AST July 2018 Magazine AST July 2018 Magazine Issue 24 | Page 17

regulated 25 nature of these bands means you have
Volume
those found in vehicle dashboards)
25
July which
2018 have
Edition
no control. Even sophisticated FHSS radios eventu-
watts of transmit power. With a 6 dB antenna, you
get 100 times the ERP of an ISM band radio.
al get overwhelmed by the noise.
• ISM bands are limited to 1-watt Effective Radiated • The lower frequencies have greater ability to go
around or thru minor obstructions. If the topog-
Power (ERP) at most (some countries are even
less).
raphy is favorable, a control station in the center
• Higher radio frequencies provide more bandwidth
of town may be able to directly hit all the sirens
for applications like a high def video but have less
in the surrounding area without depending on
and less ability to go thru or around obstructions.
any 3rd party infrastructure like the cell system or
Basically, the higher the frequency of the radio
network providers.
wave, the more it’s like light. It wants to travel
in a straight line and a wall or other obstruction
Since all ATI RTUs and CCUs have built-in bat-
severely reduces the signal. In one extreme case, a teries, your system works, period, even if local
link that worked fine in the winter stopped work-
power or communication networks are down.
ing in the spring when the leaves came out on the
trees between buildings.
The relatively narrow licensed frequency channel
is not going to transport high def video but is per-
The relatively limited Line-Of-Sight nature
fectly adequate to control and monitor a group of
of most wireless IP links means that a large outdoor or indoor speaker units.
installation needs to either:
• Depend on an extensive 3rd
party infrastructure (WiFi access
points, cell towers, etc.)
• Or install an extensive mesh
network with lots of local repeat-
ers, multiple radios, etc. This
can require a large effort which
may need to be adjusted if the
physical environment (or the RF
environment) changes.
Using an “old fashioned”
licensed VHF (~150 MHz)
or UHF (~450 MHz) channel
to transmit encoded digital
packets has several advantag-
es:
• Much higher power transmitters
MassAlert® is customized for each client’s specific system and utilizes field unit icons
can be used. ATI units typically layered onto location maps and building diagrams of the system to provide system
use standard mobile radios (like overview and real-time status.
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