for some weeks now, I'm glad to have
an Agilent 54754A based TDR in my lab to analyze
PCB structures. On one PCB I analyzed the transition
from the PCB wave guide into an RF connector and
found a positive bump indicating a more or less
inductive behaviour for this section.
allows the positioning of two markers and calculates
the excessive reactance in between these markers.
This is really valuable to determine the correct
compensation, or to find a way to reduce the excess.
For the section of interest I get round about 630nH
of inductance if I place the markers left and right
of it. So far so good.
Questionable to me is
the behaviour that I see if I move the markers closer
together to cover only a part of this inductive
discontinuity. At a certain point, when the left
quarter of the discontinuity is outside the markers
the display jumps over and starts showing fF and
further in pF values. I'd like to make clear, that
all the curve in between the markers is clearly >50Ohm.
I have started a support case and received a number
of AppNotes on TDR measurements, but no clear statement
yet. The system is in the market for quite some
time and I checked I use the latest software from
I will try to make screenshots visible here
in this thread to illustrate the description and
I'm still searching the solution in between screen
an chair fo course.
I wonder if somebody has a similar system
available, or has a good explanation for this observation.
Many Thanks, Thomas.