Hi Folks

RE:TDR Several years ago (1971) I worked at a Hospital in New York. They had a coax cable going up 21 stories to an antenna on the roof for WWV time. The Coax was damaged and stopped working. I used a pulse generator and a scope to shoot a pulse up the line. I then got the "round trip time" and divided by 2. I then used .86 as a velocity factor and calculated the exact distance to the short.

1. You need to terminate the pulse gen with the same impedance as the line, in my case (RG-8) was 50 ohms.
2. Fire the scope trace at the instant the pulse gen fires. You will see the initial pulse on the left.
Ste the scope time to recieve the reflected pulse.
3. Figure 300,000,000 meteres per second times the "Velocity factor", for me and using RG8 cable was .86 or "86" percent.
4. Use very short pulse width. The pulse travels several feet(meteres) per nanosecond.

About 5 years ago I needed to check some 75 ohm video lines. I used a "555" timer to generate the pule. It worked great.
Hope this helps.... Tom