Figure 15: Tdr Step And Reflection (50 Ω Line Terminated In 75 Ω) - Tektronix 80E02 User Manual

50 Ω line
Figure 15: TDR step and reflection (50 Ω line terminated in 75 Ω)
80E00 Electrical Sampling Modules User Manual
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 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 0.2ρ (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:
1
Z Z
L O
1
50 1 0.2
Z
L
1–0.2
Notice that the instrument automatically performs this calculation and displays
the impedance (Ω) or reflection coefficient (ρ) for each cursor and the difference
between the two cursors.
75 Ω line
75 Ω
50 Ω line
Reference
75 Ω line
31