1000BASE-T/100BASE-TX/10BASE-T Physical Layer Compliance Tests Manual
Intel Confidential
105
Test Fixture Construction Tips and Information
Appendix B: Test Fixture Construction
Tips and Information
B.1
General Test Fixture Construction Guidelines
1. Unless otherwise specified, always use solid 22 AWG wire or solid 24 AWG wire. Ideally, the
wires for differential test fixtures can be taken from a scrap piece of high-quality, solid-
conductor, Category 5 cable.
— Keep both sides of each differential pair balanced.
— Keep lead lengths the same on each side of each differential pair.
— Route both leads, within a differential pair, next to each other.
— Center resistors and other components that are soldered between differential pairs
between the pair of wires or traces.
— Match values and lengths as closely as possible when two of same value components are
shown in an illustration.
2. Always keep lead lengths as short as possible, without violating the rules listed under the
second bullet in guideline 1 (above).
3. If the differential leads on a test fixture need to be more than one or two inches long and if
possible, twist the two leads (of the differential pair) around each other.
4. Tightly toleranced components should be used wherever possible.
— When using an ohm meter to “cherry-pick” best resistor values, subtract the meter’s lead
resistance from the measured resistance values.
— As a starting point, resistors should be 1% or better tolerance. Use an ohm meter, and
select resistors that are within 0.1
Ω
of the required value. When a pair of the same value
is used, they should be matched within 0.1
Ω
before soldering, and within 0.2
Ω
after
soldering. If an illustration shows a tighter tolerance, follow the illustration.
— Capacitors should be 5% or better tolerance. When a pair of the same value is used, they
should be matched as close as possible. If an illustration shows a tighter tolerance, follow
the illustration.
— Inductors should be 10% or better tolerance. When a pair of the same value is used, they
should be matched as close as possible. If an illustration shows a tighter tolerance, follow
the illustration.
5. Each test fixture and cable should be labeled with its function and identity.
6. When using twisted pair Ethernet cable to build test fixtures (or very short test cables), use
solid conductor Category 5 cable. The impedance is better controlled than Category 5 patch
cable and Category 3 cable. Also, solid conductor Category 5 cable has lower insertion loss.