Clear-Com SB-704 - Manual (Page 19)

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INSTALLATION
This chapter describes installation of the SB-704 in an intercom system.
INSTALLATION OVERVIEW
This section describes the Clear-Com concept in intercom line
interconnection under the following topics:
• Intercom Line Connection
• Line Termination
• Station Powering
• Cable Considerations
INTERCOM LINE CONNECTION
The SB-704 provides one male XLR-3 connector for each main intercom line
and ten male XLR-3 connectors for the separate assignable intercom
channels.
LINE TERMINATION
The fundamental concept of the Clear-Com party-line intercom is that all
stations provide high impedance into a single system termination.
Note: An intercom line must be terminated. Care must be taken not to
“double” terminate a line. All unused intercom inputs must be
terminated to keep the line drive circuits stable.
The SB-704 provides switchable terminations of the intercom lines.
Clear-Com main stations and power supplies provide switch-selectable
termination networks on all intercom output lines. It is up to the user to
determine where the termination will be provided. An unterminated line will
cause excessive levels, possible oscillation of line drivers, and severe
imbalance of hybrid null networks. A double- or multiple-terminated line will
cause low levels and severe imbalance of hybrid null circuits.
Switching of the termination on and off on the SB-704 is with back-panel
switches. The SB-704 is shipped from the factory with all four lines
terminated.
USING THE LINK FUNCTION
The link function in the SB-704 uses relays to connect the four party lines
together. In doing so, it also removes the terminations from channels B, C, and
D such that the new party line on channel A has only one termination when