10Base-T TD Circuit Impedance (Transmitter Return Loss)
1000BASE-T/100BASE-TX/10BASE-T Physical Layer Compliance Tests Manual
74
Intel Confidential
2. Adjust the spectrum analyzer to the following settings.
3. From the 10 BASE-T PHY Configuration Tests menu in gigconf.exe, select the Harmonic
Content: 1411.10.07 test.
4. Connect the CAT 5 cable to the UUT as shown above.
5. Perform a calibration on the S11, S-parameter, port and turn correction on.
6. 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.
Table 19-1. Analyzer Configuration for TD Circuit Impedance
Scope Parameters
Settings
Start Frequency
3 MHz
Stop Frequency
13 MHz
IF BW or Resolution BW
Lowest practical bandwidth supported by
equipment in the range of 100 KHz and
200 KHz.
Number of Points (Resolution)
Maximum for instrument (
≥
401)
Acquire
Average (if necessary)
Vertical Division
10 dB/division
Mode
Network Analyzer
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
=