Network Medium

The thick Ethernet segment is based on a thick (approx 1 cm or 0.4 inch diameter) and relatively inflexible coaxial cable. The outer insulation (jacket) of the cable may be plain PVC (yellow color) or Teflon (orange-brown color). Teflon is used for "plenum rated" cable, which is often required for installation in air handling spaces (also called plenums) to meet fire regulations. Thick Ethernet coaxial cable must be designed especially for use in Ethernet systems so that it meets the specifications, including a 50 ohms characteristic impedance rating and a solid center conductor. Examples of thick coaxial cables specifically designed for Ethernet are Belden numbers 9880 (PVC) and 89880 (plenum rated).

Thick coaxial segments are equipped with male type "N" coaxial connectors at each end. Installing the coaxial connectors onto the cable requires special stripping and crimping tools and must be done carefully or signal problems may result. For this reason, the correct operation of thick coaxial segments depends very much on the correct installation of the coaxial connectors.

The specifications note that the thick coaxial segment should ideally be built using a single piece of cable from the same cable spool or from cable spools all manufactured at the same time (known as a cable lot). If cable from different lots is used to build up a thick coax segment, then the specifications note that the sections of cable used should be 23.4 meters, 70.2 meters, or 117 meters in length (all lengths may be +/- 0.5 meters). The reason for using these lengths of cable is to minimize the chance of having excessive signal reflections build up due to the slight variations in electrical characteristics that can occur between different cable manufacturers or cable lots.

Quick Reference Guide to 10BASE5 Thick Ethernet - 04 SEP 95

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