Coaxial

Overview

The term "coaxial" is used to describe a type of electrical interconnect which has a central inner signal conductor surrounded by a tubular insulating layer, which is surrounded by a tubular conductor that serves as both a “shield” and as the signal “return.” The term “coaxial” comes from the inner conductor and the outer shield having a common axis.

Basics

• Coaxial cable is used for both analog audio and digital audio, as well as Word Clock connections in digital audio systems. The type of cable differs for analog and digital audio applications, with the digital audio and Word Clock cable employing more tightly controlled spacing of the center conductor and shield as well as selection of insulating material separating them, to maintain more constant characteristic impedance. Digital audio and Word Clock coaxial cable tends to be lower in capacitance than average audio coaxial cable; although low capacitance is also desirable to minimize high frequency loss in longer audio cables.
• Coaxial audio cables can have either RCA or T.S. connectors, and are used for unbalanced connections. Signal level in this type of connection is typically “-10dBV” consumer level; although T.S. cables can also be used for relatively short professional “+4dBu” signal connections.
• Coaxial digital interconnects are typically constructed with 75 Ohm cable and RCA connectors or, in some cases BNC connectors. They are used for unbalanced connections to transmit S-PDIF format and with a relatively low 0.5 – 0.6 Volt p-p level; so cable length is limited.
• Coaxial Word Clock cables are essentially the same as 75 Ohm video cables with BNC connectors, and are designed to carry high frequency signals up to hundreds of feet (depending on the frequency of the signal).