are not to be confused with the party-line loop (McCulloh circuit) which are
prone to cross talk and indecipherable message transmissions.
7.2.3 Telephone Line to On- or Off-Site. Very long alarm communication
wiring can be managed by existing or specially installed telephone company
wiring. Connections between buildings and within large facilities often can
be cost-effectively accommodated by the telephone utility wiring, since most
IDS communications needs are conducted via low-voltage wire pairs. Lease
and installation costs, physical protection of wire routes, expansion
capabilities, and availability of services are a few of the major
considerations in comparing telephone facilities to proprietary wiring.
Responsibility for maintenance can also be a problem. Caution must be
observed on installations within air return plenum ceilings, which must be
explicitly noted for conduit or plenum cable applications as required by
local and national electrical codes and fire regulations. Various
communications techniques can effectively extend the IDS information
communications to points which are limited only by location of telephone
communications instrumentation. These may include international satellite
7.2.4 Radio Frequency. Radio frequency (RF) communication techniques may
be used for IDS information transfer. Although most often used for two-way
voice communications, there have been significant new developments in the RF
alarm transmitter subsystems within the past 10 years. The primary use of
RF alarm transmissions has been to provide for mobile duress alarms and for
an inexpensive method for alarm signalling where wiring applications are
impractical due to remote locations. "Wireless" systems work in conjunction
with detection sensors to provide transmissions of the detected event from
the device location to the monitor location. The signal codes permit
separation of reporting for one to 10,000 distinct alarm reporting
transmitters. Extreme caution should be exercised when using this type of
device since transmissions are affected by interference (electric circuit
transients, motors, transformers, ignitions, heating, static, weather, and
other radio frequency signals). The output and power regulations of the RF
devices must be licensed by the Federal Communications Commission (FCC).
systems, and methods of power supply or batteries require frequent
supervision and maintenance.
7.2.5 Microwave. Microwave transmissions are extremely short radio waves.
on/off pulses rather than varying frequency are indicative of information.
This differentiation permits high-speed information transfer rates for data,
television signal, multiplexed telephone, and multiplexed alarm signals.
Microwave is limited to line-of-sight transmitter to receiver (or
reflector), behaves very much the same as light signals, and will not pass
through buildings, trees or hills. There are very few atmospheric
influences on microwave, and the system withstands adverse weather
conditions. Systems are licensed through the FCC for IDS alarm and
assessment (CCTV) equipment. The system designer may wish to explore the
cost benefits of microwave data and video links, particularly in large or
complex sites where cabling costs are