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12
Understanding Scanning
this was the primary way that radio systems
operated.
Even today, there are many 2-way radio users who
operate using a conventional system:
•Aircraft
• Amateur radio
• PRS (UHF CB) users
• Broadcast AM/FM/TV stations
• Many business radio users
When you want to store a conventional system, all
you need to know is the frequencies they operate
on. When you are scanning a conventional system,
the scanner stops very briefly on each channel to
see if there is activity. If there isn’t, the scanner
quickly moves to the next channel. If there is, then
the scanner pauses on the transmission until it is over.
Simplex Operation
Simplex systems use a single frequency for both
transmit and receive. Most radios using this type of
operation are limited to line-of-sight operation. This
type of radio is frequently used at construction job
sites, and with inexpensive consumer radios such as
PRS (UHF CB) radios. The range is typically 1.5-12
km, depending upon the terrain and many other factors.
Repeater Operation
Repeater systems use two frequencies: one transmits
from the radio to a central repeater; the other
transmits from the repeater to other radios in the
system. With a repeater-based system, the repeater
is located on top of a tall building or on a radio tower
that provides great visibility to the area of operation.
When a user transmits (on an input frequency), the
signal is picked up by the repeater and retransmitted
(on an output frequency). The user’s radios always
UBC93XLT Paper OM.fm Page 12 Monday, May 14, 2007 9:01 AM