How Radio Scanners Work

Photo courtesy HowStuffWorks Shopper

The air around you is bursting with radio waves. You know that you can flip on the AM/FM radio in your car and receive dozens of stations. You can flip on a CB radio and receive 40 more. You can flip on a TV and receive numerous broadcast channels. Cell phones can send and receive hundreds of frequencies. And this is just the tip of the radio spectrum iceberg. Literally tens of thousands of other radio broadcasts and conversations are zipping past you as you read this article -- police officers, firefighters, ambulance drivers, paramedics, sanitation workers, space shuttle astronauts, race car drivers, and even babies with their monitors are transmitting radio waves all around you at this very moment!

To tap into this ocean of electromagnetic dialogue and hear what all of these people are talking about, all you need is a scanner. A scanner is basically a radio receiver capable of receiving multiple signals. Generally, scanners pick up signals in the VHF to UHF range (see How the Radio Spectrum Works for details on these frequency bands).


Radio scanners are very portable and affordable. In this article, we will look at the basics of scanner operation, examine radio scanning as a hobby, and show you how to get started listening to public airwaves you may not have known existed!

Scanner Basics

Scanners typically operate in three modes:

  • Scan
  • Manual scan
  • Search

In scan mode, the receiver constantly changes frequencies in a set order looking for a frequency that has someone transmitting. Lights or panel-mounted displays show what channel or frequency is in use as the scanner stops on a given frequency. The frequencies can be preprogrammed on some models or manually set on practically all models.

In manual scan mode, the user taps a button or turns a dial to manually step through preprogrammed frequencies one frequency at a time.

In search mode, the receiver is set to search between two sets of frequencies within a given band. This mode is useful when a user does not know a frequency, but wants to know what frequencies are active in a given area. If the frequency the scanner stops at during a search is interesting, the user can store that frequency in the radio scanner and use it in scan mode.


Scanner Features

Radio scanners can be either portable, with rechargeable battery packs, or desktop, like a regular radio. Scanners are gaining popularity with consumers. With the huge popularity of NASCAR racing, many people now use scanners at auto racing events to eavesdrop on the crew-driver communications at races. At a typical race, there are hundreds of frequencies in use. Each team has two or three frequencies, while race control, the sanctioning organization, the medical, fire and track crews and many others each have assigned frequencies during the race.

Some of the recently released scanners are capable of tracking municipalities and police frequencies in the 800-megahertz (MHz) range. This is known as trunk tracking of computer-controlled trunked radio networks.


Higher-end scanners can be controlled by the serial port of a personal computer using special software. This helps the user with the logging of stations as well as with duplicating the scanner controls within the software application.

Many models receive the NOAA weather radio broadcasts. This can be a very useful feature during pending tornadoes or hurricanes.

The controls on a radio scanner can vary, but practically all of them have:

  • Volume
  • Squelch - This is an adjustable control that keeps the speaker muted (quiet and free from static) when a station is not transmitting. It works whether the radio is scanning, searching or manually stepping through stored frequencies. CB radios also have this control.
  • WX button - This is common on some newer models. This button typically does a mini-scan of some factory-written frequencies that receive the nationwide NOAA weather broadcast reports.
  • Numeric keypad - This is used for entering frequencies or in combination with the "Limit" button, used for entering upper and lower ranges of a search between two frequencies. The keypad also lets you enter frequencies found during a search. More expensive models automatically store frequencies found during a search. Buy a copy of "Police Call" (you can get a used one for next to nothing at or the CD-ROM version at Radio Shack) to get some frequencies for your area. See these Frequently Asked Frequencies, too. Useful Book Scanners & Secret Frequencies by Henry L. Eisenson and Bill Cheek Thanks to frequency synthesizers, most scanners can receive frequency bands in the 29-MHz to 512-MHz range. If you enter a frequency outside that range, you typically see an error indication on the display. More expensive models often have a higher range and often include military aircraft frequencies. (Earlier scanners did not have numeric keypads and required the owner to purchase individual crystals manufactured for a given frequency. Most early scanners only held six or 10 crystals. The cost of filling up a scanner with individual channel crystals often approached the cost of the scanner, much like buying ink cartridges for today’s low-priced color inkjet printers.)
  • Search button - This starts the scanner on a continuous loop between two frequency limits, finding unknown frequencies within a given range. The searches typically are in the same automatic increments that the Federal Communications Commission (FCC) assigns for the given frequency band being searched. U.S. scanners cannot search the frequency bands assigned for analog cellular telephone calls. If you were at a car race, for example, you could do a search from 460 to 470 MHz and note when the scanner stops (or look in the race program for assigned frequencies). You could make a note of the displayed frequency or store it at that time, and then continue the search. The instruction manual that comes with a scanner typically shows what frequency bands are for government, business, aviation, and other users.
  • Manual button - This lets the user manually step through a range of frequencies stored in the scanner. Modern scanners have 100 to 300 channels for storing frequencies in the built-in memory. More expensive models have even more.
  • Scan button - This starts the scanner on a continuous loop through all of the frequency banks (containing stored frequencies). The scanner stops when it detects a radio signal on a stored frequency; it moves to the next stored frequency when the radio signal ends. The user can typically enable or disable certain banks of frequencies for scanning. Each bank can hold 10 to 30 frequencies, depending on the brand and model of the radio scanner. Often, banks contain frequencies according to the type of radio service. Types include emergency, police, fire, aviation, marine and business.
  • Delay button - This makes the scanner stall for a short duration on a frequency before moving to the next one. This delay helps the user hear the other part of the radio conversation on that frequency.
  • Lockout button - This temporarily disables the radio scanner from stopping on a stored frequency. For example, you might want to lockout the frequency of a busy airport tower at peak travel time during the day when you're really trying to hear the traffic helicopters in your area.

