Marcus Jenkins blogged about his TDR pulse generator build:
I saw an excellent YouTube video from Alan W2AEW and thought I’d have a go at making a prettier version of the tool myself. After all, checking 50 Ohm coax cables is a pretty common need for an amateur radio enthusiast.
Alan’s video says it all, but here’s a top-level overview. You feed a fast-edged pulse into one end of a coax cable and use your oscilloscope to measure the time it takes for the pulse to travel all the way to the other (unconnected) end, bounce, and come back. If you know the characteristics of the cable, you can calculate the length of the cable (or the distance from your measurement point to the first break in the cable). The circuit described in Alan’s video and this article makes such a fast-edged pulse.
With this setup you can measure the length of cable, find breaks in cable and also tell if your cable has become waterlogged. You can also characterise a sample of cable (assumed to not be broken, waterlogged, etc.).
Project info at Marcus’ blog.