Return Loss Analysis For RJ Connectors


Xmultiple's Engineering Department

Return Loss (RL)

Return Loss is a parameters regulated by the requirements established for Category 5e and 6 cables. Return loss is specified in the newly ratified TIA/EIA TSB-95 standard. Return Loss is a measure of the reflected energy from a transmitted signal. Any energy that is reflected reduces the power of the transmitted signal. It is expressed in positive dB's. The larger the value, the less energy that is reflected. In local area networks the signal transmits over the network cables. As the signal travels down the pair there are portions of the signal which are reflected back to the transmitter. These reflections are caused by impedance discontinuities in the channel. Discontinuities may be caused by many part of the equipment or cable being used in the network. Connectors are one of the items. However most causes of discontinuities are improper installation and cable. The cable can be mishandling or improperly manufacture as well.

Connector Return Loss

When looking at return loss related to connectors the return loss i the reflection or echo caused by impedance mismatches which occur when a high-speed signal enters or exists the connector. Connectors in the past have been the weak link in the channel's performance. Specifically, the split pair in the RJ-45type connector is the major culprit. The physical separation of the conductors degrades the RL performance by disturbing the pair geometry. This separation of the pair generates an impedance discontinuity, causing signal reflections. Additionally, the near-end crosstalk (NEXT) compensation that some manufacturers performed on their older connectors aggravated the RL performance of the split pair. However, large improvements have been made to the new versions of magnetic connectors as well as non magnetic connectors and this is becoming less of an issue making the cable performance more critical. Xmultiple has designed our contact pins with return loss considerations being made with how pins are arranged inside the connector. Today connectors are no longer the weak link.

A connector designed on a printed circuit board wants the signal to have a clean path and therefore the return loss is desired to be minimal. Engineers designing products target íV10dB as the critical value of connector performance. They also attempt to reduce the return loss lower than íV10dB at the desired signal speeds.

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