Overdrive Recovery
The
is due to skin effect loss in the longer cable. What is
total cable delay is only 5
At
loss is still 0.02%.
This experiment shows
importance
of using a short cable to test overdrive
A second surprise is that skin
loss disappears
completely (after
two cable delays) when one end is unterminated.
To observe
use the short cable again, and
1
input impedance on
the llA34. Insert a
attenuator between the cable and the pulse generator to
improve the reverse termination and to provide the same amplitude signal as
before. Observe the
and
again. Even at 0.1% per
division the skin effect loss is hard to detect without
forward termination.
The reason for this
the skin effect loss is an increase in the
series resistance of the cable.
voltage drop. see
23.
Without current,
cable develops no series
Figure
Overdrive recovery using long (top) and short
cables
unterminated Traces are offset
divisions and the photograph is a double
exposure.
2-6
