Tektronix 1502C User Manual
Appendix D: Application Note
D–2
1502C MTDR User Manual
Relationships
Z
O
= (138 /
pκ
)*
(log
10
D / d) for coaxial cable
%
=
r
*
100
VSWR = (1 +
r) + (1 – r) for the case where VSWR is the same for all
frequencies
c
= 30 cm / nanosecond = 0.984 ft / ns
V
F
= 1 /
pκ
V
P
= 30 /
pκ cm / ns = 0.984 / pκ ft /ns
C
= 7.36
κ + (log
10
D / d)
L
= 140 log
10
D / d
1 in
= 2.54 cm
1 ft
= 30.48 cm
1 m
= 3.28 ft
VSWR vs. Percent Reflected Voltage
To find the Voltage Standing Wave Ratio (VSWR), knowing the percent reflected
voltage (%), or vice versa, use the Frequency Domain Conversions section of the
slide rule (see Figure D–1).
voltage (%), or vice versa, use the Frequency Domain Conversions section of the
slide rule (see Figure D–1).
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)
1.04 VSWR = 2% REFLECTION
20% = 1.5 VSWR
Figure D–1: Slide Rule of VSWR vs. Percent Reflected Voltage
On the upper scale, locate the known value of VSWR (or %). Adjacent to that
point is the corresponding value for % (or VSWR). VSWR is the peak-to-valley
ratio of standing sine waves.
point is the corresponding value for % (or VSWR). VSWR is the peak-to-valley
ratio of standing sine waves.