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20
Understanding Scanning
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 GMRS/FRS radios.
The range is typically 1-8 miles, 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 listen for activity on the output frequency and
transmit on the input frequency. Since the repeater is
located very high, there is a very large line of sight.
Typical repeater systems provide coverage out to about a
25-mile radius from the repeater location.
Where To Get More Information
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