Operator Troubleshooting
1503C MTDR User Manual
D–3
Return Loss (dB) vs. Percent Reflected Voltage
To find return loss in decibels, knowing the % (or vice versa), use the bottom scale
of the Frequency Domain Conversions section of the slide rule (see Figure AN–2).
0
2
4
6
8
10
12
14
16
18
20 %
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35 1.40 1.45 1.50 VWSR
80
75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
0
.01 .02.03 .05 .10
.2 .3
.5 .7 1.0
2 3
5 7 10
20
50
100 %
30
SINGLE
RESISTIVE
DISCONTINUITY
ONLY
RETURN LOSS
(IMPULSE ONLY)
1% REFLECTION = 40 dB RETURN LOSS
Figure D–2: Slide Rule of Return Loss vs. Percent Reflected Voltage
Locate the known value of % or the known dB return loss, then locate the value of
the corresponding expression on the adjacent scale.
NOTE
. Only the impulse mode of Time-Domain Reflectometry can be accurately
expressed in terms of return loss.
A narrow impulse will be attenuated by losses in the cable and reflections will be
attenuated likewise.
As with measurements on VSWR, there is only a simple mathematical relationship
between reflection measurements using sine waves and reflection measurements
using pulses when one resistive discontinuity is the whole cause for the sizable
reflections.
Percent Reflected Voltage vs. Characteristic Line Impedance
(50 or 75 Source)
To find the characteristic impedance of a line, or section of a line, knowing the
reflection coefficient or the %, you should first know the impedance of the pulse
generator. It should be as close as possible to the nominal impedance of the line and
should be connected to the line through a length of cable having the same impedance
as the source. Select the side of the slide rule that corresponds to the source
resistance (R
S
) of the generator used, then select the longest scale as follows:
Summary of Contents for 1503C
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Page 92: ...Appendix A Specifications A 6 1503C MTDR User Manual...
Page 104: ...Appendis B Operator Performance Checks B 12 1503C MTDR User Manual...
Page 122: ...Glossary Glossary 6 1503C MTDR User Manual...
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