Option 100 Fault Location and SRL 1-9
Introduction and Measurement Theory
Cable Impedance and Structural Return Loss Measurement Theory
Method 3 (Z-average normalization). The mathematics for the
Z-average normalization as performed by the analyzer are shown below.
Equation 4
Z
0
= system impedance, 50 or 75 Ω
Equation 5
Equation 6
In Equation 4, ρ(ω) is the reflection coefficient from the analyzer
measured at each frequency and Z
in
(ω) is the impedance of the cable for
that measured reflection coefficient.
The calculation of Z
cable
, described in Equation 5, is the Z-average
impedance of the cable over the number of frequency points (N). The
default frequency range is approximately 5 MHz to 200 MHz. This
frequency range is chosen because mismatch effects of the input
connector are small. High quality connectors must be used if the average
impedance is calculated over a wider span. The frequency range for this
calculation can be modified by using the softkey
in the connector model menu to change the cable impedance cutoff
frequency.
Equation 6 is the structural return loss for the cable. This calculation
can be done by the analyzer or an external computer.
Z
in
ω() Z
0
1 ρω()+()
1 ρω()–()
--------------------------
×=
Z
cable
Z
in
ω
n
()
n 1=
N
∑
N
---------------------------------=
ρ
SRL
ω()
Z
in
ω() Z
cable
–
Z
in
ω() Z
cable
+
--------------------------------------=
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