Motorola BC796D - Manual (Page 12)

Understanding Scanning
This section provides you with the background on how scanning works. You don’t really
need to know all of this to use your scanner, but some background knowledge will help you
to get the most from your BC796D.
Conventional Scanning
Conventional scanning is a relatively simple concept. Each group of users in a conventional
system is assigned a single frequency (for simplex systems) or two frequencies (for repeater
systems) to use. Any time one of them transmits, their transmission always goes out on the
same frequency. Up until the late 1980’s this was the primary way that radio systems
operated. Even today, there are a lot of 2-way radio users who operate using a conventional
system:
• Aircraft
• Amateur Radio
• FRS/GMRS 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 frequency 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 1-5 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.
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