Tektronix 11A32 User's Reference Manual page 20

Operating the 11A32 in 11300 -series mainframes
Figure 2-2. Overdrive recovery using long (top) and short (bottom) cables
terminated in 50 Q. Traces are offset two divisions and the photograph is a double
exposure.
The waveform change is due to skin effect loss in the longer cable. What is
surprising is that the skin effect loss persists for over 200 ns even though the
total cable delay is only 5 ns. At 400 ns the loss is still 0.02%.
This experiment shows the importance of using a short cable to test overdrive
recovery.
A second surprise is that skin effect loss disappears almost completely (after two
cable delays) when one end is unterminated.
To observe this, use the short cable again, and select 1 MQ input impedance on
the 11A32. Insert a 2X attenuator between the cable and the pulse generator to
improve the reverse termination and to provide the same amplitude signal as
before. Observe the response and change cables again. Even at 0.1% per division
the skin effect loss is hard to detect without the forward termination. The reason
for this is that the skin effect loss is an increase in the effective series resistance
of the cable. Without current, the cable develops no series voltage drop. See
Figure 2-3.
2-6
11A32 User Reference Supplement