Most radios that you see in your everyday life are single-purpose radios. For example, an AM radio can listen to any AM radio station in the frequency band from 535 kilohertz to 1.7 megahertz, but nothing else. An FM radio can listen to any FM radio station in the band from 88 to 108 megahertz and nothing else. A CB radio can listen to the 40 channels devoted to citizens band radio and nothing else. Scanners are different.
Scanners are radio receivers that have extremely wide frequency ranges so you can listen to all kinds of radio signals. Typically, scanners are used to tune in to police, fire and emergency radio in the local area (so scanners are often called "police scanners"), but you can use a scanner to listen to all kinds of conversations. Generally, you will either:
- Set a scanner up to scan (switch between) a whole range of frequencies and then stop scanning when it detects a signal on any of the frequencies it is scanning - If you're interested in learning what the police are doing, you can scan the police radio frequencies in your local area. When a patrol car calls in to report a problem, the scanner will stop on that frequency and let you hear the conversation.
- Set a scanner to a specific frequency and listen to that channel - For example, say you want to listen to the transmissions between the control tower and airplanes at the local airport -- you can do this by listening to the specific frequency used at the airport. Because a scanner can receive a huge range of frequencies, you can set it to receive nearly anything on the air.
In order to use a scanner, you need to have good frequency tables so you know where the action is. For more information, check out the links below.