Tektronix 1502C Manual Do Utilizador
Appendix D: Application Note
1502C MTDR User Manual
D–3
NOTE. The relationship between % holds only when the loss is a single imped-
ance discontinuity with negligible capacitive or inductive components (e.g., a
75
ance discontinuity with negligible capacitive or inductive components (e.g., a
75
W termination at the end of a 50 W cable). The VSWR must be essentially the
same for all sine-wave frequencies.
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
D–2).
scale of the Frequency Domain Conversions section of the slide rule (see Figure
D–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.
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.
expressed in terms of return loss.
A narrow impulse will be attenuated by losses in the cable and reflections will be
attenuated likewise.
attenuated likewise.
As with measurements on VSWR, there is only a simple mathematical relation-
ship between reflection measurements using sine waves and reflection measure-
ments using pulses when one resistive discontinuity is the whole cause for the
sizable reflections.
ship between reflection measurements using sine waves and reflection measure-
ments using pulses when one resistive discontinuity is the whole cause for the
sizable reflections.