Single-Lane Duplex Communication System; Dual-Lane Duplex Communication System; Cross-Lane Communication System; Operating Theory - 3M C860 Service Information

Theory of Operation and Diagrams

Single-Lane Duplex Communication System

This system provides duplex communication
(simultaneous talk/listen) for facilities that have one
menu sign. It consists of one base station and one or
more headsets and battery chargers.

Dual-Lane Duplex Communication System

This system provides duplex communication
(simultaneous talk/listen) for facilities that have two
menu signs. It consists of two base stations and two
or more headsets and battery chargers.

Cross-Lane Communication System

This system provides duplex communication
(simultaneous talk/listen) for facilities that have two
menu signs. It consists of two duplex systems that are
connected to a cross-lane module. The headsets are
programmed for both lane 1 and lane 2.
During off-peak hours, the cross-lane module is
turned on to link the two systems and enable one
operator to talk to customers at menu sign 1 or menu
sign 2 or with other headset operators.
During peak hours, the cross-lane module is turned off
to separate the systems. With the cross-lane module
off, one system is dedicated to menu sign 1 and the
other to menu sign 2. Menu sign 1 operators can talk
to customers at menu sign 1 or with other headset
operators. Menu sign 2 operators can talk to
customers at menu sign 2 or with other headset
operators.

Operating Theory

The 3M Wireless Intercom System has two basic
functions. First, it processes vehicle alert signals that
are supplied by a hard-wired vehicle detection system.
Second, it transmits and receives radio signals to
provide the following communication:
Talk/listen communication
S
Page communication
S

Processing Vehicle Alert Signals

The vehicle alert system provides a signal to the base
station to indicate a customer is present at the menu
sign.
1-2
Wireless Intercom System
There are two types of vehicle detectors. Presence
detectors (such as magnetic loops) provide a signal
for as long as a vehicle is present at the detector.
Pulse detectors, such as air hoses, provide only a
momentary signal—signalling vehicle arrival with no
indication of whether or not the vehicle remains at the
detector station.
If a presence detector is used, menu sign audio is
S
turned off automatically when the vehicle leaves.
If a pulse detector is used, menu sign audio is
S
silenced by pressing and releasing a headset page
switch.
When a vehicle detection signal is presented to the
base station, the base station broadcasts a repeating
alert tone to all headsets. The alert tone continues
until the talk switch [on an active headset] is pressed.

Transmitting and Receiving

The transmitting and receiving functions are
accomplished by two separate sets of radio
transmitters and receivers. One set is located in the
headset and the other in the base station.
The headset receives microphone audio signals from
the base station on frequency B and transmits both
audio signals and control tones on frequency A. The
control tones are above the audible range, and
function to turn the menu sign speaker's amplifier ON
during the talk operation. The base station receiver is
also always ON when the base station is powered.
Similarly, when the headset is powered, the headset
receiver is always ON to enable the listen mode. The
headset modulator turns ON only when a talk or page
switch is pressed.
The transmitter in the base station is always
transmitting a "no signal" transmitter carrier, even
when there is no microphone audio from the menu
sign or headset operator being broadcast. This "no
signal" carrier is continually broadcast to and received
by all headset receivers. It serves to block out other
radio-frequency signals or noises from headset
receivers.
E 3M 2003 March