Radio Shack PRO-2055 User Manual page 21

The Basics
AM mode
The AM mode sets the scanner to receive
transmissions using amplitude modulation (AM),
primarily used for aircraft, military, some amateur
radio, and some government transmissions. (Refer to
"Specifi cations" for a list of the frequencies covered.)
When the scanner receives a transmission on a
channel set to the AM mode, it always stops on the
transmission.
FM mode
The FM mode sets the scanner to receive transmissions
using frequency modulation (FM), used for most public
safety transmissions, as well as broadcast, business,
and amateur radio transmissions. When the scanner
receives a transmission on a channel set to the FM
mode, it always stops on the transmission.
CTCSS (CT) mode
CTCSS mode sets the scanner to receive transmissions
using frequency modulation (FM) with Continuous
Tone Coded Squelch System (CTCSS) subaudible
tone codes. CTCSS allows multiple users to share a
single radio frequency without hearing each other's
transmissions. CTCSS mode also features a Code
Search setting that allows you to instantly display and
store unknown codes into the channel memory. CTCSS
tones can sometimes be heard as a low "hum" in the
background of a voice transmission.
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