs...test tone generation, telephone loop measurements, Volt-Ohmmeter functions, and so forth. The membrane buttons on the front of the unit are limited and you have to "cruise around" in the menus quite a bit to get a feel for everything it can do. It uses an internal 6-volt lead-acid battery that can be charged through a coaxial power connector on the front panel. The case is made of very heavy leather with a ring for hanging it at a convenient location. The unit seems to be pretty accurate on the cables I've tested, especially the functions that measure distance to a short circuit on two conductors. (This is hard to do, but this unit gets it to within a few feet.) I wish it had a serial data port, though.

This unit generally stays in the office. Since you can't compare two pairs in a cable simultaneously, this is not as useful in the field as the Canoga-Perkins unit.

While it's a little large, the Tektronix combines many nice features. It's built into a nice solid carrying case with locking cover. The display is an LCD that is very easy to read. The unit will work on internal batteries or on external power. Controls and menus are clear and easy to use. There is an option bay that allows you to add a printer, a parallel printer port, or a serial data port. This is an excellent TDR to learn on.

I guess this is a TDR, but only in the sense that a frequency counter can be considered an oscilloscope. Don't get me wrong, the Triplett unit is extremely helpful in identifying faults in cables and is quite accurate. But there's no substitute for viewing the test results showing the cable "profile" on a real TDR, where you can tell so much about the condition of the cable and what devices are connected to it. This is a basic unit that allows you to select a cable type (or enter the V of P manually) and then test a cable. The results are basically an alphanumeric display of cable length or the distance to the fault. In a structured cabling environment, this is pretty helpful, but it is not so helpful sometimes in the real world where the cable is old or unknown.

This unit stays in the office and is not used very frequently.