Intercoms 1569retrieved from the foundation of tracer software. The
multitasking Microsoft Windows operating system is
used, which creates an open system.
Three presentation methods are available. Tracer-
LIST handles multiple floors and hundreds of tags.
Features include a living directory presentation, fast
alphabetic search, usual location and extension, current
location, occupants currently in the room, and system
condition heartbeat.
Tracer VR (voice response) uses a voice response
card and allows users to dial into the system to audibly
learn location. Tracer VR extends the tracer capability
to before and after-hours callers, and personnel without
workstations.
TracerMap is a living floor plan that gives a graph-
ical location of Tags within an area.
43.1.7 Wireless Intercoms
When areas are constantly being reorganized, a wire-
less intercom may be useful. A wireless intercom may
use RF for transmitting the signal or it may be trans-
mitted through the 120 Vac lines. When the transmitting
system is RF, two frequencies are required per unit, one
for talking and one for listening unless the system oper-
ates like walkie talkies where simultaneous two-way
communication is not possible. If each unit must have
its own private communication, then each unit would
require a different transmit and receive frequency or use
a system of subaudio modulation to key the appropriate
unit. The subaudio modulation system can have only
one conversation at a time. The biggest drawbacks of
wireless intercoms is their ability to pick up noise and
stray signals and fewer bells and whistles are available.
However, if the area is confined and relatively free from
electrical noise, wireless intercoms can greatly reduce
installation costs.
When the ac power lines are used to connect the
audio between units, the frequency response must be
limited to reduce noise and hum. If the two units are on
different legs of the two phase 220/110 Vac transformer,
communications may not be possible without some
means to transfer the audio signal between the legs.43.2 Broadcast Intercoms
The need for rapid, reliable, and flexible communica-
tions is required in broadcast intercoms. Fortunately,
intercom equipment is capable of meeting almost any
need that might arise.
Telephones are usually used for less than 20 minutes
per call. Intercoms are often used for many hours at a
time. The people involved in teleproduction work often
can’t take a break or remove their headsets. If the
system has limited frequency response, then the
system’s filter effects create distortion. This unnatural
sound can cause fatigue, which can be eliminated with a
full-frequency intercom.
Broadcast intercoms can be point-to-point, party line,
or matrix. The audio line can be balanced or unbalanced.
Balanced line operation provides maximum protection
from electromagnetic interference generated from
sources such as fluorescent lights, patch panels, or light
dimmers. The 24 Vdc phantom power is fed down the
audio line with the minus voltage on the shield and the
positive voltage bridged between the two shielded lines.
The bridging is accomplished by connecting two resis-
tors in series and across the balanced line and
connecting the positive voltage to the junction between
the resistors. It is important that the resistors be at least
1% tolerance or better. A balanced system can run as
much as 5000 ft with standard two-conductor shielded
microphone cable.
An unbalanced line, sometimes called a three-wire
system, is easier to switch and operate special circuits as
the audio and signal are on different lines, only using
the ground (shield) as a common line. A second method
provides two channels of unbalanced audio, one channel
between each conductor and shield, and combining the
dc operating power with one of the audio channels.Figure 43-9. Hardware elements of a tracer system.ConcentratorV.R. card(any phone can
call for tracer
location)
Tracer V.R. Tracer map
Tracer listDisplay
softwareOptional LAN
connectionPCCeilingInfrared light
Tracer
tagFloorCollectorTelephoneSensor