100Base-TX Receiver Return Loss
1000BASE-T/100BASE-TX/10BASE-T Physical Layer Compliance Tests Manual
64
Intel Confidential
2. Reset network analyzer to factory default settings.
3. Select the S11 measurement parameter if necessary.
4. Connect the test equipment and UUT as shown in
Figure 16-1. Test Setup for 100BASE-TX Receiver Return Loss
5. Disconnect the test fixture, but keep it close to the UUT.
6. Perform a 1-port, full calibration with an open, short, and 100
Ω
load by connecting the
calibration fixture to the RJ-45 connection in place of the UUT.
Note:
It is important to try to keep the test setup as close as possible to its original position to achieve the
best calibration.
7. Test the calibration by connecting the 50
Ω
load and confirming the results are close to the
theoretical value of 9.54 dB. Also verify that the open and short loads produce the expected
results.
8. From the 100 BASE-TX PHY Configuration Tests menu in gigconf.exe, select the RX Return
Loss: 9.2.2 test.
9. Reconnect the test fixture to the UUT.
The resulting network analyzer display should be similar to
UUT
RJ-45
Network/Spectrum
Analyzer
Cat-5 Cable
50 Ohm BNC Cable
RJ-45
50
Ohms
100
Ohms
Transmission/Reflection Test Set
50 Ohm Termination on
unused balun
100
Ohms
50
Ohms
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
100
Ω
Z
load
+
100
Ω
Z
load
–
------------------------------------
log
=
20
100
Ω
50
Ω
+
100
Ω
50
Ω
–
----------------------------------
log
=