A radio scanner is a communication device that can tune or scan several discrete frequencies and is intended to be used for monitoring the UHF and VHF land mobile radio systems. This device also has the capability to tune to other types of modulation like AM and FM. Though commonly used by the police and emergencies service personnel, scanners are increasingly being used in auto racing events for monitoring races.
Scanners often have small whip antennas and external antenna connectors. The outside antenna enables one to hear more transmissions over a greater distance.
Some models are portable and come with rechargeable battery packs, allowing them to be used in different areas. However, some are desktop, much like the regular radio.
Some of the modern scanners have the capability to track police and municipality frequencies within the 800-megahertz (MHz) range. They operate as computer-controlled trunked networks and the process is known as trunk tracking.
Scanners have many different controls including;
1. Squelch: This keeps the speaker in a mute state when there are no transmissions from a station .Squelch can work if the radio is searching or scanning.
2. Numeric keypad: This control is used to enter frequencies and can also be used together with the "Limit" button to enter upper or lower ranges of a given search between 2 frequencies.
3. Search button: This is used to find unknown frequencies over a given range. It works by starting the scanner on continuous loops between 2 frequency limits.
4. Scan button – This can be used to scan signals from the stored frequencies. It starts the radio on continuous loops through the stored frequencies (located in frequency banks) with the scanner stopping when it detects a signal.
5. Manual button - This allows the user to manually scan a given range of stored frequencies. Most scanners have between 100 and 300 channels for storing frequencies in their built-in memory.
6. Lockout button: This button temporarily disables the scanner from stopping on stored frequencies.
How do scanners operate?
These generally operate in 3 modes: scan, manual scan and search.
In this mode, the receiver keeps changing frequencies in a given order to look for a frequency which has transmissions. When a certain frequency if found, the scanner will stop and lights on the device will show that particular frequency .Frequencies can be manually entered in almost all scanners though there are some models that allow pre-programming of frequencies.
Manual scan mode
In a manual scan, the user taps a button to manually go through the preprogrammed frequencies, one after another.
With this mode, the scanner is usually set to search over several sets of frequencies. If the receiver stops at a frequency the user finds interesting, he or she can store it in the device and then use it in the scan mode. The search mode is particularly useful when the user wants to find out the frequencies that are active within a given area.
Most of the modern models can receive NOAA weather broadcasts. This feature can be very useful especially during pending hurricanes or tornadoes.