As standards organizations progress in the development of test requirements and specification limits for Category 8 cabling components for frequencies up to 2 GHz, a recent white paper from Hitachi Cable USA, entitled Category 8 Cable Transmission Measurements, presents a comparative study between 4-port single wire measurements and 2-port balun measurements.
Specifically, the paper seeks to compare and analyze Category 8 cable transmission data obtained from a 4-port Vector Network Analyzer (VNA) with data obtained from a 2-port VNA system with baluns.
"Previous to Category 8 cabling specifications, the transmission measurement test procedures were based on 2-port VNAs and conventional balun (balanced-unbalanced) transformers," explains the technical paper's abstract. "These baluns were used to interface the unbalanced ports of the VNA to the differential device under test. Conventional balun transformers use flux linkages to transmit the energy from the input circuit to the output circuit. Conventional baluns with a 1 MHz lower frequency tend to be limited at frequencies above 1 GHz."
"In one method to overcome this balun limitation, 4-port VNAs are used to perform Category 8 testing to 2 GHz," continues the brief. "On this 4-port technique, the VNA measures full 4-port, single-ended S-parameters by considering the device under test a 4-port device."
In the brief, test data acquired with the 4-port method is compared against data acquired using a balun-based system capable of extending the test frequency to at least 2 GHz. Advantages and disadvantages of the two testing methods are reviewed.
View/Download the white paper.