[fancyketchup]

Aside from the things camperbob identified, this is pretty neat. The tricky parts are getting the pulse generator right (you want a sharp leading edge and flat top, with no ringing) and having an oscilloscope with a flat response well into the GHz range.

One solution to the second challenge is to home-brew a sampling adapter, like this one from 2000[1]. This is a good fit for TDR because of two factors inherent in the TDR process: a) it is repetitive, so the usual drawbacks to "sub-nyquist" sampling don't apply; and b) you have ready access to a pre-trigger, so it is easy to see the leading edge of the signal of interest.

The first challenge requires a lot of cleverness or access to expensive test equipment.

[1] http://electronicdesign.com/boards/1-ghz-sampling-oscillosco...

[CamperBob2]

That's pretty neat. If you built a similar circuit with off-the-shelf parts available today, it could be good for 8 GHz or so.