インピーダンスの測定 - DTX CableAnalyzer

Enterprise links, of which the DTX CableAnalyzer is designed to test, are typically less than 100 m (328 ft). Measuring the characteristic impedance of an enterprise link is arguably not a valid measurement. That's because your characteristic impedance measurement will be dominated by the remote unit's termination. For this reason, it is not a field test requirement in any of the enterprise cabling standards.

What is found within the enterprise cabling standards is Return Loss. This is the difference between the power of a transmitted signal and the power of the signals reflected back on the same pair. The signal reflections are caused by variations in the cable’s impedance. This is a more meaningful measurement of the link's impedance properties than a characteristic impedance measurement.

However, the DTX CableAnalyzer does have the ability to measure impedance when selecting application standards such as 100BASE-TX and 1000BASE-T. The DTX CableAnalyzer will look at the impedance of the cable at a point approximately 4 m (13 ft) from the tester. If the link is less than 4 m (13 ft), the impedance for the link will be reported as unknown. No PASS/FAIL is provided for this test; it is recorded with an "i" indicating "information only".

The stated accuracy of this measurement is: ± (5 Ω + 5 % of ⏐100 Ω – Measured⏐)