Hi Alan -

Reflections measured by a TDR are caused by physical impedance
discontinuities. Virtual impedances are defined by the superposition
of forward and reflected voltages in the steady state. Pulsed systems
offer the ability to study the transient effects of a system by
viewing reflections caused only by changes in the characteristic
impedance of the transmission line. Since TDR doesn't use CW (not to
be confused with Morse Code) it does not operate under steady state
conditions and can therefore neither prove nor disprove the claim for
reflections from virtual impedances.

73, Jim AC6XG

Yes, I had a bit of LNBF (Late Night Brain Fade) when I threw in the
rotary joint example.
What I was trying underline was that there will be a real reflection at
the point where a stub is attached - simply because it becomes a
discontinuity in the TL. A TDR can show this but of course, I agree that
a single pulse won't see the same discontinuity as a CW.
So how does one prove or disprove the existence of a real reflection
from a virtual discontinuity?
Alan