Tektronix 8.00E+04 User Manual
Reference
80E00 Electrical Sampling Modules User Manual
31
Figure 15 shows a typical waveform from a Tektronix CSA8200 mainframe
equipped with an 80E04 TDR/sampling module. In this case, the instrument is
connected through a 50
equipped with an 80E04 TDR/sampling module. In this case, the instrument is
connected through a 50
Ω coaxial cable to a 75 Ω device under test. The incident
step is about 2 divisions in amplitude, and the reflection from the device under
test is about 0.4 division high. These numbers equate to a reflection coefficient
of 0.2
test is about 0.4 division high. These numbers equate to a reflection coefficient
of 0.2
ρ (0.4 divisions divided by 2 divisions). Plugging the known 50 Ω level
and the reflection coefficient into the above equation yields the 75
Ω value:
Z
L
= Z
O
Ꮛ
1
+
1
−
Ꮠ
Z
L
= 50
Ꮛ
1
+ 0.2
1–0.2
Ꮠ
= 75 Ω
Notice that the instrument automatically performs this calculation and displays
the impedance (
the impedance (
Ω) or reflection coefficient (ρ) for each cursor and the difference
between the two cursors.
75
Ω line
50
Ω line
75
Ω line
50
Ω line
Figure 15: TDR step and reflection (50
Ω line terminated in 75 Ω)