Radio scanners usually come with small whip antennas as well as an external antenna connector. An outside antenna or attic antenna enables you to hear more transmissions at a greater distance.

Scanners cannot hear everything. The typical consumer-grade scanner cannot listen in on 900-MHz cordless phones that use digital spread spectrum (DSS) technology. Analog cell phone frequencies are also blocked by law on all scanners.

Some law enforcement agencies also use audio inversion and other scrambling technologies to prevent the reception of sensitive communications. You will not be able to decipher these conversations.

Even so, there is an unbelievable number of radio services that use frequencies most scanners can hear.

Until you buy your own scanner, you can try out scanning frequencies on Web-controlled receivers.


Getting Started With Your Scanner

Frequency lists are easy to obtain, often via the Internet. You can find a free frequency list for your area at this Web site.

If you buy a portable scanner, park near an airport sometime and search the VHF AM aviation-band range, from approximately 118 MHz to 135.975 MHz, to hear all the activity that is going on. In some areas, programming 123.45 MHz into your scanner will let you hear some pilot-to-pilot communications.


Many desktop models work on a 12-volt power supply, so a cigarette-lighter adapter will allow you to take one on a trip.

Community Service with a Scanner

Scanners have helped law enforcement track down criminals. For instance:

  • A scanner listener hears the police conversation about a recent robbery description, spots the perpetrator’s car and calls the police to report it.
  • A scanner listener hears criminal activity being discussed on the scanner and reports it to the local police.

Often, family members of those in fire protection, emergency medical services and law enforcement have a scanner so they can hear what is going on.

Scanner users sometimes receive negative publicity when they use information that they have heard for private personal gain. Be sure to obey the scanner laws when scanning.

Join a neighborhood watch team or a crime watch team and use the information you hear for awareness and safety.

Listening in via the Internet

If you wish to get a taste of radio scanning, and have a sound card in your PC, try the various radio scanner live broadcasts for police, fire, rail and aviation.

Reception over the Internet may be erratic when there is network congestion, but this is an inexpensive way to try out radio scanning via your PC and the Internet.

Scanner Tips

Once you buy a scanner, read the manual from cover to cover so you know all of the capabilities. Ask questions in one of the many scanner newsgroups on the Internet -- there are active USENET newsgroups that many scanner hobbyists visit. You can use or, easily accessed through your Web browser. Check out some of the scanning resources on the Internet, then try these tips:

  • Become a frequency collector. Start with index cards or perhaps a small database program on your computer. Learn how to do searches within a given band -- search a 1-MHz segment at a time and record the interesting frequencies you find.
  • Consider finding a way to run your radio from emergency power if you have a desktop model. That way, you can listen to police and fire crews during power failures and severe weather. Typically, a very small 12-volt battery is all that is needed.
  • Consider storing frequencies of a similar type all in the same bank. That way, if you just want to listen to police, fire, or aviation, you can scan just the frequency memory bank you're interested in and "lockout" the others.
  • Take your scanner on a trip and listen from the hotel or motel room.
  • Take your scanner to all sporting events where radios are used.
  • Listen to local amateur radio operators at 144 to 148 MHz. Volunteer ham radio spotters are often heard during a weather watch or a weather warning.

For lots more information on radio scanners and related topics, check out the links on the next page!