Filter
Top Products
1502C MTDR User Manual
D–1
Appendix D: Application Note
Pulse Echo Testing of Electrical Transmission Lines
Using the Tektronix Time-Domain Reflectometry Slide Rule
Most people who make quantitative reflectometry tests or measurements should
find the Tektronix TDR Slide Rule helpful. Those new to the subject will find
the slide rule graphically summarizes a wealth of information on reflectometry.
H Voltage Standing Wave Ratio vs. Percent Reflected Voltage
H Return Loss, dB, vs. Percent Reflected Voltage
H Percent Reflected Voltage vs. Characteristic Line Impedance (for either 50 W
or 75 W source)
H Percent Reflected Voltage vs. Load Resistance (for either 50 W or 75 W
source)
H Characteristic Line Impedance or Load Resistance vs. Reflection Amplitude
(as seen on your TDR)
H Dielectric Constant vs. Velocity Factor
H Time vs. Short Distance in centimeters or inches (any dielectric)
H Time vs. Long Distances in meters or feet (any dielectric)
Terms and Symbols
R
S
Source Resistance of a signal generator
Z
S
Source Impedance of a signal generator
Z
O
Characteristic Impedance of a transmission line
Z
L
Load Impedance for a transmission line
R
L
Load Resistance for a transmission line
r Reflection Coefficient (rho): the ratio of incident to reflected voltage
mr Reflection Coefficient divided by 1,000 (millirho)
% Ratio of the incident voltage to reflected voltage multiplied by 100
VSWR Voltage Standing Wave Ration (peak-to-valley)
c Velocity of light in air
V
P
Propagation Velocity of a signal in a transmission line
V
t
Velocity Factor (fraction of the velocity of light)
κ Dielectric Constant
D Outer Diameter of the dielectric in a coaxial cable
d Diameter of the center conductor in a coaxial cable
L Inductance in nanoHenries (nH) per foot
C Capacitance in picoFarads (pF) per foot