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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 briey
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.