1000BASE-T/100BASE-TX/10BASE-T Physical Layer Compliance Tests Manual
Intel Confidential 25
1000BASE-T MDI Return Loss
5. Measure a 50-ohm resistor standard when the calibration is completed. Its return loss should
be 9.54 dB ±0.05 dB. If the 50-ohm standard measures outside of that tolerance, check the
cable, connection points and other calibration standards, and repeat the calibration process.
6. Connect fixture 40.8.3.1.C to the UUT’s RJ-45 and measure the LAN interface’s return loss on
channel A.
7. Repeat the calibration and measurement process for the remaining three channels.
Calculating Theoretical Return Loss
To solve for theoretical return loss given known impedances:
Z
transmitter
Balanced output impedance of the balun (for example, 100 Ω).
Z
load
The impedance of any load connected to the output of the balun.
RL_in_dB
For any load on the 100 Ω output of the balun, this simplifies to:
RL_in_dB
For a 50 Ω load with the 100 Ω output of the balun, this becomes:
RL_in_dB
which simplifies to:
RL_in_dB = 20log
10
3 = 20 * 0.477 = 9.54 dB
20
Z
transmitter
Z
load
+
Z
transmitter
Z
load
–
--------------------------------------------------log=
20
100Ω Z
load
+
100Ω Z
load
–
------------------------------------log=
20
100Ω 50Ω+
100Ω 50Ω–
----------------------------------log=
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