Notes
a)
Note that a positive dB value (or mrho value <1000) indicates a return loss (i.e. the
reflection is smaller than the transmit pulse). Under certain conditions it is possible for the
reflection to have a greater voltage amplitude than the transmit pulse. In this case the dB
value will be shown as negative and the mrho figure will be greater than 1000.
b)
If the return loss is outside the range of the instrument then XXX dB and XXX m
ρ
will be
displayed.
c)
The position of the cursor prior to pressing dBRL is important as the signal level at that
point is used as the zero reference. Be sure to place the cursor on the flat section of the
trace just before the pulse.
d)
When measuring very small reflections switching the filter in can improve the performance
of the return loss function.
7.9.2
MEASUREMENT OF PULSE ATTENUATION
This should be determined using a sample length of the same type of cable as that under test.
Connect the cable directly to the T631 with the end shorted or open.
Measure the Return Loss and the length. Since the cable ends provides a 100% (0dB)
reflection, the loss measured is entirely due to the pulse attenuation.
T631 OPERATING MANUAL
37
Radiodetection Ltd. 00901209-6
