When a gooseneck microphone is inserted in the panel microphone connector, the built-in panel microphone is automatically bypassed. Use either of these microphones for talk back, then use the internal speaker for listening, or connect a pair of headphones to the headset connector for private listening.
Intercom Channel Connections
The method of connection depends on the type of box. The S box, P box, and RM versions connect to the intercom system using pre-fabricated cables in a phantom powered configuration. The U box version is designed for permanent installation, and it can be either phantom powered or locally powered.
Description of Phantom-Powered Connection
In phantom-powered connections the operating power and intercom audio for the entire system are carried over the same wires. The advantage of this method is simplicity of connection. The system power supply (PS-2001L, SPS-2001A, etc.) automatically provides what is known as a terminating impedance for the intercom system. Without this terminating impedance, the sound quality becomes distorted, and the levels shift every time additional stations are connected. The disadvantage of the phantom power method is some operating power is lost over very long intercom cable runs, and performance at distant intercom station may be reduced. Generally, if intercom stations are within a few hundred feet from the system power supply, phantom power is sufficient. Also, increasing the number of stations reduces the overall operating distance. Phantom-power is generally the only method used to connect the S box, P box, and RM versions. Figure 4 illustrates a phantom-power intercom system.
NOTE: The distance over which power can be delivered is less than the distance over which audio can be delivered. Audio can be delivered for several miles to locally powered stations as described below.
FIGURE 4. Phantom Powered Example
Example: Figure 4 is an example of a phantom-powered system. In this system, a PS-2001L power supply is set to isolate mode. Each channel is a separate party line and current per channel is limited to 1Amp. Both single and two-channel intercom stations may be connected by using Y cables (or JB2 Junction boxes). Pre-fabricated cables may be used, or cables may be constructed using the diagrams in Figure 10 on page 14.
