I spent a good part of my career as part of a team designing samplers,
step generators, TDR systems, and associated circuitry with rise times
down to a few ps. Among the projects I designed were two delay line
compensators which compensated for the distortion of a fast step by the
skin effect loss in transmission lines (one to 2 GHz bandwidth and the
other to 9, both to very high precision). These designs were used in
production Tektronix instruments. I also often helped the customer
support group with difficult TDR application problems, and I wrote and
taught several classes on TDR techniques. One of the many skills
necessary to succeed at this was to gain a very good understanding of
rise times, time constants, frequency responses, the relationships among
them, and the physical factors which influence them. From that
background, the discussion in this newsgroup seems to be taking place in
an alternate universe. I feel out of place there, so I'll leave it to
its usual and rightful inhabitants, and bow out.

Roy Lewallen, W7EL

Everything should be made as simple as possible, but not simpler.
-Albert Einstein