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 is is 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 retrun loss considerations being
made with how pins are arranged and angeled inside
the connector. Today connectors are not 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 ¡V10dB as the critical value
of connector performance. They also attempt to reduce
the return loss lower than ¡V10dB at the desired signal
speeds.
CAT5,
CAT5e, CAT6 and CAT7 Information