Sound powered network with 4 stations and extension devices selective signaling

SPT Selective Signaling

This application shows 4 call-signal stations in a sound powered network. The call-signal stations in this configuration contain a station selector rotary switch with either 8 or 16 positions.

Operating the hand crank at the calling station generates a howler tone at only the selected station. This is called "selective signaling". All handsets are wired in parallel on a single pair of wires - meaning that everyone on the network can hear and talk to everyone else.

Also shown in this application:

• A generator-operated relay driving a visual signal device. The relay operates from the current supplied by the hand-cranked generator at the calling station. The visual signal device (an incandescent lamp) requires separate 120 VAC, 60 Hz power.
• An extension howler off the station in the upper right
• A double jackbox connected to the common audio pair.